Merge pull request #18335 from gregomni/8337

Author: swift-ci

lib/Sema/TypeCheckProtocolInference.cpp

@@ -176,6 +176,13 @@ AssociatedTypeInference::inferTypeWitnessesViaValueWitnesses(
   InferredAssociatedTypesByWitnesses result;
 
   auto isExtensionUsableForInference = [&](ExtensionDecl *extension) -> bool {
+
+    // The extension where the conformance being checked is declared.
+    auto conformanceExtension = checker.Conformance->
+      getDeclContext()->getAsDeclOrDeclExtensionContext();
+    if (extension == conformanceExtension)
+      return true;
+
     // Assume unconstrained concrete extensions we found witnesses in are
     // always viable.
     if (!extension->getExtendedType()->isAnyExistentialType()) {

test/Generics/conditional_conformances.swift

@@ -413,3 +413,15 @@ extension Array: NestedArrayProtocol where Element: ElementProtocol, Element: Ar
   // with the typealias uncommented you do not get a crash.
   // typealias BaseElement = Element.BaseElement
 }
+
+// SR-8337
+struct Foo<Bar> {}
+
+protocol P {
+  associatedtype A
+  var foo: Foo<A> { get }
+}
+
+extension Foo: P where Bar: P {
+  var foo: Foo { return self }
+}