Fix line number for slices, clean up old logic (#18397)

Fixes #17655

The decorator cleanup moves a type ignore, but so does the bug fix for
decorators in #18392 , so might as well batch into a single release

Author: hauntsaninja

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Next release
 
+### Performance improvements
+
+TODO
+
 ### Drop Support for Python 3.8
 
 Mypy no longer supports running with Python 3.8, which has reached end-of-life.
@@ -40,6 +44,14 @@ Contributed by Christoph Tyralla (PR [18180](https://github.com/python/mypy/pull
 (Speaking of partial types, another reminder that mypy plans on enabling `--local-partial-types`
 by default in **mypy 2.0**).
 
+### Better line numbers for decorators and slice expressions
+
+Mypy now uses more correct line numbers for decorators and slice expressions. In some cases, this
+may necessitate changing the location of a `# type: ignore` comment.
+
+Contributed by Shantanu Jain (PR [18392](https://github.com/python/mypy/pull/18392),
+PR [18397](https://github.com/python/mypy/pull/18397)).
+
 ## Mypy 1.14
 
 We’ve just uploaded mypy 1.14 to the Python Package Index ([PyPI](https://pypi.org/project/mypy/)).

mypy/fastparse.py

@@ -1009,28 +1009,22 @@ def do_func_def(
             func_def.is_coroutine = True
         if func_type is not None:
             func_type.definition = func_def
-            func_type.line = lineno
+            func_type.set_line(lineno)
 
         if n.decorator_list:
-            # Set deco_line to the old pre-3.8 lineno, in order to keep
-            # existing "# type: ignore" comments working:
-            deco_line = n.decorator_list[0].lineno
-
             var = Var(func_def.name)
             var.is_ready = False
             var.set_line(lineno)
 
             func_def.is_decorated = True
-            func_def.deco_line = deco_line
-            func_def.set_line(lineno, n.col_offset, end_line, end_column)
+            self.set_line(func_def, n)
 
             deco = Decorator(func_def, self.translate_expr_list(n.decorator_list), var)
             first = n.decorator_list[0]
             deco.set_line(first.lineno, first.col_offset, end_line, end_column)
             retval: FuncDef | Decorator = deco
         else:
-            # FuncDef overrides set_line -- can't use self.set_line
-            func_def.set_line(lineno, n.col_offset, end_line, end_column)
+            self.set_line(func_def, n)
             retval = func_def
         if self.options.include_docstrings:
             func_def.docstring = ast3.get_docstring(n, clean=False)
@@ -1149,10 +1143,7 @@ def visit_ClassDef(self, n: ast3.ClassDef) -> ClassDef:
             type_args=explicit_type_params,
         )
         cdef.decorators = self.translate_expr_list(n.decorator_list)
-        # Set lines to match the old mypy 0.700 lines, in order to keep
-        # existing "# type: ignore" comments working:
-        cdef.line = n.lineno
-        cdef.deco_line = n.decorator_list[0].lineno if n.decorator_list else None
+        self.set_line(cdef, n)
 
         if self.options.include_docstrings:
             cdef.docstring = ast3.get_docstring(n, clean=False)
@@ -1247,8 +1238,7 @@ def visit_AnnAssign(self, n: ast3.AnnAssign) -> AssignmentStmt:
         line = n.lineno
         if n.value is None:  # always allow 'x: int'
             rvalue: Expression = TempNode(AnyType(TypeOfAny.special_form), no_rhs=True)
-            rvalue.line = line
-            rvalue.column = n.col_offset
+            self.set_line(rvalue, n)
         else:
             rvalue = self.visit(n.value)
         typ = TypeConverter(self.errors, line=line).visit(n.annotation)
@@ -1675,19 +1665,7 @@ def visit_Attribute(self, n: Attribute) -> MemberExpr | SuperExpr:
     # Subscript(expr value, slice slice, expr_context ctx)
     def visit_Subscript(self, n: ast3.Subscript) -> IndexExpr:
         e = IndexExpr(self.visit(n.value), self.visit(n.slice))
-        self.set_line(e, n)
-        # alias to please mypyc
-        is_py38_or_earlier = sys.version_info < (3, 9)
-        if isinstance(n.slice, ast3.Slice) or (
-            is_py38_or_earlier and isinstance(n.slice, ast3.ExtSlice)
-        ):
-            # Before Python 3.9, Slice has no line/column in the raw ast. To avoid incompatibility
-            # visit_Slice doesn't set_line, even in Python 3.9 on.
-            # ExtSlice also has no line/column info. In Python 3.9 on, line/column is set for
-            # e.index when visiting n.slice.
-            e.index.line = e.line
-            e.index.column = e.column
-        return e
+        return self.set_line(e, n)
 
     # Starred(expr value, expr_context ctx)
     def visit_Starred(self, n: Starred) -> StarExpr:
@@ -1718,7 +1696,8 @@ def visit_Tuple(self, n: ast3.Tuple) -> TupleExpr:
 
