From 8ce23eb615ace823cd45d9c4934c316c58cfe0e3 Mon Sep 17 00:00:00 2001
From: Eric Traut <eric@traut.com>
Date: Sun, 18 Jun 2023 12:55:22 -0700
Subject: [PATCH] =?UTF-8?q?Improved=20`reportUnnecessaryCast`=20so=20it=20?=
 =?UTF-8?q?works=20with=20types=20other=20than=20cl=E2=80=A6=20(#5336)?=
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Improved `reportUnnecessaryCast` so it works with types other than class instances. This addresses https://github.com/microsoft/pyright/issues/5333.
---
 .../src/analyzer/typeEvaluator.ts             |  4 +-
 .../src/tests/checker.test.ts                 |  2 +-
 .../src/tests/samples/unnecessaryCast1.py     | 51 +++++++++++++++++--
 3 files changed, 49 insertions(+), 8 deletions(-)

diff --git a/packages/pyright-internal/src/analyzer/typeEvaluator.ts b/packages/pyright-internal/src/analyzer/typeEvaluator.ts
index e86c7a37b864..594d1966ab57 100644
--- a/packages/pyright-internal/src/analyzer/typeEvaluator.ts
+++ b/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,
                                     })
                                 ) {
diff --git a/packages/pyright-internal/src/tests/checker.test.ts b/packages/pyright-internal/src/tests/checker.test.ts
index 24764cb1c36b..f420585e991e 100644
--- a/packages/pyright-internal/src/tests/checker.test.ts
+++ b/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', () => {
diff --git a/packages/pyright-internal/src/tests/samples/unnecessaryCast1.py b/packages/pyright-internal/src/tests/samples/unnecessaryCast1.py
index fe3d447e3c8e..f63eddabb27d 100644
--- a/packages/pyright-internal/src/tests/samples/unnecessaryCast1.py
+++ b/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)