Improved reportUnnecessaryCast so it works with types other than cl… (

microsoft#5336)

Improved `reportUnnecessaryCast` so it works with types other than class instances. This addresses microsoft#5333.

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

@@ -8913,9 +8913,9 @@ export function createTypeEvaluator(importLookup: ImportLookup, evaluatorOptions
                             // Verify that the cast is necessary.
                             const castToType = getTypeOfArgumentExpectingType(argList[0]).type;
                             const castFromType = getTypeOfArgument(argList[1]).type;
-                            if (isInstantiableClass(castToType) && isClassInstance(castFromType)) {
+                            if (TypeBase.isInstantiable(castToType) && !isUnknown(castToType)) {
                                 if (
-                                    isTypeSame(castToType, ClassType.cloneAsInstantiable(castFromType), {
+                                    isTypeSame(convertToInstance(castToType), castFromType, {
                                         ignorePseudoGeneric: true,
                                     })
                                 ) {

packages/pyright-internal/src/tests/checker.test.ts

@@ -261,7 +261,7 @@ test('UnnecessaryCast1', () => {
     // Turn on errors.
     configOptions.diagnosticRuleSet.reportUnnecessaryCast = 'error';
     analysisResults = TestUtils.typeAnalyzeSampleFiles(['unnecessaryCast1.py'], configOptions);
-    TestUtils.validateResults(analysisResults, 1);
+    TestUtils.validateResults(analysisResults, 6);
 });
 
 test('UnnecessaryContains1', () => {

packages/pyright-internal/src/tests/samples/unnecessaryCast1.py

@@ -1,13 +1,54 @@
 # This sample tests the type checker's reportUnnecessaryCast feature.
 
-from typing import cast, Union
+from typing import Never, NoReturn, TypeVar, cast
 
 
-def foo(a: int):
+def func1(a: int):
     # This should generate an error if
     # reportUnnecessaryCast is enabled.
-    b = cast(int, a)
+    v1 = cast(int, a)
 
 
-c: Union[int, str] = "hello"
-d = cast(int, c)
+def func2(a: int | str):
+    v1 = cast(int, a)
+
+    b: str = "hello"
+    v2 = cast(int, b)
+
+
+def func3(a: int | None):
+    v1 = cast(int, a)
+
+    # This should generate an error if
+    # reportUnnecessaryCast is enabled.
+    v2 = cast(int | None, a)
+
+
+T = TypeVar("T")
+
+
+def func4(a: list[T]) -> list[T]:
+    # This should generate an error if
+    # reportUnnecessaryCast is enabled.
+    v1 = cast(list[T], a)
+
+    return a
+
+
+def func5(a: Never):
+    # This should generate an error if
+    # reportUnnecessaryCast is enabled.
+    v1 = cast(NoReturn, a)
+
+
+def func6(a: type[int], b: int):
+    v1 = cast(int, a)
+    v2 = cast(type[int], b)
+
+    # This should generate an error if
+    # reportUnnecessaryCast is enabled.
+    v3 = cast(type[int], a)
+
+    # This should generate an error if
+    # reportUnnecessaryCast is enabled.
+    v4 = cast(int, b)