[Modules] Implement ODR-like semantics for tag types in C/ObjC

Allow ODR for ObjC/C in the sense that we won't keep more that
one definition around (merge them). However, ensure the decl
pass the structural compatibility check in C11 6.2.7/1, for that,
reuse the structural equivalence checks used by the ASTImporter.

Few other considerations:
- Create error diagnostics for tag types mismatches and thread
them into the structural equivalence checks.
- Note that by doing this we only support redefinition between types
that are considered "compatible types" by C.

This is mixed approach of the suggestions discussed in
http://lists.llvm.org/pipermail/cfe-dev/2017-March/053257.html

Differential Revision: https://reviews.llvm.org/D31778

rdar://problem/31909368

llvm-svn: 306918

4 files changed, 34 insertions, 0 deletions

diff --git a/clang/test/Modules/Inputs/F.framework/Headers/F.h b/clang/test/Modules/Inputs/F.framework/Headers/F.h
new file mode 100644
index 00000000000..4f705f00e1a
--- /dev/null
+++ b/clang/test/Modules/Inputs/F.framework/Headers/F.h
@@ -0,0 +1 @@
+// F.h
diff --git a/clang/test/Modules/Inputs/F.framework/Modules/module.modulemap b/clang/test/Modules/Inputs/F.framework/Modules/module.modulemap
new file mode 100644
index 00000000000..e414776c536
--- /dev/null
+++ b/clang/test/Modules/Inputs/F.framework/Modules/module.modulemap
@@ -0,0 +1,7 @@
+framework module F [extern_c] [system] {
+  umbrella header "F.h"
+  module * {
+      export *
+  }
+  export *
+}
diff --git a/clang/test/Modules/Inputs/F.framework/Modules/module.private.modulemap b/clang/test/Modules/Inputs/F.framework/Modules/module.private.modulemap
new file mode 100644
index 00000000000..69486a2a641
--- /dev/null
+++ b/clang/test/Modules/Inputs/F.framework/Modules/module.private.modulemap
@@ -0,0 +1,7 @@
+module F.Private [system] {
+  explicit module NS {
+      header "NS.h"
+      export *
+  }
+  export *
+}
diff --git a/clang/test/Modules/Inputs/F.framework/PrivateHeaders/NS.h b/clang/test/Modules/Inputs/F.framework/PrivateHeaders/NS.h
new file mode 100644
index 00000000000..5e947ba9051
--- /dev/null
+++ b/clang/test/Modules/Inputs/F.framework/PrivateHeaders/NS.h
@@ -0,0 +1,19 @@
+struct NS {
+  int a;
+  int b;
+};
+
+enum NSE {
+  FST = 22,
+  SND = 43,
+  TRD = 55
+};
+
+#define NS_ENUM(_type, _name) \
+  enum _name : _type _name;   \
+  enum _name : _type
+
+typedef NS_ENUM(int, NSMyEnum) {
+  MinX = 11,
+  MinXOther = MinX,
+};