Fixed a bug that results in a false negative for a method override that uses Self in a contravariant position. This addresses https://discuss.python.org/t/unsoundness-of-contravariant-self-type/86338. (#10209)

erictraut · web-flow · commit 4e847ba729b3 · 2025-03-29T12:19:05.000-07:00
diff --git a/packages/pyright-internal/src/analyzer/checker.ts b/packages/pyright-internal/src/analyzer/checker.ts
@@ -6635,6 +6635,7 @@ export class Checker extends ParseTreeWalker {
         }
 
         const baseClass = baseClassAndSymbol.classType;
+        const baseClassSelf = ClassType.cloneAsInstance(selfSpecializeClass(baseClass, { useBoundTypeVars: true }));
         const childClassSelf = ClassType.cloneAsInstance(
             selfSpecializeClass(childClassType, { useBoundTypeVars: true })
         );
@@ -6643,7 +6644,7 @@ export class Checker extends ParseTreeWalker {
             this._evaluator.getEffectiveTypeOfSymbol(baseClassAndSymbol.symbol),
             baseClass,
             this._evaluator.getTypeClassType(),
-            childClassSelf
+            baseClassSelf
         );
 
         overrideType = partiallySpecializeType(
diff --git a/packages/pyright-internal/src/tests/samples/methodOverride2.py b/packages/pyright-internal/src/tests/samples/methodOverride2.py
@@ -6,112 +6,89 @@
 
 
 class Base1:
-    def f1(self, *, kwarg0: int) -> None:
-        ...
+    def f1(self, *, kwarg0: int) -> None: ...
 
-    def f2(self, *, kwarg0: int) -> None:
-        ...
+    def f2(self, *, kwarg0: int) -> None: ...
 
-    def f3(self, *, kwarg0: int) -> None:
-        ...
+    def f3(self, *, kwarg0: int) -> None: ...
 
-    def f4(self, *, kwarg0: int) -> None:
-        ...
+    def f4(self, *, kwarg0: int) -> None: ...
 
-    def g1(self, a: int, /, b: str, *, kwarg0: int) -> None:
-        ...
+    def g1(self, a: int, /, b: str, *, kwarg0: int) -> None: ...
 
-    def g2(self, a: int, /, b: str, *, kwarg0: int) -> None:
-        ...
+    def g2(self, a: int, /, b: str, *, kwarg0: int) -> None: ...
 
-    def g3(self, a: int, /, b: str, *, kwarg0: int) -> None:
-        ...
+    def g3(self, a: int, /, b: str, *, kwarg0: int) -> None: ...
 
-    def g4(self, a: int, /, b: str, *, kwarg0: int) -> None:
-        ...
+    def g4(self, a: int, /, b: str, *, kwarg0: int) -> None: ...
 
-    def g5(self, a: int, /, b: str, *, kwarg0: int) -> None:
-        ...
+    def g5(self, a: int, /, b: str, *, kwarg0: int) -> None: ...
 
-    def g6(self, a: int, /, b: str, *, kwarg0: int) -> None:
-        ...
+    def g6(self, a: int, /, b: str, *, kwarg0: int) -> None: ...
 
-    def h1(self, a: int, *args: int) -> None:
-        ...
+    def h1(self, a: int, *args: int) -> None: ...
 
 
 class Derived1(Base1):
-    def f1(self, arg0: int = 0, *, kwarg0: int, kwarg1: int = 0) -> None:
-        ...
+    def f1(self, arg0: int = 0, *, kwarg0: int, kwarg1: int = 0) -> None: ...
 
     # This should generate an error because of a positional parameter mismatch.
-    def f2(self, arg0: int, *, kwarg0: int, kwarg1: int = 0) -> None:
-        ...
+    def f2(self, arg0: int, *, kwarg0: int, kwarg1: int = 0) -> None: ...
 
     # This should generate an error because of a missing kwarg1.
-    def f3(self, arg0: int = 0, *, kwarg0: int, kwarg1: int) -> None:
-        ...
+    def f3(self, arg0: int = 0, *, kwarg0: int, kwarg1: int) -> None: ...
 
