From 5d690beac48faf5e6d7f20deacffbc0e47dd1519 Mon Sep 17 00:00:00 2001
From: A5rocks <git@helvetica.moe>
Date: Sun, 26 Jan 2025 19:29:08 +0900
Subject: [PATCH 1/3] Make default return value for NodeVisitor explicitly
 optional

---
 mypy/checkexpr.py          |   4 +-
 mypy/checkpattern.py       |   1 +
 mypy/nodes.py              | 156 +++++++++---------
 mypy/patterns.py           |  18 +-
 mypy/strconv.py            |  22 ++-
 mypy/stubgen.py            |  93 ++++++++---
 mypy/test/testmerge.py     |   1 +
 mypy/treetransform.py      |   1 +
 mypy/visitor.py            | 327 ++++++++++++++++++-------------------
 mypy_self_check.ini        |   4 -
 mypyc/irbuild/builder.py   |   1 +
 mypyc/irbuild/statement.py |   1 +
 12 files changed, 341 insertions(+), 288 deletions(-)

diff --git a/mypy/checkexpr.py b/mypy/checkexpr.py
index a10dc00bb1de..c4156e2c6cfa 100644
--- a/mypy/checkexpr.py
+++ b/mypy/checkexpr.py
@@ -5944,7 +5944,9 @@ def accept(
             elif allow_none_return and isinstance(node, AwaitExpr):
                 typ = self.visit_await_expr(node, allow_none_return=True)
             else:
-                typ = node.accept(self)
+                typ_ = node.accept(self)
+                assert typ_ is not None
+                typ = typ_
         except Exception as err:
             report_internal_error(
                 err, self.chk.errors.file, node.line, self.chk.errors, self.chk.options
diff --git a/mypy/checkpattern.py b/mypy/checkpattern.py
index 4b34c0ddb54b..cd47fb13df4c 100644
--- a/mypy/checkpattern.py
+++ b/mypy/checkpattern.py
@@ -130,6 +130,7 @@ def accept(self, o: Pattern, type_context: Type) -> PatternType:
         result = o.accept(self)
         self.type_context.pop()
 
+        assert result is not None
         return result
 
     def visit_as_pattern(self, o: AsPattern) -> PatternType:
diff --git a/mypy/nodes.py b/mypy/nodes.py
index b7b09f506c35..ee6431c179e5 100644
--- a/mypy/nodes.py
+++ b/mypy/nodes.py
@@ -181,7 +181,7 @@ def str_with_options(self, options: Options) -> str:
         assert ans
         return ans
 
-    def accept(self, visitor: NodeVisitor[T]) -> T:
+    def accept(self, visitor: NodeVisitor[T]) -> T | None:
         raise RuntimeError("Not implemented", type(self))
 
 
@@ -191,7 +191,7 @@ class Statement(Node):
 
     __slots__ = ()
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         raise RuntimeError("Not implemented", type(self))
 
 
@@ -201,7 +201,7 @@ class Expression(Node):
 
     __slots__ = ()
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         raise RuntimeError("Not implemented", type(self))
 
 
@@ -355,7 +355,7 @@ def name(self) -> str:
     def fullname(self) -> str:
         return self._fullname
 
-    def accept(self, visitor: NodeVisitor[T]) -> T:
+    def accept(self, visitor: NodeVisitor[T]) -> T | None:
         return visitor.visit_mypy_file(self)
 
     def is_package_init_file(self) -> bool:
@@ -433,7 +433,7 @@ def __init__(self, ids: list[tuple[str, str | None]]) -> None:
         super().__init__()
         self.ids = ids
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_import(self)
 
 
@@ -454,7 +454,7 @@ def __init__(self, id: str, relative: int, names: list[tuple[str, str | None]])
         self.names = names
         self.relative = relative
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_import_from(self)
 
 
@@ -473,7 +473,7 @@ def __init__(self, id: str, relative: int) -> None:
         self.id = id
         self.relative = relative
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_import_all(self)
 
 
@@ -574,7 +574,7 @@ def name(self) -> str:
             assert self.impl is not None
             return self.impl.name
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_overloaded_func_def(self)
 
     def serialize(self) -> JsonDict:
@@ -807,7 +807,7 @@ def __init__(
     def name(self) -> str:
         return self._name
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_func_def(self)
 
     def serialize(self) -> JsonDict:
@@ -919,7 +919,7 @@ def info(self) -> TypeInfo:
     def type(self) -> mypy.types.Type | None:
         return self.var.type
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_decorator(self)
 
     def serialize(self) -> JsonDict:
@@ -1065,7 +1065,7 @@ def name(self) -> str:
     def fullname(self) -> str:
         return self._fullname
 
-    def accept(self, visitor: NodeVisitor[T]) -> T:
+    def accept(self, visitor: NodeVisitor[T]) -> T | None:
         return visitor.visit_var(self)
 
     def serialize(self) -> JsonDict:
@@ -1173,7 +1173,7 @@ def fullname(self) -> str:
     def fullname(self, v: str) -> None:
         self._fullname = v
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_class_def(self)
 
     def is_generic(self) -> bool:
@@ -1218,7 +1218,7 @@ def __init__(self, names: list[str]) -> None:
         super().__init__()
         self.names = names
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_global_decl(self)
 
 
@@ -1235,7 +1235,7 @@ def __init__(self, names: list[str]) -> None:
         super().__init__()
         self.names = names
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_nonlocal_decl(self)
 
 
@@ -1254,7 +1254,7 @@ def __init__(self, body: list[Statement], *, is_unreachable: bool = False) -> No
         # in those cases.
         self.is_unreachable = is_unreachable
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_block(self)
 
 
@@ -1274,7 +1274,7 @@ def __init__(self, expr: Expression) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_expression_stmt(self)
 
 
@@ -1341,7 +1341,7 @@ def __init__(
         self.is_final_def = False
         self.invalid_recursive_alias = False
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_assignment_stmt(self)
 
 
@@ -1362,7 +1362,7 @@ def __init__(self, op: str, lvalue: Lvalue, rvalue: Expression) -> None:
         self.lvalue = lvalue
         self.rvalue = rvalue
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_operator_assignment_stmt(self)
 
 
@@ -1381,7 +1381,7 @@ def __init__(self, expr: Expression, body: Block, else_body: Block | None) -> No
         self.body = body
         self.else_body = else_body
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_while_stmt(self)
 
 
@@ -1435,7 +1435,7 @@ def __init__(
         self.else_body = else_body
         self.is_async = False
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_for_stmt(self)
 
 
@@ -1450,7 +1450,7 @@ def __init__(self, expr: Expression | None) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_return_stmt(self)
 
 
@@ -1467,7 +1467,7 @@ def __init__(self, expr: Expression, msg: Expression | None = None) -> None:
         self.expr = expr
         self.msg = msg
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_assert_stmt(self)
 
 
@@ -1482,28 +1482,28 @@ def __init__(self, expr: Lvalue) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_del_stmt(self)
 
 
 class BreakStmt(Statement):
     __slots__ = ()
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_break_stmt(self)
 
 
 class ContinueStmt(Statement):
     __slots__ = ()
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_continue_stmt(self)
 
 
 class PassStmt(Statement):
     __slots__ = ()
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_pass_stmt(self)
 
 
@@ -1522,7 +1522,7 @@ def __init__(self, expr: list[Expression], body: list[Block], else_body: Block |
         self.body = body
         self.else_body = else_body
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_if_stmt(self)
 
 
@@ -1540,7 +1540,7 @@ def __init__(self, expr: Expression | None, from_expr: Expression | None) -> Non
         self.expr = expr
         self.from_expr = from_expr
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_raise_stmt(self)
 
 
@@ -1577,7 +1577,7 @@ def __init__(
         self.finally_body = finally_body
         self.is_star = False
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_try_stmt(self)
 
 
@@ -1610,7 +1610,7 @@ def __init__(
         self.body = body
         self.is_async = False
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_with_stmt(self)
 
 
@@ -1638,7 +1638,7 @@ def __init__(
         self.guards = guards
         self.bodies = bodies
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_match_stmt(self)
 
 
@@ -1661,7 +1661,7 @@ def __init__(self, name: NameExpr, type_args: list[TypeParam], value: LambdaExpr
         self.invalid_recursive_alias = False
         self.alias_node = None
 
-    def accept(self, visitor: StatementVisitor[T]) -> T:
+    def accept(self, visitor: StatementVisitor[T]) -> T | None:
         return visitor.visit_type_alias_stmt(self)
 
 
@@ -1681,7 +1681,7 @@ def __init__(self, value: int) -> None:
         super().__init__()
         self.value = value
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_int_expr(self)
 
 
@@ -1704,7 +1704,7 @@ def __init__(self, value: str) -> None:
         super().__init__()
         self.value = value
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_str_expr(self)
 
 
@@ -1734,7 +1734,7 @@ def __init__(self, value: str) -> None:
         super().__init__()
         self.value = value
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_bytes_expr(self)
 
 
@@ -1751,7 +1751,7 @@ def __init__(self, value: float) -> None:
         super().__init__()
         self.value = value
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_float_expr(self)
 
 
@@ -1768,7 +1768,7 @@ def __init__(self, value: complex) -> None:
         super().__init__()
         self.value = value
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_complex_expr(self)
 
 
@@ -1777,7 +1777,7 @@ class EllipsisExpr(Expression):
 
     __slots__ = ()
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_ellipsis(self)
 
 
@@ -1798,7 +1798,7 @@ def __init__(self, expr: Expression) -> None:
         # Whether this starred expression is used in a tuple/list and as lvalue
         self.valid = False
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_star_expr(self)
 
 
@@ -1863,7 +1863,7 @@ def __init__(self, name: str) -> None:
         # Is this a l.h.s. of a special form assignment like typed dict or type variable?
         self.is_special_form = False
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_name_expr(self)
 
     def serialize(self) -> JsonDict:
@@ -1885,7 +1885,7 @@ def __init__(self, expr: Expression, name: str) -> None:
         # The nodes of other kinds of member expressions are resolved during type checking.
         self.def_var: Var | None = None
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_member_expr(self)
 
 
@@ -1961,7 +1961,7 @@ def __init__(
         # cast(...) this is a CastExpr.
         self.analyzed = analyzed
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_call_expr(self)
 
 
@@ -1976,7 +1976,7 @@ def __init__(self, expr: Expression) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_yield_from_expr(self)
 
 
@@ -1991,7 +1991,7 @@ def __init__(self, expr: Expression | None) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_yield_expr(self)
 
 
@@ -2020,7 +2020,7 @@ def __init__(self, base: Expression, index: Expression) -> None:
         self.method_type = None
         self.analyzed = None
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_index_expr(self)
 
 
@@ -2042,7 +2042,7 @@ def __init__(self, op: str, expr: Expression) -> None:
         self.expr = expr
         self.method_type = None
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_unary_expr(self)
 
 
@@ -2058,7 +2058,7 @@ def __init__(self, target: Expression, value: Expression) -> None:
         self.target = target
         self.value = value
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_assignment_expr(self)
 
 
@@ -2104,7 +2104,7 @@ def __init__(
         self.right_unreachable = False
         self.analyzed = analyzed
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_op_expr(self)
 
 
@@ -2133,7 +2133,7 @@ def pairwise(self) -> Iterator[tuple[str, Expression, Expression]]:
         for i, operator in enumerate(self.operators):
             yield operator, self.operands[i], self.operands[i + 1]
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_comparison_expr(self)
 
 
@@ -2162,7 +2162,7 @@ def __init__(
         self.end_index = end_index
         self.stride = stride
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_slice_expr(self)
 
 
@@ -2181,7 +2181,7 @@ def __init__(self, expr: Expression, typ: mypy.types.Type) -> None:
         self.expr = expr
         self.type = typ
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_cast_expr(self)
 
 
@@ -2200,7 +2200,7 @@ def __init__(self, expr: Expression, typ: mypy.types.Type) -> None:
         self.expr = expr
         self.type = typ
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_assert_type_expr(self)
 
 
@@ -2228,7 +2228,7 @@ def __init__(
         self.local_nodes = local_nodes
         self.is_imported = is_imported
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_reveal_expr(self)
 
 
@@ -2249,7 +2249,7 @@ def __init__(self, name: str, call: CallExpr) -> None:
         self.call = call
         self.info = None
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_super_expr(self)
 
 
@@ -2270,7 +2270,7 @@ def expr(self) -> Expression:
         assert expr is not None  # lambda can't have empty body
         return expr
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_lambda_expr(self)
 
     def is_dynamic(self) -> bool:
@@ -2290,7 +2290,7 @@ def __init__(self, items: list[Expression]) -> None:
         super().__init__()
         self.items = items
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_list_expr(self)
 
 
@@ -2307,7 +2307,7 @@ def __init__(self, items: list[tuple[Expression | None, Expression]]) -> None:
         super().__init__()
         self.items = items
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_dict_expr(self)
 
 
@@ -2326,7 +2326,7 @@ def __init__(self, items: list[Expression]) -> None:
         super().__init__()
         self.items = items
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_tuple_expr(self)
 
 
@@ -2343,7 +2343,7 @@ def __init__(self, items: list[Expression]) -> None:
         super().__init__()
         self.items = items
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_set_expr(self)
 
 
@@ -2375,7 +2375,7 @@ def __init__(
         self.indices = indices
         self.is_async = is_async
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_generator_expr(self)
 
 
@@ -2392,7 +2392,7 @@ def __init__(self, generator: GeneratorExpr) -> None:
         super().__init__()
         self.generator = generator
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_list_comprehension(self)
 
 
@@ -2409,7 +2409,7 @@ def __init__(self, generator: GeneratorExpr) -> None:
         super().__init__()
         self.generator = generator
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_set_comprehension(self)
 
 
@@ -2444,7 +2444,7 @@ def __init__(
         self.indices = indices
         self.is_async = is_async
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_dictionary_comprehension(self)
 
 
@@ -2465,7 +2465,7 @@ def __init__(self, cond: Expression, if_expr: Expression, else_expr: Expression)
         self.if_expr = if_expr
         self.else_expr = else_expr
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_conditional_expr(self)
 
 
@@ -2484,7 +2484,7 @@ def __init__(self, expr: Expression, types: list[mypy.types.Type]) -> None:
         self.expr = expr
         self.types = types
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_type_application(self)
 
 
@@ -2586,7 +2586,7 @@ def __init__(
         super().__init__(name, fullname, upper_bound, default, variance, is_new_style, line=line)
         self.values = values
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_type_var_expr(self)
 
     def serialize(self) -> JsonDict:
@@ -2618,7 +2618,7 @@ class ParamSpecExpr(TypeVarLikeExpr):
 
     __match_args__ = ("name", "upper_bound", "default")
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_paramspec_expr(self)
 
     def serialize(self) -> JsonDict:
@@ -2666,7 +2666,7 @@ def __init__(
         super().__init__(name, fullname, upper_bound, default, variance, is_new_style, line=line)
         self.tuple_fallback = tuple_fallback
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_type_var_tuple_expr(self)
 
     def serialize(self) -> JsonDict:
@@ -2706,7 +2706,7 @@ def __init__(self, node: TypeAlias) -> None:
         super().__init__()
         self.node = node
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_type_alias_expr(self)
 
 
@@ -2727,7 +2727,7 @@ def __init__(self, info: TypeInfo, is_typed: bool = False) -> None:
         self.info = info
         self.is_typed = is_typed
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_namedtuple_expr(self)
 
 
@@ -2745,7 +2745,7 @@ def __init__(self, info: TypeInfo) -> None:
         super().__init__()
         self.info = info
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_typeddict_expr(self)
 
 
@@ -2768,7 +2768,7 @@ def __init__(self, info: TypeInfo, items: list[str], values: list[Expression | N
         self.items = items
         self.values = values
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_enum_call_expr(self)
 
 
@@ -2783,7 +2783,7 @@ def __init__(self, type: mypy.types.ProperType) -> None:
         super().__init__()
         self.type = type
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit__promote_expr(self)
 
 
@@ -2808,7 +2808,7 @@ def __init__(
         self.old_type = old_type
         self.info = None
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_newtype_expr(self)
 
 
@@ -2825,7 +2825,7 @@ def __init__(self, expr: Expression) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_await_expr(self)
 
 
@@ -2861,7 +2861,7 @@ def __init__(
     def __repr__(self) -> str:
         return "TempNode:%d(%s)" % (self.line, str(self.type))
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
         return visitor.visit_temp_node(self)
 
 
@@ -3705,7 +3705,7 @@ def serialize(self) -> JsonDict:
         }
         return data
 
-    def accept(self, visitor: NodeVisitor[T]) -> T:
+    def accept(self, visitor: NodeVisitor[T]) -> T | None:
         return visitor.visit_type_alias(self)
 
     @classmethod
@@ -3802,7 +3802,7 @@ def fullname(self) -> str:
     def serialize(self) -> JsonDict:
         assert False, "PlaceholderNode can't be serialized"
 
-    def accept(self, visitor: NodeVisitor[T]) -> T:
+    def accept(self, visitor: NodeVisitor[T]) -> T | None:
         return visitor.visit_placeholder_node(self)
 
 
diff --git a/mypy/patterns.py b/mypy/patterns.py
index a01bf6acc876..47a290f60902 100644
--- a/mypy/patterns.py
+++ b/mypy/patterns.py
@@ -18,7 +18,7 @@ class Pattern(Node):
 
     __slots__ = ()
 
-    def accept(self, visitor: PatternVisitor[T]) -> T:
+    def accept(self, visitor: PatternVisitor[T]) -> T | None:
         raise RuntimeError("Not implemented", type(self))
 
 
@@ -38,7 +38,7 @@ def __init__(self, pattern: Pattern | None, name: NameExpr | None) -> None:
         self.pattern = pattern
         self.name = name
 
-    def accept(self, visitor: PatternVisitor[T]) -> T:
+    def accept(self, visitor: PatternVisitor[T]) -> T | None:
         return visitor.visit_as_pattern(self)
 
 
@@ -51,7 +51,7 @@ def __init__(self, patterns: list[Pattern]) -> None:
         super().__init__()
         self.patterns = patterns
 
-    def accept(self, visitor: PatternVisitor[T]) -> T:
+    def accept(self, visitor: PatternVisitor[T]) -> T | None:
         return visitor.visit_or_pattern(self)
 
 
@@ -64,7 +64,7 @@ def __init__(self, expr: Expression) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: PatternVisitor[T]) -> T:
+    def accept(self, visitor: PatternVisitor[T]) -> T | None:
         return visitor.visit_value_pattern(self)
 
 
@@ -76,7 +76,7 @@ def __init__(self, value: bool | None) -> None:
         super().__init__()
         self.value = value
 
-    def accept(self, visitor: PatternVisitor[T]) -> T:
+    def accept(self, visitor: PatternVisitor[T]) -> T | None:
         return visitor.visit_singleton_pattern(self)
 
 
@@ -89,7 +89,7 @@ def __init__(self, patterns: list[Pattern]) -> None:
         super().__init__()
         self.patterns = patterns
 
-    def accept(self, visitor: PatternVisitor[T]) -> T:
+    def accept(self, visitor: PatternVisitor[T]) -> T | None:
         return visitor.visit_sequence_pattern(self)
 
