2 files changed, 22 insertions, 9 deletions
diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index d314f6d18a6..991e9ef990a 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -1393,8 +1393,21 @@ bool CompilerInstance::loadModuleFile(StringRef FileName) {
         if (Module *M = CI.getPreprocessor()
                             .getHeaderSearchInfo()
                             .getModuleMap()
-                            .findModule(II->getName()))
+                            .findModule(II->getName())) {
           M->HasIncompatibleModuleFile = true;
+
+          // Mark module as available if the only reason it was unavailable
+          // was missing headers.
+          SmallVector<Module *, 2> Stack;
+          Stack.push_back(M);
+          while (!Stack.empty()) {
+            Module *Current = Stack.pop_back_val();
+            if (Current->IsMissingRequirement) continue;
+            Current->IsAvailable = true;
+            Stack.insert(Stack.end(),
+                         Current->submodule_begin(), Current->submodule_end());
+          }
+        }
       }
       LoadedModules.clear();
     }
@@ -1498,7 +1511,7 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
       if (Module && Module->HasIncompatibleModuleFile) {
         // We tried and failed to load a module file for this module. Fall
         // back to textual inclusion for its headers.
-        return ModuleLoadResult(nullptr, /*missingExpected*/true);
+        return ModuleLoadResult::ConfigMismatch;
       }
 
       getDiagnostics().Report(ModuleNameLoc, diag::err_module_build_disabled)
@@ -1705,7 +1718,7 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
         << Module->getFullModuleName()
         << SourceRange(Path.front().second, Path.back().second);
 
-      return ModuleLoadResult(nullptr, true);
+      return ModuleLoadResult::MissingExpected;
     }
 
     // Check whether this module is available.
@@ -1739,7 +1752,7 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
   }
 
   LastModuleImportLoc = ImportLoc;
-  LastModuleImportResult = ModuleLoadResult(Module, false);
+  LastModuleImportResult = ModuleLoadResult(Module);
   return LastModuleImportResult;
 }
 
diff --git a/clang/lib/Lex/PPDirectives.cpp b/clang/lib/Lex/PPDirectives.cpp
index 7fc008274bd..85504de3d15 100644
--- a/clang/lib/Lex/PPDirectives.cpp
+++ b/clang/lib/Lex/PPDirectives.cpp
@@ -1866,10 +1866,7 @@ void Preprocessor::HandleIncludeDirective(SourceLocation HashLoc,
     // unavailable, diagnose the situation and bail out.
     // FIXME: Remove this; loadModule does the same check (but produces
     // slightly worse diagnostics).
-    if (!SuggestedModule.getModule()->isAvailable() &&
-        !SuggestedModule.getModule()
-             ->getTopLevelModule()
-             ->HasIncompatibleModuleFile) {
+    if (!SuggestedModule.getModule()->isAvailable()) {
       Module::Requirement Requirement;
       Module::UnresolvedHeaderDirective MissingHeader;
       Module *M = SuggestedModule.getModule();
@@ -1918,9 +1915,12 @@ void Preprocessor::HandleIncludeDirective(SourceLocation HashLoc,
     else if (Imported.isMissingExpected()) {
       // We failed to find a submodule that we assumed would exist (because it
       // was in the directory of an umbrella header, for instance), but no
-      // actual module exists for it (because the umbrella header is
+      // actual module containing it exists (because the umbrella header is
       // incomplete).  Treat this as a textual inclusion.
       SuggestedModule = ModuleMap::KnownHeader();
+    } else if (Imported.isConfigMismatch()) {
+      // On a configuration mismatch, enter the header textually. We still know
+      // that it's part of the corresponding module.
     } else {
       // We hit an error processing the import. Bail out.
       if (hadModuleLoaderFatalFailure()) {