Sep 2, 2025 · Sep 1, 2025 · Sep 2, 2025 · Sep 2, 2025
diff --git a/mypyc/irbuild/prepare.py b/mypyc/irbuild/prepare.py
    ir = mapper.type_to_ir[cdef.info]
    info = cdef.info

    attrs = get_mypyc_attrs(cdef)
    attrs, attrs_lines = get_mypyc_attrs(cdef)
    if attrs.get("allow_interpreted_subclasses") is True:
        ir.allow_interpreted_subclasses = True
    if attrs.get("serializable") is True:
        # Supports copy.copy and pickle (including subclasses)
        ir._serializable = True

    free_list_len = attrs.get("free_list_len")
    if free_list_len is not None:
        line = attrs_lines["free_list_len"]
        if ir.is_trait:
            errors.error('"free_list_len" can\'t be used with traits', path, line)
        if free_list_len == 1:
            ir.reuse_freed_instance = True
        else:
            errors.error(f'Unsupported value for "free_list_len": {free_list_len}', path, line)

    # Check for subclassing from builtin types
    for cls in info.mro:
        # Special case exceptions and dicts
diff --git a/mypyc/irbuild/util.py b/mypyc/irbuild/util.py
        return False
    elif isinstance(e, RefExpr) and e.fullname == "builtins.None":
        return None
    elif isinstance(e, IntExpr):
        return e.value
    return NotImplemented


    return None


 def get_mypyc_attrs(stmt: ClassDef | Decorator) -> dict[str, Any]:
 def get_mypyc_attrs(stmt: ClassDef | Decorator) ->tuple[dict[str, Any], dict[str, int]]:
    """Collect all the mypyc_attr attributes on a class definition or a function."""
    attrs: dict[str, Any] = {}
    lines: dict[str, int] = {}
    for dec in stmt.decorators:
        d = get_mypyc_attr_call(dec)
        if d:
            for name, arg in zip(d.arg_names, d.args):
                if name is None:
                    if isinstance(arg, StrExpr):
                        attrs[arg.value] = True
                        lines[arg.value] = d.line
                else:
                    attrs[name] = get_mypyc_attr_literal(arg)
                    lines[name] = d.line

    return attrs
    return attrs, lines


 def is_extension_class(path: str, cdef: ClassDef, errors: Errors) -> bool:
diff --git a/mypyc/test-data/irbuild-classes.test b/mypyc/test-data/irbuild-classes.test
 class InheritsPython(dict):
    def __new__(cls) -> InheritsPython:
        return super().__new__(cls)  # E: super().__new__() not supported for classes inheriting from non-native classes

 [case testClassWithFreeList]
 from mypy_extensions import mypyc_attr, trait

 @mypyc_attr(free_list_len=1)
 class UsesFreeList:
    pass

 @mypyc_attr(free_list_len=None)
 class NoFreeList:
    pass

 @mypyc_attr(free_list_len=2)  # E: Unsupported value for "free_list_len": 2
 class FreeListError:
    pass

 @trait
 @mypyc_attr(free_list_len=1)  # E: "free_list_len" can't be used with traits
 class NonNative:
    pass
diff --git a/mypyc/test-data/run-classes.test b/mypyc/test-data/run-classes.test
 assert t.generic == "{}"
 assert t.bitfield == 0x0C
 assert t.default == 10

 [case testPerTypeFreeList]
 from mypy_extensions import mypyc_attr

 a = []

 @mypyc_attr(free_list=1)
 class Foo:
    def __init__(self, x: int) -> None:
        self.x = x
        a.append(x)

 def test_alloc() -> None:
    x: Foo | None
    y: Foo | None

    x = Foo(1)
    assert x.x == 1
    x = None

    x = Foo(2)
    assert x.x == 2
    y = Foo(3)
    assert x.x == 2
    assert y.x == 3
    x = None
    y = None
    assert a == [1, 2, 3]

