Fixed a bug that results in a hang under certain circumstances when u…

…sing a recursive type alias. This addresses #9497.
microsoft · Nov 29, 2024 · abf178b · abf178b
1 parent 4042841
commit abf178b
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Showing 3 changed files with 40 additions and 5 deletions.
diff --git a/packages/pyright-internal/src/analyzer/typeEvaluator.ts b/packages/pyright-internal/src/analyzer/typeEvaluator.ts
@@ -7717,15 +7717,18 @@ export function createTypeEvaluator(
         }
 
         const transformedType = transformPossibleRecursiveTypeAlias(type);
+        const isRecursiveTypeAlias = transformedType !== type;
 
         // If this is a recursive type alias, see if we've already recursed
         // seen it once before in the recursion stack. If so, don't recurse
         // further.
-        if (transformedType !== type) {
+        if (isRecursiveTypeAlias) {
             const pendingOverlaps = pendingTypes.filter((pendingType) => isTypeSame(pendingType, type));
             if (pendingOverlaps.length > 1) {
                 return;
             }
+
+            pendingTypes.push(type);
         }
 
         recursionCount++;
@@ -7737,8 +7740,6 @@ export function createTypeEvaluator(
                 if (typeParamIndex >= 0) {
                     usageVariances[typeParamIndex] = combineVariances(usageVariances[typeParamIndex], variance);
                 } else {
-                    pendingTypes.push(type);
-
                     updateUsageVariancesRecursive(
                         subtype,
                         typeAliasTypeParams,
@@ -7747,8 +7748,6 @@ export function createTypeEvaluator(
                         pendingTypes,
                         recursionCount
                     );
-
-                    pendingTypes.pop();
                 }
             });
         }
@@ -7796,6 +7795,10 @@ export function createTypeEvaluator(
                 }
             }
         });
+
+        if (isRecursiveTypeAlias) {
+            pendingTypes.pop();
+        }
     }
 
     function getIndexAccessMagicMethodName(usage: EvaluatorUsage): string {

diff --git a/packages/pyright-internal/src/tests/samples/recursiveTypeAlias16.py b/packages/pyright-internal/src/tests/samples/recursiveTypeAlias16.py
@@ -0,0 +1,23 @@
+# This sample tests a case that previously resulted in infinite recursion.
+
+from typing import TypeVar, Generic
+
+U = TypeVar("U")
+T = TypeVar("T")
+
+
+class A(Generic[T]):
+    pass
+
+
+class B(Generic[T]):
+    pass
+
+
+class C(Generic[T]):
+    pass
+
+
+TA1 = A["TA2[U]"] | B["TA2[U]"]
+TA2 = TA1[U] | C[TA1[U]]
+TA3 = TA2[U]
diff --git a/packages/pyright-internal/src/tests/typeEvaluator3.test.ts b/packages/pyright-internal/src/tests/typeEvaluator3.test.ts
@@ -850,6 +850,15 @@ test('RecursiveTypeAlias15', () => {
     TestUtils.validateResults(analysisResults, 4);
 });
 
+test('RecursiveTypeAlias16', () => {
+    const configOptions = new ConfigOptions(Uri.empty());
+
+    configOptions.defaultPythonVersion = pythonVersion3_12;
+    const analysisResults = TestUtils.typeAnalyzeSampleFiles(['recursiveTypeAlias16.py'], configOptions);
+
+    TestUtils.validateResults(analysisResults, 0);
+});
+
 test('Classes1', () => {
     const analysisResults = TestUtils.typeAnalyzeSampleFiles(['classes1.py']);