Include method base class in error message

mypy/checker.py

@@ -643,15 +643,17 @@ def _visit_overloaded_func_def(self, defn: OverloadedFuncDef) -> None:
         if defn.impl:
             defn.impl.accept(self)
         if defn.info:
-            found_base_method = self.check_method_override(defn)
-            if defn.is_explicit_override and found_base_method is False:
+            method_base_class = self.check_method_override(defn)
+            if defn.is_explicit_override and not method_base_class:
                 self.msg.no_overridable_method(defn.name, defn)
             elif (
-                found_base_method
+                method_base_class
                 and self.options.strict_override_decorator
                 and not defn.is_explicit_override
             ):
-                self.msg.override_decorator_missing(defn.name, defn.impl or defn)
+                self.msg.override_decorator_missing(
+                    defn.name, method_base_class.fullname, defn.impl or defn
+                )
             self.check_inplace_operator_method(defn)
         if not defn.is_property:
             self.check_overlapping_overloads(defn)
@@ -978,13 +980,15 @@ def _visit_func_def(self, defn: FuncDef) -> None:
                 # overload, the legality of the override has already
                 # been typechecked, and decorated methods will be
                 # checked when the decorator is.
-                found_base_method = self.check_method_override(defn)
+                method_base_class = self.check_method_override(defn)
                 if (
-                    found_base_method
+                    method_base_class
                     and self.options.strict_override_decorator
                     and defn.name not in ("__init__", "__new__")
                 ):
-                    self.msg.override_decorator_missing(defn.name, defn)
+                    self.msg.override_decorator_missing(
+                        defn.name, method_base_class.fullname, defn
+                    )
             self.check_inplace_operator_method(defn)
         if defn.original_def:
             # Override previous definition.
@@ -1826,23 +1830,26 @@ def expand_typevars(
         else:
             return [(defn, typ)]
 
-    def check_method_override(self, defn: FuncDef | OverloadedFuncDef | Decorator) -> bool | None:
+    def check_method_override(
+        self, defn: FuncDef | OverloadedFuncDef | Decorator
+    ) -> TypeInfo | None:
         """Check if function definition is compatible with base classes.
 
         This may defer the method if a signature is not available in at least one base class.
         Return ``None`` if that happens.
 
+        Return the first base class if an attribute with the method name was found within it.
         Return ``True`` if an attribute with the method name was found in the base class.
         """
         # Check against definitions in base classes.
-        found_base_method = False
         for base in defn.info.mro[1:]:
             result = self.check_method_or_accessor_override_for_base(defn, base)
             if result is None:
                 # Node was deferred, we will have another attempt later.
                 return None
-            found_base_method |= result
-        return found_base_method
+            if result:
+                return base
+        return None
 
     def check_method_or_accessor_override_for_base(
         self, defn: FuncDef | OverloadedFuncDef | Decorator, base: TypeInfo
@@ -4752,15 +4759,17 @@ def visit_decorator(self, e: Decorator) -> None:
             self.check_incompatible_property_override(e)
         # For overloaded functions we already checked override for overload as a whole.
         if e.func.info and not e.func.is_dynamic() and not e.is_overload:
-            found_base_method = self.check_method_override(e)
-            if e.func.is_explicit_override and found_base_method is False:
+            method_base_class = self.check_method_override(e)
+            if e.func.is_explicit_override and not method_base_class:
                 self.msg.no_overridable_method(e.func.name, e.func)
             elif (
-                found_base_method
+                method_base_class
                 and self.options.strict_override_decorator
                 and not e.func.is_explicit_override
             ):
-                self.msg.override_decorator_missing(e.func.name, e.func)
+                self.msg.override_decorator_missing(
+                    e.func.name, method_base_class.fullname, e.func
+                )
 
         if e.func.info and e.func.name in ("__init__", "__new__"):
             if e.type and not isinstance(get_proper_type(e.type), (FunctionLike, AnyType)):

mypy/messages.py

@@ -1525,10 +1525,10 @@ def no_overridable_method(self, name: str, context: Context) -> None:
             context,
         )
 
-    def override_decorator_missing(self, name: str, context: Context) -> None:
+    def override_decorator_missing(self, name: str, base_name: str, context: Context) -> None:
         self.fail(
             f'Method "{name}" is not marked as override '
-            "but is overriding a method in a base class",
+            f'but is overriding a method in class "{base_name}"',
             context,
         )
 

test-data/unit/check-functions.test

@@ -3013,7 +3013,10 @@ class B(A):
     def f(self, y: int) -> str: pass
 
 class C(A):
-    def f(self, y: int) -> str: pass  # E: Method "f" is not marked as override but is overriding a method in a base class
+    def f(self, y: int) -> str: pass  # E: Method "f" is not marked as override but is overriding a method in class "__main__.A"
+
+class D(B):
+    def f(self, y: int) -> str: pass  # E: Method "f" is not marked as override but is overriding a method in class "__main__.B"
 [typing fixtures/typing-override.pyi]
 
 [case requireExplicitOverrideSpecialMethod]
@@ -3042,7 +3045,7 @@ class B(A):
 
 class C(A):
     @property
-    def prop(self) -> int: pass  # E: Method "prop" is not marked as override but is overriding a method in a base class
+    def prop(self) -> int: pass  # E: Method "prop" is not marked as override but is overriding a method in class "__main__.A"
 [typing fixtures/typing-override.pyi]
 [builtins fixtures/property.pyi]
 
@@ -3070,5 +3073,22 @@ class C(A):
     def f(self, y: int) -> str: ...
     @overload
     def f(self, y: str) -> str: ...
-    def f(self, y): pass  # E: Method "f" is not marked as override but is overriding a method in a base class
+    def f(self, y): pass  # E: Method "f" is not marked as override but is overriding a method in class "__main__.A"
+[typing fixtures/typing-override.pyi]
+
+[case requireExplicitOverrideMultipleInheritance]
+# flags: --strict-override-decorator --python-version 3.12
+from typing import override
+
+class A:
+    def f(self, x: int) -> str: pass
+class B:
+    def f(self, y: int) -> str: pass
+
+class C(A, B):
+    @override
+    def f(self, z: int) -> str: pass
+
+class D(A, B):
+    def f(self, z: int) -> str: pass  # E: Method "f" is not marked as override but is overriding a method in class "__main__.A"
 [typing fixtures/typing-override.pyi]