 
@@ -102,7 +102,7 @@ def __init__(self, capture: NameExpr | None) -> None:
         super().__init__()
         self.capture = capture
 
-    def accept(self, visitor: PatternVisitor[T]) -> T:
+    def accept(self, visitor: PatternVisitor[T]) -> T | None:
         return visitor.visit_starred_pattern(self)
 
 
@@ -120,7 +120,7 @@ def __init__(
         self.values = values
         self.rest = rest
 
-    def accept(self, visitor: PatternVisitor[T]) -> T:
+    def accept(self, visitor: PatternVisitor[T]) -> T | None:
         return visitor.visit_mapping_pattern(self)
 
 
@@ -146,5 +146,5 @@ def __init__(
         self.keyword_keys = keyword_keys
         self.keyword_values = keyword_values
 
-    def accept(self, visitor: PatternVisitor[T]) -> T:
+    def accept(self, visitor: PatternVisitor[T]) -> T | None:
         return visitor.visit_class_pattern(self)
diff --git a/mypy/strconv.py b/mypy/strconv.py
index 3e9d37586f72..2102c76c66c4 100644
--- a/mypy/strconv.py
+++ b/mypy/strconv.py
@@ -182,7 +182,8 @@ def visit_class_def(self, o: mypy.nodes.ClassDef) -> str:
         if o.type_vars:
             a.insert(1, ("TypeVars", o.type_vars))
         if o.metaclass:
-            a.insert(1, f"Metaclass({o.metaclass.accept(self)})")
+            inner = o.metaclass.accept(self)
+            a.insert(1, f"Metaclass({inner})")
         if o.decorators:
             a.insert(1, ("Decorators", o.decorators))
         if o.info and o.info._promote:
@@ -430,13 +431,16 @@ def visit_yield_expr(self, o: mypy.nodes.YieldExpr) -> str:
 
     def visit_yield_from_expr(self, o: mypy.nodes.YieldFromExpr) -> str:
         if o.expr:
-            return self.dump([o.expr.accept(self)], o)
+            inner = o.expr.accept(self)
+            return self.dump([inner], o)
         else:
             return self.dump([], o)
 
     def visit_call_expr(self, o: mypy.nodes.CallExpr) -> str:
         if o.analyzed:
-            return o.analyzed.accept(self)
+            result = o.analyzed.accept(self)
+            assert result is not None
+            return result
         args: list[mypy.nodes.Expression] = []
         extra: list[str | tuple[str, list[Any]]] = []
         for i, kind in enumerate(o.arg_kinds):
@@ -455,7 +459,9 @@ def visit_call_expr(self, o: mypy.nodes.CallExpr) -> str:
 
     def visit_op_expr(self, o: mypy.nodes.OpExpr) -> str:
         if o.analyzed:
-            return o.analyzed.accept(self)
+            result = o.analyzed.accept(self)
+            assert result is not None
+            return result
         return self.dump([o.op, o.left, o.right], o)
 
     def visit_comparison_expr(self, o: mypy.nodes.ComparisonExpr) -> str:
@@ -494,7 +500,9 @@ def visit_tuple_expr(self, o: mypy.nodes.TupleExpr) -> str:
 
     def visit_index_expr(self, o: mypy.nodes.IndexExpr) -> str:
         if o.analyzed:
-            return o.analyzed.accept(self)
+            result = o.analyzed.accept(self)
+            assert result is not None
+            return result
         return self.dump([o.base, o.index], o)
 
     def visit_super_expr(self, o: mypy.nodes.SuperExpr) -> str:
@@ -653,7 +661,9 @@ def dump_tagged(nodes: Sequence[object], tag: str | None, str_conv: StrConv) ->
             s = dump_tagged(n[1], n[0], str_conv)
             a.append(indent(s, 2))
         elif isinstance(n, mypy.nodes.Node):
-            a.append(indent(n.accept(str_conv), 2))
+            indented = n.accept(str_conv)
+            assert indented is not None
+            a.append(indent(indented, 2))
         elif isinstance(n, Type):
             a.append(
                 indent(n.accept(TypeStrVisitor(str_conv.id_mapper, options=str_conv.options)), 2)
diff --git a/mypy/stubgen.py b/mypy/stubgen.py
index 1f8a1a4740f1..9df68b762eee 100755
--- a/mypy/stubgen.py
+++ b/mypy/stubgen.py
@@ -285,14 +285,16 @@ def visit_call_expr(self, node: CallExpr) -> str:
         callee = node.callee.accept(self)
         args = []
         for name, arg, kind in zip(node.arg_names, node.args, node.arg_kinds):
+            arg_str = arg.accept(self)
+            assert arg_str is not None
             if kind == ARG_POS:
-                args.append(arg.accept(self))
+                args.append(arg_str)
             elif kind == ARG_STAR:
-                args.append("*" + arg.accept(self))
+                args.append("*" + arg_str)
             elif kind == ARG_STAR2:
-                args.append("**" + arg.accept(self))
+                args.append("**" + arg_str)
             elif kind == ARG_NAMED:
-                args.append(f"{name}={arg.accept(self)}")
+                args.append(f"{name}={arg_str}")
             else:
                 raise ValueError(f"Unknown argument kind {kind} in call")
         return f"{callee}({', '.join(args)})"
@@ -335,41 +337,65 @@ def visit_index_expr(self, node: IndexExpr) -> str:
         base_fullname = self.stubgen.get_fullname(node.base)
         if base_fullname == "typing.Union":
             if isinstance(node.index, TupleExpr):
-                return " | ".join([item.accept(self) for item in node.index.items])
-            return node.index.accept(self)
+                items = []
+                for item in node.index.items:
+                    item_str = item.accept(self)
+                    assert item_str is not None
+                    items.append(item_str)
+                return " | ".join(items)
+            result = node.index.accept(self)
+            assert result is not None
+            return result
         if base_fullname == "typing.Optional":
             if isinstance(node.index, TupleExpr):
                 return self.stubgen.add_name("_typeshed.Incomplete")
-            return f"{node.index.accept(self)} | None"
+            inner = node.index.accept(self)
+            return f"{inner} | None"
         base = node.base.accept(self)
         index = node.index.accept(self)
+        assert index is not None
         if len(index) > 2 and index.startswith("(") and index.endswith(")"):
             index = index[1:-1].rstrip(",")
         return f"{base}[{index}]"
 
     def visit_tuple_expr(self, node: TupleExpr) -> str:
         suffix = "," if len(node.items) == 1 else ""
-        return f"({', '.join(n.accept(self) for n in node.items)}{suffix})"
+        items = []
+        for item in node.items:
+            item_str = item.accept(self)
+            assert item_str is not None
+            items.append(item_str)
+        return f"({', '.join(items)}{suffix})"
 
     def visit_list_expr(self, node: ListExpr) -> str:
-        return f"[{', '.join(n.accept(self) for n in node.items)}]"
+        items = []
+        for item in node.items:
+            item_str = item.accept(self)
+            assert item_str is not None
+            items.append(item_str)
+        return f"[{', '.join(items)}]"
 
     def visit_dict_expr(self, o: DictExpr) -> str:
         dict_items = []
         for key, value in o.items:
             # This is currently only used for TypedDict where all keys are strings.
             assert isinstance(key, StrExpr)
-            dict_items.append(f"{key.accept(self)}: {value.accept(self)}")
+            inner1 = key.accept(self)
+            inner2 = value.accept(self)
+            dict_items.append(f"{inner1}: {inner2}")
         return f"{{{', '.join(dict_items)}}}"
 
     def visit_ellipsis(self, node: EllipsisExpr) -> str:
         return "..."
 
     def visit_op_expr(self, o: OpExpr) -> str:
-        return f"{o.left.accept(self)} {o.op} {o.right.accept(self)}"
+        inner1 = o.left.accept(self)
+        inner2 = o.right.accept(self)
+        return f"{inner1} {o.op} {inner2}"
 
     def visit_star_expr(self, o: StarExpr) -> str:
-        return f"*{o.expr.accept(self)}"
+        inner = o.expr.accept(self)
+        return f"*{inner}"
 
     def visit_lambda_expr(self, o: LambdaExpr) -> str:
         # TODO: Required for among other things dataclass.field default_factory
@@ -754,7 +780,8 @@ def process_decorator(self, o: Decorator) -> None:
                 self.add_decorator(qualname, require_name=False)
             elif fullname in DATACLASS_TRANSFORM_NAMES:
                 p = AliasPrinter(self)
-                self._decorators.append(f"@{decorator.accept(p)}")
+                inner = decorator.accept(p)
+                self._decorators.append(f"@{inner}")
 
     def get_fullname(self, expr: Expression) -> str:
         """Return the expression's full name."""
@@ -787,7 +814,7 @@ def visit_class_def(self, o: ClassDef) -> None:
             self.processing_enum = True
         if isinstance(o.metaclass, (NameExpr, MemberExpr)):
             meta = o.metaclass.accept(AliasPrinter(self))
-            base_types.append("metaclass=" + meta)
+            base_types.append(f"metaclass={meta}")
         elif self.analyzed and o.info.is_abstract and not o.info.is_protocol:
             base_types.append("metaclass=abc.ABCMeta")
             self.import_tracker.add_import("abc")
@@ -831,7 +858,9 @@ def get_base_types(self, cdef: ClassDef) -> list[str]:
                 if self.get_fullname(base) != "builtins.object":
                     base_types.append(get_qualified_name(base))
             elif isinstance(base, IndexExpr):
-                base_types.append(base.accept(p))
+                base_str = base.accept(p)
+                assert base_str is not None
+                base_types.append(base_str)
             elif isinstance(base, CallExpr):
                 # namedtuple(typename, fields), NamedTuple(typename, fields) calls can
                 # be used as a base class. The first argument is a string literal that
@@ -854,7 +883,9 @@ def get_base_types(self, cdef: ClassDef) -> list[str]:
                     namedtuple_name = self.add_name("typing.NamedTuple")
                     base_types.append(f"{namedtuple_name}({typename!r}, [{fields_str}])")
                 elif self.is_typed_namedtuple(base):
-                    base_types.append(base.accept(p))
+                    base_str = base.accept(p)
+                    assert base_str is not None
+                    base_types.append(base_str)
                 else:
                     # At this point, we don't know what the base class is, so we
                     # just use Incomplete as the base class.
@@ -871,11 +902,15 @@ def get_class_decorators(self, cdef: ClassDef) -> list[str]:
         p = AliasPrinter(self)
         for d in cdef.decorators:
             if self.is_dataclass(d):
-                decorators.append(d.accept(p))
+                d_str = d.accept(p)
+                assert d_str is not None
+                decorators.append(d_str)
                 self.import_tracker.require_name(get_qualified_name(d))
                 self.processing_dataclass = True
             if self.is_dataclass_transform(d):
-                decorators.append(d.accept(p))
+                d_str = d.accept(p)
+                assert d_str is not None
+                decorators.append(d_str)
                 self.import_tracker.require_name(get_qualified_name(d))
         return decorators
 
@@ -986,7 +1021,9 @@ def _get_namedtuple_fields(self, call: CallExpr) -> list[tuple[str, str]] | None
                 field_name, field_type = field.items
                 if not isinstance(field_name, StrExpr):
                     return None
-                fields.append((field_name.value, field_type.accept(p)))
+                field_type_str = field_type.accept(p)
+                assert field_type_str is not None
+                fields.append((field_name.value, field_type_str))
             return fields
         else:
             return None  # Not a named tuple call
@@ -1056,13 +1093,15 @@ def process_typeddict(self, lvalue: NameExpr, rvalue: CallExpr) -> None:
         p = AliasPrinter(self)
         if any(not key.isidentifier() or keyword.iskeyword(key) for key, _ in items):
             # Keep the call syntax if there are non-identifier or reserved keyword keys.
-            self.add(f"{self._indent}{lvalue.name} = {rvalue.accept(p)}\n")
+            inner = rvalue.accept(p)
+            self.add(f"{self._indent}{lvalue.name} = {inner}\n")
             self._state = VAR
         else:
             bases = self.add_name("typing_extensions.TypedDict")
             # TODO: Add support for generic TypedDicts. Requires `Generic` as base class.
             if total is not None:
-                bases += f", total={total.accept(p)}"
+                inner = total.accept(p)
+                bases += f", total={inner}"
             class_def = f"{self._indent}class {lvalue.name}({bases}):"
             if len(items) == 0:
                 self.add(f"{class_def} ...\n")
@@ -1072,7 +1111,8 @@ def process_typeddict(self, lvalue: NameExpr, rvalue: CallExpr) -> None:
                     self.add("\n")
                 self.add(f"{class_def}\n")
                 for key, key_type in items:
-                    self.add(f"{self._indent}    {key}: {key_type.accept(p)}\n")
+                    inner = key_type.accept(p)
+                    self.add(f"{self._indent}    {key}: {inner}\n")
                 self._state = CLASS
 
     def annotate_as_incomplete(self, lvalue: NameExpr) -> None:
@@ -1144,7 +1184,8 @@ def is_alias_expression(self, expr: Expression, top_level: bool = True) -> bool:
 
     def process_typealias(self, lvalue: NameExpr, rvalue: Expression) -> None:
         p = AliasPrinter(self)
-        self.add(f"{self._indent}{lvalue.name} = {rvalue.accept(p)}\n")
+        inner = rvalue.accept(p)
+        self.add(f"{self._indent}{lvalue.name} = {inner}\n")
         self.record_name(lvalue.name)
         self._vars[-1].append(lvalue.name)
 
@@ -1154,7 +1195,8 @@ def visit_type_alias_stmt(self, o: TypeAliasStmt) -> None:
         name = o.name.name
         rvalue = o.value.expr()
         type_args = self.format_type_args(o)
-        self.add(f"{self._indent}type {name}{type_args} = {rvalue.accept(p)}\n")
+        inner = rvalue.accept(p)
+        self.add(f"{self._indent}type {name}{type_args} = {inner}\n")
         self.record_name(name)
         self._vars[-1].append(name)
 
@@ -1275,7 +1317,8 @@ def get_assign_initializer(self, rvalue: Expression) -> str:
                 fullname = self.get_fullname(rvalue.callee)
                 if fullname in (self.dataclass_field_specifier or DATACLASS_FIELD_SPECIFIERS):
                     p = AliasPrinter(self)
-                    return f" = {rvalue.accept(p)}"
+                    inner = rvalue.accept(p)
+                    return f" = {inner}"
             if not (isinstance(rvalue, TempNode) and rvalue.no_rhs):
                 return " = ..."
         # TODO: support other possible cases, where initializer is important
diff --git a/mypy/test/testmerge.py b/mypy/test/testmerge.py
index 0582c9ed5882..65d1ca8d1ed1 100644
--- a/mypy/test/testmerge.py
+++ b/mypy/test/testmerge.py
@@ -150,6 +150,7 @@ def dump_asts(self, modules: dict[str, MypyFile]) -> list[str]:
         a = []
         for m in sorted(modules):
             s = modules[m].accept(self.str_conv)
+            assert s is not None
             a.extend(s.splitlines())
         return a
 
diff --git a/mypy/treetransform.py b/mypy/treetransform.py
index 3e5a7ef3f2ca..ec488fd89d39 100644
--- a/mypy/treetransform.py
+++ b/mypy/treetransform.py
@@ -695,6 +695,7 @@ def visit_temp_node(self, node: TempNode) -> TempNode:
 
     def node(self, node: Node) -> Node:
         new = node.accept(self)
+        assert new is not None
         new.set_line(node)
         return new
 
diff --git a/mypy/visitor.py b/mypy/visitor.py
index 6613b6cbb144..52d386fec708 100644
--- a/mypy/visitor.py
+++ b/mypy/visitor.py
@@ -20,179 +20,179 @@
 @mypyc_attr(allow_interpreted_subclasses=True)
 class ExpressionVisitor(Generic[T]):
     @abstractmethod
-    def visit_int_expr(self, o: mypy.nodes.IntExpr, /) -> T:
+    def visit_int_expr(self, o: mypy.nodes.IntExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_str_expr(self, o: mypy.nodes.StrExpr, /) -> T:
+    def visit_str_expr(self, o: mypy.nodes.StrExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_bytes_expr(self, o: mypy.nodes.BytesExpr, /) -> T:
+    def visit_bytes_expr(self, o: mypy.nodes.BytesExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_float_expr(self, o: mypy.nodes.FloatExpr, /) -> T:
+    def visit_float_expr(self, o: mypy.nodes.FloatExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_complex_expr(self, o: mypy.nodes.ComplexExpr, /) -> T:
+    def visit_complex_expr(self, o: mypy.nodes.ComplexExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_ellipsis(self, o: mypy.nodes.EllipsisExpr, /) -> T:
+    def visit_ellipsis(self, o: mypy.nodes.EllipsisExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_star_expr(self, o: mypy.nodes.StarExpr, /) -> T:
+    def visit_star_expr(self, o: mypy.nodes.StarExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_name_expr(self, o: mypy.nodes.NameExpr, /) -> T:
+    def visit_name_expr(self, o: mypy.nodes.NameExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_member_expr(self, o: mypy.nodes.MemberExpr, /) -> T:
+    def visit_member_expr(self, o: mypy.nodes.MemberExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_yield_from_expr(self, o: mypy.nodes.YieldFromExpr, /) -> T:
+    def visit_yield_from_expr(self, o: mypy.nodes.YieldFromExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_yield_expr(self, o: mypy.nodes.YieldExpr, /) -> T:
+    def visit_yield_expr(self, o: mypy.nodes.YieldExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_call_expr(self, o: mypy.nodes.CallExpr, /) -> T:
+    def visit_call_expr(self, o: mypy.nodes.CallExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_op_expr(self, o: mypy.nodes.OpExpr, /) -> T:
+    def visit_op_expr(self, o: mypy.nodes.OpExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_comparison_expr(self, o: mypy.nodes.ComparisonExpr, /) -> T:
+    def visit_comparison_expr(self, o: mypy.nodes.ComparisonExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_cast_expr(self, o: mypy.nodes.CastExpr, /) -> T:
+    def visit_cast_expr(self, o: mypy.nodes.CastExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_assert_type_expr(self, o: mypy.nodes.AssertTypeExpr, /) -> T:
+    def visit_assert_type_expr(self, o: mypy.nodes.AssertTypeExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_reveal_expr(self, o: mypy.nodes.RevealExpr, /) -> T:
+    def visit_reveal_expr(self, o: mypy.nodes.RevealExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_super_expr(self, o: mypy.nodes.SuperExpr, /) -> T:
+    def visit_super_expr(self, o: mypy.nodes.SuperExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_unary_expr(self, o: mypy.nodes.UnaryExpr, /) -> T:
+    def visit_unary_expr(self, o: mypy.nodes.UnaryExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_assignment_expr(self, o: mypy.nodes.AssignmentExpr, /) -> T:
+    def visit_assignment_expr(self, o: mypy.nodes.AssignmentExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_list_expr(self, o: mypy.nodes.ListExpr, /) -> T:
+    def visit_list_expr(self, o: mypy.nodes.ListExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_dict_expr(self, o: mypy.nodes.DictExpr, /) -> T:
+    def visit_dict_expr(self, o: mypy.nodes.DictExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_tuple_expr(self, o: mypy.nodes.TupleExpr, /) -> T:
+    def visit_tuple_expr(self, o: mypy.nodes.TupleExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_set_expr(self, o: mypy.nodes.SetExpr, /) -> T:
+    def visit_set_expr(self, o: mypy.nodes.SetExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_index_expr(self, o: mypy.nodes.IndexExpr, /) -> T:
+    def visit_index_expr(self, o: mypy.nodes.IndexExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_type_application(self, o: mypy.nodes.TypeApplication, /) -> T:
+    def visit_type_application(self, o: mypy.nodes.TypeApplication, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_lambda_expr(self, o: mypy.nodes.LambdaExpr, /) -> T:
+    def visit_lambda_expr(self, o: mypy.nodes.LambdaExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_list_comprehension(self, o: mypy.nodes.ListComprehension, /) -> T:
+    def visit_list_comprehension(self, o: mypy.nodes.ListComprehension, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_set_comprehension(self, o: mypy.nodes.SetComprehension, /) -> T:
+    def visit_set_comprehension(self, o: mypy.nodes.SetComprehension, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_dictionary_comprehension(self, o: mypy.nodes.DictionaryComprehension, /) -> T:
+    def visit_dictionary_comprehension(self, o: mypy.nodes.DictionaryComprehension, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_generator_expr(self, o: mypy.nodes.GeneratorExpr, /) -> T:
+    def visit_generator_expr(self, o: mypy.nodes.GeneratorExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_slice_expr(self, o: mypy.nodes.SliceExpr, /) -> T:
+    def visit_slice_expr(self, o: mypy.nodes.SliceExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_conditional_expr(self, o: mypy.nodes.ConditionalExpr, /) -> T:
+    def visit_conditional_expr(self, o: mypy.nodes.ConditionalExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_type_var_expr(self, o: mypy.nodes.TypeVarExpr, /) -> T:
+    def visit_type_var_expr(self, o: mypy.nodes.TypeVarExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_paramspec_expr(self, o: mypy.nodes.ParamSpecExpr, /) -> T:
+    def visit_paramspec_expr(self, o: mypy.nodes.ParamSpecExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_type_var_tuple_expr(self, o: mypy.nodes.TypeVarTupleExpr, /) -> T:
+    def visit_type_var_tuple_expr(self, o: mypy.nodes.TypeVarTupleExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_type_alias_expr(self, o: mypy.nodes.TypeAliasExpr, /) -> T:
+    def visit_type_alias_expr(self, o: mypy.nodes.TypeAliasExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_namedtuple_expr(self, o: mypy.nodes.NamedTupleExpr, /) -> T:
+    def visit_namedtuple_expr(self, o: mypy.nodes.NamedTupleExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_enum_call_expr(self, o: mypy.nodes.EnumCallExpr, /) -> T:
+    def visit_enum_call_expr(self, o: mypy.nodes.EnumCallExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_typeddict_expr(self, o: mypy.nodes.TypedDictExpr, /) -> T:
+    def visit_typeddict_expr(self, o: mypy.nodes.TypedDictExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_newtype_expr(self, o: mypy.nodes.NewTypeExpr, /) -> T:
+    def visit_newtype_expr(self, o: mypy.nodes.NewTypeExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit__promote_expr(self, o: mypy.nodes.PromoteExpr, /) -> T:
+    def visit__promote_expr(self, o: mypy.nodes.PromoteExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_await_expr(self, o: mypy.nodes.AwaitExpr, /) -> T:
+    def visit_await_expr(self, o: mypy.nodes.AwaitExpr, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_temp_node(self, o: mypy.nodes.TempNode, /) -> T:
+    def visit_temp_node(self, o: mypy.nodes.TempNode, /) -> T | None:
         pass
 
