Fixed bug that leads to a hang when returning a tuple from a lambda a…

…rgument expression in certain circumstances. This addresses #9558 and #9536. (#9560)

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

@@ -222,6 +222,13 @@ export interface AddConditionOptions {
     skipBoundTypeVars?: boolean;
 }
 
+// There are cases where tuple types can be infinitely nested. The
+// recursion count limit will eventually be hit, but this will create
+// deep types that will effectively hang the analyzer. To prevent this,
+// we'll limit the depth of the tuple type arguments. This value is
+// large enough that we should never hit it in legitimate circumstances.
+const maxTupleTypeArgRecursionDepth = 10;
+
 // Tracks whether a function signature has been seen before within
 // an expression. For example, in the expression "foo(foo, foo)", the
 // signature for "foo" will be seen three times at three different
@@ -3654,6 +3661,10 @@ export class TypeVarTransformer {
 
         // Handle tuples specially.
         if (ClassType.isTupleClass(classType)) {
+            if (getContainerDepth(classType) > maxTupleTypeArgRecursionDepth) {
+                return classType;
+            }
+
             if (classType.priv.tupleTypeArgs) {
                 newTupleTypeArgs = [];
 

packages/pyright-internal/src/tests/samples/tuple19.py

@@ -0,0 +1,11 @@
+# This sample tests a case where the constraint solver generates a very
+# "deep" tuple type. Previously, this caused a hang in the evaluator.
+
+from typing import Callable
+
+
+def func1[T](c: Callable[[T], T]): ...
+
+
+# This should generate an error, not hang.
+func1(lambda v: (v, v))

packages/pyright-internal/src/tests/typeEvaluator8.test.ts

@@ -539,6 +539,12 @@ test('Tuple18', () => {
     TestUtils.validateResults(analysisResults, 2);
 });
 
+test('Tuple19', () => {
+    const analysisResults = TestUtils.typeAnalyzeSampleFiles(['tuple19.py']);
+
+    TestUtils.validateResults(analysisResults, 1);
+});
+
 test('NamedTuple1', () => {
     const analysisResults = TestUtils.typeAnalyzeSampleFiles(['namedTuple1.py']);