Extended support for union expansion of constrained type variables when performing overload matching.

msfterictraut · msfterictraut · commit eaac1d341975 · 2022-08-11T18:38:45.000-07:00
diff --git a/packages/pyright-internal/src/analyzer/typeEvaluator.ts b/packages/pyright-internal/src/analyzer/typeEvaluator.ts
@@ -7770,12 +7770,15 @@ export function createTypeEvaluator(importLookup: ImportLookup, evaluatorOptions
             return undefined;
         }
 
-        let unionToExpand: UnionType | undefined;
+        let unionToExpand: Type | undefined;
         while (indexToExpand < contextFreeArgTypes.length) {
             // Is this a union type? If so, we can expand it.
             const argType = contextFreeArgTypes[indexToExpand];
             if (isUnion(argType)) {
-                unionToExpand = argType;
+                unionToExpand = makeTopLevelTypeVarsConcrete(argType);
+                break;
+            } else if (isTypeVar(argType) && argType.details.constraints.length > 1) {
+                unionToExpand = makeTopLevelTypeVarsConcrete(argType);
                 break;
             }
             indexToExpand++;
diff --git a/packages/pyright-internal/src/tests/samples/overload8.py b/packages/pyright-internal/src/tests/samples/overload8.py
@@ -87,3 +87,24 @@ def func2(a: LargeUnion, b: Literal[2, 3, 4], c: Literal[2, 3, 4, 9, 10]):
     # will exceed the max number of expansions (64).
     v3 = overloaded2(a, c)
     reveal_type(v2, expected_text="str | float")
+
+
+_T2 = TypeVar("_T2", str, bytes)
+
+
+@overload
+def overloaded3(x: str) -> str:
+    ...
+
+
+@overload
+def overloaded3(x: bytes) -> bytes:
+    ...
+
+
+def overloaded3(x: str | bytes) -> str | bytes:
+    ...
+
+
+def func3(y: _T2):
+    overloaded3(y)
