Fix implementation of C11 6.2.7/4 and C++11 [dcl.array]p3:

When a local extern declaration redeclares some other entity, the type of that
entity is merged with the prior type if the prior declaration is visible (in C)
or is declared in the same scope (in C++).

 - Make LookupRedeclarationWithLinkage actually work in C++, use it in the right
   set of cases, and make it track whether it found a shadowed declaration.
 - Track whether we found a declaration in the same scope (for C++) including
   across serialization and template instantiation.

llvm-svn: 188307

1 files changed, 13 insertions, 5 deletions

diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 5766afa1011..c7242aa5f99 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -973,7 +973,8 @@ Decl *TemplateDeclInstantiator::VisitVarTemplateDecl(VarTemplateDecl *D) {
 
   // FIXME: This, and ForVarTemplate, is a hack that is probably unnecessary.
   // We should use a simplified version of VisitVarDecl.
-  VarDecl *VarInst = cast_or_null<VarDecl>(VisitVarDecl(Pattern, /*ForVarTemplate=*/true));
+  VarDecl *VarInst =
+      cast_or_null<VarDecl>(VisitVarDecl(Pattern, /*ForVarTemplate=*/ true));
 
   DeclContext *DC = Owner;
 
@@ -3336,6 +3337,8 @@ void Sema::BuildVariableInstantiation(
   NewVar->setInitStyle(OldVar->getInitStyle());
   NewVar->setCXXForRangeDecl(OldVar->isCXXForRangeDecl());
   NewVar->setConstexpr(OldVar->isConstexpr());
+  NewVar->setPreviousDeclInSameBlockScope(
+      OldVar->isPreviousDeclInSameBlockScope());
   NewVar->setAccess(OldVar->getAccess());
 
   if (!OldVar->isStaticDataMember()) {
@@ -3348,13 +3351,18 @@ void Sema::BuildVariableInstantiation(
   if (NewVar->hasAttrs())
     CheckAlignasUnderalignment(NewVar);
 
-  // FIXME: In theory, we could have a previous declaration for variables that
-  // are not static data members.
-  // FIXME: having to fake up a LookupResult is dumb.
   LookupResult Previous(*this, NewVar->getDeclName(), NewVar->getLocation(),
                         Sema::LookupOrdinaryName, Sema::ForRedeclaration);
 
-  if (!isa<VarTemplateSpecializationDecl>(NewVar))
+  if (NewVar->getLexicalDeclContext()->isFunctionOrMethod() &&
+      OldVar->getPreviousDecl()) {
+    // We have a previous declaration. Use that one, so we merge with the
+    // right type.
+    if (NamedDecl *NewPrev = FindInstantiatedDecl(
+            NewVar->getLocation(), OldVar->getPreviousDecl(), TemplateArgs))
+      Previous.addDecl(NewPrev);
+  } else if (!isa<VarTemplateSpecializationDecl>(NewVar) &&
+             OldVar->hasLinkage())
     LookupQualifiedName(Previous, NewVar->getDeclContext(), false);
 
   CheckVariableDeclaration(NewVar, Previous);