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

1 files changed, 13 insertions, 0 deletions

diff --git a/clang/lib/AST/ASTDumper.cpp b/clang/lib/AST/ASTDumper.cpp
index 3dec23d0065..c95922b141e 100644
--- a/clang/lib/AST/ASTDumper.cpp
+++ b/clang/lib/AST/ASTDumper.cpp
@@ -1475,6 +1475,19 @@ void ASTDumper::VisitObjCMethodDecl(const ObjCMethodDecl *D) {
 
 void ASTDumper::VisitObjCTypeParamDecl(const ObjCTypeParamDecl *D) {
   dumpName(D);
+  switch (D->getVariance()) {
+  case ObjCTypeParamVariance::Invariant:
+    break;
+
+  case ObjCTypeParamVariance::Covariant:
+    OS << " covariant";
+    break;
+
+  case ObjCTypeParamVariance::Contravariant:
+    OS << " contravariant";
+    break;
+  }
+
   if (D->hasExplicitBound())
     OS << " bounded";
   dumpType(D->getUnderlyingType());