[Objective-c] Fix a crash

[ahatanak]

Summary

This patch fixes a crash that occurs when __kindof is incorrectly used in the type parameter list of an interface. The crash occurs because ObjCTypeParamList::back() is called in checkTypeParamListConsistency on an empty list:

00762 diagLoc = S.getLocForEndOfToken(newTypeParams->back()->getLocEnd());

cfe/trunk/lib/Parse/ParseObjc.cpp

ObjCTypeParamList *list = Actions.actOnObjCTypeParamList(
                               typeParams,
                               rAngleLoc);
   Scope.enter(list);
 
   // Clear out the angle locations; they're used by the caller to indicate
   // whether there are any protocol references.
   lAngleLoc = SourceLocation();
   rAngleLoc = SourceLocation();
-  return list;
+  return invalid ? nullptr : list;
 }
 
 /// Parse an objc-type-parameter-list.
 ObjCTypeParamList *Parser::parseObjCTypeParamList() {
   SourceLocation lAngleLoc;
   SmallVector<IdentifierLocPair, 1> protocolIdents;
   SourceLocation rAngleLoc;
 

cfe/trunk/test/SemaObjC/kindof.m

 void testNullability() {
   // The base type being a pointer type tickles the bug.
   extern __kindof id <NSCopying> _Nonnull getSomeCopyable();
   NSString *string = getSomeCopyable(); // no-warning
 
   void processCopyable(__typeof(getSomeCopyable()) string);
   processCopyable(0); // expected-warning{{null passed to a callee that requires a non-null argument}}
 }
+
+// Check that clang doesn't crash when a type parameter is illegal.
+@interface Array1<T> : NSObject
+@end
+
+@interface I1 : NSObject
+@end
+
+@interface Array1<__kindof I1*>(extensions1) // expected-error{{expected type parameter name}}
+@end
+
+@interface Array2<T1, T2, T3> : NSObject
+@end
+
+@interface Array2<T, T, __kindof I1*>(extensions2) // expected-error{{expected type parameter name}} expected-error{{redeclaration of type parameter 'T'}}
+@end