commit d16663d412a3f5401b79f78adbf8a46a4893cffb
Author: Ben Langmuir <blangmuir@apple.com>
Date:   Fri Nov 13 15:47:31 2015

    [modules] Allow "redefinition" of typedef from unimported submodule
    
    r233345 started being stricter about typedef names for linkage purposes
    in non-visible modules, but broke languages without the ODR.
    
    rdar://23527954

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 009fe16..1ff82b8 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -1828,7 +1828,8 @@ static void filterNonConflictingPreviousTypedefDecls(Sema &S,
 
       // If both declarations give a tag declaration a typedef name for linkage
       // purposes, then they declare the same entity.
-      if (OldTD->getAnonDeclWithTypedefName(/*AnyRedecl*/true) &&
+      if (S.getLangOpts().CPlusPlus &&
+          OldTD->getAnonDeclWithTypedefName(/*AnyRedecl*/true) &&
           Decl->getAnonDeclWithTypedefName())
         continue;
     }
diff --git a/test/Modules/Inputs/module.map b/test/Modules/Inputs/module.map
index d195e2f..226d45f 100644
--- a/test/Modules/Inputs/module.map
+++ b/test/Modules/Inputs/module.map
@@ -379,3 +379,10 @@ module DebugSubmodules {
 module ExtensionTestA {
   header "ExtensionTestA.h"
 }
+
+module TypedefTag {
+  header "typedef-tag.h"
+  explicit module Hidden {
+    header "typedef-tag-hidden.h"
+  }
+}
diff --git a/test/Modules/Inputs/typedef-tag-hidden.h b/test/Modules/Inputs/typedef-tag-hidden.h
new file mode 100644
index 0000000..eb59d69
--- /dev/null
+++ b/test/Modules/Inputs/typedef-tag-hidden.h
@@ -0,0 +1 @@
+typedef struct { int x; } TypedefStructHidden_t;
diff --git a/test/Modules/Inputs/typedef-tag.h b/test/Modules/Inputs/typedef-tag.h
new file mode 100644
index 0000000..77dff95
--- /dev/null
+++ b/test/Modules/Inputs/typedef-tag.h
@@ -0,0 +1 @@
+typedef struct { int x; } TypedefStructVisible_t;
diff --git a/test/Modules/typedef-tag-not-visible.m b/test/Modules/typedef-tag-not-visible.m
new file mode 100644
index 0000000..e1a6406
--- /dev/null
+++ b/test/Modules/typedef-tag-not-visible.m
@@ -0,0 +1,8 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -I %S/Inputs %s -verify
+
+@import TypedefTag;
+
+typedef struct { int x; } TypedefStructHidden_t;
+typedef struct { int x; } TypedefStructVisible_t; // expected-error{{typedef redefinition}}
+// expected-note@typedef-tag.h:1 {{here}}