Fix bug in overload compatibility checking

Discovered as part of python#14017

Author: hauntsaninja

mypy/subtypes.py

@@ -840,6 +840,7 @@ def visit_overloaded(self, left: Overloaded) -> bool:
                             found_match = True
                             matched_overloads.add(left_item)
                             possible_invalid_overloads.discard(left_item)
+                            break
                     else:
                         # If this one overlaps with the supertype in any way, but it wasn't
                         # an exact match, then it's a potential error.

test-data/unit/check-classes.test

@@ -3872,28 +3872,37 @@ class Super:
     def foo(self, a: C) -> C: pass
 
 class Sub(Super):
-    @overload  # Fail
+    @overload
     def foo(self, a: A) -> A: pass
     @overload
     def foo(self, a: B) -> C: pass  # Fail
     @overload
     def foo(self, a: C) -> C: pass
+
+class Sub2(Super):
+    @overload
+    def foo(self, a: B) -> C: pass  # Fail
+    @overload
+    def foo(self, a: A) -> A: pass
+    @overload
+    def foo(self, a: C) -> C: pass
 [builtins fixtures/classmethod.pyi]
 [out]
-tmp/foo.pyi:16: error: Signature of "foo" incompatible with supertype "Super"
-tmp/foo.pyi:16: note:      Superclass:
-tmp/foo.pyi:16: note:          @overload
-tmp/foo.pyi:16: note:          def foo(self, a: A) -> A
-tmp/foo.pyi:16: note:          @overload
-tmp/foo.pyi:16: note:          def foo(self, a: C) -> C
-tmp/foo.pyi:16: note:      Subclass:
-tmp/foo.pyi:16: note:          @overload
-tmp/foo.pyi:16: note:          def foo(self, a: A) -> A
-tmp/foo.pyi:16: note:          @overload
-tmp/foo.pyi:16: note:          def foo(self, a: B) -> C
-tmp/foo.pyi:16: note:          @overload
-tmp/foo.pyi:16: note:          def foo(self, a: C) -> C
 tmp/foo.pyi:19: error: Overloaded function signature 2 will never be matched: signature 1's parameter type(s) are the same or broader
+tmp/foo.pyi:24: error: Signature of "foo" incompatible with supertype "Super"
+tmp/foo.pyi:24: note:      Superclass:
+tmp/foo.pyi:24: note:          @overload
+tmp/foo.pyi:24: note:          def foo(self, a: A) -> A
+tmp/foo.pyi:24: note:          @overload
+tmp/foo.pyi:24: note:          def foo(self, a: C) -> C
+tmp/foo.pyi:24: note:      Subclass:
+tmp/foo.pyi:24: note:          @overload
+tmp/foo.pyi:24: note:          def foo(self, a: B) -> C
+tmp/foo.pyi:24: note:          @overload
+tmp/foo.pyi:24: note:          def foo(self, a: A) -> A
+tmp/foo.pyi:24: note:          @overload
+tmp/foo.pyi:24: note:          def foo(self, a: C) -> C
+tmp/foo.pyi:25: error: Overloaded function signatures 1 and 2 overlap with incompatible return types
 
 [case testTypeTypeOverlapsWithObjectAndType]
 from foo import *

test-data/unit/check-selftype.test

@@ -128,6 +128,34 @@ reveal_type(cast(A, C()).copy())  # N: Revealed type is "__main__.A"
 
 [builtins fixtures/bool.pyi]
 
+[case testSelfTypeOverrideCompatibility]
+from typing import overload, TypeVar, Generic
+
+T = TypeVar("T")
+
+class A(Generic[T]):
+    @overload
+    def f(self: A[int]) -> int: ...
+    @overload
+    def f(self: A[str]) -> str: ...
+    def f(self): ...
+
+class B(A[T]):
+    @overload
+    def f(self: A[int]) -> int: ...
+    @overload
+    def f(self: A[str]) -> str: ...
+    def f(self): ...
+
+class B2(A[T]):
+    @overload
+    def f(self: A[int]) -> int: ...
+    @overload
+    def f(self: A[str]) -> str: ...
+    @overload
+    def f(self: A[bytes]) -> bytes: ...
+    def f(self): ...
+
 [case testSelfTypeSuper]
 from typing import TypeVar, cast