 
@@ -202,115 +202,115 @@ class StatementVisitor(Generic[T]):
     # Definitions
 
     @abstractmethod
-    def visit_assignment_stmt(self, o: mypy.nodes.AssignmentStmt, /) -> T:
+    def visit_assignment_stmt(self, o: mypy.nodes.AssignmentStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_for_stmt(self, o: mypy.nodes.ForStmt, /) -> T:
+    def visit_for_stmt(self, o: mypy.nodes.ForStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_with_stmt(self, o: mypy.nodes.WithStmt, /) -> T:
+    def visit_with_stmt(self, o: mypy.nodes.WithStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_del_stmt(self, o: mypy.nodes.DelStmt, /) -> T:
+    def visit_del_stmt(self, o: mypy.nodes.DelStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_func_def(self, o: mypy.nodes.FuncDef, /) -> T:
+    def visit_func_def(self, o: mypy.nodes.FuncDef, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_overloaded_func_def(self, o: mypy.nodes.OverloadedFuncDef, /) -> T:
+    def visit_overloaded_func_def(self, o: mypy.nodes.OverloadedFuncDef, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_class_def(self, o: mypy.nodes.ClassDef, /) -> T:
+    def visit_class_def(self, o: mypy.nodes.ClassDef, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_global_decl(self, o: mypy.nodes.GlobalDecl, /) -> T:
+    def visit_global_decl(self, o: mypy.nodes.GlobalDecl, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_nonlocal_decl(self, o: mypy.nodes.NonlocalDecl, /) -> T:
+    def visit_nonlocal_decl(self, o: mypy.nodes.NonlocalDecl, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_decorator(self, o: mypy.nodes.Decorator, /) -> T:
+    def visit_decorator(self, o: mypy.nodes.Decorator, /) -> T | None:
         pass
 
     # Module structure
 
     @abstractmethod
-    def visit_import(self, o: mypy.nodes.Import, /) -> T:
+    def visit_import(self, o: mypy.nodes.Import, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_import_from(self, o: mypy.nodes.ImportFrom, /) -> T:
+    def visit_import_from(self, o: mypy.nodes.ImportFrom, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_import_all(self, o: mypy.nodes.ImportAll, /) -> T:
+    def visit_import_all(self, o: mypy.nodes.ImportAll, /) -> T | None:
         pass
 
     # Statements
 
     @abstractmethod
-    def visit_block(self, o: mypy.nodes.Block, /) -> T:
+    def visit_block(self, o: mypy.nodes.Block, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_expression_stmt(self, o: mypy.nodes.ExpressionStmt, /) -> T:
+    def visit_expression_stmt(self, o: mypy.nodes.ExpressionStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_operator_assignment_stmt(self, o: mypy.nodes.OperatorAssignmentStmt, /) -> T:
+    def visit_operator_assignment_stmt(self, o: mypy.nodes.OperatorAssignmentStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_while_stmt(self, o: mypy.nodes.WhileStmt, /) -> T:
+    def visit_while_stmt(self, o: mypy.nodes.WhileStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_return_stmt(self, o: mypy.nodes.ReturnStmt, /) -> T:
+    def visit_return_stmt(self, o: mypy.nodes.ReturnStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_assert_stmt(self, o: mypy.nodes.AssertStmt, /) -> T:
+    def visit_assert_stmt(self, o: mypy.nodes.AssertStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_if_stmt(self, o: mypy.nodes.IfStmt, /) -> T:
+    def visit_if_stmt(self, o: mypy.nodes.IfStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_break_stmt(self, o: mypy.nodes.BreakStmt, /) -> T:
+    def visit_break_stmt(self, o: mypy.nodes.BreakStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_continue_stmt(self, o: mypy.nodes.ContinueStmt, /) -> T:
+    def visit_continue_stmt(self, o: mypy.nodes.ContinueStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_pass_stmt(self, o: mypy.nodes.PassStmt, /) -> T:
+    def visit_pass_stmt(self, o: mypy.nodes.PassStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_raise_stmt(self, o: mypy.nodes.RaiseStmt, /) -> T:
+    def visit_raise_stmt(self, o: mypy.nodes.RaiseStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_try_stmt(self, o: mypy.nodes.TryStmt, /) -> T:
+    def visit_try_stmt(self, o: mypy.nodes.TryStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_match_stmt(self, o: mypy.nodes.MatchStmt, /) -> T:
+    def visit_match_stmt(self, o: mypy.nodes.MatchStmt, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_type_alias_stmt(self, o: mypy.nodes.TypeAliasStmt, /) -> T:
+    def visit_type_alias_stmt(self, o: mypy.nodes.TypeAliasStmt, /) -> T | None:
         pass
 
 
@@ -318,35 +318,35 @@ def visit_type_alias_stmt(self, o: mypy.nodes.TypeAliasStmt, /) -> T:
 @mypyc_attr(allow_interpreted_subclasses=True)
 class PatternVisitor(Generic[T]):
     @abstractmethod
-    def visit_as_pattern(self, o: mypy.patterns.AsPattern, /) -> T:
+    def visit_as_pattern(self, o: mypy.patterns.AsPattern, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_or_pattern(self, o: mypy.patterns.OrPattern, /) -> T:
+    def visit_or_pattern(self, o: mypy.patterns.OrPattern, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_value_pattern(self, o: mypy.patterns.ValuePattern, /) -> T:
+    def visit_value_pattern(self, o: mypy.patterns.ValuePattern, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_singleton_pattern(self, o: mypy.patterns.SingletonPattern, /) -> T:
+    def visit_singleton_pattern(self, o: mypy.patterns.SingletonPattern, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_sequence_pattern(self, o: mypy.patterns.SequencePattern, /) -> T:
+    def visit_sequence_pattern(self, o: mypy.patterns.SequencePattern, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_starred_pattern(self, o: mypy.patterns.StarredPattern, /) -> T:
+    def visit_starred_pattern(self, o: mypy.patterns.StarredPattern, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_mapping_pattern(self, o: mypy.patterns.MappingPattern, /) -> T:
+    def visit_mapping_pattern(self, o: mypy.patterns.MappingPattern, /) -> T | None:
         pass
 
     @abstractmethod
-    def visit_class_pattern(self, o: mypy.patterns.ClassPattern, /) -> T:
+    def visit_class_pattern(self, o: mypy.patterns.ClassPattern, /) -> T | None:
         pass
 
 
@@ -358,271 +358,268 @@ class NodeVisitor(Generic[T], ExpressionVisitor[T], StatementVisitor[T], Pattern
     The T type argument specifies the return type of the visit
     methods. As all methods defined here return None by default,
     subclasses do not always need to override all the methods.
-
-    TODO: make the default return value explicit, then turn on
-          empty body checking in mypy_self_check.ini.
     """
 
     # Not in superclasses:
 
-    def visit_mypy_file(self, o: mypy.nodes.MypyFile, /) -> T:
+    def visit_mypy_file(self, o: mypy.nodes.MypyFile, /) -> T | None:
         pass
 
     # TODO: We have a visit_var method, but no visit_typeinfo or any
     # other non-Statement SymbolNode (accepting those will raise a
     # runtime error). Maybe this should be resolved in some direction.
-    def visit_var(self, o: mypy.nodes.Var, /) -> T:
+    def visit_var(self, o: mypy.nodes.Var, /) -> T | None:
         pass
 
     # Module structure
 
-    def visit_import(self, o: mypy.nodes.Import, /) -> T:
+    def visit_import(self, o: mypy.nodes.Import, /) -> T | None:
         pass
 
-    def visit_import_from(self, o: mypy.nodes.ImportFrom, /) -> T:
+    def visit_import_from(self, o: mypy.nodes.ImportFrom, /) -> T | None:
         pass
 
-    def visit_import_all(self, o: mypy.nodes.ImportAll, /) -> T:
+    def visit_import_all(self, o: mypy.nodes.ImportAll, /) -> T | None:
         pass
 
     # Definitions
 
-    def visit_func_def(self, o: mypy.nodes.FuncDef, /) -> T:
+    def visit_func_def(self, o: mypy.nodes.FuncDef, /) -> T | None:
         pass
 
-    def visit_overloaded_func_def(self, o: mypy.nodes.OverloadedFuncDef, /) -> T:
+    def visit_overloaded_func_def(self, o: mypy.nodes.OverloadedFuncDef, /) -> T | None:
         pass
 
-    def visit_class_def(self, o: mypy.nodes.ClassDef, /) -> T:
+    def visit_class_def(self, o: mypy.nodes.ClassDef, /) -> T | None:
         pass
 
-    def visit_global_decl(self, o: mypy.nodes.GlobalDecl, /) -> T:
+    def visit_global_decl(self, o: mypy.nodes.GlobalDecl, /) -> T | None:
         pass
 
-    def visit_nonlocal_decl(self, o: mypy.nodes.NonlocalDecl, /) -> T:
+    def visit_nonlocal_decl(self, o: mypy.nodes.NonlocalDecl, /) -> T | None:
         pass
 
-    def visit_decorator(self, o: mypy.nodes.Decorator, /) -> T:
+    def visit_decorator(self, o: mypy.nodes.Decorator, /) -> T | None:
         pass
 
-    def visit_type_alias(self, o: mypy.nodes.TypeAlias, /) -> T:
+    def visit_type_alias(self, o: mypy.nodes.TypeAlias, /) -> T | None:
         pass
 
-    def visit_placeholder_node(self, o: mypy.nodes.PlaceholderNode, /) -> T:
+    def visit_placeholder_node(self, o: mypy.nodes.PlaceholderNode, /) -> T | None:
         pass
 
     # Statements
 
-    def visit_block(self, o: mypy.nodes.Block, /) -> T:
+    def visit_block(self, o: mypy.nodes.Block, /) -> T | None:
         pass
 
-    def visit_expression_stmt(self, o: mypy.nodes.ExpressionStmt, /) -> T:
+    def visit_expression_stmt(self, o: mypy.nodes.ExpressionStmt, /) -> T | None:
         pass
 
-    def visit_assignment_stmt(self, o: mypy.nodes.AssignmentStmt, /) -> T:
+    def visit_assignment_stmt(self, o: mypy.nodes.AssignmentStmt, /) -> T | None:
         pass
 
-    def visit_operator_assignment_stmt(self, o: mypy.nodes.OperatorAssignmentStmt, /) -> T:
+    def visit_operator_assignment_stmt(self, o: mypy.nodes.OperatorAssignmentStmt, /) -> T | None:
         pass
 
-    def visit_while_stmt(self, o: mypy.nodes.WhileStmt, /) -> T:
+    def visit_while_stmt(self, o: mypy.nodes.WhileStmt, /) -> T | None:
         pass
 
-    def visit_for_stmt(self, o: mypy.nodes.ForStmt, /) -> T:
+    def visit_for_stmt(self, o: mypy.nodes.ForStmt, /) -> T | None:
         pass
 
-    def visit_return_stmt(self, o: mypy.nodes.ReturnStmt, /) -> T:
+    def visit_return_stmt(self, o: mypy.nodes.ReturnStmt, /) -> T | None:
         pass
 
-    def visit_assert_stmt(self, o: mypy.nodes.AssertStmt, /) -> T:
+    def visit_assert_stmt(self, o: mypy.nodes.AssertStmt, /) -> T | None:
         pass
 
-    def visit_del_stmt(self, o: mypy.nodes.DelStmt, /) -> T:
+    def visit_del_stmt(self, o: mypy.nodes.DelStmt, /) -> T | None:
         pass
 
-    def visit_if_stmt(self, o: mypy.nodes.IfStmt, /) -> T:
+    def visit_if_stmt(self, o: mypy.nodes.IfStmt, /) -> T | None:
         pass
 
-    def visit_break_stmt(self, o: mypy.nodes.BreakStmt, /) -> T:
+    def visit_break_stmt(self, o: mypy.nodes.BreakStmt, /) -> T | None:
         pass
 
-    def visit_continue_stmt(self, o: mypy.nodes.ContinueStmt, /) -> T:
+    def visit_continue_stmt(self, o: mypy.nodes.ContinueStmt, /) -> T | None:
         pass
 
-    def visit_pass_stmt(self, o: mypy.nodes.PassStmt, /) -> T:
+    def visit_pass_stmt(self, o: mypy.nodes.PassStmt, /) -> T | None:
         pass
 
-    def visit_raise_stmt(self, o: mypy.nodes.RaiseStmt, /) -> T:
+    def visit_raise_stmt(self, o: mypy.nodes.RaiseStmt, /) -> T | None:
         pass
 
-    def visit_try_stmt(self, o: mypy.nodes.TryStmt, /) -> T:
+    def visit_try_stmt(self, o: mypy.nodes.TryStmt, /) -> T | None:
         pass
 
-    def visit_with_stmt(self, o: mypy.nodes.WithStmt, /) -> T:
+    def visit_with_stmt(self, o: mypy.nodes.WithStmt, /) -> T | None:
         pass
 
-    def visit_match_stmt(self, o: mypy.nodes.MatchStmt, /) -> T:
+    def visit_match_stmt(self, o: mypy.nodes.MatchStmt, /) -> T | None:
         pass
 
-    def visit_type_alias_stmt(self, o: mypy.nodes.TypeAliasStmt, /) -> T:
+    def visit_type_alias_stmt(self, o: mypy.nodes.TypeAliasStmt, /) -> T | None:
         pass
 
     # Expressions (default no-op implementation)
 
-    def visit_int_expr(self, o: mypy.nodes.IntExpr, /) -> T:
+    def visit_int_expr(self, o: mypy.nodes.IntExpr, /) -> T | None:
         pass
 
-    def visit_str_expr(self, o: mypy.nodes.StrExpr, /) -> T:
+    def visit_str_expr(self, o: mypy.nodes.StrExpr, /) -> T | None:
         pass
 
-    def visit_bytes_expr(self, o: mypy.nodes.BytesExpr, /) -> T:
+    def visit_bytes_expr(self, o: mypy.nodes.BytesExpr, /) -> T | None:
         pass
 
-    def visit_float_expr(self, o: mypy.nodes.FloatExpr, /) -> T:
+    def visit_float_expr(self, o: mypy.nodes.FloatExpr, /) -> T | None:
         pass
 
-    def visit_complex_expr(self, o: mypy.nodes.ComplexExpr, /) -> T:
+    def visit_complex_expr(self, o: mypy.nodes.ComplexExpr, /) -> T | None:
         pass
 
-    def visit_ellipsis(self, o: mypy.nodes.EllipsisExpr, /) -> T:
+    def visit_ellipsis(self, o: mypy.nodes.EllipsisExpr, /) -> T | None:
         pass
 
-    def visit_star_expr(self, o: mypy.nodes.StarExpr, /) -> T:
+    def visit_star_expr(self, o: mypy.nodes.StarExpr, /) -> T | None:
         pass
 
-    def visit_name_expr(self, o: mypy.nodes.NameExpr, /) -> T:
+    def visit_name_expr(self, o: mypy.nodes.NameExpr, /) -> T | None:
         pass
 
-    def visit_member_expr(self, o: mypy.nodes.MemberExpr, /) -> T:
+    def visit_member_expr(self, o: mypy.nodes.MemberExpr, /) -> T | None:
         pass
 
-    def visit_yield_from_expr(self, o: mypy.nodes.YieldFromExpr, /) -> T:
+    def visit_yield_from_expr(self, o: mypy.nodes.YieldFromExpr, /) -> T | None:
         pass
 
-    def visit_yield_expr(self, o: mypy.nodes.YieldExpr, /) -> T:
+    def visit_yield_expr(self, o: mypy.nodes.YieldExpr, /) -> T | None:
         pass
 
