Implement variance for Objective-C type parameters.

Introduce co- and contra-variance for Objective-C type parameters,
which allows us to express that (for example) an NSArray is covariant
in its type parameter. This means that NSArray<NSMutableString *> * is
a subtype of NSArray<NSString *> *, which is expected of the immutable
Foundation collections.

Type parameters can be annotated with __covariant or __contravariant
to make them co- or contra-variant, respectively. This feature can be
detected by __has_feature(objc_generics_variance). Implements
rdar://problem/20217490.

llvm-svn: 241549

2 files changed, 4 insertions, 0 deletions

diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index c54c5697e59..52019fcd328 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -904,7 +904,9 @@ void ASTDeclReader::VisitObjCMethodDecl(ObjCMethodDecl *MD) {
 
 void ASTDeclReader::VisitObjCTypeParamDecl(ObjCTypeParamDecl *D) {
   VisitTypedefNameDecl(D);
+  D->Variance = Record[Idx++];
   D->Index = Record[Idx++];
+  D->VarianceLoc = ReadSourceLocation(Record, Idx);
   D->ColonLoc = ReadSourceLocation(Record, Idx);
 }
 
diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index 4d3fb78b080..371aea8088a 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -581,7 +581,9 @@ void ASTDeclWriter::VisitObjCMethodDecl(ObjCMethodDecl *D) {
 
 void ASTDeclWriter::VisitObjCTypeParamDecl(ObjCTypeParamDecl *D) {
   VisitTypedefNameDecl(D);
+  Record.push_back(D->Variance);
   Record.push_back(D->Index);
+  Writer.AddSourceLocation(D->VarianceLoc, Record);
   Writer.AddSourceLocation(D->ColonLoc, Record);
 
   Code = serialization::DECL_OBJC_TYPE_PARAM;