Fixed bug that leads to false positive when a method is overridden by…

… a polymorphic method. This addresses #9417. (#9434)

packages/pyright-internal/src/analyzer/typeEvaluator.ts

@@ -27275,7 +27275,8 @@ export function createTypeEvaluator(
 
         // Now check the return type.
         const baseReturnType = getEffectiveReturnType(baseMethod);
-        const overrideReturnType = getEffectiveReturnType(overrideMethod);
+        const overrideReturnType = solveAndApplyConstraints(getEffectiveReturnType(overrideMethod), constraints);
+
         if (
             !assignType(
                 baseReturnType,

packages/pyright-internal/src/tests/samples/methodOverride4.py

@@ -14,23 +14,31 @@
 _T3 = TypeVar("_T3")
 
 
-class Base(Generic[_TSource]):
+class BaseA(Generic[_TSource]):
     @abstractmethod
     def method1(
-        self, mapper: Callable[[_TSource, _T1], _TResult], other: "Base[_T1]"
-    ) -> "Base[_TResult]":
+        self, mapper: Callable[[_TSource, _T1], _TResult], other: "BaseA[_T1]"
+    ) -> "BaseA[_TResult]":
         raise NotImplementedError
 
 
-class Subclass1(Base[_TSource]):
+class SubclassA1(BaseA[_TSource]):
     def method1(
-        self, mapper: Callable[[_TSource, _T2], _TResult], other: Base[_T2]
-    ) -> Base[_TResult]:
-        return Subclass2()
+        self, mapper: Callable[[_TSource, _T2], _TResult], other: BaseA[_T2]
+    ) -> BaseA[_TResult]:
+        return SubclassA2()
 
 
-class Subclass2(Base[_TSource]):
+class SubclassA2(BaseA[_TSource]):
     def method1(
-        self, mapper: Callable[[_TSource, _T3], _TResult], other: Base[_T3]
-    ) -> Base[_TResult]:
-        return Subclass2()
+        self, mapper: Callable[[_TSource, _T3], _TResult], other: BaseA[_T3]
+    ) -> BaseA[_TResult]:
+        return SubclassA2()
+
+
+class BaseB:
+    def f(self, v: str) -> str: ...
+
+
+class SubclassB1(BaseB):
+    def f[T](self, v: T) -> T: ...