-    def visit_call_expr(self, o: mypy.nodes.CallExpr, /) -> T:
+    def visit_call_expr(self, o: mypy.nodes.CallExpr, /) -> T | None:
         pass
 
-    def visit_op_expr(self, o: mypy.nodes.OpExpr, /) -> T:
+    def visit_op_expr(self, o: mypy.nodes.OpExpr, /) -> T | None:
         pass
 
-    def visit_comparison_expr(self, o: mypy.nodes.ComparisonExpr, /) -> T:
+    def visit_comparison_expr(self, o: mypy.nodes.ComparisonExpr, /) -> T | None:
         pass
 
-    def visit_cast_expr(self, o: mypy.nodes.CastExpr, /) -> T:
+    def visit_cast_expr(self, o: mypy.nodes.CastExpr, /) -> T | None:
         pass
 
-    def visit_assert_type_expr(self, o: mypy.nodes.AssertTypeExpr, /) -> T:
+    def visit_assert_type_expr(self, o: mypy.nodes.AssertTypeExpr, /) -> T | None:
         pass
 
-    def visit_reveal_expr(self, o: mypy.nodes.RevealExpr, /) -> T:
+    def visit_reveal_expr(self, o: mypy.nodes.RevealExpr, /) -> T | None:
         pass
 
-    def visit_super_expr(self, o: mypy.nodes.SuperExpr, /) -> T:
+    def visit_super_expr(self, o: mypy.nodes.SuperExpr, /) -> T | None:
         pass
 
-    def visit_assignment_expr(self, o: mypy.nodes.AssignmentExpr, /) -> T:
+    def visit_assignment_expr(self, o: mypy.nodes.AssignmentExpr, /) -> T | None:
         pass
 
-    def visit_unary_expr(self, o: mypy.nodes.UnaryExpr, /) -> T:
+    def visit_unary_expr(self, o: mypy.nodes.UnaryExpr, /) -> T | None:
         pass
 
-    def visit_list_expr(self, o: mypy.nodes.ListExpr, /) -> T:
+    def visit_list_expr(self, o: mypy.nodes.ListExpr, /) -> T | None:
         pass
 
-    def visit_dict_expr(self, o: mypy.nodes.DictExpr, /) -> T:
+    def visit_dict_expr(self, o: mypy.nodes.DictExpr, /) -> T | None:
         pass
 
-    def visit_tuple_expr(self, o: mypy.nodes.TupleExpr, /) -> T:
+    def visit_tuple_expr(self, o: mypy.nodes.TupleExpr, /) -> T | None:
         pass
 
-    def visit_set_expr(self, o: mypy.nodes.SetExpr, /) -> T:
+    def visit_set_expr(self, o: mypy.nodes.SetExpr, /) -> T | None:
         pass
 
-    def visit_index_expr(self, o: mypy.nodes.IndexExpr, /) -> T:
+    def visit_index_expr(self, o: mypy.nodes.IndexExpr, /) -> T | None:
         pass
 
-    def visit_type_application(self, o: mypy.nodes.TypeApplication, /) -> T:
+    def visit_type_application(self, o: mypy.nodes.TypeApplication, /) -> T | None:
         pass
 
-    def visit_lambda_expr(self, o: mypy.nodes.LambdaExpr, /) -> T:
+    def visit_lambda_expr(self, o: mypy.nodes.LambdaExpr, /) -> T | None:
         pass
 
-    def visit_list_comprehension(self, o: mypy.nodes.ListComprehension, /) -> T:
+    def visit_list_comprehension(self, o: mypy.nodes.ListComprehension, /) -> T | None:
         pass
 
-    def visit_set_comprehension(self, o: mypy.nodes.SetComprehension, /) -> T:
+    def visit_set_comprehension(self, o: mypy.nodes.SetComprehension, /) -> T | None:
         pass
 
-    def visit_dictionary_comprehension(self, o: mypy.nodes.DictionaryComprehension, /) -> T:
+    def visit_dictionary_comprehension(self, o: mypy.nodes.DictionaryComprehension, /) -> T | None:
         pass
 
-    def visit_generator_expr(self, o: mypy.nodes.GeneratorExpr, /) -> T:
+    def visit_generator_expr(self, o: mypy.nodes.GeneratorExpr, /) -> T | None:
         pass
 
-    def visit_slice_expr(self, o: mypy.nodes.SliceExpr, /) -> T:
+    def visit_slice_expr(self, o: mypy.nodes.SliceExpr, /) -> T | None:
         pass
 
-    def visit_conditional_expr(self, o: mypy.nodes.ConditionalExpr, /) -> T:
+    def visit_conditional_expr(self, o: mypy.nodes.ConditionalExpr, /) -> T | None:
         pass
 
-    def visit_type_var_expr(self, o: mypy.nodes.TypeVarExpr, /) -> T:
+    def visit_type_var_expr(self, o: mypy.nodes.TypeVarExpr, /) -> T | None:
         pass
 
-    def visit_paramspec_expr(self, o: mypy.nodes.ParamSpecExpr, /) -> T:
+    def visit_paramspec_expr(self, o: mypy.nodes.ParamSpecExpr, /) -> T | None:
         pass
 
-    def visit_type_var_tuple_expr(self, o: mypy.nodes.TypeVarTupleExpr, /) -> T:
+    def visit_type_var_tuple_expr(self, o: mypy.nodes.TypeVarTupleExpr, /) -> T | None:
         pass
 
-    def visit_type_alias_expr(self, o: mypy.nodes.TypeAliasExpr, /) -> T:
+    def visit_type_alias_expr(self, o: mypy.nodes.TypeAliasExpr, /) -> T | None:
         pass
 
-    def visit_namedtuple_expr(self, o: mypy.nodes.NamedTupleExpr, /) -> T:
+    def visit_namedtuple_expr(self, o: mypy.nodes.NamedTupleExpr, /) -> T | None:
         pass
 
-    def visit_enum_call_expr(self, o: mypy.nodes.EnumCallExpr, /) -> T:
+    def visit_enum_call_expr(self, o: mypy.nodes.EnumCallExpr, /) -> T | None:
         pass
 
-    def visit_typeddict_expr(self, o: mypy.nodes.TypedDictExpr, /) -> T:
+    def visit_typeddict_expr(self, o: mypy.nodes.TypedDictExpr, /) -> T | None:
         pass
 
-    def visit_newtype_expr(self, o: mypy.nodes.NewTypeExpr, /) -> T:
+    def visit_newtype_expr(self, o: mypy.nodes.NewTypeExpr, /) -> T | None:
         pass
 
-    def visit__promote_expr(self, o: mypy.nodes.PromoteExpr, /) -> T:
+    def visit__promote_expr(self, o: mypy.nodes.PromoteExpr, /) -> T | None:
         pass
 
-    def visit_await_expr(self, o: mypy.nodes.AwaitExpr, /) -> T:
+    def visit_await_expr(self, o: mypy.nodes.AwaitExpr, /) -> T | None:
         pass
 
-    def visit_temp_node(self, o: mypy.nodes.TempNode, /) -> T:
+    def visit_temp_node(self, o: mypy.nodes.TempNode, /) -> T | None:
         pass
 
     # Patterns
 
-    def visit_as_pattern(self, o: mypy.patterns.AsPattern, /) -> T:
+    def visit_as_pattern(self, o: mypy.patterns.AsPattern, /) -> T | None:
         pass
 
-    def visit_or_pattern(self, o: mypy.patterns.OrPattern, /) -> T:
+    def visit_or_pattern(self, o: mypy.patterns.OrPattern, /) -> T | None:
         pass
 
-    def visit_value_pattern(self, o: mypy.patterns.ValuePattern, /) -> T:
+    def visit_value_pattern(self, o: mypy.patterns.ValuePattern, /) -> T | None:
         pass
 
-    def visit_singleton_pattern(self, o: mypy.patterns.SingletonPattern, /) -> T:
+    def visit_singleton_pattern(self, o: mypy.patterns.SingletonPattern, /) -> T | None:
         pass
 
-    def visit_sequence_pattern(self, o: mypy.patterns.SequencePattern, /) -> T:
+    def visit_sequence_pattern(self, o: mypy.patterns.SequencePattern, /) -> T | None:
         pass
 
-    def visit_starred_pattern(self, o: mypy.patterns.StarredPattern, /) -> T:
+    def visit_starred_pattern(self, o: mypy.patterns.StarredPattern, /) -> T | None:
         pass
 
-    def visit_mapping_pattern(self, o: mypy.patterns.MappingPattern, /) -> T:
+    def visit_mapping_pattern(self, o: mypy.patterns.MappingPattern, /) -> T | None:
         pass
 
-    def visit_class_pattern(self, o: mypy.patterns.ClassPattern, /) -> T:
+    def visit_class_pattern(self, o: mypy.patterns.ClassPattern, /) -> T | None:
         pass
diff --git a/mypy_self_check.ini b/mypy_self_check.ini
index f54c1f17f025..7198a1f6f342 100644
--- a/mypy_self_check.ini
+++ b/mypy_self_check.ini
@@ -12,7 +12,3 @@ exclude = mypy/typeshed/|mypyc/test-data/|mypyc/lib-rt/
 enable_error_code = ignore-without-code,redundant-expr
 enable_incomplete_feature = PreciseTupleTypes
 show_error_code_links = True
-
-[mypy-mypy.visitor]
-# See docstring for NodeVisitor for motivation.
-disable_error_code = empty-body
diff --git a/mypyc/irbuild/builder.py b/mypyc/irbuild/builder.py
index b0597617bdc5..154e0cd9798e 100644
--- a/mypyc/irbuild/builder.py
+++ b/mypyc/irbuild/builder.py
@@ -274,6 +274,7 @@ def accept(self, node: Statement | Expression, *, can_borrow: bool = False) -> V
                 self.can_borrow = can_borrow
                 try:
                     res = node.accept(self.visitor)
+                    assert res is not None
                     res = self.coerce(res, self.node_type(node), node.line)
                 # If we hit an error during compilation, we want to
                 # keep trying, so we can produce more error
diff --git a/mypyc/irbuild/statement.py b/mypyc/irbuild/statement.py
index cdc1d54589eb..d5801dbcf619 100644
--- a/mypyc/irbuild/statement.py
+++ b/mypyc/irbuild/statement.py
@@ -1048,6 +1048,7 @@ def transform_type_alias_stmt(builder: IRBuilder, s: TypeAliasStmt) -> None:
     # The value needs to be lazily computed to match Python runtime behavior, but
     # Python public APIs don't support this, so we use a C primitive.
     compute_fn = s.value.accept(builder.visitor)
+    assert compute_fn is not None
     builder.builder.primitive_op(set_type_alias_compute_function_op, [alias, compute_fn], line)
 
     target = builder.get_assignment_target(s.name)

From d80e041db4034262aae5ff676f9727398c58c586 Mon Sep 17 00:00:00 2001
From: A5rocks <git@helvetica.moe>
Date: Tue, 28 Jan 2025 05:28:21 +0900
Subject: [PATCH 2/3] Revert "Make default return value for NodeVisitor
 explicitly optional"

This reverts commit 5d690beac48faf5e6d7f20deacffbc0e47dd1519.
---
 mypy/checkexpr.py          |   4 +-
 mypy/checkpattern.py       |   1 -
 mypy/nodes.py              | 156 +++++++++---------
 mypy/patterns.py           |  18 +-
 mypy/strconv.py            |  22 +--
 mypy/stubgen.py            |  93 +++--------
 mypy/test/testmerge.py     |   1 -
 mypy/treetransform.py      |   1 -
 mypy/visitor.py            | 327 +++++++++++++++++++------------------
 mypy_self_check.ini        |   4 +
 mypyc/irbuild/builder.py   |   1 -
 mypyc/irbuild/statement.py |   1 -
 12 files changed, 288 insertions(+), 341 deletions(-)

diff --git a/mypy/checkexpr.py b/mypy/checkexpr.py
index c4156e2c6cfa..a10dc00bb1de 100644
--- a/mypy/checkexpr.py
+++ b/mypy/checkexpr.py
@@ -5944,9 +5944,7 @@ def accept(
             elif allow_none_return and isinstance(node, AwaitExpr):
                 typ = self.visit_await_expr(node, allow_none_return=True)
             else:
-                typ_ = node.accept(self)
-                assert typ_ is not None
-                typ = typ_
+                typ = node.accept(self)
         except Exception as err:
             report_internal_error(
                 err, self.chk.errors.file, node.line, self.chk.errors, self.chk.options
diff --git a/mypy/checkpattern.py b/mypy/checkpattern.py
index cd47fb13df4c..4b34c0ddb54b 100644
--- a/mypy/checkpattern.py
+++ b/mypy/checkpattern.py
@@ -130,7 +130,6 @@ def accept(self, o: Pattern, type_context: Type) -> PatternType:
         result = o.accept(self)
         self.type_context.pop()
 
-        assert result is not None
         return result
 
     def visit_as_pattern(self, o: AsPattern) -> PatternType:
diff --git a/mypy/nodes.py b/mypy/nodes.py
index ee6431c179e5..b7b09f506c35 100644
--- a/mypy/nodes.py
+++ b/mypy/nodes.py
@@ -181,7 +181,7 @@ def str_with_options(self, options: Options) -> str:
         assert ans
         return ans
 
-    def accept(self, visitor: NodeVisitor[T]) -> T | None:
+    def accept(self, visitor: NodeVisitor[T]) -> T:
         raise RuntimeError("Not implemented", type(self))
 
 
@@ -191,7 +191,7 @@ class Statement(Node):
 
     __slots__ = ()
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         raise RuntimeError("Not implemented", type(self))
 
 
@@ -201,7 +201,7 @@ class Expression(Node):
 
     __slots__ = ()
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         raise RuntimeError("Not implemented", type(self))
 
 
@@ -355,7 +355,7 @@ def name(self) -> str:
     def fullname(self) -> str:
         return self._fullname
 
-    def accept(self, visitor: NodeVisitor[T]) -> T | None:
+    def accept(self, visitor: NodeVisitor[T]) -> T:
         return visitor.visit_mypy_file(self)
 
     def is_package_init_file(self) -> bool:
@@ -433,7 +433,7 @@ def __init__(self, ids: list[tuple[str, str | None]]) -> None:
         super().__init__()
         self.ids = ids
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_import(self)
 
 
@@ -454,7 +454,7 @@ def __init__(self, id: str, relative: int, names: list[tuple[str, str | None]])
         self.names = names
         self.relative = relative
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_import_from(self)
 
 
@@ -473,7 +473,7 @@ def __init__(self, id: str, relative: int) -> None:
         self.id = id
         self.relative = relative
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_import_all(self)
 
 
@@ -574,7 +574,7 @@ def name(self) -> str:
             assert self.impl is not None
             return self.impl.name
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_overloaded_func_def(self)
 
     def serialize(self) -> JsonDict:
@@ -807,7 +807,7 @@ def __init__(
     def name(self) -> str:
         return self._name
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_func_def(self)
 
     def serialize(self) -> JsonDict:
@@ -919,7 +919,7 @@ def info(self) -> TypeInfo:
     def type(self) -> mypy.types.Type | None:
         return self.var.type
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_decorator(self)
 
     def serialize(self) -> JsonDict:
@@ -1065,7 +1065,7 @@ def name(self) -> str:
     def fullname(self) -> str:
         return self._fullname
 
-    def accept(self, visitor: NodeVisitor[T]) -> T | None:
+    def accept(self, visitor: NodeVisitor[T]) -> T:
         return visitor.visit_var(self)
 
     def serialize(self) -> JsonDict:
@@ -1173,7 +1173,7 @@ def fullname(self) -> str:
     def fullname(self, v: str) -> None:
         self._fullname = v
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_class_def(self)
 
     def is_generic(self) -> bool:
@@ -1218,7 +1218,7 @@ def __init__(self, names: list[str]) -> None:
         super().__init__()
         self.names = names
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_global_decl(self)
 
 
@@ -1235,7 +1235,7 @@ def __init__(self, names: list[str]) -> None:
         super().__init__()
         self.names = names
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_nonlocal_decl(self)
 
 
@@ -1254,7 +1254,7 @@ def __init__(self, body: list[Statement], *, is_unreachable: bool = False) -> No
         # in those cases.
         self.is_unreachable = is_unreachable
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_block(self)
 
 
@@ -1274,7 +1274,7 @@ def __init__(self, expr: Expression) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_expression_stmt(self)
 
 
@@ -1341,7 +1341,7 @@ def __init__(
         self.is_final_def = False
         self.invalid_recursive_alias = False
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_assignment_stmt(self)
 
 
@@ -1362,7 +1362,7 @@ def __init__(self, op: str, lvalue: Lvalue, rvalue: Expression) -> None:
         self.lvalue = lvalue
         self.rvalue = rvalue
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_operator_assignment_stmt(self)
 
 
@@ -1381,7 +1381,7 @@ def __init__(self, expr: Expression, body: Block, else_body: Block | None) -> No
         self.body = body
         self.else_body = else_body
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_while_stmt(self)
 
 
@@ -1435,7 +1435,7 @@ def __init__(
         self.else_body = else_body
         self.is_async = False
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_for_stmt(self)
 
 
@@ -1450,7 +1450,7 @@ def __init__(self, expr: Expression | None) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_return_stmt(self)
 
 
@@ -1467,7 +1467,7 @@ def __init__(self, expr: Expression, msg: Expression | None = None) -> None:
         self.expr = expr
         self.msg = msg
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_assert_stmt(self)
 
 
@@ -1482,28 +1482,28 @@ def __init__(self, expr: Lvalue) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_del_stmt(self)
 
 
 class BreakStmt(Statement):
     __slots__ = ()
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_break_stmt(self)
 
 
 class ContinueStmt(Statement):
     __slots__ = ()
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_continue_stmt(self)
 
 
 class PassStmt(Statement):
     __slots__ = ()
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_pass_stmt(self)
 
 
@@ -1522,7 +1522,7 @@ def __init__(self, expr: list[Expression], body: list[Block], else_body: Block |
         self.body = body
         self.else_body = else_body
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_if_stmt(self)
 
 
@@ -1540,7 +1540,7 @@ def __init__(self, expr: Expression | None, from_expr: Expression | None) -> Non
         self.expr = expr
         self.from_expr = from_expr
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_raise_stmt(self)
 
 
@@ -1577,7 +1577,7 @@ def __init__(
         self.finally_body = finally_body
         self.is_star = False
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_try_stmt(self)
 
 
@@ -1610,7 +1610,7 @@ def __init__(
         self.body = body
         self.is_async = False
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_with_stmt(self)
 
 
@@ -1638,7 +1638,7 @@ def __init__(
         self.guards = guards
         self.bodies = bodies
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_match_stmt(self)
 
 
@@ -1661,7 +1661,7 @@ def __init__(self, name: NameExpr, type_args: list[TypeParam], value: LambdaExpr
         self.invalid_recursive_alias = False
         self.alias_node = None
 
-    def accept(self, visitor: StatementVisitor[T]) -> T | None:
+    def accept(self, visitor: StatementVisitor[T]) -> T:
         return visitor.visit_type_alias_stmt(self)
 
