Fix diagnostic for static methods referencing fields from using decls

Previously we thought the instance member was a function, not a field,
and we'd say something silly like:
  t.cpp:4:27: error: call to non-static member function without an object argument
    static int f() { return n; }
                            ^

Noticed in PR21923.

llvm-svn: 224480

clang/lib/Sema/SemaExprMember.cpp

@@ -90,7 +90,6 @@ enum IMAKind {
 /// conservatively answer "yes", in which case some errors will simply
 /// not be caught until template-instantiation.
 static IMAKind ClassifyImplicitMemberAccess(Sema &SemaRef,
-                                            Scope *CurScope,
                                             const LookupResult &R) {
   assert(!R.empty() && (*R.begin())->isCXXClassMember());
 
@@ -205,6 +204,9 @@ static void diagnoseInstanceReference(Sema &SemaRef,
   SourceRange Range(Loc);
   if (SS.isSet()) Range.setBegin(SS.getRange().getBegin());
 
+  // Look through using shadow decls and aliases.
+  Rep = Rep->getUnderlyingDecl();
+
   DeclContext *FunctionLevelDC = SemaRef.getFunctionLevelDeclContext();
   CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(FunctionLevelDC);
   CXXRecordDecl *ContextClass = Method ? Method->getParent() : nullptr;
@@ -237,7 +239,7 @@ Sema::BuildPossibleImplicitMemberExpr(const CXXScopeSpec &SS,
                                       SourceLocation TemplateKWLoc,
                                       LookupResult &R,
                                 const TemplateArgumentListInfo *TemplateArgs) {
-  switch (ClassifyImplicitMemberAccess(*this, CurScope, R)) {
+  switch (ClassifyImplicitMemberAccess(*this, R)) {
   case IMA_Instance:
     return BuildImplicitMemberExpr(SS, TemplateKWLoc, R, TemplateArgs, true);
 

clang/test/SemaCXX/using-decl-1.cpp

@@ -255,3 +255,11 @@ namespace TypoCorrectTemplateMember {
     using A::goobar; // expected-error {{no member named 'goobar' in 'TypoCorrectTemplateMember::A'; did you mean 'foobar'?}}
   };
 }
+
+namespace use_instance_in_static {
+struct A { int n; };
+struct B : A {
+  using A::n;
+  static int f() { return n; } // expected-error {{invalid use of member 'n' in static member function}}
+};
+}