remove method is_private by mangling "__mypy-replace" and "__mypy-post_init".

Author: tyralla

mypy/checker.py

@@ -1336,7 +1336,7 @@ def check_func_def(
                         if (
                             arg_type.variance == COVARIANT
                             and defn.name not in ("__init__", "__new__", "__post_init__")
-                            and not is_private(defn.name)  # private methods are not inherited
+                            and "mypy-" not in defn.name  # skip internally added methods
                         ):
                             ctx: Context = arg_type
                             if ctx.line < 0:
@@ -1979,7 +1979,6 @@ def check_explicit_override_decorator(
             and found_method_base_classes
             and not defn.is_explicit_override
             and defn.name not in ("__init__", "__new__")
-            and not is_private(defn.name)
         ):
             self.msg.explicit_override_decorator_missing(
                 defn.name, found_method_base_classes[0].fullname, context or defn
@@ -2036,7 +2035,7 @@ def check_method_or_accessor_override_for_base(
             base_attr = base.names.get(name)
             if base_attr:
                 # First, check if we override a final (always an error, even with Any types).
-                if is_final_node(base_attr.node) and not is_private(name):
+                if is_final_node(base_attr.node):
                     self.msg.cant_override_final(name, base.name, defn)
                 # Second, final can't override anything writeable independently of types.
                 if defn.is_final:
@@ -2393,9 +2392,6 @@ def check_override(
                 if original.type_is is not None and override.type_is is None:
                     fail = True
 
-        if is_private(name):
-            fail = False
-
         if fail:
             emitted_msg = False
 
@@ -2828,12 +2824,8 @@ def check_multiple_inheritance(self, typ: TypeInfo) -> None:
         # Verify that inherited attributes are compatible.
         mro = typ.mro[1:]
         all_names = {name for base in mro for name in base.names}
+        # Sort for reproducible message order.
         for name in sorted(all_names - typ.names.keys()):
-            # Sort for reproducible message order.
-            # Attributes defined in both the type and base are skipped.
-            # Normal checks for attribute compatibility should catch any problems elsewhere.
-            if is_private(name):
-                continue
             # Compare the first base defining a name with the rest.
             # Remaining bases may not be pairwise compatible as the first base provides
             # the used definition.
@@ -2945,7 +2937,7 @@ class C(B, A[int]): ...  # this is unsafe because...
             ok = True
         # Final attributes can never be overridden, but can override
         # non-final read-only attributes.
-        if is_final_node(second.node) and not is_private(name):
+        if is_final_node(second.node):
             self.msg.cant_override_final(name, base2.name, ctx)
         if is_final_node(first.node):
             self.check_if_final_var_override_writable(name, second.node, ctx)
@@ -3415,9 +3407,6 @@ def check_compatibility_all_supers(
                 ):
                     continue
 
-                if is_private(lvalue_node.name):
-                    continue
-
                 base_type, base_node = self.lvalue_type_from_base(lvalue_node, base)
                 custom_setter = is_custom_settable_property(base_node)
                 if isinstance(base_type, PartialType):
@@ -3621,8 +3610,6 @@ def check_compatibility_final_super(
         """
         if not isinstance(base_node, (Var, FuncBase, Decorator)):
             return True
-        if is_private(node.name):
-            return True
         if base_node.is_final and (node.is_final or not isinstance(base_node, Var)):
             # Give this error only for explicit override attempt with `Final`, or
             # if we are overriding a final method with variable.
@@ -8908,15 +8895,6 @@ def is_overlapping_types_for_overload(left: Type, right: Type) -> bool:
     )
 
 
-def is_private(node_name: str) -> bool:
-    """Check if node is private to class definition.
-
-    Since Mypy supports name mangling, `is_private` is likely only required for
-    internally introduced names like `__mypy-replace` and `__mypy-post_init`.
-    """
-    return node_name.startswith("__") and not node_name.endswith("__")
-
-
 def is_string_literal(typ: Type) -> bool:
     strs = try_getting_str_literals_from_type(typ)
     return strs is not None and len(strs) == 1

mypy/plugins/dataclasses.py

@@ -422,20 +422,22 @@ def _add_internal_replace_method(self, attributes: list[DataclassAttribute]) ->
         Stashes the signature of 'dataclasses.replace(...)' for this specific dataclass
         to be used later whenever 'dataclasses.replace' is called for this dataclass.
         """
+        mangled_name = f"_{self._cls.name.lstrip('_')}{_INTERNAL_REPLACE_SYM_NAME}"
         add_method_to_class(
             self._api,
             self._cls,
-            _INTERNAL_REPLACE_SYM_NAME,
+            mangled_name,
             args=[attr.to_argument(self._cls.info, of="replace") for attr in attributes],
             return_type=NoneType(),
             is_staticmethod=True,
         )
 
