[modules] Apply ODR merging for function scoped tags only in C++ mode.

In C mode, if we have a visible declaration but not a visible definition, a tag
defined in the declaration should be have a visible definition. In C++ we rely
on the ODR merging, whereas in C we cannot because each declaration of a
function gets its own set of declarations in its prototype scope.

Patch developed in collaboration with Richard Smith!

llvm-svn: 280984

4 files changed, 12 insertions, 0 deletions

diff --git a/clang/test/Modules/Inputs/merge-fn-prototype-tags/a.h b/clang/test/Modules/Inputs/merge-fn-prototype-tags/a.h
new file mode 100644
index 00000000000..8dd717cba62
--- /dev/null
+++ b/clang/test/Modules/Inputs/merge-fn-prototype-tags/a.h
@@ -0,0 +1,2 @@
+#include "c.h"
+void ftw(struct stat);
diff --git a/clang/test/Modules/Inputs/merge-fn-prototype-tags/b.h b/clang/test/Modules/Inputs/merge-fn-prototype-tags/b.h
new file mode 100644
index 00000000000..566381f2edf
--- /dev/null
+++ b/clang/test/Modules/Inputs/merge-fn-prototype-tags/b.h
@@ -0,0 +1 @@
+struct stat;
diff --git a/clang/test/Modules/Inputs/merge-fn-prototype-tags/c.h b/clang/test/Modules/Inputs/merge-fn-prototype-tags/c.h
new file mode 100644
index 00000000000..cb526241743
--- /dev/null
+++ b/clang/test/Modules/Inputs/merge-fn-prototype-tags/c.h
@@ -0,0 +1,4 @@
+#ifndef _STAT_H_
+#define _STAT_H_
+struct stat {};
+#endif
diff --git a/clang/test/Modules/Inputs/merge-fn-prototype-tags/module.modulemap b/clang/test/Modules/Inputs/merge-fn-prototype-tags/module.modulemap
new file mode 100644
index 00000000000..b324f05abf1
--- /dev/null
+++ b/clang/test/Modules/Inputs/merge-fn-prototype-tags/module.modulemap
@@ -0,0 +1,5 @@
+module M {
+  header "a.h"
+  module mod_c { header "c.h" }
+  header "b.h"
+}