3 files changed, 17 insertions, 8 deletions
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 5123601d8a6..5215a7e0dc4 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -1834,8 +1834,7 @@ static void filterNonConflictingPreviousTypedefDecls(Sema &S,
         continue;
     }
 
-    if (!Old->isExternallyVisible())
-      Filter.erase();
+    Filter.erase();
   }
 
   Filter.done();
@@ -3344,6 +3343,9 @@ void Sema::MergeVarDecl(VarDecl *New, LookupResult &Previous) {
   if (New->isInvalidDecl())
     return;
 
+  if (!shouldLinkPossiblyHiddenDecl(Previous, New))
+    return;
+
   VarTemplateDecl *NewTemplate = New->getDescribedVarTemplate();
 
   // Verify the old decl was also a variable or variable template.
@@ -3375,9 +3377,6 @@ void Sema::MergeVarDecl(VarDecl *New, LookupResult &Previous) {
     return New->setInvalidDecl();
   }
 
-  if (!shouldLinkPossiblyHiddenDecl(Old, New))
-    return;
-
   // Ensure the template parameters are compatible.
   if (NewTemplate &&
       !TemplateParameterListsAreEqual(NewTemplate->getTemplateParameters(),
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index b7278904185..eb010e9e39a 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -8684,9 +8684,11 @@ Decl *Sema::ActOnNamespaceAliasDef(Scope *S, SourceLocation NamespaceLoc,
   assert(!R.isAmbiguous() && !R.empty());
 
   // Check if we have a previous declaration with the same name.
-  NamedDecl *PrevDecl = LookupSingleName(S, Alias, AliasLoc, LookupOrdinaryName,
-                                         ForRedeclaration);
-  if (PrevDecl && !isDeclInScope(PrevDecl, CurContext, S))
+  LookupResult PrevR(*this, Alias, AliasLoc, LookupOrdinaryName,
+                     ForRedeclaration);
+  LookupQualifiedName(PrevR, CurContext->getRedeclContext());
+  NamedDecl *PrevDecl = PrevR.getAsSingle<NamedDecl>();
+  if (PrevDecl && !isVisible(PrevDecl))
     PrevDecl = nullptr;
 
   NamedDecl *ND = R.getFoundDecl();
diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index 7236e99942b..9b5d511818e 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -1547,6 +1547,14 @@ bool Sema::isVisibleSlow(const NamedDecl *D) {
   return LookupResult::isVisible(*this, const_cast<NamedDecl*>(D));
 }
 
+bool Sema::shouldLinkPossiblyHiddenDecl(LookupResult &R, const NamedDecl *New) {
+  for (auto *D : R) {
+    if (isVisible(D))
+      return true;
+  }
+  return New->isExternallyVisible();
+}
+
 /// \brief Retrieve the visible declaration corresponding to D, if any.
 ///
 /// This routine determines whether the declaration D is visible in the current