     def _add_internal_post_init_method(self, attributes: list[DataclassAttribute]) -> None:
+        mangled_name = f"_{self._cls.name.lstrip('_')}{_INTERNAL_POST_INIT_SYM_NAME}"
         add_method_to_class(
             self._api,
             self._cls,
-            _INTERNAL_POST_INIT_SYM_NAME,
+            mangled_name,
             args=[
                 attr.to_argument(self._cls.info, of="__post_init__")
                 for attr in attributes
@@ -1027,7 +1029,8 @@ def _get_expanded_dataclasses_fields(
             ctx, get_proper_type(typ.upper_bound), display_typ, parent_typ
         )
     elif isinstance(typ, Instance):
-        replace_sym = typ.type.get_method(_INTERNAL_REPLACE_SYM_NAME)
+        mangled_name = f"_{typ.type.name.lstrip('_')}{_INTERNAL_REPLACE_SYM_NAME}"
+        replace_sym = typ.type.get_method(mangled_name)
         if replace_sym is None:
             return None
         replace_sig = replace_sym.type
@@ -1111,7 +1114,8 @@ def check_post_init(api: TypeChecker, defn: FuncItem, info: TypeInfo) -> None:
         return
     assert isinstance(defn.type, FunctionLike)
 
-    ideal_sig_method = info.get_method(_INTERNAL_POST_INIT_SYM_NAME)
+    mangled_name = f"_{info.name.lstrip('_')}{_INTERNAL_POST_INIT_SYM_NAME}"
+    ideal_sig_method = info.get_method(mangled_name)
     assert ideal_sig_method is not None and ideal_sig_method.type is not None
     ideal_sig = ideal_sig_method.type
     assert isinstance(ideal_sig, ProperType)  # we set it ourselves

test-data/unit/deps.test

@@ -1389,15 +1389,16 @@ class B(A):
 
 [out]
 <m.A.(abstract)> -> <m.B.__init__>, m
+<m.A._A__mypy-replace> -> <m.B._A__mypy-replace>, m
+<m.A._B__mypy-replace> -> m.B._B__mypy-replace
 <m.A.__dataclass_fields__> -> <m.B.__dataclass_fields__>
 <m.A.__init__> -> <m.B.__init__>, m.B.__init__
-<m.A.__mypy-replace> -> <m.B.__mypy-replace>, m, m.B.__mypy-replace
 <m.A.__new__> -> <m.B.__new__>
 <m.A.x> -> <m.B.x>
 <m.A.y> -> <m.B.y>
 <m.A> -> m, m.A, m.B
 <m.A[wildcard]> -> m
-<m.B.__mypy-replace> -> m
+<m.B._B__mypy-replace> -> m
 <m.B.y> -> m
 <m.B> -> m.B
 <m.Z> -> m
@@ -1421,10 +1422,11 @@ class B(A):
 
 [out]
 <m.A.(abstract)> -> <m.B.__init__>, m
+<m.A._A__mypy-replace> -> <m.B._A__mypy-replace>, m
+<m.A._B__mypy-replace> -> m.B._B__mypy-replace
 <m.A.__dataclass_fields__> -> <m.B.__dataclass_fields__>
 <m.A.__init__> -> <m.B.__init__>, m.B.__init__
 <m.A.__match_args__> -> <m.B.__match_args__>
-<m.A.__mypy-replace> -> <m.B.__mypy-replace>, m, m.B.__mypy-replace
 <m.A.__new__> -> <m.B.__new__>
 <m.A.x> -> <m.B.x>
 <m.A.y> -> <m.B.y>

test-data/unit/pythoneval.test

@@ -1963,17 +1963,33 @@ from dataclasses import dataclass, replace
 class A:
     x: int
 
+@dataclass
+class B(A):
+    y: str
+
 a = A(x=42)
 a2 = replace(a, x=42)
 reveal_type(a2)
 a2 = replace()
-a2 = replace(a, x='spam')
+a2 = replace(a, x="spam")
 a2 = replace(a, x=42, q=42)
-[out]
-_testDataclassReplace.py:9: note: Revealed type is "_testDataclassReplace.A"
-_testDataclassReplace.py:10: error: Too few arguments for "replace"
-_testDataclassReplace.py:11: error: Argument "x" to "replace" of "A" has incompatible type "str"; expected "int"
-_testDataclassReplace.py:12: error: Unexpected keyword argument "q" for "replace" of "A"
+
+b = B(x=42, y="egg")
+b2 = replace(b, x=42, y="egg")
+reveal_type(b2)
+replace()
+replace(b, x="egg", y=42)
+replace(b, x=42, y="egg", q=42)
+[out]
+_testDataclassReplace.py:13: note: Revealed type is "_testDataclassReplace.A"
+_testDataclassReplace.py:14: error: Too few arguments for "replace"
+_testDataclassReplace.py:15: error: Argument "x" to "replace" of "A" has incompatible type "str"; expected "int"
+_testDataclassReplace.py:16: error: Unexpected keyword argument "q" for "replace" of "A"
+_testDataclassReplace.py:20: note: Revealed type is "_testDataclassReplace.B"
+_testDataclassReplace.py:21: error: Too few arguments for "replace"
+_testDataclassReplace.py:22: error: Argument "x" to "replace" of "B" has incompatible type "str"; expected "int"
+_testDataclassReplace.py:22: error: Argument "y" to "replace" of "B" has incompatible type "int"; expected "str"
+_testDataclassReplace.py:23: error: Unexpected keyword argument "q" for "replace" of "B"
 
 [case testGenericInferenceWithTuple]
 # flags: --new-type-inference