Fixed bug that resulted in a false positive error when doing protocol matching where the object type (i.e. the self value) is a literal value. This addresses microsoft/pyright#4844.

Author: msfterictraut

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

@@ -150,7 +150,8 @@ function assignClassToProtocolInternal(
     const genericDestTypeVarContext = new TypeVarContext(getTypeVarScopeId(destType));
 
     const selfTypeVarContext = new TypeVarContext(getTypeVarScopeId(destType));
-    populateTypeVarContextForSelfType(selfTypeVarContext, destType, srcType);
+    const noLiteralSrcType = evaluator.stripLiteralValue(srcType) as ClassType;
+    populateTypeVarContextForSelfType(selfTypeVarContext, destType, noLiteralSrcType);
 
     // If the source is a TypedDict, use the _TypedDict placeholder class
     // instead. We don't want to use the TypedDict members for protocol
@@ -248,7 +249,11 @@ function assignClassToProtocolInternal(
                                 evaluator.inferReturnTypeIfNecessary(symbolType);
                             }
 
-                            srcMemberType = partiallySpecializeType(symbolType, srcMemberInfo.classType, srcType);
+                            srcMemberType = partiallySpecializeType(
+                                symbolType,
+                                srcMemberInfo.classType,
+                                noLiteralSrcType
+                            );
                         } else {
                             srcMemberType = UnknownType.create();
                         }

packages/pyright-internal/src/tests/samples/protocol38.py

@@ -0,0 +1,20 @@
+# This sample tests the case where a protocol is specialized with
+# a literal type.
+
+from typing import Literal, Protocol, Self
+
+
+class Negatable(Protocol):
+    def __neg__(self) -> Self:
+        ...
+
+
+def func1(x: Negatable) -> None:
+    ...
+
+
+func1(0)
+
+
+def func2(val: Literal[0, 1]):
+    func1(val)

packages/pyright-internal/src/tests/typeEvaluator2.test.ts

@@ -1263,6 +1263,12 @@ test('Protocol37', () => {
     TestUtils.validateResults(analysisResults, 0);
 });
 
+test('Protocol38', () => {
+    const analysisResults = TestUtils.typeAnalyzeSampleFiles(['protocol38.py']);
+
+    TestUtils.validateResults(analysisResults, 0);
+});
+
 test('TypedDict1', () => {
     const analysisResults = TestUtils.typeAnalyzeSampleFiles(['typedDict1.py']);