 
@@ -1681,7 +1681,7 @@ def __init__(self, value: int) -> None:
         super().__init__()
         self.value = value
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_int_expr(self)
 
 
@@ -1704,7 +1704,7 @@ def __init__(self, value: str) -> None:
         super().__init__()
         self.value = value
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_str_expr(self)
 
 
@@ -1734,7 +1734,7 @@ def __init__(self, value: str) -> None:
         super().__init__()
         self.value = value
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_bytes_expr(self)
 
 
@@ -1751,7 +1751,7 @@ def __init__(self, value: float) -> None:
         super().__init__()
         self.value = value
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_float_expr(self)
 
 
@@ -1768,7 +1768,7 @@ def __init__(self, value: complex) -> None:
         super().__init__()
         self.value = value
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_complex_expr(self)
 
 
@@ -1777,7 +1777,7 @@ class EllipsisExpr(Expression):
 
     __slots__ = ()
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_ellipsis(self)
 
 
@@ -1798,7 +1798,7 @@ def __init__(self, expr: Expression) -> None:
         # Whether this starred expression is used in a tuple/list and as lvalue
         self.valid = False
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_star_expr(self)
 
 
@@ -1863,7 +1863,7 @@ def __init__(self, name: str) -> None:
         # Is this a l.h.s. of a special form assignment like typed dict or type variable?
         self.is_special_form = False
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_name_expr(self)
 
     def serialize(self) -> JsonDict:
@@ -1885,7 +1885,7 @@ def __init__(self, expr: Expression, name: str) -> None:
         # The nodes of other kinds of member expressions are resolved during type checking.
         self.def_var: Var | None = None
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_member_expr(self)
 
 
@@ -1961,7 +1961,7 @@ def __init__(
         # cast(...) this is a CastExpr.
         self.analyzed = analyzed
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_call_expr(self)
 
 
@@ -1976,7 +1976,7 @@ def __init__(self, expr: Expression) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_yield_from_expr(self)
 
 
@@ -1991,7 +1991,7 @@ def __init__(self, expr: Expression | None) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_yield_expr(self)
 
 
@@ -2020,7 +2020,7 @@ def __init__(self, base: Expression, index: Expression) -> None:
         self.method_type = None
         self.analyzed = None
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_index_expr(self)
 
 
@@ -2042,7 +2042,7 @@ def __init__(self, op: str, expr: Expression) -> None:
         self.expr = expr
         self.method_type = None
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_unary_expr(self)
 
 
@@ -2058,7 +2058,7 @@ def __init__(self, target: Expression, value: Expression) -> None:
         self.target = target
         self.value = value
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_assignment_expr(self)
 
 
@@ -2104,7 +2104,7 @@ def __init__(
         self.right_unreachable = False
         self.analyzed = analyzed
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_op_expr(self)
 
 
@@ -2133,7 +2133,7 @@ def pairwise(self) -> Iterator[tuple[str, Expression, Expression]]:
         for i, operator in enumerate(self.operators):
             yield operator, self.operands[i], self.operands[i + 1]
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_comparison_expr(self)
 
 
@@ -2162,7 +2162,7 @@ def __init__(
         self.end_index = end_index
         self.stride = stride
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_slice_expr(self)
 
 
@@ -2181,7 +2181,7 @@ def __init__(self, expr: Expression, typ: mypy.types.Type) -> None:
         self.expr = expr
         self.type = typ
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_cast_expr(self)
 
 
@@ -2200,7 +2200,7 @@ def __init__(self, expr: Expression, typ: mypy.types.Type) -> None:
         self.expr = expr
         self.type = typ
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_assert_type_expr(self)
 
 
@@ -2228,7 +2228,7 @@ def __init__(
         self.local_nodes = local_nodes
         self.is_imported = is_imported
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_reveal_expr(self)
 
 
@@ -2249,7 +2249,7 @@ def __init__(self, name: str, call: CallExpr) -> None:
         self.call = call
         self.info = None
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_super_expr(self)
 
 
@@ -2270,7 +2270,7 @@ def expr(self) -> Expression:
         assert expr is not None  # lambda can't have empty body
         return expr
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_lambda_expr(self)
 
     def is_dynamic(self) -> bool:
@@ -2290,7 +2290,7 @@ def __init__(self, items: list[Expression]) -> None:
         super().__init__()
         self.items = items
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_list_expr(self)
 
 
@@ -2307,7 +2307,7 @@ def __init__(self, items: list[tuple[Expression | None, Expression]]) -> None:
         super().__init__()
         self.items = items
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_dict_expr(self)
 
 
@@ -2326,7 +2326,7 @@ def __init__(self, items: list[Expression]) -> None:
         super().__init__()
         self.items = items
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_tuple_expr(self)
 
 
@@ -2343,7 +2343,7 @@ def __init__(self, items: list[Expression]) -> None:
         super().__init__()
         self.items = items
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_set_expr(self)
 
 
@@ -2375,7 +2375,7 @@ def __init__(
         self.indices = indices
         self.is_async = is_async
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_generator_expr(self)
 
 
@@ -2392,7 +2392,7 @@ def __init__(self, generator: GeneratorExpr) -> None:
         super().__init__()
         self.generator = generator
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_list_comprehension(self)
 
 
@@ -2409,7 +2409,7 @@ def __init__(self, generator: GeneratorExpr) -> None:
         super().__init__()
         self.generator = generator
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_set_comprehension(self)
 
 
@@ -2444,7 +2444,7 @@ def __init__(
         self.indices = indices
         self.is_async = is_async
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_dictionary_comprehension(self)
 
 
@@ -2465,7 +2465,7 @@ def __init__(self, cond: Expression, if_expr: Expression, else_expr: Expression)
         self.if_expr = if_expr
         self.else_expr = else_expr
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_conditional_expr(self)
 
 
@@ -2484,7 +2484,7 @@ def __init__(self, expr: Expression, types: list[mypy.types.Type]) -> None:
         self.expr = expr
         self.types = types
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_type_application(self)
 
 
@@ -2586,7 +2586,7 @@ def __init__(
         super().__init__(name, fullname, upper_bound, default, variance, is_new_style, line=line)
         self.values = values
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_type_var_expr(self)
 
     def serialize(self) -> JsonDict:
@@ -2618,7 +2618,7 @@ class ParamSpecExpr(TypeVarLikeExpr):
 
     __match_args__ = ("name", "upper_bound", "default")
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_paramspec_expr(self)
 
     def serialize(self) -> JsonDict:
@@ -2666,7 +2666,7 @@ def __init__(
         super().__init__(name, fullname, upper_bound, default, variance, is_new_style, line=line)
         self.tuple_fallback = tuple_fallback
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_type_var_tuple_expr(self)
 
     def serialize(self) -> JsonDict:
@@ -2706,7 +2706,7 @@ def __init__(self, node: TypeAlias) -> None:
         super().__init__()
         self.node = node
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_type_alias_expr(self)
 
 
@@ -2727,7 +2727,7 @@ def __init__(self, info: TypeInfo, is_typed: bool = False) -> None:
         self.info = info
         self.is_typed = is_typed
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_namedtuple_expr(self)
 
 
@@ -2745,7 +2745,7 @@ def __init__(self, info: TypeInfo) -> None:
         super().__init__()
         self.info = info
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_typeddict_expr(self)
 
 
@@ -2768,7 +2768,7 @@ def __init__(self, info: TypeInfo, items: list[str], values: list[Expression | N
         self.items = items
         self.values = values
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_enum_call_expr(self)
 
 
@@ -2783,7 +2783,7 @@ def __init__(self, type: mypy.types.ProperType) -> None:
         super().__init__()
         self.type = type
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit__promote_expr(self)
 
 
@@ -2808,7 +2808,7 @@ def __init__(
         self.old_type = old_type
         self.info = None
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_newtype_expr(self)
 
 
@@ -2825,7 +2825,7 @@ def __init__(self, expr: Expression) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_await_expr(self)
 
 
@@ -2861,7 +2861,7 @@ def __init__(
     def __repr__(self) -> str:
         return "TempNode:%d(%s)" % (self.line, str(self.type))
 
-    def accept(self, visitor: ExpressionVisitor[T]) -> T | None:
+    def accept(self, visitor: ExpressionVisitor[T]) -> T:
         return visitor.visit_temp_node(self)
 
 
@@ -3705,7 +3705,7 @@ def serialize(self) -> JsonDict:
         }
         return data
 
-    def accept(self, visitor: NodeVisitor[T]) -> T | None:
+    def accept(self, visitor: NodeVisitor[T]) -> T:
         return visitor.visit_type_alias(self)
 
     @classmethod
@@ -3802,7 +3802,7 @@ def fullname(self) -> str:
     def serialize(self) -> JsonDict:
         assert False, "PlaceholderNode can't be serialized"
 
-    def accept(self, visitor: NodeVisitor[T]) -> T | None:
+    def accept(self, visitor: NodeVisitor[T]) -> T:
         return visitor.visit_placeholder_node(self)
 
 
diff --git a/mypy/patterns.py b/mypy/patterns.py
index 47a290f60902..a01bf6acc876 100644
--- a/mypy/patterns.py
+++ b/mypy/patterns.py
@@ -18,7 +18,7 @@ class Pattern(Node):
 
     __slots__ = ()
 
-    def accept(self, visitor: PatternVisitor[T]) -> T | None:
+    def accept(self, visitor: PatternVisitor[T]) -> T:
         raise RuntimeError("Not implemented", type(self))
 
 
@@ -38,7 +38,7 @@ def __init__(self, pattern: Pattern | None, name: NameExpr | None) -> None:
         self.pattern = pattern
         self.name = name
 
-    def accept(self, visitor: PatternVisitor[T]) -> T | None:
+    def accept(self, visitor: PatternVisitor[T]) -> T:
         return visitor.visit_as_pattern(self)
 
 
@@ -51,7 +51,7 @@ def __init__(self, patterns: list[Pattern]) -> None:
         super().__init__()
         self.patterns = patterns
 
-    def accept(self, visitor: PatternVisitor[T]) -> T | None:
+    def accept(self, visitor: PatternVisitor[T]) -> T:
         return visitor.visit_or_pattern(self)
 
 
@@ -64,7 +64,7 @@ def __init__(self, expr: Expression) -> None:
         super().__init__()
         self.expr = expr
 
-    def accept(self, visitor: PatternVisitor[T]) -> T | None:
+    def accept(self, visitor: PatternVisitor[T]) -> T:
         return visitor.visit_value_pattern(self)
 
 
@@ -76,7 +76,7 @@ def __init__(self, value: bool | None) -> None:
         super().__init__()
         self.value = value
 
-    def accept(self, visitor: PatternVisitor[T]) -> T | None:
+    def accept(self, visitor: PatternVisitor[T]) -> T:
         return visitor.visit_singleton_pattern(self)
 
 
@@ -89,7 +89,7 @@ def __init__(self, patterns: list[Pattern]) -> None:
         super().__init__()
         self.patterns = patterns
 
-    def accept(self, visitor: PatternVisitor[T]) -> T | None:
+    def accept(self, visitor: PatternVisitor[T]) -> T:
         return visitor.visit_sequence_pattern(self)
 
 
@@ -102,7 +102,7 @@ def __init__(self, capture: NameExpr | None) -> None:
         super().__init__()
         self.capture = capture
 
-    def accept(self, visitor: PatternVisitor[T]) -> T | None:
+    def accept(self, visitor: PatternVisitor[T]) -> T:
         return visitor.visit_starred_pattern(self)
 
 
@@ -120,7 +120,7 @@ def __init__(
         self.values = values
         self.rest = rest
 
-    def accept(self, visitor: PatternVisitor[T]) -> T | None:
+    def accept(self, visitor: PatternVisitor[T]) -> T:
         return visitor.visit_mapping_pattern(self)
 
 
@@ -146,5 +146,5 @@ def __init__(
         self.keyword_keys = keyword_keys
         self.keyword_values = keyword_values
 
-    def accept(self, visitor: PatternVisitor[T]) -> T | None:
+    def accept(self, visitor: PatternVisitor[T]) -> T:
         return visitor.visit_class_pattern(self)
diff --git a/mypy/strconv.py b/mypy/strconv.py
index 2102c76c66c4..3e9d37586f72 100644
--- a/mypy/strconv.py
+++ b/mypy/strconv.py
@@ -182,8 +182,7 @@ def visit_class_def(self, o: mypy.nodes.ClassDef) -> str:
         if o.type_vars:
             a.insert(1, ("TypeVars", o.type_vars))
         if o.metaclass:
-            inner = o.metaclass.accept(self)
-            a.insert(1, f"Metaclass({inner})")
+            a.insert(1, f"Metaclass({o.metaclass.accept(self)})")
         if o.decorators:
             a.insert(1, ("Decorators", o.decorators))
         if o.info and o.info._promote:
@@ -431,16 +430,13 @@ def visit_yield_expr(self, o: mypy.nodes.YieldExpr) -> str:
 
     def visit_yield_from_expr(self, o: mypy.nodes.YieldFromExpr) -> str:
         if o.expr:
-            inner = o.expr.accept(self)
-            return self.dump([inner], o)
+            return self.dump([o.expr.accept(self)], o)
         else:
             return self.dump([], o)
 
     def visit_call_expr(self, o: mypy.nodes.CallExpr) -> str:
         if o.analyzed:
-            result = o.analyzed.accept(self)
-            assert result is not None
-            return result
+            return o.analyzed.accept(self)
         args: list[mypy.nodes.Expression] = []
         extra: list[str | tuple[str, list[Any]]] = []
         for i, kind in enumerate(o.arg_kinds):
@@ -459,9 +455,7 @@ def visit_call_expr(self, o: mypy.nodes.CallExpr) -> str:
 
     def visit_op_expr(self, o: mypy.nodes.OpExpr) -> str:
         if o.analyzed:
-            result = o.analyzed.accept(self)
-            assert result is not None
-            return result
+            return o.analyzed.accept(self)
         return self.dump([o.op, o.left, o.right], o)
 
     def visit_comparison_expr(self, o: mypy.nodes.ComparisonExpr) -> str:
@@ -500,9 +494,7 @@ def visit_tuple_expr(self, o: mypy.nodes.TupleExpr) -> str:
 
     def visit_index_expr(self, o: mypy.nodes.IndexExpr) -> str:
         if o.analyzed:
-            result = o.analyzed.accept(self)
-            assert result is not None
-            return result
+            return o.analyzed.accept(self)
         return self.dump([o.base, o.index], o)
 
     def visit_super_expr(self, o: mypy.nodes.SuperExpr) -> str:
@@ -661,9 +653,7 @@ def dump_tagged(nodes: Sequence[object], tag: str | None, str_conv: StrConv) ->
             s = dump_tagged(n[1], n[0], str_conv)
             a.append(indent(s, 2))
         elif isinstance(n, mypy.nodes.Node):
-            indented = n.accept(str_conv)
-            assert indented is not None
-            a.append(indent(indented, 2))
+            a.append(indent(n.accept(str_conv), 2))
         elif isinstance(n, Type):
             a.append(
                 indent(n.accept(TypeStrVisitor(str_conv.id_mapper, options=str_conv.options)), 2)
diff --git a/mypy/stubgen.py b/mypy/stubgen.py
index 9df68b762eee..1f8a1a4740f1 100755
--- a/mypy/stubgen.py
+++ b/mypy/stubgen.py
@@ -285,16 +285,14 @@ def visit_call_expr(self, node: CallExpr) -> str:
         callee = node.callee.accept(self)
         args = []
         for name, arg, kind in zip(node.arg_names, node.args, node.arg_kinds):
-            arg_str = arg.accept(self)
-            assert arg_str is not None
             if kind == ARG_POS:
-                args.append(arg_str)
+                args.append(arg.accept(self))
             elif kind == ARG_STAR:
-                args.append("*" + arg_str)
+                args.append("*" + arg.accept(self))
             elif kind == ARG_STAR2:
-                args.append("**" + arg_str)
+                args.append("**" + arg.accept(self))
             elif kind == ARG_NAMED:
-                args.append(f"{name}={arg_str}")
+                args.append(f"{name}={arg.accept(self)}")
             else:
                 raise ValueError(f"Unknown argument kind {kind} in call")
         return f"{callee}({', '.join(args)})"
@@ -337,65 +335,41 @@ def visit_index_expr(self, node: IndexExpr) -> str:
         base_fullname = self.stubgen.get_fullname(node.base)
         if base_fullname == "typing.Union":
             if isinstance(node.index, TupleExpr):
-                items = []
-                for item in node.index.items:
-                    item_str = item.accept(self)
-                    assert item_str is not None
-                    items.append(item_str)
-                return " | ".join(items)
-            result = node.index.accept(self)
-            assert result is not None
-            return result
+                return " | ".join([item.accept(self) for item in node.index.items])
+            return node.index.accept(self)
         if base_fullname == "typing.Optional":
             if isinstance(node.index, TupleExpr):
                 return self.stubgen.add_name("_typeshed.Incomplete")
-            inner = node.index.accept(self)
-            return f"{inner} | None"
+            return f"{node.index.accept(self)} | None"
         base = node.base.accept(self)
         index = node.index.accept(self)
-        assert index is not None
         if len(index) > 2 and index.startswith("(") and index.endswith(")"):
             index = index[1:-1].rstrip(",")
         return f"{base}[{index}]"
 
     def visit_tuple_expr(self, node: TupleExpr) -> str:
         suffix = "," if len(node.items) == 1 else ""
-        items = []
-        for item in node.items:
-            item_str = item.accept(self)
-            assert item_str is not None
-            items.append(item_str)
-        return f"({', '.join(items)}{suffix})"
+        return f"({', '.join(n.accept(self) for n in node.items)}{suffix})"
 
     def visit_list_expr(self, node: ListExpr) -> str:
-        items = []
-        for item in node.items:
-            item_str = item.accept(self)
-            assert item_str is not None
-            items.append(item_str)
-        return f"[{', '.join(items)}]"
+        return f"[{', '.join(n.accept(self) for n in node.items)}]"
 
     def visit_dict_expr(self, o: DictExpr) -> str:
         dict_items = []
         for key, value in o.items:
             # This is currently only used for TypedDict where all keys are strings.
             assert isinstance(key, StrExpr)
-            inner1 = key.accept(self)
-            inner2 = value.accept(self)
-            dict_items.append(f"{inner1}: {inner2}")
+            dict_items.append(f"{key.accept(self)}: {value.accept(self)}")
         return f"{{{', '.join(dict_items)}}}"
 
     def visit_ellipsis(self, node: EllipsisExpr) -> str:
         return "..."
 
