From fceda7d31062da61f20ac369843d390d9ff4fc20 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Sat, 27 Feb 2016 02:36:43 +0000
Subject: [PATCH] Fix bug in using shadow decl checking: a using shadow decl
 should not conflict with a prior UsingDecl -- those should not even really be
 found by the lookup here, except that we use the same lookup results for two
 different checks, and the other check needs them.

This happens to work in *almost all* cases, because either the lookup results
list the UsingDecl first (and the NonTag result gets replaced by something
else) or because the problematic declaration is a function (which causes us to
use different logic to detect conflicts). This can also be triggered from a
state only reachable through modules (where the name lookup results can contain
multiple UsingDecls in the same scope).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@262105 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaDeclCXX.cpp      |  6 ++++++
 test/SemaCXX/using-decl-1.cpp | 23 +++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index 3890120341..e7c3b6af02 100644
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -7796,6 +7796,12 @@ bool Sema::CheckUsingShadowDecl(UsingDecl *Using, NamedDecl *Orig,
   for (LookupResult::iterator I = Previous.begin(), E = Previous.end();
          I != E; ++I) {
     NamedDecl *D = (*I)->getUnderlyingDecl();
+    // We can have UsingDecls in our Previous results because we use the same
+    // LookupResult for checking whether the UsingDecl itself is a valid
+    // redeclaration.
+    if (isa<UsingDecl>(D))
+      continue;
+
     if (IsEquivalentForUsingDecl(Context, D, Target)) {
       if (UsingShadowDecl *Shadow = dyn_cast<UsingShadowDecl>(*I))
         PrevShadow = Shadow;
diff --git a/test/SemaCXX/using-decl-1.cpp b/test/SemaCXX/using-decl-1.cpp
index ec45b3109a..e17612d277 100644
--- a/test/SemaCXX/using-decl-1.cpp
+++ b/test/SemaCXX/using-decl-1.cpp
@@ -338,3 +338,26 @@ struct B : A {
   enum { X = sizeof(field) };
 };
 }
+
+namespace tag_vs_var {
+  namespace N {
+    struct X {};
+
+    struct Y {};
+    int Y;
+
+    int Z;
+  }
+  using N::X;
+  using N::Y;
+  using N::Z;
+
+  namespace N {
+    int X;
+
+    struct Z {};
+  }
+  using N::X;
+  using N::Y;
+  using N::Z;
+}
-- 
2.40.0