[Modules] Improve error message when cannot find parent module for submodule definition.

Before the change the diagnostic for

    module unknown.submodule {}

was "error: expected module name" which is incorrect and misleading
because both "unknown" and "submodule" are valid module names.

We already have a better error message when a parent module is a
submodule itself and is missing. Make the error for a missing top-level
module more like the one for a submodule.

rdar://problem/64424407

Reviewed By: bruno

Differential Revision: https://reviews.llvm.org/D84458

1 files changed, 7 insertions, 9 deletions

diff --git a/clang/lib/Lex/ModuleMap.cpp b/clang/lib/Lex/ModuleMap.cpp
index bcdc5b8..12da5a8 100644
--- a/clang/lib/Lex/ModuleMap.cpp
+++ b/clang/lib/Lex/ModuleMap.cpp
@@ -1903,18 +1903,16 @@ void ModuleMapParser::parseModuleDecl() {
         continue;
       }
 
-      if (ActiveModule) {
-        Diags.Report(Id[I].second, diag::err_mmap_missing_module_qualified)
-          << Id[I].first
-          << ActiveModule->getTopLevelModule()->getFullModuleName();
-      } else {
-        Diags.Report(Id[I].second, diag::err_mmap_expected_module_name);
-      }
+      Diags.Report(Id[I].second, diag::err_mmap_missing_parent_module)
+          << Id[I].first << (ActiveModule != nullptr)
+          << (ActiveModule
+                  ? ActiveModule->getTopLevelModule()->getFullModuleName()
+                  : "");
       HadError = true;
-      return;
     }
 
-    if (ModuleMapFile != Map.getContainingModuleMapFile(TopLevelModule)) {
+    if (TopLevelModule &&
+        ModuleMapFile != Map.getContainingModuleMapFile(TopLevelModule)) {
       assert(ModuleMapFile != Map.getModuleMapFileForUniquing(TopLevelModule) &&
              "submodule defined in same file as 'module *' that allowed its "
              "top-level module");