     def visit_op_expr(self, o: OpExpr) -> str:
-        inner1 = o.left.accept(self)
-        inner2 = o.right.accept(self)
-        return f"{inner1} {o.op} {inner2}"
+        return f"{o.left.accept(self)} {o.op} {o.right.accept(self)}"
 
     def visit_star_expr(self, o: StarExpr) -> str:
-        inner = o.expr.accept(self)
-        return f"*{inner}"
+        return f"*{o.expr.accept(self)}"
 
     def visit_lambda_expr(self, o: LambdaExpr) -> str:
         # TODO: Required for among other things dataclass.field default_factory
@@ -780,8 +754,7 @@ def process_decorator(self, o: Decorator) -> None:
                 self.add_decorator(qualname, require_name=False)
             elif fullname in DATACLASS_TRANSFORM_NAMES:
                 p = AliasPrinter(self)
-                inner = decorator.accept(p)
-                self._decorators.append(f"@{inner}")
+                self._decorators.append(f"@{decorator.accept(p)}")
 
     def get_fullname(self, expr: Expression) -> str:
         """Return the expression's full name."""
@@ -814,7 +787,7 @@ def visit_class_def(self, o: ClassDef) -> None:
             self.processing_enum = True
         if isinstance(o.metaclass, (NameExpr, MemberExpr)):
             meta = o.metaclass.accept(AliasPrinter(self))
-            base_types.append(f"metaclass={meta}")
+            base_types.append("metaclass=" + meta)
         elif self.analyzed and o.info.is_abstract and not o.info.is_protocol:
             base_types.append("metaclass=abc.ABCMeta")
             self.import_tracker.add_import("abc")
@@ -858,9 +831,7 @@ def get_base_types(self, cdef: ClassDef) -> list[str]:
                 if self.get_fullname(base) != "builtins.object":
                     base_types.append(get_qualified_name(base))
             elif isinstance(base, IndexExpr):
-                base_str = base.accept(p)
-                assert base_str is not None
-                base_types.append(base_str)
+                base_types.append(base.accept(p))
             elif isinstance(base, CallExpr):
                 # namedtuple(typename, fields), NamedTuple(typename, fields) calls can
                 # be used as a base class. The first argument is a string literal that
@@ -883,9 +854,7 @@ def get_base_types(self, cdef: ClassDef) -> list[str]:
                     namedtuple_name = self.add_name("typing.NamedTuple")
                     base_types.append(f"{namedtuple_name}({typename!r}, [{fields_str}])")
                 elif self.is_typed_namedtuple(base):
-                    base_str = base.accept(p)
-                    assert base_str is not None
-                    base_types.append(base_str)
+                    base_types.append(base.accept(p))
                 else:
                     # At this point, we don't know what the base class is, so we
                     # just use Incomplete as the base class.
@@ -902,15 +871,11 @@ def get_class_decorators(self, cdef: ClassDef) -> list[str]:
         p = AliasPrinter(self)
         for d in cdef.decorators:
             if self.is_dataclass(d):
-                d_str = d.accept(p)
-                assert d_str is not None
-                decorators.append(d_str)
+                decorators.append(d.accept(p))
                 self.import_tracker.require_name(get_qualified_name(d))
                 self.processing_dataclass = True
             if self.is_dataclass_transform(d):
-                d_str = d.accept(p)
-                assert d_str is not None
-                decorators.append(d_str)
+                decorators.append(d.accept(p))
                 self.import_tracker.require_name(get_qualified_name(d))
         return decorators
 
@@ -1021,9 +986,7 @@ def _get_namedtuple_fields(self, call: CallExpr) -> list[tuple[str, str]] | None
                 field_name, field_type = field.items
                 if not isinstance(field_name, StrExpr):
                     return None
-                field_type_str = field_type.accept(p)
-                assert field_type_str is not None
-                fields.append((field_name.value, field_type_str))
+                fields.append((field_name.value, field_type.accept(p)))
             return fields
         else:
             return None  # Not a named tuple call
@@ -1093,15 +1056,13 @@ def process_typeddict(self, lvalue: NameExpr, rvalue: CallExpr) -> None:
         p = AliasPrinter(self)
         if any(not key.isidentifier() or keyword.iskeyword(key) for key, _ in items):
             # Keep the call syntax if there are non-identifier or reserved keyword keys.
-            inner = rvalue.accept(p)
-            self.add(f"{self._indent}{lvalue.name} = {inner}\n")
+            self.add(f"{self._indent}{lvalue.name} = {rvalue.accept(p)}\n")
             self._state = VAR
         else:
             bases = self.add_name("typing_extensions.TypedDict")
             # TODO: Add support for generic TypedDicts. Requires `Generic` as base class.
             if total is not None:
-                inner = total.accept(p)
-                bases += f", total={inner}"
+                bases += f", total={total.accept(p)}"
             class_def = f"{self._indent}class {lvalue.name}({bases}):"
             if len(items) == 0:
                 self.add(f"{class_def} ...\n")
@@ -1111,8 +1072,7 @@ def process_typeddict(self, lvalue: NameExpr, rvalue: CallExpr) -> None:
                     self.add("\n")
                 self.add(f"{class_def}\n")
                 for key, key_type in items:
-                    inner = key_type.accept(p)
-                    self.add(f"{self._indent}    {key}: {inner}\n")
+                    self.add(f"{self._indent}    {key}: {key_type.accept(p)}\n")
                 self._state = CLASS
 
     def annotate_as_incomplete(self, lvalue: NameExpr) -> None:
@@ -1184,8 +1144,7 @@ def is_alias_expression(self, expr: Expression, top_level: bool = True) -> bool:
 
     def process_typealias(self, lvalue: NameExpr, rvalue: Expression) -> None:
         p = AliasPrinter(self)
-        inner = rvalue.accept(p)
-        self.add(f"{self._indent}{lvalue.name} = {inner}\n")
+        self.add(f"{self._indent}{lvalue.name} = {rvalue.accept(p)}\n")
         self.record_name(lvalue.name)
         self._vars[-1].append(lvalue.name)
 
@@ -1195,8 +1154,7 @@ def visit_type_alias_stmt(self, o: TypeAliasStmt) -> None:
         name = o.name.name
         rvalue = o.value.expr()
         type_args = self.format_type_args(o)
-        inner = rvalue.accept(p)
-        self.add(f"{self._indent}type {name}{type_args} = {inner}\n")
+        self.add(f"{self._indent}type {name}{type_args} = {rvalue.accept(p)}\n")
         self.record_name(name)
         self._vars[-1].append(name)
 
@@ -1317,8 +1275,7 @@ def get_assign_initializer(self, rvalue: Expression) -> str:
                 fullname = self.get_fullname(rvalue.callee)
                 if fullname in (self.dataclass_field_specifier or DATACLASS_FIELD_SPECIFIERS):
                     p = AliasPrinter(self)
-                    inner = rvalue.accept(p)
-                    return f" = {inner}"
+                    return f" = {rvalue.accept(p)}"
             if not (isinstance(rvalue, TempNode) and rvalue.no_rhs):
                 return " = ..."
         # TODO: support other possible cases, where initializer is important
diff --git a/mypy/test/testmerge.py b/mypy/test/testmerge.py
index 65d1ca8d1ed1..0582c9ed5882 100644
--- a/mypy/test/testmerge.py
+++ b/mypy/test/testmerge.py
@@ -150,7 +150,6 @@ def dump_asts(self, modules: dict[str, MypyFile]) -> list[str]:
         a = []
         for m in sorted(modules):
             s = modules[m].accept(self.str_conv)
-            assert s is not None
             a.extend(s.splitlines())
         return a
 
diff --git a/mypy/treetransform.py b/mypy/treetransform.py
index ec488fd89d39..3e5a7ef3f2ca 100644
--- a/mypy/treetransform.py
+++ b/mypy/treetransform.py
@@ -695,7 +695,6 @@ def visit_temp_node(self, node: TempNode) -> TempNode:
 
     def node(self, node: Node) -> Node:
         new = node.accept(self)
-        assert new is not None
         new.set_line(node)
         return new
 
diff --git a/mypy/visitor.py b/mypy/visitor.py
index 52d386fec708..6613b6cbb144 100644
--- a/mypy/visitor.py
+++ b/mypy/visitor.py
@@ -20,179 +20,179 @@
 @mypyc_attr(allow_interpreted_subclasses=True)
 class ExpressionVisitor(Generic[T]):
     @abstractmethod
-    def visit_int_expr(self, o: mypy.nodes.IntExpr, /) -> T | None:
+    def visit_int_expr(self, o: mypy.nodes.IntExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_str_expr(self, o: mypy.nodes.StrExpr, /) -> T | None:
+    def visit_str_expr(self, o: mypy.nodes.StrExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_bytes_expr(self, o: mypy.nodes.BytesExpr, /) -> T | None:
+    def visit_bytes_expr(self, o: mypy.nodes.BytesExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_float_expr(self, o: mypy.nodes.FloatExpr, /) -> T | None:
+    def visit_float_expr(self, o: mypy.nodes.FloatExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_complex_expr(self, o: mypy.nodes.ComplexExpr, /) -> T | None:
+    def visit_complex_expr(self, o: mypy.nodes.ComplexExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_ellipsis(self, o: mypy.nodes.EllipsisExpr, /) -> T | None:
+    def visit_ellipsis(self, o: mypy.nodes.EllipsisExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_star_expr(self, o: mypy.nodes.StarExpr, /) -> T | None:
+    def visit_star_expr(self, o: mypy.nodes.StarExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_name_expr(self, o: mypy.nodes.NameExpr, /) -> T | None:
+    def visit_name_expr(self, o: mypy.nodes.NameExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_member_expr(self, o: mypy.nodes.MemberExpr, /) -> T | None:
+    def visit_member_expr(self, o: mypy.nodes.MemberExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_yield_from_expr(self, o: mypy.nodes.YieldFromExpr, /) -> T | None:
+    def visit_yield_from_expr(self, o: mypy.nodes.YieldFromExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_yield_expr(self, o: mypy.nodes.YieldExpr, /) -> T | None:
+    def visit_yield_expr(self, o: mypy.nodes.YieldExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_call_expr(self, o: mypy.nodes.CallExpr, /) -> T | None:
+    def visit_call_expr(self, o: mypy.nodes.CallExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_op_expr(self, o: mypy.nodes.OpExpr, /) -> T | None:
+    def visit_op_expr(self, o: mypy.nodes.OpExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_comparison_expr(self, o: mypy.nodes.ComparisonExpr, /) -> T | None:
+    def visit_comparison_expr(self, o: mypy.nodes.ComparisonExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_cast_expr(self, o: mypy.nodes.CastExpr, /) -> T | None:
+    def visit_cast_expr(self, o: mypy.nodes.CastExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_assert_type_expr(self, o: mypy.nodes.AssertTypeExpr, /) -> T | None:
+    def visit_assert_type_expr(self, o: mypy.nodes.AssertTypeExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_reveal_expr(self, o: mypy.nodes.RevealExpr, /) -> T | None:
+    def visit_reveal_expr(self, o: mypy.nodes.RevealExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_super_expr(self, o: mypy.nodes.SuperExpr, /) -> T | None:
+    def visit_super_expr(self, o: mypy.nodes.SuperExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_unary_expr(self, o: mypy.nodes.UnaryExpr, /) -> T | None:
+    def visit_unary_expr(self, o: mypy.nodes.UnaryExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_assignment_expr(self, o: mypy.nodes.AssignmentExpr, /) -> T | None:
+    def visit_assignment_expr(self, o: mypy.nodes.AssignmentExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_list_expr(self, o: mypy.nodes.ListExpr, /) -> T | None:
+    def visit_list_expr(self, o: mypy.nodes.ListExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_dict_expr(self, o: mypy.nodes.DictExpr, /) -> T | None:
+    def visit_dict_expr(self, o: mypy.nodes.DictExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_tuple_expr(self, o: mypy.nodes.TupleExpr, /) -> T | None:
+    def visit_tuple_expr(self, o: mypy.nodes.TupleExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_set_expr(self, o: mypy.nodes.SetExpr, /) -> T | None:
+    def visit_set_expr(self, o: mypy.nodes.SetExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_index_expr(self, o: mypy.nodes.IndexExpr, /) -> T | None:
+    def visit_index_expr(self, o: mypy.nodes.IndexExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_type_application(self, o: mypy.nodes.TypeApplication, /) -> T | None:
+    def visit_type_application(self, o: mypy.nodes.TypeApplication, /) -> T:
         pass
 
     @abstractmethod
-    def visit_lambda_expr(self, o: mypy.nodes.LambdaExpr, /) -> T | None:
+    def visit_lambda_expr(self, o: mypy.nodes.LambdaExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_list_comprehension(self, o: mypy.nodes.ListComprehension, /) -> T | None:
+    def visit_list_comprehension(self, o: mypy.nodes.ListComprehension, /) -> T:
         pass
 
     @abstractmethod
-    def visit_set_comprehension(self, o: mypy.nodes.SetComprehension, /) -> T | None:
+    def visit_set_comprehension(self, o: mypy.nodes.SetComprehension, /) -> T:
         pass
 
     @abstractmethod
-    def visit_dictionary_comprehension(self, o: mypy.nodes.DictionaryComprehension, /) -> T | None:
+    def visit_dictionary_comprehension(self, o: mypy.nodes.DictionaryComprehension, /) -> T:
         pass
 
     @abstractmethod
-    def visit_generator_expr(self, o: mypy.nodes.GeneratorExpr, /) -> T | None:
+    def visit_generator_expr(self, o: mypy.nodes.GeneratorExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_slice_expr(self, o: mypy.nodes.SliceExpr, /) -> T | None:
+    def visit_slice_expr(self, o: mypy.nodes.SliceExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_conditional_expr(self, o: mypy.nodes.ConditionalExpr, /) -> T | None:
+    def visit_conditional_expr(self, o: mypy.nodes.ConditionalExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_type_var_expr(self, o: mypy.nodes.TypeVarExpr, /) -> T | None:
+    def visit_type_var_expr(self, o: mypy.nodes.TypeVarExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_paramspec_expr(self, o: mypy.nodes.ParamSpecExpr, /) -> T | None:
+    def visit_paramspec_expr(self, o: mypy.nodes.ParamSpecExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_type_var_tuple_expr(self, o: mypy.nodes.TypeVarTupleExpr, /) -> T | None:
+    def visit_type_var_tuple_expr(self, o: mypy.nodes.TypeVarTupleExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_type_alias_expr(self, o: mypy.nodes.TypeAliasExpr, /) -> T | None:
+    def visit_type_alias_expr(self, o: mypy.nodes.TypeAliasExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_namedtuple_expr(self, o: mypy.nodes.NamedTupleExpr, /) -> T | None:
+    def visit_namedtuple_expr(self, o: mypy.nodes.NamedTupleExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_enum_call_expr(self, o: mypy.nodes.EnumCallExpr, /) -> T | None:
+    def visit_enum_call_expr(self, o: mypy.nodes.EnumCallExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_typeddict_expr(self, o: mypy.nodes.TypedDictExpr, /) -> T | None:
+    def visit_typeddict_expr(self, o: mypy.nodes.TypedDictExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_newtype_expr(self, o: mypy.nodes.NewTypeExpr, /) -> T | None:
+    def visit_newtype_expr(self, o: mypy.nodes.NewTypeExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit__promote_expr(self, o: mypy.nodes.PromoteExpr, /) -> T | None:
+    def visit__promote_expr(self, o: mypy.nodes.PromoteExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_await_expr(self, o: mypy.nodes.AwaitExpr, /) -> T | None:
+    def visit_await_expr(self, o: mypy.nodes.AwaitExpr, /) -> T:
         pass
 
     @abstractmethod
-    def visit_temp_node(self, o: mypy.nodes.TempNode, /) -> T | None:
+    def visit_temp_node(self, o: mypy.nodes.TempNode, /) -> T:
         pass
 
 
@@ -202,115 +202,115 @@ class StatementVisitor(Generic[T]):
     # Definitions
 
     @abstractmethod
-    def visit_assignment_stmt(self, o: mypy.nodes.AssignmentStmt, /) -> T | None:
+    def visit_assignment_stmt(self, o: mypy.nodes.AssignmentStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_for_stmt(self, o: mypy.nodes.ForStmt, /) -> T | None:
+    def visit_for_stmt(self, o: mypy.nodes.ForStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_with_stmt(self, o: mypy.nodes.WithStmt, /) -> T | None:
+    def visit_with_stmt(self, o: mypy.nodes.WithStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_del_stmt(self, o: mypy.nodes.DelStmt, /) -> T | None:
+    def visit_del_stmt(self, o: mypy.nodes.DelStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_func_def(self, o: mypy.nodes.FuncDef, /) -> T | None:
+    def visit_func_def(self, o: mypy.nodes.FuncDef, /) -> T:
         pass
 
     @abstractmethod
-    def visit_overloaded_func_def(self, o: mypy.nodes.OverloadedFuncDef, /) -> T | None:
+    def visit_overloaded_func_def(self, o: mypy.nodes.OverloadedFuncDef, /) -> T:
         pass
 
     @abstractmethod
-    def visit_class_def(self, o: mypy.nodes.ClassDef, /) -> T | None:
+    def visit_class_def(self, o: mypy.nodes.ClassDef, /) -> T:
         pass
 
     @abstractmethod
-    def visit_global_decl(self, o: mypy.nodes.GlobalDecl, /) -> T | None:
+    def visit_global_decl(self, o: mypy.nodes.GlobalDecl, /) -> T:
         pass
 
     @abstractmethod
-    def visit_nonlocal_decl(self, o: mypy.nodes.NonlocalDecl, /) -> T | None:
+    def visit_nonlocal_decl(self, o: mypy.nodes.NonlocalDecl, /) -> T:
         pass
 
     @abstractmethod
-    def visit_decorator(self, o: mypy.nodes.Decorator, /) -> T | None:
+    def visit_decorator(self, o: mypy.nodes.Decorator, /) -> T:
         pass
 
     # Module structure
 
     @abstractmethod
-    def visit_import(self, o: mypy.nodes.Import, /) -> T | None:
+    def visit_import(self, o: mypy.nodes.Import, /) -> T:
         pass
 
     @abstractmethod
-    def visit_import_from(self, o: mypy.nodes.ImportFrom, /) -> T | None:
+    def visit_import_from(self, o: mypy.nodes.ImportFrom, /) -> T:
         pass
 
     @abstractmethod
-    def visit_import_all(self, o: mypy.nodes.ImportAll, /) -> T | None:
+    def visit_import_all(self, o: mypy.nodes.ImportAll, /) -> T:
         pass
 
     # Statements
 
     @abstractmethod
-    def visit_block(self, o: mypy.nodes.Block, /) -> T | None:
+    def visit_block(self, o: mypy.nodes.Block, /) -> T:
         pass
 
