[Clang importer] Make sure that the first argument of Set/Dictionary types are Hashable.

Extend the check to make sure that the first type argument to an
imported Set or Dictionary type is Hashable actually checks
struct/enum types for Hashable conformances.

Fixes rdar://problem/30622665.

lib/ClangImporter/ImportType.cpp

@@ -984,13 +984,12 @@ namespace {
               return Type();
 
             // The first type argument for Dictionary or Set needs
-            // to be Hashable. Everything that inherits NSObject has a
-            // -hash code in ObjC, but if something isn't NSObject, fall back
+            // to be Hashable. If something isn't Hashable, fall back
             // to AnyHashable as a key type.
             if (unboundDecl == Impl.SwiftContext.getDictionaryDecl() ||
                 unboundDecl == Impl.SwiftContext.getSetDecl()) {
               auto &keyType = importedTypeArgs[0];
-              if (!Impl.matchesNSObjectBound(keyType)) {
+              if (!Impl.matchesHashableBound(keyType)) {
                 if (auto anyHashable = Impl.SwiftContext.getAnyHashableDecl())
                   keyType = anyHashable->getDeclaredType();
                 else
@@ -2413,7 +2412,7 @@ Type ClangImporter::Implementation::getNSObjectType() {
   return Type();
 }
 
-bool ClangImporter::Implementation::matchesNSObjectBound(Type type) {
+bool ClangImporter::Implementation::matchesHashableBound(Type type) {
   Type NSObjectType = getNSObjectType();
   if (!NSObjectType)
     return false;
@@ -2425,8 +2424,14 @@ bool ClangImporter::Implementation::matchesNSObjectBound(Type type) {
   // Struct or enum type must have been bridged.
   // TODO: Check that the bridged type is Hashable?
   if (type->getStructOrBoundGenericStruct() ||
-      type->getEnumOrBoundGenericEnum())
-    return true;
+      type->getEnumOrBoundGenericEnum()) {
+    auto nominal = type->getAnyNominal();
+    auto hashable = SwiftContext.getProtocol(KnownProtocolKind::Hashable);
+    SmallVector<ProtocolConformance *, 2> conformances;
+    return hashable &&
+      nominal->lookupConformance(nominal->getParentModule(), hashable,
+                                 conformances);
+  }
 
   return false;
 }

lib/ClangImporter/ImporterImpl.h

@@ -886,7 +886,7 @@ public:
 
   /// \brief Determines whether the given type matches an implicit type
   /// bound of "Hashable", which is used to validate NSDictionary/NSSet.
-  bool matchesNSObjectBound(Type type);
+  bool matchesHashableBound(Type type);
 
   /// \brief Look up and attempt to import a Clang declaration with
   /// the given name.

test/ClangImporter/Inputs/custom-modules/ObjCBridgeNonconforming.h

@@ -0,0 +1,6 @@
+@import ObjectiveC;
+@import Foundation;
+
+@interface ObjCBridgeNonconforming
+@property NSSet<NSDictionary<NSString *, id> *> * _Nonnull foo;
+@end

test/ClangImporter/Inputs/custom-modules/module.map

@@ -175,3 +175,7 @@ module MacrosRedefB {
 module IndirectFields {
   header "IndirectFields.h"
 }
+
+module ObjCBridgeNonconforming {
+  header "ObjCBridgeNonconforming.h"
+}

test/ClangImporter/objc_bridging_generics.swift

@@ -1,9 +1,10 @@
-// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -parse-as-library -verify -swift-version 4 %s
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -parse-as-library -verify -swift-version 4 -I %S/Inputs/custom-modules %s
 
 // REQUIRES: objc_interop
 
 import Foundation
 import objc_generics
+import ObjCBridgeNonconforming
 
 func testNSArrayBridging(_ hive: Hive) {
   _ = hive.bees as [Bee]
@@ -392,3 +393,8 @@ let third: Third! = Third()
 func useThird() {
   _ = third.description
 }
+
+
+func testNonconforming(bnc: ObjCBridgeNonconforming) {
+  let _: Int = bnc.foo // expected-error{{cannot convert value of type 'Set<AnyHashable>' to specified type 'Int'}}
+}