[c++2a] Improve diagnostic for use of declaration from another TU's

global module fragment.

We know that the declaration in question should have been introduced by
a '#include', so try to figure out which one and suggest it. Don't
suggest importing the global module fragment itself!

llvm-svn: 358631

1 files changed, 15 insertions, 1 deletions

diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index b3778c1d6f8..5d5cae5fd0f 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -614,9 +614,16 @@ Preprocessor::getModuleHeaderToIncludeForDiagnostics(SourceLocation IncLoc,
                                                      SourceLocation Loc) {
   assert(M && "no module to include");
 
+  // If the context is the global module fragment of some module, we never
+  // want to return that file; instead, we want the innermost include-guarded
+  // header that it included.
+  bool InGlobalModuleFragment = M->Kind == Module::GlobalModuleFragment;
+
   // If we have a module import syntax, we shouldn't include a header to
   // make a particular module visible.
-  if (getLangOpts().ObjC)
+  if ((getLangOpts().ObjC || getLangOpts().CPlusPlusModules ||
+       getLangOpts().ModulesTS) &&
+      !InGlobalModuleFragment)
     return nullptr;
 
   Module *TopM = M->getTopLevelModule();
@@ -633,6 +640,13 @@ Preprocessor::getModuleHeaderToIncludeForDiagnostics(SourceLocation IncLoc,
     if (!FE)
       break;
 
+    if (InGlobalModuleFragment) {
+      if (getHeaderSearchInfo().isFileMultipleIncludeGuarded(FE))
+        return FE;
+      Loc = SM.getIncludeLoc(ID);
+      continue;
+    }
+
     bool InTextualHeader = false;
     for (auto Header : HeaderInfo.getModuleMap().findAllModulesForHeader(FE)) {
       if (!Header.getModule()->isSubModuleOf(TopM))