Limit our MSVC compat hack for nested names from dependent bases

Previously, any undeclared unqualified id starting a nested name
specifier in a dependent context would have its lookup retried during
template instantiation.  Now we limit that retry hack to methods of a
class with dependent bases.  Free function templates in particular are
no longer affected by this hack.

Also, diagnose this as a Microsoft extension. This has the downside that
template authors may see this warning *and* an error during
instantiation time about this identifier. Fixing that will probably
require formalizing some kind of "delayed" identifier, instead of our
ad-hoc solutions of forming dependent AST nodes when lookup fails.

Based on a patch by Kim Gräsman!

Differential Revision: http://reviews.llvm.org/D4854

llvm-svn: 215683

clang/lib/Sema/SemaCXXScopeSpec.cpp

@@ -703,8 +703,13 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S,
   if (getLangOpts().MSVCCompat) {
     DeclContext *DC = LookupCtx ? LookupCtx : CurContext;
     if (DC->isDependentContext() && DC->isFunctionOrMethod()) {
-      SS.Extend(Context, &Identifier, IdentifierLoc, CCLoc);
-      return false;
+      CXXRecordDecl *ContainingClass = dyn_cast<CXXRecordDecl>(DC->getParent());
+      if (ContainingClass && ContainingClass->hasAnyDependentBases()) {
+        Diag(IdentifierLoc, diag::ext_undeclared_unqual_id_with_dependent_base)
+            << &Identifier << ContainingClass;
+        SS.Extend(Context, &Identifier, IdentifierLoc, CCLoc);
+        return false;
+      }
     }
   }
 

clang/test/SemaTemplate/lookup-dependent-bases.cpp

@@ -1,20 +1,55 @@
 // RUN: %clang_cc1 -fms-compatibility -fsyntax-only -verify %s
-// expected-no-diagnostics
 
-class C {
-public:
-   static void foo2() {  }
+namespace basic {
+struct C {
+  static void foo2() {}
 };
-template <class T>
-class A {
-public:
-   typedef C D;
+template <typename T>
+struct A {
+  typedef C D;
 };
 
-template <class T>
-class B : public A<T> {
-public:
-   void foo() {
-    D::foo2();
-   }
+template <typename T>
+struct B : A<T> {
+  void foo() {
+    D::foo2(); // expected-warning {{use of undeclared identifier 'D'; unqualified lookup into dependent bases of class template 'B' is a Microsoft extension}}
+  }
 };
+
+template struct B<int>; // Instantiation has no warnings.
+}
+
+namespace nested_nodep_base {
+// There are limits to our hacks, MSVC accepts this, but we don't.
+struct A {
+  struct D { static void foo2(); };
+};
+template <typename T>
+struct B : T {
+  struct C {
+    void foo() {
+      D::foo2(); // expected-error {{use of undeclared identifier 'D'}}
+    }
+  };
+};
+
+template struct B<A>; // Instantiation has no warnings.
+}
+
+namespace nested_dep_base {
+// We actually accept this because the inner class has a dependent base even
+// though it isn't a template.
+struct A {
+  struct D { static void foo2(); };
+};
+template <typename T>
+struct B {
+  struct C : T {
+    void foo() {
+      D::foo2(); // expected-warning {{use of undeclared identifier 'D'; unqualified lookup into dependent bases of class template 'C' is a Microsoft extension}}
+    }
+  };
+};
+
+template struct B<A>; // Instantiation has no warnings.
+}

clang/test/SemaTemplate/ms-lookup-template-base-classes.cpp

@@ -220,7 +220,8 @@ template <typename T> struct C : T {
   int    *bar() { return &b; }     // expected-error {{no member named 'b' in 'PR16014::C<PR16014::A>'}} expected-warning {{lookup into dependent bases}}
   int     baz() { return T::b; }   // expected-error {{no member named 'b' in 'PR16014::A'}}
   int T::*qux() { return &T::b; }  // expected-error {{no member named 'b' in 'PR16014::A'}}
-  int T::*fuz() { return &U::a; }  // expected-error {{use of undeclared identifier 'U'}}
+  int T::*fuz() { return &U::a; }  // expected-error {{use of undeclared identifier 'U'}} \
+  // expected-warning {{unqualified lookup into dependent bases of class template 'C'}}
 };
 
 template struct B<A>;
@@ -249,7 +250,8 @@ struct A : T {
     ::UndefClass::undef(); // expected-error {{no member named 'UndefClass' in the global namespace}}
   }
   void baz() {
-    B::qux(); // expected-error {{use of undeclared identifier 'B'}}
+    B::qux(); // expected-error {{use of undeclared identifier 'B'}} \
+    // expected-warning {{unqualified lookup into dependent bases of class template 'A'}}
   }
 };
 
@@ -460,3 +462,11 @@ template <typename T> struct D : C<T> {
   int x = f<NameFromBase>();
 };
 }
+
+namespace function_template_undef_impl {
+template<class T>
+void f() {
+  Undef::staticMethod(); // expected-error {{use of undeclared identifier 'Undef'}}
+  UndefVar.method(); // expected-error {{use of undeclared identifier 'UndefVar'}}
+}
+}