From d17e9c681bc448391b6a85fe7abdf6e180143393 Mon Sep 17 00:00:00 2001
From: Ben Langmuir <blangmuir@apple.com>
Date: Fri, 11 Dec 2015 01:44:43 +0000
Subject: [PATCH] Revert "[Modules] Fix regression when an
 elaborated-type-specifier mentions a hidden tag"

This is causing assertion failures; reverting until I can fix.

This reverts commit r255267

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@255324 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaDecl.cpp                          | 10 ++++------
 test/Modules/Inputs/elaborated-type-structs.h  |  3 ---
 test/Modules/Inputs/module.map                 |  7 -------
 ...borated-type-specifier-from-hidden-module.m | 18 ------------------
 4 files changed, 4 insertions(+), 34 deletions(-)
 delete mode 100644 test/Modules/Inputs/elaborated-type-structs.h
 delete mode 100644 test/Modules/elaborated-type-specifier-from-hidden-module.m

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 1d8f9b7d20..af5fdc95c9 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -12121,12 +12121,10 @@ Decl *Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
 
     // In C++, we need to do a redeclaration lookup to properly
     // diagnose some problems.
-    // FIXME: this lookup is also used (with and without C++) to find a hidden
-    // declaration so that we don't get ambiguity errors when using a type
-    // declared by an elaborated-type-specifier.  In C that is not correct and
-    // we should instead merge compatible types found by lookup.
-    Previous.setRedeclarationKind(ForRedeclaration);
-    LookupQualifiedName(Previous, SearchDC);
+    if (getLangOpts().CPlusPlus) {
+      Previous.setRedeclarationKind(ForRedeclaration);
+      LookupQualifiedName(Previous, SearchDC);
+    }
   }
 
   // If we have a known previous declaration to use, then use it.
diff --git a/test/Modules/Inputs/elaborated-type-structs.h b/test/Modules/Inputs/elaborated-type-structs.h
deleted file mode 100644
index da3940998f..0000000000
--- a/test/Modules/Inputs/elaborated-type-structs.h
+++ /dev/null
@@ -1,3 +0,0 @@
-struct S1;
-struct S2 { int x; };
-struct S3 { int x; };
diff --git a/test/Modules/Inputs/module.map b/test/Modules/Inputs/module.map
index 632517dd36..226d45fdf4 100644
--- a/test/Modules/Inputs/module.map
+++ b/test/Modules/Inputs/module.map
@@ -386,10 +386,3 @@ module TypedefTag {
     header "typedef-tag-hidden.h"
   }
 }
-
-module ElaboratedTypeStructs {
-  module Empty {}
-  module Structs {
-    header "elaborated-type-structs.h"
-  }
-}
diff --git a/test/Modules/elaborated-type-specifier-from-hidden-module.m b/test/Modules/elaborated-type-specifier-from-hidden-module.m
deleted file mode 100644
index 0ca1c24bba..0000000000
--- a/test/Modules/elaborated-type-specifier-from-hidden-module.m
+++ /dev/null
@@ -1,18 +0,0 @@
-// RUN: rm -rf %t
-// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs %s -verify
-
-@import ElaboratedTypeStructs.Empty; // The structs are now hidden.
-struct S1 *x;
-struct S2 *y;
-// FIXME: compatible definition should not be an error.
-struct S2 { int x; }; // expected-error {{redefinition}}
-struct S3 *z;
-// Incompatible definition.
-struct S3 { float y; }; // expected-error {{redefinition}}
-// expected-note@elaborated-type-structs.h:* 2 {{previous definition is here}}
-
-@import ElaboratedTypeStructs.Structs;
-
-void useS1(struct S1 *x);
-void useS2(struct S2 *x);
-void useS2(struct S2 *x);
-- 
2.40.0