[cfe-dev] UsingDirectiveDecl inconsistently (not) added to their DeclContext.

[John McCall]

On Aug 6, 2012, at 7:30 AM, Enea Zaffanella wrote:
> We are observing an inconsistency (affecting our AST visitors) in the 
> addition of UsingDirectiveDecl to their DeclContext.
> 
> When parsing a using directive, it gets added to its DeclContext only if 
> it is NOT a function/method:
> 
> ===================== SemaDeclCXX.cpp
> void Sema::PushUsingDirective(Scope *S, UsingDirectiveDecl *UDir) {
>   // If the scope has an associated entity and the using directive is at
>   // namespace or translation unit scope, add the UsingDirectiveDecl into
>   // its lookup structure so qualified name lookup can find it.
>   DeclContext *Ctx = static_cast<DeclContext*>(S->getEntity());
>   if (Ctx && !Ctx->isFunctionOrMethod())
>     Ctx->addDecl(UDir);
> =====================
> 
> 
> However, when such a using declaration is subject to template 
> instantiations, it is unconditionally added to its DeclContext, no 
> matter if it is a function/method or not:
> 
> ===================== SemaTemplateInstantiateDecl.cpp
> Decl 
> *TemplateDeclInstantiator::VisitUsingDirectiveDecl(UsingDirectiveDecl *D) {
>   // Using directives are never dependent (and never contain any types or
>   // expressions), so they require no explicit instantiation work.
> 
>   UsingDirectiveDecl *Inst
>     = UsingDirectiveDecl::Create(SemaRef.Context, Owner, D->getLocation(),
>                                  D->getNamespaceKeyLocation(),
>                                  D->getQualifierLoc(),
>                                  D->getIdentLocation(),
>                                  D->getNominatedNamespace(),
>                                  D->getCommonAncestor());
>   Owner->addDecl(Inst);
> =====================
> 
> Therefore, when visiting the instantiated DeclContext we will see more 
> declarations than when visiting its instantiation pattern.
> We would like to remove this inconsistency, but it is unclear to us 
> which is the right fix to apply: should we always add the using 
> declaration to its DeclContext or should we repeat the check for 
> function/method when instantiating?

Repeat the check;  I don't see any value to having the UsingDirectiveDecl
in the DC for a function.

John.