Add function explicit instantiations to owning context

[davrec]

Summary

template <typename T> T func() { return T(); }
template int func<int>();

The second line is not currently represented in AST in its lexical context, though it is among the FunctionTemplateDecl's specializations (with getTemplateSpecializationKind() == TSK_ExplicitInstantiationDefinition). By contrast, explicit instantiations for classes and variables are represented in their lexical context, in addition to being among their owning TemplateDecl's specializations.

This patch simply adds function explicit instantiations to the lexical context to match the behavior of classes/vars.

Not well tested.

[davrec]

clang/include/clang/AST/RecursiveASTVisitor.h

2124

This switch should actually be conditioned on if (!getDerived.shouldVisitTemplateInstantiations()):

clang/include/clang/AST/RecursiveASTVisitor.h

for (auto *FD : D->specializations()) {
     for (auto *RD : FD->redecls()) {
       switch (RD->getTemplateSpecializationKind()) {
       case TSK_Undeclared:
       case TSK_ImplicitInstantiation:
         // We don't know what kind of FunctionDecl this is.
         TRY_TO(TraverseDecl(RD));
         break;
 
-      // FIXME: For now traverse explicit instantiations here. Change that
-      // once they are represented as dedicated nodes in the AST.
       case TSK_ExplicitInstantiationDeclaration:
       case TSK_ExplicitInstantiationDefinition:
-        TRY_TO(TraverseDecl(RD));
-        break;
-
       case TSK_ExplicitSpecialization:
         break;
       }
     }
   }
 
   return true;
 }
bool RecursiveASTVisitor<Derived>::TraverseFunctionHelper(FunctionDecl *D) {
   if (const auto *MD = dyn_cast<CXXMethodDecl>(D)) {
     if (const CXXRecordDecl *RD = MD->getParent()) {
       if (RD->isLambda() &&
           declaresSameEntity(RD->getLambdaCallOperator(), MD)) {
         VisitBody = VisitBody && getDerived().shouldVisitLambdaBody();
       }
     }
   }
 
+  switch(D->getTemplateSpecializationKind()) {
+    case TSK_ExplicitInstantiationDeclaration:
+    case TSK_ExplicitInstantiationDefinition:
+      VisitBody = false;
+      break;
+    default:
+      break;
+  }
+
   if (VisitBody) {
     TRY_TO(TraverseStmt(D->getBody()));
     // Body may contain using declarations whose shadows are parented to the
     // FunctionDecl itself.
     for (auto *Child : D->decls()) {
       if (isa<UsingShadowDecl>(Child))
         TRY_TO(TraverseDecl(Child));
     }

clang/lib/Sema/SemaTemplate.cpp

if (D.getName().getKind() != UnqualifiedIdKind::IK_TemplateId && !FunTmpl &&
     << Specialization << D.getCXXScopeSpec().getRange();
 
   CheckExplicitInstantiation(
       *this,
       FunTmpl ? (NamedDecl *)FunTmpl
               : Specialization->getInstantiatedFromMemberFunction(),
       D.getIdentifierLoc(), D.getCXXScopeSpec().isSet(), TSK);
 
-  // FIXME: Create some kind of ExplicitInstantiationDecl here.
+  CurContext->addDecl(Specialization);
   return (Decl*) nullptr;
 }
 
 TypeResult
 Sema::ActOnDependentTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                         const CXXScopeSpec &SS, IdentifierInfo *Name,
                         SourceLocation TagLoc, SourceLocation NameLoc) {
   // This has to hold, because SS is expected to be defined.