Fix PR12960 by not attempting to correct cases when we're not actually instantiatiating a template.

This comes up in the begin/end calls of a range-for (see the included test
case). Other suggestions are welcome, though this seems to do the trick without
regressing anything.

llvm-svn: 157553

clang/lib/Sema/SemaExpr.cpp

@@ -1371,7 +1371,8 @@ bool Sema::DiagnoseEmptyLookup(Scope *S, CXXScopeSpec &SS, LookupResult &R,
   // unqualified lookup.  This is useful when (for example) the
   // original lookup would not have found something because it was a
   // dependent name.
-  DeclContext *DC = SS.isEmpty() ? CurContext : 0;
+  DeclContext *DC = (SS.isEmpty() && !CallsUndergoingInstantiation.empty())
+    ? CurContext : 0;
   while (DC) {
     if (isa<CXXRecordDecl>(DC)) {
       LookupQualifiedName(R, DC);

clang/test/CXX/stmt.stmt/stmt.iter/stmt.ranged/p1.cpp

@@ -1,5 +1,13 @@
 // RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify %s
 
+struct pr12960 {
+  int begin;
+  void foo(int x) {
+    for (int& it : x) { // expected-error {{use of undeclared identifier 'begin'}} expected-note {{range has type 'int'}}
+    }
+  }
+};
+
 namespace std {
   template<typename T>
     auto begin(T &&t) -> decltype(t.begin()) { return t.begin(); } // expected-note 4{{ignored: substitution failure}}
@@ -207,3 +215,4 @@ void example() {
   for (int &x : array)
     x *= 2;
 }
+