Add stopgap option -fmodule-implementation-of <name>

This flag specifies that we are building an implementation file of the
module <name>, preventing importing <name> as a module. This does not
consider this to be the 'current module' for the purposes of doing
modular checks like decluse or non-modular-include warnings, unlike
-fmodule-name.

This is needed as a stopgap until:
1) we can resolve relative includes to a VFS-mapped module (or can
   safely import a header textually and as part of a module)

and ideally
2) we can safely do incremental rebuilding when implementation files
   import submodules.

llvm-svn: 213767

1 files changed, 3 insertions, 1 deletions

diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index 1741c302f33..a8e27c71da8 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -1539,7 +1539,9 @@ void Preprocessor::HandleIncludeDirective(SourceLocation HashLoc,
 
   // If we are supposed to import a module rather than including the header,
   // do so now.
-  if (SuggestedModule && getLangOpts().Modules) {
+  if (SuggestedModule && getLangOpts().Modules &&
+      SuggestedModule.getModule()->getTopLevelModuleName() !=
+      getLangOpts().ImplementationOfModule) {
     // Compute the module access path corresponding to this module.
     // FIXME: Should we have a second loadModule() overload to avoid this
     // extra lookup step?