    x = Foo(4)
    assert x.x == 4
    y = Foo(5)
    assert x.x == 4
    assert y.x == 5
Original file line number	Diff line number	Diff line change
Expand Up		@@ -351,13 +351,23 @@ def prepare_class_def(
		ir = mapper.type_to_ir[cdef.info]
		info = cdef.info

		attrs = get_mypyc_attrs(cdef)
		attrs, attrs_lines = get_mypyc_attrs(cdef)
		if attrs.get("allow_interpreted_subclasses") is True:
		ir.allow_interpreted_subclasses = True
		if attrs.get("serializable") is True:
		# Supports copy.copy and pickle (including subclasses)
		ir._serializable = True

		free_list_len = attrs.get("free_list_len")
		if free_list_len is not None:
		line = attrs_lines["free_list_len"]
		if ir.is_trait:
		errors.error('"free_list_len" can\'t be used with traits', path, line)
		if free_list_len == 1:
		ir.reuse_freed_instance = True
		else:
		errors.error(f'Unsupported value for "free_list_len": {free_list_len}', path, line)

		# Check for subclassing from builtin types
		for cls in info.mro:
		# Special case exceptions and dicts
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -96,6 +96,8 @@ def get_mypyc_attr_literal(e: Expression) -> Any:
		return False
		elif isinstance(e, RefExpr) and e.fullname == "builtins.None":
		return None
		elif isinstance(e, IntExpr):
		return e.value
		return NotImplemented


Expand All		@@ -110,20 +112,23 @@ def get_mypyc_attr_call(d: Expression) -> CallExpr \| None:
		return None


		def get_mypyc_attrs(stmt: ClassDef \| Decorator) -> dict[str, Any]:
		def get_mypyc_attrs(stmt: ClassDef \| Decorator) ->tuple[dict[str, Any], dict[str, int]]:
		"""Collect all the mypyc_attr attributes on a class definition or a function."""
		attrs: dict[str, Any] = {}
		lines: dict[str, int] = {}
		for dec in stmt.decorators:
		d = get_mypyc_attr_call(dec)
		if d:
		for name, arg in zip(d.arg_names, d.args):
		if name is None:
		if isinstance(arg, StrExpr):
		attrs[arg.value] = True
		lines[arg.value] = d.line
		else:
		attrs[name] = get_mypyc_attr_literal(arg)
		lines[name] = d.line

		return attrs
		return attrs, lines


		def is_extension_class(path: str, cdef: ClassDef, errors: Errors) -> bool:
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1734,3 +1734,23 @@ class NonNative:
		class InheritsPython(dict):
		def __new__(cls) -> InheritsPython:
		return super().__new__(cls) # E: super().__new__() not supported for classes inheriting from non-native classes

		[case testClassWithFreeList]
		from mypy_extensions import mypyc_attr, trait

		@mypyc_attr(free_list_len=1)
		class UsesFreeList:
		pass

		@mypyc_attr(free_list_len=None)
		class NoFreeList:
		pass

		@mypyc_attr(free_list_len=2) # E: Unsupported value for "free_list_len": 2
		class FreeListError:
		pass

		@trait
		@mypyc_attr(free_list_len=1) # E: "free_list_len" can't be used with traits
		class NonNative:
		pass
Original file line number	Diff line number	Diff line change
Expand Up		@@ -3794,3 +3794,37 @@ assert t.native == 43
		assert t.generic == "{}"
		assert t.bitfield == 0x0C
		assert t.default == 10

		[case testPerTypeFreeList]
		from mypy_extensions import mypyc_attr

		a = []

		@mypyc_attr(free_list=1)
		class Foo:
		def __init__(self, x: int) -> None:
		self.x = x
		a.append(x)

		def test_alloc() -> None:
		x: Foo \| None
		y: Foo \| None

		x = Foo(1)
		assert x.x == 1
		x = None

		x = Foo(2)
		assert x.x == 2
		y = Foo(3)
		assert x.x == 2
		assert y.x == 3
		x = None
		y = None
		assert a == [1, 2, 3]

		x = Foo(4)
		assert x.x == 4
		y = Foo(5)
		assert x.x == 4
		assert y.x == 5