[modules] Fix macro hiding bug exposed if:

 * A submodule of module A is imported into module B
 * Another submodule of module A that is not imported into B exports a macro
 * Some submodule of module B also exports a definition of the macro, and
   happens to be the first submodule of B that imports module A.

In this case, we would incorrectly determine that A's macro redefines B's
macro, and so we don't need to re-export B's macro at all.

This happens with the 'assert' macro in an LLVM self-host. =(

llvm-svn: 213348

1 files changed, 6 insertions, 0 deletions

diff --git a/clang/test/Modules/macro-hiding.cpp b/clang/test/Modules/macro-hiding.cpp
new file mode 100644
index 00000000000..a7a6064e64d
--- /dev/null
+++ b/clang/test/Modules/macro-hiding.cpp
@@ -0,0 +1,6 @@
+// RUN: rm -rf %t
+// RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -I%S/Inputs/macro-hiding %s
+#include "c1.h"
+#include "b2.h"
+
+void h() { assert(true); }