     # Slice(expr? lower, expr? upper, expr? step)
     def visit_Slice(self, n: ast3.Slice) -> SliceExpr:
-        return SliceExpr(self.visit(n.lower), self.visit(n.upper), self.visit(n.step))
+        e = SliceExpr(self.visit(n.lower), self.visit(n.upper), self.visit(n.step))
+        return self.set_line(e, n)
 
     # ExtSlice(slice* dims)
     def visit_ExtSlice(self, n: ast3.ExtSlice) -> TupleExpr:

mypy/messages.py

@@ -244,7 +244,7 @@ def span_from_context(ctx: Context) -> Iterable[int]:
             TODO: address this in follow up PR
             """
             if isinstance(ctx, (ClassDef, FuncDef)):
-                return range(ctx.deco_line or ctx.line, ctx.line + 1)
+                return range(ctx.line, ctx.line + 1)
             elif not isinstance(ctx, Expression):
                 return [ctx.line]
             else:

mypy/nodes.py

@@ -768,7 +768,6 @@ class FuncDef(FuncItem, SymbolNode, Statement):
         "is_conditional",
         "abstract_status",
         "original_def",
-        "deco_line",
         "is_trivial_body",
         "is_mypy_only",
         # Present only when a function is decorated with @typing.dataclass_transform or similar
@@ -798,8 +797,6 @@ def __init__(
         self.is_trivial_body = False
         # Original conditional definition
         self.original_def: None | FuncDef | Var | Decorator = None
-        # Used for error reporting (to keep backward compatibility with pre-3.8)
-        self.deco_line: int | None = None
         # Definitions that appear in if TYPE_CHECKING are marked with this flag.
         self.is_mypy_only = False
         self.dataclass_transform_spec: DataclassTransformSpec | None = None
@@ -1115,7 +1112,6 @@ class ClassDef(Statement):
         "keywords",
         "analyzed",
         "has_incompatible_baseclass",
-        "deco_line",
         "docstring",
         "removed_statements",
     )
@@ -1166,8 +1162,6 @@ def __init__(
         self.keywords = dict(keywords) if keywords else {}
         self.analyzed = None
         self.has_incompatible_baseclass = False
-        # Used for error reporting (to keep backward compatibility with pre-3.8)
-        self.deco_line: int | None = None
         self.docstring: str | None = None
         self.removed_statements = []
 

mypy/plugins/common.py

@@ -282,7 +282,6 @@ def add_overloaded_method_to_class(
             var = Var(func.name, func.type)
             var.set_line(func.line)
             func.is_decorated = True
-            func.deco_line = func.line
 
             deco = Decorator(func, [], var)
         else:

test-data/unit/check-python38.test

@@ -17,8 +17,8 @@ def f(): ...  # E: Function is missing a return type annotation \
 # flags: --disallow-untyped-defs --warn-unused-ignores
 def d(f): ...  # type: ignore
 @d
-# type: ignore
-def f(): ...  # type: ignore  # E: Unused "type: ignore" comment
+# type: ignore  # E: Unused "type: ignore" comment
+def f(): ...  # type: ignore
 
 [case testIgnoreDecoratedFunction2]
 # flags: --disallow-untyped-defs

test-data/unit/parse.test

@@ -3171,10 +3171,10 @@ MypyFile:1(
     IndexExpr:1(
       NameExpr(a)
       TupleExpr:1(
-        SliceExpr:-1(
+        SliceExpr:1(
           <empty>
           <empty>)
-        SliceExpr:-1(
+        SliceExpr:1(
           <empty>
           <empty>)))))
 
@@ -3186,10 +3186,10 @@ MypyFile:1(
     IndexExpr:1(
       NameExpr(a)
       TupleExpr:1(
-        SliceExpr:-1(
+        SliceExpr:1(
           IntExpr(1)
           IntExpr(2))
-        SliceExpr:-1(
+        SliceExpr:1(
           <empty>
           <empty>)))))
 
@@ -3201,13 +3201,29 @@ MypyFile:1(
     IndexExpr:1(
       NameExpr(a)
       TupleExpr:1(
-        SliceExpr:-1(
+        SliceExpr:1(
           IntExpr(1)
           IntExpr(2)
           IntExpr(3))
         Ellipsis
         IntExpr(1)))))
 
+[case testParseExtendedSlicing4]
+m[*index, :]
+[out]
+main:1: error: invalid syntax
+[out version>=3.11]
+MypyFile:1(
+  ExpressionStmt:1(
+    IndexExpr:1(
+      NameExpr(m)
+      TupleExpr:1(
+        StarExpr:1(
+          NameExpr(index))
+        SliceExpr:1(
+          <empty>
+          <empty>)))))
+
 [case testParseIfExprInDictExpr]
 test =  { 'spam': 'eggs' if True else 'bacon' }
 [out]