[Sema] Fix crash-on-invalid-code issue:

@class I;
@implementation I(cat) // crashes here
@end

rdar://10968158

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@151931 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/DeclObjC.cpp b/lib/AST/DeclObjC.cpp
index 996e93a..7822eb2 100644
--- a/lib/AST/DeclObjC.cpp
+++ b/lib/AST/DeclObjC.cpp
@@ -806,6 +806,10 @@
 ///
 ObjCCategoryDecl *
 ObjCInterfaceDecl::FindCategoryDeclaration(IdentifierInfo *CategoryId) const {
+  // FIXME: Should make sure no callers ever do this.
+  if (!hasDefinition())
+    return 0;
+
   if (data().ExternallyCompleted)
     LoadExternalDefinition();
 
diff --git a/lib/Sema/SemaDeclObjC.cpp b/lib/Sema/SemaDeclObjC.cpp
index 9b49260..4df5ab3 100644
--- a/lib/Sema/SemaDeclObjC.cpp
+++ b/lib/Sema/SemaDeclObjC.cpp
@@ -820,7 +820,7 @@
                       IdentifierInfo *CatName, SourceLocation CatLoc) {
   ObjCInterfaceDecl *IDecl = getObjCInterfaceDecl(ClassName, ClassLoc, true);
   ObjCCategoryDecl *CatIDecl = 0;
-  if (IDecl) {
+  if (IDecl && IDecl->hasDefinition()) {
     CatIDecl = IDecl->FindCategoryDeclaration(CatName);
     if (!CatIDecl) {
       // Category @implementation with no corresponding @interface.
diff --git a/test/SemaObjC/category-1.m b/test/SemaObjC/category-1.m
index 137309f..d5ca0e2 100644
--- a/test/SemaObjC/category-1.m
+++ b/test/SemaObjC/category-1.m
@@ -95,3 +95,7 @@
 @synthesize name = _name;
 @end
 
+// rdar://10968158
+@class I; // expected-note {{forward declaration}}
+@implementation I(cat) // expected-error{{cannot find interface declaration}}
+@end