     @abstractmethod
-    def visit_expression_stmt(self, o: mypy.nodes.ExpressionStmt, /) -> T | None:
+    def visit_expression_stmt(self, o: mypy.nodes.ExpressionStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_operator_assignment_stmt(self, o: mypy.nodes.OperatorAssignmentStmt, /) -> T | None:
+    def visit_operator_assignment_stmt(self, o: mypy.nodes.OperatorAssignmentStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_while_stmt(self, o: mypy.nodes.WhileStmt, /) -> T | None:
+    def visit_while_stmt(self, o: mypy.nodes.WhileStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_return_stmt(self, o: mypy.nodes.ReturnStmt, /) -> T | None:
+    def visit_return_stmt(self, o: mypy.nodes.ReturnStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_assert_stmt(self, o: mypy.nodes.AssertStmt, /) -> T | None:
+    def visit_assert_stmt(self, o: mypy.nodes.AssertStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_if_stmt(self, o: mypy.nodes.IfStmt, /) -> T | None:
+    def visit_if_stmt(self, o: mypy.nodes.IfStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_break_stmt(self, o: mypy.nodes.BreakStmt, /) -> T | None:
+    def visit_break_stmt(self, o: mypy.nodes.BreakStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_continue_stmt(self, o: mypy.nodes.ContinueStmt, /) -> T | None:
+    def visit_continue_stmt(self, o: mypy.nodes.ContinueStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_pass_stmt(self, o: mypy.nodes.PassStmt, /) -> T | None:
+    def visit_pass_stmt(self, o: mypy.nodes.PassStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_raise_stmt(self, o: mypy.nodes.RaiseStmt, /) -> T | None:
+    def visit_raise_stmt(self, o: mypy.nodes.RaiseStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_try_stmt(self, o: mypy.nodes.TryStmt, /) -> T | None:
+    def visit_try_stmt(self, o: mypy.nodes.TryStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_match_stmt(self, o: mypy.nodes.MatchStmt, /) -> T | None:
+    def visit_match_stmt(self, o: mypy.nodes.MatchStmt, /) -> T:
         pass
 
     @abstractmethod
-    def visit_type_alias_stmt(self, o: mypy.nodes.TypeAliasStmt, /) -> T | None:
+    def visit_type_alias_stmt(self, o: mypy.nodes.TypeAliasStmt, /) -> T:
         pass
 
 
@@ -318,35 +318,35 @@ def visit_type_alias_stmt(self, o: mypy.nodes.TypeAliasStmt, /) -> T | None:
 @mypyc_attr(allow_interpreted_subclasses=True)
 class PatternVisitor(Generic[T]):
     @abstractmethod
-    def visit_as_pattern(self, o: mypy.patterns.AsPattern, /) -> T | None:
+    def visit_as_pattern(self, o: mypy.patterns.AsPattern, /) -> T:
         pass
 
     @abstractmethod
-    def visit_or_pattern(self, o: mypy.patterns.OrPattern, /) -> T | None:
+    def visit_or_pattern(self, o: mypy.patterns.OrPattern, /) -> T:
         pass
 
     @abstractmethod
-    def visit_value_pattern(self, o: mypy.patterns.ValuePattern, /) -> T | None:
+    def visit_value_pattern(self, o: mypy.patterns.ValuePattern, /) -> T:
         pass
 
     @abstractmethod
-    def visit_singleton_pattern(self, o: mypy.patterns.SingletonPattern, /) -> T | None:
+    def visit_singleton_pattern(self, o: mypy.patterns.SingletonPattern, /) -> T:
         pass
 
     @abstractmethod
-    def visit_sequence_pattern(self, o: mypy.patterns.SequencePattern, /) -> T | None:
+    def visit_sequence_pattern(self, o: mypy.patterns.SequencePattern, /) -> T:
         pass
 
     @abstractmethod
-    def visit_starred_pattern(self, o: mypy.patterns.StarredPattern, /) -> T | None:
+    def visit_starred_pattern(self, o: mypy.patterns.StarredPattern, /) -> T:
         pass
 
     @abstractmethod
-    def visit_mapping_pattern(self, o: mypy.patterns.MappingPattern, /) -> T | None:
+    def visit_mapping_pattern(self, o: mypy.patterns.MappingPattern, /) -> T:
         pass
 
     @abstractmethod
-    def visit_class_pattern(self, o: mypy.patterns.ClassPattern, /) -> T | None:
+    def visit_class_pattern(self, o: mypy.patterns.ClassPattern, /) -> T:
         pass
 
 
@@ -358,268 +358,271 @@ class NodeVisitor(Generic[T], ExpressionVisitor[T], StatementVisitor[T], Pattern
     The T type argument specifies the return type of the visit
     methods. As all methods defined here return None by default,
     subclasses do not always need to override all the methods.
+
+    TODO: make the default return value explicit, then turn on
+          empty body checking in mypy_self_check.ini.
     """
 
     # Not in superclasses:
 
-    def visit_mypy_file(self, o: mypy.nodes.MypyFile, /) -> T | None:
+    def visit_mypy_file(self, o: mypy.nodes.MypyFile, /) -> T:
         pass
 
     # TODO: We have a visit_var method, but no visit_typeinfo or any
     # other non-Statement SymbolNode (accepting those will raise a
     # runtime error). Maybe this should be resolved in some direction.
-    def visit_var(self, o: mypy.nodes.Var, /) -> T | None:
+    def visit_var(self, o: mypy.nodes.Var, /) -> T:
         pass
 
     # Module structure
 
-    def visit_import(self, o: mypy.nodes.Import, /) -> T | None:
+    def visit_import(self, o: mypy.nodes.Import, /) -> T:
         pass
 
-    def visit_import_from(self, o: mypy.nodes.ImportFrom, /) -> T | None:
+    def visit_import_from(self, o: mypy.nodes.ImportFrom, /) -> T:
         pass
 
-    def visit_import_all(self, o: mypy.nodes.ImportAll, /) -> T | None:
+    def visit_import_all(self, o: mypy.nodes.ImportAll, /) -> T:
         pass
 
     # Definitions
 
-    def visit_func_def(self, o: mypy.nodes.FuncDef, /) -> T | None:
+    def visit_func_def(self, o: mypy.nodes.FuncDef, /) -> T:
         pass
 
-    def visit_overloaded_func_def(self, o: mypy.nodes.OverloadedFuncDef, /) -> T | None:
+    def visit_overloaded_func_def(self, o: mypy.nodes.OverloadedFuncDef, /) -> T:
         pass
 
-    def visit_class_def(self, o: mypy.nodes.ClassDef, /) -> T | None:
+    def visit_class_def(self, o: mypy.nodes.ClassDef, /) -> T:
         pass
 
-    def visit_global_decl(self, o: mypy.nodes.GlobalDecl, /) -> T | None:
+    def visit_global_decl(self, o: mypy.nodes.GlobalDecl, /) -> T:
         pass
 
-    def visit_nonlocal_decl(self, o: mypy.nodes.NonlocalDecl, /) -> T | None:
+    def visit_nonlocal_decl(self, o: mypy.nodes.NonlocalDecl, /) -> T:
         pass
 
-    def visit_decorator(self, o: mypy.nodes.Decorator, /) -> T | None:
+    def visit_decorator(self, o: mypy.nodes.Decorator, /) -> T:
         pass
 
-    def visit_type_alias(self, o: mypy.nodes.TypeAlias, /) -> T | None:
+    def visit_type_alias(self, o: mypy.nodes.TypeAlias, /) -> T:
         pass
 
-    def visit_placeholder_node(self, o: mypy.nodes.PlaceholderNode, /) -> T | None:
+    def visit_placeholder_node(self, o: mypy.nodes.PlaceholderNode, /) -> T:
         pass
 
     # Statements
 
-    def visit_block(self, o: mypy.nodes.Block, /) -> T | None:
+    def visit_block(self, o: mypy.nodes.Block, /) -> T:
         pass
 
-    def visit_expression_stmt(self, o: mypy.nodes.ExpressionStmt, /) -> T | None:
+    def visit_expression_stmt(self, o: mypy.nodes.ExpressionStmt, /) -> T:
         pass
 
-    def visit_assignment_stmt(self, o: mypy.nodes.AssignmentStmt, /) -> T | None:
+    def visit_assignment_stmt(self, o: mypy.nodes.AssignmentStmt, /) -> T:
         pass
 
-    def visit_operator_assignment_stmt(self, o: mypy.nodes.OperatorAssignmentStmt, /) -> T | None:
+    def visit_operator_assignment_stmt(self, o: mypy.nodes.OperatorAssignmentStmt, /) -> T:
         pass
 
-    def visit_while_stmt(self, o: mypy.nodes.WhileStmt, /) -> T | None:
+    def visit_while_stmt(self, o: mypy.nodes.WhileStmt, /) -> T:
         pass
 
-    def visit_for_stmt(self, o: mypy.nodes.ForStmt, /) -> T | None:
+    def visit_for_stmt(self, o: mypy.nodes.ForStmt, /) -> T:
         pass
 
-    def visit_return_stmt(self, o: mypy.nodes.ReturnStmt, /) -> T | None:
+    def visit_return_stmt(self, o: mypy.nodes.ReturnStmt, /) -> T:
         pass
 
-    def visit_assert_stmt(self, o: mypy.nodes.AssertStmt, /) -> T | None:
+    def visit_assert_stmt(self, o: mypy.nodes.AssertStmt, /) -> T:
         pass
 
-    def visit_del_stmt(self, o: mypy.nodes.DelStmt, /) -> T | None:
+    def visit_del_stmt(self, o: mypy.nodes.DelStmt, /) -> T:
         pass
 
-    def visit_if_stmt(self, o: mypy.nodes.IfStmt, /) -> T | None:
+    def visit_if_stmt(self, o: mypy.nodes.IfStmt, /) -> T:
         pass
 
-    def visit_break_stmt(self, o: mypy.nodes.BreakStmt, /) -> T | None:
+    def visit_break_stmt(self, o: mypy.nodes.BreakStmt, /) -> T:
         pass
 
-    def visit_continue_stmt(self, o: mypy.nodes.ContinueStmt, /) -> T | None:
+    def visit_continue_stmt(self, o: mypy.nodes.ContinueStmt, /) -> T:
         pass
 
-    def visit_pass_stmt(self, o: mypy.nodes.PassStmt, /) -> T | None:
+    def visit_pass_stmt(self, o: mypy.nodes.PassStmt, /) -> T:
         pass
 
-    def visit_raise_stmt(self, o: mypy.nodes.RaiseStmt, /) -> T | None:
+    def visit_raise_stmt(self, o: mypy.nodes.RaiseStmt, /) -> T:
         pass
 
-    def visit_try_stmt(self, o: mypy.nodes.TryStmt, /) -> T | None:
+    def visit_try_stmt(self, o: mypy.nodes.TryStmt, /) -> T:
         pass
 
-    def visit_with_stmt(self, o: mypy.nodes.WithStmt, /) -> T | None:
+    def visit_with_stmt(self, o: mypy.nodes.WithStmt, /) -> T:
         pass
 
-    def visit_match_stmt(self, o: mypy.nodes.MatchStmt, /) -> T | None:
+    def visit_match_stmt(self, o: mypy.nodes.MatchStmt, /) -> T:
         pass
 
-    def visit_type_alias_stmt(self, o: mypy.nodes.TypeAliasStmt, /) -> T | None:
+    def visit_type_alias_stmt(self, o: mypy.nodes.TypeAliasStmt, /) -> T:
         pass
 
     # Expressions (default no-op implementation)
 
-    def visit_int_expr(self, o: mypy.nodes.IntExpr, /) -> T | None:
+    def visit_int_expr(self, o: mypy.nodes.IntExpr, /) -> T:
         pass
 
-    def visit_str_expr(self, o: mypy.nodes.StrExpr, /) -> T | None:
+    def visit_str_expr(self, o: mypy.nodes.StrExpr, /) -> T:
         pass
 
-    def visit_bytes_expr(self, o: mypy.nodes.BytesExpr, /) -> T | None:
+    def visit_bytes_expr(self, o: mypy.nodes.BytesExpr, /) -> T:
         pass
 
-    def visit_float_expr(self, o: mypy.nodes.FloatExpr, /) -> T | None:
+    def visit_float_expr(self, o: mypy.nodes.FloatExpr, /) -> T:
         pass
 
-    def visit_complex_expr(self, o: mypy.nodes.ComplexExpr, /) -> T | None:
+    def visit_complex_expr(self, o: mypy.nodes.ComplexExpr, /) -> T:
         pass
 
-    def visit_ellipsis(self, o: mypy.nodes.EllipsisExpr, /) -> T | None:
+    def visit_ellipsis(self, o: mypy.nodes.EllipsisExpr, /) -> T:
         pass
 
-    def visit_star_expr(self, o: mypy.nodes.StarExpr, /) -> T | None:
+    def visit_star_expr(self, o: mypy.nodes.StarExpr, /) -> T:
         pass
 
-    def visit_name_expr(self, o: mypy.nodes.NameExpr, /) -> T | None:
+    def visit_name_expr(self, o: mypy.nodes.NameExpr, /) -> T:
         pass
 
-    def visit_member_expr(self, o: mypy.nodes.MemberExpr, /) -> T | None:
+    def visit_member_expr(self, o: mypy.nodes.MemberExpr, /) -> T:
         pass
 
-    def visit_yield_from_expr(self, o: mypy.nodes.YieldFromExpr, /) -> T | None:
+    def visit_yield_from_expr(self, o: mypy.nodes.YieldFromExpr, /) -> T:
         pass
 
-    def visit_yield_expr(self, o: mypy.nodes.YieldExpr, /) -> T | None:
+    def visit_yield_expr(self, o: mypy.nodes.YieldExpr, /) -> T:
         pass
 
-    def visit_call_expr(self, o: mypy.nodes.CallExpr, /) -> T | None:
+    def visit_call_expr(self, o: mypy.nodes.CallExpr, /) -> T:
         pass
 
-    def visit_op_expr(self, o: mypy.nodes.OpExpr, /) -> T | None:
+    def visit_op_expr(self, o: mypy.nodes.OpExpr, /) -> T:
         pass
 
-    def visit_comparison_expr(self, o: mypy.nodes.ComparisonExpr, /) -> T | None:
+    def visit_comparison_expr(self, o: mypy.nodes.ComparisonExpr, /) -> T:
         pass
 
-    def visit_cast_expr(self, o: mypy.nodes.CastExpr, /) -> T | None:
+    def visit_cast_expr(self, o: mypy.nodes.CastExpr, /) -> T:
         pass
 
-    def visit_assert_type_expr(self, o: mypy.nodes.AssertTypeExpr, /) -> T | None:
+    def visit_assert_type_expr(self, o: mypy.nodes.AssertTypeExpr, /) -> T:
         pass
 
-    def visit_reveal_expr(self, o: mypy.nodes.RevealExpr, /) -> T | None:
+    def visit_reveal_expr(self, o: mypy.nodes.RevealExpr, /) -> T:
         pass
 
-    def visit_super_expr(self, o: mypy.nodes.SuperExpr, /) -> T | None:
+    def visit_super_expr(self, o: mypy.nodes.SuperExpr, /) -> T:
         pass
 
-    def visit_assignment_expr(self, o: mypy.nodes.AssignmentExpr, /) -> T | None:
+    def visit_assignment_expr(self, o: mypy.nodes.AssignmentExpr, /) -> T:
         pass
 
-    def visit_unary_expr(self, o: mypy.nodes.UnaryExpr, /) -> T | None:
+    def visit_unary_expr(self, o: mypy.nodes.UnaryExpr, /) -> T:
         pass
 
-    def visit_list_expr(self, o: mypy.nodes.ListExpr, /) -> T | None:
+    def visit_list_expr(self, o: mypy.nodes.ListExpr, /) -> T:
         pass
 
-    def visit_dict_expr(self, o: mypy.nodes.DictExpr, /) -> T | None:
+    def visit_dict_expr(self, o: mypy.nodes.DictExpr, /) -> T:
         pass
 
-    def visit_tuple_expr(self, o: mypy.nodes.TupleExpr, /) -> T | None:
+    def visit_tuple_expr(self, o: mypy.nodes.TupleExpr, /) -> T:
         pass
 
-    def visit_set_expr(self, o: mypy.nodes.SetExpr, /) -> T | None:
+    def visit_set_expr(self, o: mypy.nodes.SetExpr, /) -> T:
         pass
 
-    def visit_index_expr(self, o: mypy.nodes.IndexExpr, /) -> T | None:
+    def visit_index_expr(self, o: mypy.nodes.IndexExpr, /) -> T:
         pass
 
-    def visit_type_application(self, o: mypy.nodes.TypeApplication, /) -> T | None:
+    def visit_type_application(self, o: mypy.nodes.TypeApplication, /) -> T:
         pass
 
-    def visit_lambda_expr(self, o: mypy.nodes.LambdaExpr, /) -> T | None:
+    def visit_lambda_expr(self, o: mypy.nodes.LambdaExpr, /) -> T:
         pass
 
-    def visit_list_comprehension(self, o: mypy.nodes.ListComprehension, /) -> T | None:
+    def visit_list_comprehension(self, o: mypy.nodes.ListComprehension, /) -> T:
         pass
 
-    def visit_set_comprehension(self, o: mypy.nodes.SetComprehension, /) -> T | None:
+    def visit_set_comprehension(self, o: mypy.nodes.SetComprehension, /) -> T:
         pass
 
-    def visit_dictionary_comprehension(self, o: mypy.nodes.DictionaryComprehension, /) -> T | None:
+    def visit_dictionary_comprehension(self, o: mypy.nodes.DictionaryComprehension, /) -> T:
         pass
 
-    def visit_generator_expr(self, o: mypy.nodes.GeneratorExpr, /) -> T | None:
+    def visit_generator_expr(self, o: mypy.nodes.GeneratorExpr, /) -> T:
         pass
 
-    def visit_slice_expr(self, o: mypy.nodes.SliceExpr, /) -> T | None:
+    def visit_slice_expr(self, o: mypy.nodes.SliceExpr, /) -> T:
         pass
 
-    def visit_conditional_expr(self, o: mypy.nodes.ConditionalExpr, /) -> T | None:
+    def visit_conditional_expr(self, o: mypy.nodes.ConditionalExpr, /) -> T:
         pass
 
-    def visit_type_var_expr(self, o: mypy.nodes.TypeVarExpr, /) -> T | None:
+    def visit_type_var_expr(self, o: mypy.nodes.TypeVarExpr, /) -> T:
         pass
 
-    def visit_paramspec_expr(self, o: mypy.nodes.ParamSpecExpr, /) -> T | None:
+    def visit_paramspec_expr(self, o: mypy.nodes.ParamSpecExpr, /) -> T:
         pass
 
-    def visit_type_var_tuple_expr(self, o: mypy.nodes.TypeVarTupleExpr, /) -> T | None:
+    def visit_type_var_tuple_expr(self, o: mypy.nodes.TypeVarTupleExpr, /) -> T:
         pass
 
-    def visit_type_alias_expr(self, o: mypy.nodes.TypeAliasExpr, /) -> T | None:
+    def visit_type_alias_expr(self, o: mypy.nodes.TypeAliasExpr, /) -> T:
         pass
 
-    def visit_namedtuple_expr(self, o: mypy.nodes.NamedTupleExpr, /) -> T | None:
+    def visit_namedtuple_expr(self, o: mypy.nodes.NamedTupleExpr, /) -> T:
         pass
 
-    def visit_enum_call_expr(self, o: mypy.nodes.EnumCallExpr, /) -> T | None:
+    def visit_enum_call_expr(self, o: mypy.nodes.EnumCallExpr, /) -> T:
         pass
 
-    def visit_typeddict_expr(self, o: mypy.nodes.TypedDictExpr, /) -> T | None:
+    def visit_typeddict_expr(self, o: mypy.nodes.TypedDictExpr, /) -> T:
         pass
 
-    def visit_newtype_expr(self, o: mypy.nodes.NewTypeExpr, /) -> T | None:
+    def visit_newtype_expr(self, o: mypy.nodes.NewTypeExpr, /) -> T:
         pass
 
