[PEP 695] Enable new type parameter syntax by default (#17798)

I think the PEP 695 syntax is supported well enough now to enable it by
default.

Author: JukkaL

docs/source/command_line.rst

@@ -1008,7 +1008,7 @@ format into the specified directory.
 Enabling incomplete/experimental features
 *****************************************
 
-.. option:: --enable-incomplete-feature {PreciseTupleTypes, NewGenericSyntax, InlineTypedDict}
+.. option:: --enable-incomplete-feature {PreciseTupleTypes, InlineTypedDict}
 
     Some features may require several mypy releases to implement, for example
     due to their complexity, potential for backwards incompatibility, or
@@ -1055,19 +1055,6 @@ List of currently incomplete/experimental features:
          # Without PreciseTupleTypes: tuple[int, ...]
          # With PreciseTupleTypes: tuple[()] | tuple[int] | tuple[int, int]
 
-* ``NewGenericSyntax``: this feature enables support for syntax defined
-  by :pep:`695`. For example:
-
-  .. code-block:: python
-
-     class Container[T]:  # defines a generic class
-         content: T
-
-     def first[T](items: list[T]) -> T:  # defines a generic function
-         return items[0]
-
-     type Items[T] = list[tuple[T, T]]  # defines a generic type alias
-
 * ``InlineTypedDict``: this feature enables non-standard syntax for inline
   :ref:`TypedDicts <typeddict>`, for example:
 

mypy/fastparse.py

@@ -92,7 +92,7 @@
     YieldFromExpr,
     check_arg_names,
 )
-from mypy.options import NEW_GENERIC_SYNTAX, Options
+from mypy.options import Options
 from mypy.patterns import (
     AsPattern,
     ClassPattern,
@@ -965,19 +965,7 @@ def do_func_def(
                 return_type = AnyType(TypeOfAny.from_error)
         else:
             if sys.version_info >= (3, 12) and n.type_params:
-                if NEW_GENERIC_SYNTAX in self.options.enable_incomplete_feature:
-                    explicit_type_params = self.translate_type_params(n.type_params)
-                else:
-                    self.fail(
-                        ErrorMessage(
-                            "PEP 695 generics are not yet supported. "
-                            "Use --enable-incomplete-feature=NewGenericSyntax for experimental support",
-                            code=codes.VALID_TYPE,
-                        ),
-                        n.type_params[0].lineno,
-                        n.type_params[0].col_offset,
-                        blocker=False,
-                    )
+                explicit_type_params = self.translate_type_params(n.type_params)
 
             arg_types = [a.type_annotation for a in args]
             return_type = TypeConverter(
@@ -1157,19 +1145,7 @@ def visit_ClassDef(self, n: ast3.ClassDef) -> ClassDef:
         explicit_type_params: list[TypeParam] | None = None
 
         if sys.version_info >= (3, 12) and n.type_params:
-            if NEW_GENERIC_SYNTAX in self.options.enable_incomplete_feature:
-                explicit_type_params = self.translate_type_params(n.type_params)
-            else:
-                self.fail(
-                    ErrorMessage(
-                        "PEP 695 generics are not yet supported. "
-                        "Use --enable-incomplete-feature=NewGenericSyntax for experimental support",
-                        code=codes.VALID_TYPE,
-                    ),
-                    n.type_params[0].lineno,
-                    n.type_params[0].col_offset,
-                    blocker=False,
-                )
+            explicit_type_params = self.translate_type_params(n.type_params)
 
         cdef = ClassDef(
             n.name,
@@ -1843,31 +1819,17 @@ def validate_type_alias(self, n: ast_TypeAlias) -> None:
     # TypeAlias(identifier name, type_param* type_params, expr value)
     def visit_TypeAlias(self, n: ast_TypeAlias) -> TypeAliasStmt | AssignmentStmt:
         node: TypeAliasStmt | AssignmentStmt
-        if NEW_GENERIC_SYNTAX in self.options.enable_incomplete_feature:
-            type_params = self.translate_type_params(n.type_params)
-            self.validate_type_alias(n)
-            value = self.visit(n.value)
-            # Since the value is evaluated lazily, wrap the value inside a lambda.
-            # This helps mypyc.
-            ret = ReturnStmt(value)
-            self.set_line(ret, n.value)
-            value_func = LambdaExpr(body=Block([ret]))
-            self.set_line(value_func, n.value)
-            node = TypeAliasStmt(self.visit_Name(n.name), type_params, value_func)
-            return self.set_line(node, n)
-        else:
-            self.fail(
-                ErrorMessage(
-                    "PEP 695 type aliases are not yet supported. "
-                    "Use --enable-incomplete-feature=NewGenericSyntax for experimental support",
-                    code=codes.VALID_TYPE,
-                ),
-                n.lineno,
-                n.col_offset,
-                blocker=False,
-            )
-            node = AssignmentStmt([NameExpr(n.name.id)], self.visit(n.value))
-            return self.set_line(node, n)
+        type_params = self.translate_type_params(n.type_params)
+        self.validate_type_alias(n)
+        value = self.visit(n.value)
+        # Since the value is evaluated lazily, wrap the value inside a lambda.
+        # This helps mypyc.
+        ret = ReturnStmt(value)
+        self.set_line(ret, n.value)
+        value_func = LambdaExpr(body=Block([ret]))
+        self.set_line(value_func, n.value)
+        node = TypeAliasStmt(self.visit_Name(n.name), type_params, value_func)
+        return self.set_line(node, n)
 
 
 class TypeConverter:

mypy/options.py

@@ -75,8 +75,8 @@ class BuildType:
 PRECISE_TUPLE_TYPES: Final = "PreciseTupleTypes"
 NEW_GENERIC_SYNTAX: Final = "NewGenericSyntax"
 INLINE_TYPEDDICT: Final = "InlineTypedDict"
-INCOMPLETE_FEATURES: Final = frozenset((PRECISE_TUPLE_TYPES, NEW_GENERIC_SYNTAX, INLINE_TYPEDDICT))
-COMPLETE_FEATURES: Final = frozenset((TYPE_VAR_TUPLE, UNPACK))
+INCOMPLETE_FEATURES: Final = frozenset((PRECISE_TUPLE_TYPES, INLINE_TYPEDDICT))
+COMPLETE_FEATURES: Final = frozenset((TYPE_VAR_TUPLE, UNPACK, NEW_GENERIC_SYNTAX))
 
 
 class Options:

mypyc/test-data/run-python312.test

@@ -1,5 +1,4 @@
 [case testPEP695Basics]
-# flags: --enable-incomplete-feature=NewGenericSyntax
 from typing import Any, TypeAliasType, cast
 
 from testutil import assertRaises
@@ -192,7 +191,6 @@ def test_recursive_type_alias() -> None:
 [typing fixtures/typing-full.pyi]
 
 [case testPEP695GenericTypeAlias]
-# flags: --enable-incomplete-feature=NewGenericSyntax
 from typing import Callable
 from types import GenericAlias
 

mypyc/test/test_run.py

@@ -196,7 +196,6 @@ def run_case_step(self, testcase: DataDrivenTestCase, incremental_step: int) ->
         options.preserve_asts = True
         options.allow_empty_bodies = True
         options.incremental = self.separate
-        options.enable_incomplete_feature.append("NewGenericSyntax")
 
         # Avoid checking modules/packages named 'unchecked', to provide a way
         # to test interacting with code we don't have types for.