     # This should generate an error because kwarg0 is the wrong type.
-    def f4(self, arg0: int = 0, *kwarg0: str) -> None:
-        ...
+    def f4(self, arg0: int = 0, *kwarg0: str) -> None: ...
 
-    def g1(self, xxx: int, /, b: str, *, kwarg0: int) -> None:
-        ...
+    def g1(self, xxx: int, /, b: str, *, kwarg0: int) -> None: ...
 
-    def g2(self, __a: int, b: str, *, kwarg0: int) -> None:
-        ...
+    def g2(self, __a: int, b: str, *, kwarg0: int) -> None: ...
 
     # This should generate an error because of a name mismatch between b and c.
-    def g3(self, __a: int, c: str, *, kwarg0: int) -> None:
-        ...
+    def g3(self, __a: int, c: str, *, kwarg0: int) -> None: ...
 
     # This should generate an error because of a type mismatch for b.
-    def g4(self, __a: int, b: int, *, kwarg0: int) -> None:
-        ...
+    def g4(self, __a: int, b: int, *, kwarg0: int) -> None: ...
 
-    def g5(self, __a: int, b: str = "hi", *, kwarg0: int) -> None:
-        ...
+    def g5(self, __a: int, b: str = "hi", *, kwarg0: int) -> None: ...
 
-    def g6(self, __a: int, b: str, c: str = "hi", *, kwarg0: int) -> None:
-        ...
+    def g6(self, __a: int, b: str, c: str = "hi", *, kwarg0: int) -> None: ...
 
 
 P = ParamSpec("P")
 R = TypeVar("R")
 
 
 class Base2(Generic[P, R]):
-    def method1(self, *args: P.args, **kwargs: P.kwargs) -> R:
-        ...
+    def method1(self, *args: P.args, **kwargs: P.kwargs) -> R: ...
 
-    def method2(self, *args: P.args, **kwargs: P.kwargs) -> R:
-        ...
+    def method2(self, *args: P.args, **kwargs: P.kwargs) -> R: ...
 
 
 class Derived2(Base2[P, R]):
-    def method1(self, *args: P.args, **kwargs: P.kwargs) -> R:
-        ...
+    def method1(self, *args: P.args, **kwargs: P.kwargs) -> R: ...
 
-    def method2(self, *args: Any, **kwargs: Any) -> R:
-        ...
+    def method2(self, *args: Any, **kwargs: Any) -> R: ...
 
 
 T = TypeVar("T")
 
 
 class Base3:
-    def method1(self, x: Self) -> Self:
-        ...
+    def method1(self, x: Self) -> Self: ...
 
-    def method2(self, x: Self) -> Self:
-        ...
+    def method2(self, x: Self) -> Self: ...
+
+    def method3(self, x: Self) -> Self: ...
 
 
 class Derived3(Generic[T], Base3):
-    def method1(self, x: "Derived3[T]") -> "Derived3[T]":
-        ...
+    # This should generate an error.
+    def method1(self, x: "Derived3[T]") -> "Derived3[T]": ...
+
+    # This should generate an error.
+    def method2(self, x: "Derived3[int]") -> "Derived3[int]": ...
 
     # This should generate an error.
-    def method2(self, x: "Derived3[int]") -> "Derived3[int]":
-        ...
+    def method3(self, x: Self) -> Self: ...
diff --git a/packages/pyright-internal/src/tests/typeEvaluator3.test.ts b/packages/pyright-internal/src/tests/typeEvaluator3.test.ts
@@ -958,7 +958,7 @@ test('MethodOverride2', () => {
 
     configOptions.diagnosticRuleSet.reportIncompatibleMethodOverride = 'error';
     analysisResults = TestUtils.typeAnalyzeSampleFiles(['methodOverride2.py'], configOptions);
-    TestUtils.validateResults(analysisResults, 6);
+    TestUtils.validateResults(analysisResults, 8);
 });
 
 test('MethodOverride3', () => {
