[ObjC generics] Fix not inheriting type bounds in categories/extensions.

When a category/extension doesn't repeat a type bound, corresponding
type parameter is substituted with `id` when used as a type argument. As
a result, in the added test case it was causing errors like

> type argument 'T' (aka 'id') does not satisfy the bound ('id<NSCopying>') of type parameter 'T'

We are already checking that type parameters should be consistent
everywhere (see `checkTypeParamListConsistency`) and update
`ObjCTypeParamDecl` to have correct underlying type. And when we use the
type parameter as a method return type or a method parameter type, it is
substituted to the bounded type. But when we use the type parameter as a
type argument, we check `ObjCTypeParamType` that wasn't updated and
remains `id`.

Fix by updating not only `ObjCTypeParamDecl` UnderlyingType but also
TypeForDecl as we use the underlying type to create a canonical type for
`ObjCTypeParamType` (see `ASTContext::getObjCTypeParamType`).

This is a different approach to fixing the issue. The previous one was
02c2ab3d8872416589bd1a6ca3dfb96ba373a3b9 which was reverted in
4c539e8da1b3de38a53ef3f7497f5c45a3243b61. The problem with the previous
approach was that `ObjCTypeParamType::desugar` was returning underlying
type for `ObjCTypeParamDecl` without applying any protocols stored in
`ObjCTypeParamType`. It caused inconsistencies in comparing types before
and after desugaring.

rdar://problem/54329242

Reviewed By: erik.pilkington

Differential Revision: https://reviews.llvm.org/D72872

clang/include/clang/AST/ASTContext.h

@@ -1442,6 +1442,8 @@ public:
 
   QualType getObjCTypeParamType(const ObjCTypeParamDecl *Decl,
                                 ArrayRef<ObjCProtocolDecl *> protocols) const;
+  void adjustObjCTypeParamBoundType(const ObjCTypeParamDecl *Orig,
+                                    ObjCTypeParamDecl *New) const;
 
   bool ObjCObjectAdoptsQTypeProtocols(QualType QT, ObjCInterfaceDecl *Decl);
 

clang/lib/AST/ASTContext.cpp

@@ -4874,6 +4874,17 @@ ASTContext::getObjCTypeParamType(const ObjCTypeParamDecl *Decl,
   return QualType(newType, 0);
 }
 
+void ASTContext::adjustObjCTypeParamBoundType(const ObjCTypeParamDecl *Orig,
+                                              ObjCTypeParamDecl *New) const {
+  New->setTypeSourceInfo(getTrivialTypeSourceInfo(Orig->getUnderlyingType()));
+  // Update TypeForDecl after updating TypeSourceInfo.
+  auto NewTypeParamTy = cast<ObjCTypeParamType>(New->getTypeForDecl());
+  SmallVector<ObjCProtocolDecl *, 8> protocols;
+  protocols.append(NewTypeParamTy->qual_begin(), NewTypeParamTy->qual_end());
+  QualType UpdatedTy = getObjCTypeParamType(New, protocols);
+  New->setTypeForDecl(UpdatedTy.getTypePtr());
+}
+
 /// ObjCObjectAdoptsQTypeProtocols - Checks that protocols in IC's
 /// protocol list adopt all protocols in QT's qualified-id protocol
 /// list.

clang/lib/AST/Type.cpp

@@ -3534,6 +3534,7 @@ void ObjCTypeParamType::Profile(llvm::FoldingSetNodeID &ID,
                                 const ObjCTypeParamDecl *OTPDecl,
                                 ArrayRef<ObjCProtocolDecl *> protocols) {
   ID.AddPointer(OTPDecl);
+  ID.AddPointer(OTPDecl->getUnderlyingType().getAsOpaquePtr());
   ID.AddInteger(protocols.size());
   for (auto proto : protocols)
     ID.AddPointer(proto);

clang/lib/Sema/SemaDeclObjC.cpp

@@ -938,8 +938,7 @@ static bool checkTypeParamListConsistency(Sema &S,
 
       // Override the new type parameter's bound type with the previous type,
       // so that it's consistent.
-      newTypeParam->setTypeSourceInfo(
-        S.Context.getTrivialTypeSourceInfo(prevTypeParam->getUnderlyingType()));
+      S.Context.adjustObjCTypeParamBoundType(prevTypeParam, newTypeParam);
       continue;
     }
 
@@ -966,8 +965,7 @@ static bool checkTypeParamListConsistency(Sema &S,
     }
 
     // Update the new type parameter's bound to match the previous one.
-    newTypeParam->setTypeSourceInfo(
-      S.Context.getTrivialTypeSourceInfo(prevTypeParam->getUnderlyingType()));
+    S.Context.adjustObjCTypeParamBoundType(prevTypeParam, newTypeParam);
   }
 
   return false;

clang/test/SemaObjC/parameterized_classes_collection_literal.m

@@ -29,7 +29,9 @@ __attribute__((objc_root_class))
 @end
 
 @interface NSDictionary<K, V> : NSObject <NSCopying>
-+ (instancetype)dictionaryWithObjects:(const V [])objects forKeys:(const K [])keys count:(NSUInteger)cnt;
++ (instancetype)dictionaryWithObjects:(const V [])objects
+                              forKeys:(const K <NSCopying> [])keys
+                                count:(NSUInteger)cnt;
 @end
 
 void testArrayLiteral(void) {
@@ -50,3 +52,9 @@ void testDictionaryLiteral(void) {
     @"world" : @"blah" // expected-warning{{object of type 'NSString *' is not compatible with dictionary value type 'NSNumber *'}}
   };
 }
+
+void testCastingInDictionaryLiteral(NSString *arg) {
+  NSDictionary *dict = @{
+    (id)arg : @"foo",
+  };
+}

clang/test/SemaObjC/parameterized_classes_subst.m

@@ -467,3 +467,17 @@ void bar(MyMutableDictionary<NSString *, NSString *> *stringsByString,
 - (void)mapUsingBlock2:(id)block { // expected-warning{{conflicting parameter types in implementation}}
 }
 @end
+
+// --------------------------------------------------------------------------
+// Use a type parameter as a type argument.
+// --------------------------------------------------------------------------
+// Type bounds in a category/extension are omitted. rdar://problem/54329242
+@interface ParameterizedContainer<T : id<NSCopying>>
+- (ParameterizedContainer<T> *)inInterface;
+@end
+@interface ParameterizedContainer<T> (Cat)
+- (ParameterizedContainer<T> *)inCategory;
+@end
+@interface ParameterizedContainer<U> ()
+- (ParameterizedContainer<U> *)inExtension;
+@end