AST: Lazily populate associated conformances with -enable-experimental-associated-type-inference

Author: slavapestov

lib/AST/ProtocolConformance.cpp

@@ -535,27 +535,48 @@ ProtocolConformance::getAssociatedConformance(Type assocType,
 ProtocolConformanceRef
 NormalProtocolConformance::getAssociatedConformance(Type assocType,
                                                  ProtocolDecl *protocol) const {
+  if (Loader)
+    resolveLazyInfo();
+
   assert(assocType->isTypeParameter() &&
          "associated type must be a type parameter");
 
   llvm::Optional<ProtocolConformanceRef> result;
 
+  auto &ctx = getDeclContext()->getASTContext();
+
   forEachAssociatedConformance(
       [&](Type t, ProtocolDecl *p, unsigned index) {
         if (t->isEqual(assocType) && p == protocol) {
-          // Fill in the signature conformances, if we haven't done so yet.
-          if (!hasComputedAssociatedConformances()) {
-            const_cast<NormalProtocolConformance *>(this)
-                ->finishSignatureConformances();
+          if (!ctx.LangOpts.hasFeature(Feature::TypeWitnessSystemInference)) {
+            // Fill in the signature conformances, if we haven't done so yet.
+            if (!hasComputedAssociatedConformances()) {
+              const_cast<NormalProtocolConformance *>(this)
+                  ->finishSignatureConformances();
+            }
+          }
+
+          // Not strictly necessary, but avoids a bit of request evaluator
+          // overhead in the happy case.
+          if (hasComputedAssociatedConformances()) {
+            result = AssociatedConformances[index];
+            if (result)
+              return true;
           }
 
-          result = getAssociatedConformance(index);
+          result = evaluateOrDefault(ctx.evaluator,
+                                     AssociatedConformanceRequest{
+                                       const_cast<NormalProtocolConformance *>(this),
+                                       t->getCanonicalType(), p, index
+                                     }, ProtocolConformanceRef::forInvalid());
           return true;
         }
 
         return false;
       });
 
+  assert(result && "Subject type must be exactly equal to left-hand side of a"
+         "conformance requirement in protocol requirement signature");
   return *result;
 }
 

validation-test/compiler_crashers_2_fixed/rdar110806272.swift

@@ -0,0 +1,15 @@
+// RUN: not %target-swift-frontend -typecheck %s -enable-experimental-associated-type-inference
+
+struct SyntaxCollectionIterator<E: SyntaxProtocol>: IteratorProtocol {
+  typealias Element = E
+}
+
+protocol SyntaxCollection: BidirectionalCollection {}
+
+extension SyntaxCollection {
+  typealias Iterator = SyntaxCollectionIterator<Element>
+}
+
+struct AccessorListSyntax: SyntaxCollection {
+  typealias Element = Int
+}