-    def visit__promote_expr(self, o: mypy.nodes.PromoteExpr, /) -> T | None:
+    def visit__promote_expr(self, o: mypy.nodes.PromoteExpr, /) -> T:
         pass
 
-    def visit_await_expr(self, o: mypy.nodes.AwaitExpr, /) -> T | None:
+    def visit_await_expr(self, o: mypy.nodes.AwaitExpr, /) -> T:
         pass
 
-    def visit_temp_node(self, o: mypy.nodes.TempNode, /) -> T | None:
+    def visit_temp_node(self, o: mypy.nodes.TempNode, /) -> T:
         pass
 
     # Patterns
 
-    def visit_as_pattern(self, o: mypy.patterns.AsPattern, /) -> T | None:
+    def visit_as_pattern(self, o: mypy.patterns.AsPattern, /) -> T:
         pass
 
-    def visit_or_pattern(self, o: mypy.patterns.OrPattern, /) -> T | None:
+    def visit_or_pattern(self, o: mypy.patterns.OrPattern, /) -> T:
         pass
 
-    def visit_value_pattern(self, o: mypy.patterns.ValuePattern, /) -> T | None:
+    def visit_value_pattern(self, o: mypy.patterns.ValuePattern, /) -> T:
         pass
 
-    def visit_singleton_pattern(self, o: mypy.patterns.SingletonPattern, /) -> T | None:
+    def visit_singleton_pattern(self, o: mypy.patterns.SingletonPattern, /) -> T:
         pass
 
-    def visit_sequence_pattern(self, o: mypy.patterns.SequencePattern, /) -> T | None:
+    def visit_sequence_pattern(self, o: mypy.patterns.SequencePattern, /) -> T:
         pass
 
-    def visit_starred_pattern(self, o: mypy.patterns.StarredPattern, /) -> T | None:
+    def visit_starred_pattern(self, o: mypy.patterns.StarredPattern, /) -> T:
         pass
 
-    def visit_mapping_pattern(self, o: mypy.patterns.MappingPattern, /) -> T | None:
+    def visit_mapping_pattern(self, o: mypy.patterns.MappingPattern, /) -> T:
         pass
 
-    def visit_class_pattern(self, o: mypy.patterns.ClassPattern, /) -> T | None:
+    def visit_class_pattern(self, o: mypy.patterns.ClassPattern, /) -> T:
         pass
diff --git a/mypy_self_check.ini b/mypy_self_check.ini
index 7198a1f6f342..f54c1f17f025 100644
--- a/mypy_self_check.ini
+++ b/mypy_self_check.ini
@@ -12,3 +12,7 @@ exclude = mypy/typeshed/|mypyc/test-data/|mypyc/lib-rt/
 enable_error_code = ignore-without-code,redundant-expr
 enable_incomplete_feature = PreciseTupleTypes
 show_error_code_links = True
+
+[mypy-mypy.visitor]
+# See docstring for NodeVisitor for motivation.
+disable_error_code = empty-body
diff --git a/mypyc/irbuild/builder.py b/mypyc/irbuild/builder.py
index 154e0cd9798e..b0597617bdc5 100644
--- a/mypyc/irbuild/builder.py
+++ b/mypyc/irbuild/builder.py
@@ -274,7 +274,6 @@ def accept(self, node: Statement | Expression, *, can_borrow: bool = False) -> V
                 self.can_borrow = can_borrow
                 try:
                     res = node.accept(self.visitor)
-                    assert res is not None
                     res = self.coerce(res, self.node_type(node), node.line)
                 # If we hit an error during compilation, we want to
                 # keep trying, so we can produce more error
diff --git a/mypyc/irbuild/statement.py b/mypyc/irbuild/statement.py
index d5801dbcf619..cdc1d54589eb 100644
--- a/mypyc/irbuild/statement.py
+++ b/mypyc/irbuild/statement.py
@@ -1048,7 +1048,6 @@ def transform_type_alias_stmt(builder: IRBuilder, s: TypeAliasStmt) -> None:
     # The value needs to be lazily computed to match Python runtime behavior, but
     # Python public APIs don't support this, so we use a C primitive.
     compute_fn = s.value.accept(builder.visitor)
-    assert compute_fn is not None
     builder.builder.primitive_op(set_type_alias_compute_function_op, [alias, compute_fn], line)
 
     target = builder.get_assignment_target(s.name)

From a06b55dd9c5ef57947b8f252b5ccb78f5de3bc1f Mon Sep 17 00:00:00 2001
From: A5rocks <git@helvetica.moe>
Date: Tue, 28 Jan 2025 10:41:51 +0900
Subject: [PATCH 3/3] Raise instead of returning None

---
 mypy/checker.py     |  13 ++++
 mypy/semanal.py     |  33 +++++++++
 mypy/traverser.py   |  82 +++++++++++++++++++++
 mypy/visitor.py     | 171 ++++++++++++++++++++++----------------------
 mypy_self_check.ini |   4 --
 5 files changed, 212 insertions(+), 91 deletions(-)

diff --git a/mypy/checker.py b/mypy/checker.py
index 7b0b88186f76..91501f66e6de 100644
--- a/mypy/checker.py
+++ b/mypy/checker.py
@@ -77,6 +77,7 @@
     FuncBase,
     FuncDef,
     FuncItem,
+    GlobalDecl,
     IfStmt,
     Import,
     ImportAll,
@@ -92,6 +93,7 @@
     MypyFile,
     NameExpr,
     Node,
+    NonlocalDecl,
     OperatorAssignmentStmt,
     OpExpr,
     OverloadedFuncDef,
@@ -7766,6 +7768,17 @@ def warn_deprecated_overload_item(
                     if candidate == target:
                         self.warn_deprecated(item.func, context)
 
+    # leafs
+
+    def visit_pass_stmt(self, o: PassStmt, /) -> None:
+        return None
+
+    def visit_nonlocal_decl(self, o: NonlocalDecl, /) -> None:
+        return None
+
+    def visit_global_decl(self, o: GlobalDecl, /) -> None:
+        return None
+
 
 class CollectArgTypeVarTypes(TypeTraverserVisitor):
     """Collects the non-nested argument types in a set."""
diff --git a/mypy/semanal.py b/mypy/semanal.py
index 034d8fb28b42..e9776325a496 100644
--- a/mypy/semanal.py
+++ b/mypy/semanal.py
@@ -97,10 +97,12 @@
     AwaitExpr,
     Block,
     BreakStmt,
+    BytesExpr,
     CallExpr,
     CastExpr,
     ClassDef,
     ComparisonExpr,
+    ComplexExpr,
     ConditionalExpr,
     Context,
     ContinueStmt,
@@ -114,6 +116,7 @@
     Expression,
     ExpressionStmt,
     FakeExpression,
+    FloatExpr,
     ForStmt,
     FuncBase,
     FuncDef,
@@ -126,6 +129,7 @@
     ImportBase,
     ImportFrom,
     IndexExpr,
+    IntExpr,
     LambdaExpr,
     ListComprehension,
     ListExpr,
@@ -193,6 +197,7 @@
     MappingPattern,
     OrPattern,
     SequencePattern,
+    SingletonPattern,
     StarredPattern,
     ValuePattern,
 )
@@ -7522,6 +7527,34 @@ def parse_dataclass_transform_field_specifiers(self, arg: Expression) -> tuple[s
             names.append(specifier.fullname)
         return tuple(names)
 
+    # leafs
+    def visit_int_expr(self, o: IntExpr, /) -> None:
+        return None
+
+    def visit_str_expr(self, o: StrExpr, /) -> None:
+        return None
+
+    def visit_bytes_expr(self, o: BytesExpr, /) -> None:
+        return None
+
+    def visit_float_expr(self, o: FloatExpr, /) -> None:
+        return None
+
+    def visit_complex_expr(self, o: ComplexExpr, /) -> None:
+        return None
+
+    def visit_ellipsis(self, o: EllipsisExpr, /) -> None:
+        return None
+
+    def visit_temp_node(self, o: TempNode, /) -> None:
+        return None
+
+    def visit_pass_stmt(self, o: PassStmt, /) -> None:
+        return None
+
+    def visit_singleton_pattern(self, o: SingletonPattern, /) -> None:
+        return None
+
 
 def replace_implicit_first_type(sig: FunctionLike, new: Type) -> FunctionLike:
     if isinstance(sig, CallableType):
diff --git a/mypy/traverser.py b/mypy/traverser.py
index 2c8ea49491bc..7d7794822396 100644
--- a/mypy/traverser.py
+++ b/mypy/traverser.py
@@ -58,6 +58,7 @@
     OverloadedFuncDef,
     ParamSpecExpr,
     PassStmt,
+    PromoteExpr,
     RaiseStmt,
     ReturnStmt,
     RevealExpr,
@@ -67,6 +68,7 @@
     StarExpr,
     StrExpr,
     SuperExpr,
+    TempNode,
     TryStmt,
     TupleExpr,
     TypeAlias,
@@ -77,6 +79,7 @@
     TypeVarExpr,
     TypeVarTupleExpr,
     UnaryExpr,
+    Var,
     WhileStmt,
     WithStmt,
     YieldExpr,
@@ -415,6 +418,85 @@ def visit_import_from(self, o: ImportFrom, /) -> None:
         for a in o.assignments:
             a.accept(self)
 
+    # leaf nodes
+    def visit_name_expr(self, o: NameExpr, /) -> None:
+        return None
+
+    def visit_str_expr(self, o: StrExpr, /) -> None:
+        return None
+
+    def visit_int_expr(self, o: IntExpr, /) -> None:
+        return None
+
+    def visit_float_expr(self, o: FloatExpr, /) -> None:
+        return None
+
+    def visit_bytes_expr(self, o: BytesExpr, /) -> None:
+        return None
+
+    def visit_ellipsis(self, o: EllipsisExpr, /) -> None:
+        return None
+
+    def visit_var(self, o: Var, /) -> None:
+        return None
+
+    def visit_continue_stmt(self, o: ContinueStmt, /) -> None:
+        return None
+
+    def visit_pass_stmt(self, o: PassStmt, /) -> None:
+        return None
+
+    def visit_break_stmt(self, o: BreakStmt, /) -> None:
+        return None
+
+    def visit_temp_node(self, o: TempNode, /) -> None:
+        return None
+
+    def visit_nonlocal_decl(self, o: NonlocalDecl, /) -> None:
+        return None
+
+    def visit_global_decl(self, o: GlobalDecl, /) -> None:
+        return None
+
+    def visit_import_all(self, o: ImportAll, /) -> None:
+        return None
+
+    def visit_type_var_expr(self, o: TypeVarExpr, /) -> None:
+        return None
+
+    def visit_paramspec_expr(self, o: ParamSpecExpr, /) -> None:
+        return None
+
+    def visit_type_var_tuple_expr(self, o: TypeVarTupleExpr, /) -> None:
+        return None
+
+    def visit_type_alias_expr(self, o: TypeAliasExpr, /) -> None:
+        return None
+
+    def visit_type_alias(self, o: TypeAlias, /) -> None:
+        return None
+
+    def visit_namedtuple_expr(self, o: NamedTupleExpr, /) -> None:
+        return None
+
+    def visit_typeddict_expr(self, o: TypedDictExpr, /) -> None:
+        return None
+
+    def visit_newtype_expr(self, o: NewTypeExpr, /) -> None:
+        return None
+
+    def visit__promote_expr(self, o: PromoteExpr, /) -> None:
+        return None
+
+    def visit_complex_expr(self, o: ComplexExpr, /) -> None:
+        return None
+
+    def visit_enum_call_expr(self, o: EnumCallExpr, /) -> None:
+        return None
+
+    def visit_singleton_pattern(self, o: SingletonPattern, /) -> None:
+        return None
+
 
 class ExtendedTraverserVisitor(TraverserVisitor):
     """This is a more flexible traverser.
diff --git a/mypy/visitor.py b/mypy/visitor.py
index 6613b6cbb144..d1b2ca416410 100644
--- a/mypy/visitor.py
+++ b/mypy/visitor.py
@@ -356,273 +356,270 @@ class NodeVisitor(Generic[T], ExpressionVisitor[T], StatementVisitor[T], Pattern
     """Empty base class for parse tree node visitors.
 
     The T type argument specifies the return type of the visit
-    methods. As all methods defined here return None by default,
+    methods. As all methods defined here raise by default,
     subclasses do not always need to override all the methods.
-
-    TODO: make the default return value explicit, then turn on
-          empty body checking in mypy_self_check.ini.
     """
 
     # Not in superclasses:
 
     def visit_mypy_file(self, o: mypy.nodes.MypyFile, /) -> T:
-        pass
+        raise NotImplementedError()
 
     # TODO: We have a visit_var method, but no visit_typeinfo or any
     # other non-Statement SymbolNode (accepting those will raise a
     # runtime error). Maybe this should be resolved in some direction.
     def visit_var(self, o: mypy.nodes.Var, /) -> T:
-        pass
+        raise NotImplementedError()
 
     # Module structure
 
     def visit_import(self, o: mypy.nodes.Import, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_import_from(self, o: mypy.nodes.ImportFrom, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_import_all(self, o: mypy.nodes.ImportAll, /) -> T:
-        pass
+        raise NotImplementedError()
 
     # Definitions
 
     def visit_func_def(self, o: mypy.nodes.FuncDef, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_overloaded_func_def(self, o: mypy.nodes.OverloadedFuncDef, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_class_def(self, o: mypy.nodes.ClassDef, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_global_decl(self, o: mypy.nodes.GlobalDecl, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_nonlocal_decl(self, o: mypy.nodes.NonlocalDecl, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_decorator(self, o: mypy.nodes.Decorator, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_type_alias(self, o: mypy.nodes.TypeAlias, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_placeholder_node(self, o: mypy.nodes.PlaceholderNode, /) -> T:
-        pass
+        raise NotImplementedError()
 
     # Statements
 
     def visit_block(self, o: mypy.nodes.Block, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_expression_stmt(self, o: mypy.nodes.ExpressionStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_assignment_stmt(self, o: mypy.nodes.AssignmentStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_operator_assignment_stmt(self, o: mypy.nodes.OperatorAssignmentStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_while_stmt(self, o: mypy.nodes.WhileStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_for_stmt(self, o: mypy.nodes.ForStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_return_stmt(self, o: mypy.nodes.ReturnStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_assert_stmt(self, o: mypy.nodes.AssertStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_del_stmt(self, o: mypy.nodes.DelStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_if_stmt(self, o: mypy.nodes.IfStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_break_stmt(self, o: mypy.nodes.BreakStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_continue_stmt(self, o: mypy.nodes.ContinueStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_pass_stmt(self, o: mypy.nodes.PassStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_raise_stmt(self, o: mypy.nodes.RaiseStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_try_stmt(self, o: mypy.nodes.TryStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_with_stmt(self, o: mypy.nodes.WithStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_match_stmt(self, o: mypy.nodes.MatchStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_type_alias_stmt(self, o: mypy.nodes.TypeAliasStmt, /) -> T:
-        pass
+        raise NotImplementedError()
 
     # Expressions (default no-op implementation)
 
     def visit_int_expr(self, o: mypy.nodes.IntExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_str_expr(self, o: mypy.nodes.StrExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_bytes_expr(self, o: mypy.nodes.BytesExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_float_expr(self, o: mypy.nodes.FloatExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_complex_expr(self, o: mypy.nodes.ComplexExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_ellipsis(self, o: mypy.nodes.EllipsisExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_star_expr(self, o: mypy.nodes.StarExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_name_expr(self, o: mypy.nodes.NameExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_member_expr(self, o: mypy.nodes.MemberExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_yield_from_expr(self, o: mypy.nodes.YieldFromExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_yield_expr(self, o: mypy.nodes.YieldExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_call_expr(self, o: mypy.nodes.CallExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_op_expr(self, o: mypy.nodes.OpExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_comparison_expr(self, o: mypy.nodes.ComparisonExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_cast_expr(self, o: mypy.nodes.CastExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_assert_type_expr(self, o: mypy.nodes.AssertTypeExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_reveal_expr(self, o: mypy.nodes.RevealExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_super_expr(self, o: mypy.nodes.SuperExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_assignment_expr(self, o: mypy.nodes.AssignmentExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_unary_expr(self, o: mypy.nodes.UnaryExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_list_expr(self, o: mypy.nodes.ListExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_dict_expr(self, o: mypy.nodes.DictExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_tuple_expr(self, o: mypy.nodes.TupleExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_set_expr(self, o: mypy.nodes.SetExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_index_expr(self, o: mypy.nodes.IndexExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_type_application(self, o: mypy.nodes.TypeApplication, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_lambda_expr(self, o: mypy.nodes.LambdaExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_list_comprehension(self, o: mypy.nodes.ListComprehension, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_set_comprehension(self, o: mypy.nodes.SetComprehension, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_dictionary_comprehension(self, o: mypy.nodes.DictionaryComprehension, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_generator_expr(self, o: mypy.nodes.GeneratorExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_slice_expr(self, o: mypy.nodes.SliceExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_conditional_expr(self, o: mypy.nodes.ConditionalExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_type_var_expr(self, o: mypy.nodes.TypeVarExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_paramspec_expr(self, o: mypy.nodes.ParamSpecExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_type_var_tuple_expr(self, o: mypy.nodes.TypeVarTupleExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_type_alias_expr(self, o: mypy.nodes.TypeAliasExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_namedtuple_expr(self, o: mypy.nodes.NamedTupleExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_enum_call_expr(self, o: mypy.nodes.EnumCallExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_typeddict_expr(self, o: mypy.nodes.TypedDictExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_newtype_expr(self, o: mypy.nodes.NewTypeExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit__promote_expr(self, o: mypy.nodes.PromoteExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_await_expr(self, o: mypy.nodes.AwaitExpr, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_temp_node(self, o: mypy.nodes.TempNode, /) -> T:
-        pass
+        raise NotImplementedError()
 
     # Patterns
 
     def visit_as_pattern(self, o: mypy.patterns.AsPattern, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_or_pattern(self, o: mypy.patterns.OrPattern, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_value_pattern(self, o: mypy.patterns.ValuePattern, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_singleton_pattern(self, o: mypy.patterns.SingletonPattern, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_sequence_pattern(self, o: mypy.patterns.SequencePattern, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_starred_pattern(self, o: mypy.patterns.StarredPattern, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_mapping_pattern(self, o: mypy.patterns.MappingPattern, /) -> T:
-        pass
+        raise NotImplementedError()
 
     def visit_class_pattern(self, o: mypy.patterns.ClassPattern, /) -> T:
-        pass
+        raise NotImplementedError()
diff --git a/mypy_self_check.ini b/mypy_self_check.ini
index f54c1f17f025..7198a1f6f342 100644
--- a/mypy_self_check.ini
+++ b/mypy_self_check.ini
@@ -12,7 +12,3 @@ exclude = mypy/typeshed/|mypyc/test-data/|mypyc/lib-rt/
 enable_error_code = ignore-without-code,redundant-expr
 enable_incomplete_feature = PreciseTupleTypes
 show_error_code_links = True
-
-[mypy-mypy.visitor]
-# See docstring for NodeVisitor for motivation.
-disable_error_code = empty-body