[clang][SemaTemplate] Fix a stack use after scope

Differential Revision: https://reviews.llvm.org/D120065

clang/include/clang/AST/DeclTemplate.h

@@ -2461,10 +2461,10 @@ private:
   SourceLocation FriendLoc;
 
   FriendTemplateDecl(DeclContext *DC, SourceLocation Loc,
-                     MutableArrayRef<TemplateParameterList *> Params,
+                     TemplateParameterList **Params, unsigned NumParams,
                      FriendUnion Friend, SourceLocation FriendLoc)
-      : Decl(Decl::FriendTemplate, DC, Loc), NumParams(Params.size()),
-        Params(Params.data()), Friend(Friend), FriendLoc(FriendLoc) {}
+      : Decl(Decl::FriendTemplate, DC, Loc), NumParams(NumParams),
+        Params(Params), Friend(Friend), FriendLoc(FriendLoc) {}
 
   FriendTemplateDecl(EmptyShell Empty) : Decl(Decl::FriendTemplate, Empty) {}
 

clang/lib/AST/DeclTemplate.cpp

@@ -28,6 +28,7 @@
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/None.h"
 #include "llvm/ADT/PointerUnion.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -1098,7 +1099,13 @@ FriendTemplateDecl::Create(ASTContext &Context, DeclContext *DC,
                            SourceLocation L,
                            MutableArrayRef<TemplateParameterList *> Params,
                            FriendUnion Friend, SourceLocation FLoc) {
-  return new (Context, DC) FriendTemplateDecl(DC, L, Params, Friend, FLoc);
+  TemplateParameterList **TPL = nullptr;
+  if (!Params.empty()) {
+    TPL = new (Context) TemplateParameterList *[Params.size()];
+    llvm::copy(Params, TPL);
+  }
+  return new (Context, DC)
+      FriendTemplateDecl(DC, L, TPL, Params.size(), Friend, FLoc);
 }
 
 FriendTemplateDecl *FriendTemplateDecl::CreateDeserialized(ASTContext &C,

clang/test/SemaTemplate/friend-template.cpp

@@ -329,3 +329,12 @@ namespace rdar12350696 {
     foo(b); // expected-note {{in instantiation}}
   }
 }
+
+namespace StackUseAfterScope {
+template <typename T> class Bar {};
+class Foo {
+  // Make sure this doesn't crash.
+  template <> friend class Bar<int>; // expected-error {{template specialization declaration cannot be a friend}}
+  bool aux;
+};
+}