Improve diagnostics for missing import / #include of module.

Fix a few bugs where we would fail to properly determine header to
module correspondence when determining whether to suggest a #include or
import, and suggest a #include more often in language modes where there
is no import syntax. Generally, if the target is in a header with
include guards or #pragma once, we should suggest either #including or
importing that header, and not importing a module that happens to
textually include it.

In passing, improve the notes we attach to the corresponding
diagnostics: calling an entity that we couldn't see "previous" is
confusing.

1 files changed, 14 insertions, 1 deletions

diff --git a/clang/lib/Lex/ModuleMap.cpp b/clang/lib/Lex/ModuleMap.cpp
index 4f7d5ab..85bf93a 100644
--- a/clang/lib/Lex/ModuleMap.cpp
+++ b/clang/lib/Lex/ModuleMap.cpp
@@ -662,7 +662,20 @@ ModuleMap::findOrCreateModuleForHeaderInUmbrellaDir(const FileEntry *File) {
 }
 
 ArrayRef<ModuleMap::KnownHeader>
-ModuleMap::findAllModulesForHeader(const FileEntry *File) const {
+ModuleMap::findAllModulesForHeader(const FileEntry *File) {
+  HeadersMap::iterator Known = findKnownHeader(File);
+  if (Known != Headers.end())
+    return Known->second;
+
+  if (findOrCreateModuleForHeaderInUmbrellaDir(File))
+    return Headers.find(File)->second;
+
+  return None;
+}
+
+ArrayRef<ModuleMap::KnownHeader>
+ModuleMap::findResolvedModulesForHeader(const FileEntry *File) const {
+  // FIXME: Is this necessary?
   resolveHeaderDirectives(File);
   auto It = Headers.find(File);
   if (It == Headers.end())