Fix a hole with nested unavailable submodules from r206664

If a module doesn't meet a requirement, neither do its submodules. If we
don't propogate that, we might think it's an error to be missing a
header in one of those submodules.

llvm-svn: 206673

clang/include/clang/Basic/Module.h

@@ -413,7 +413,7 @@ public:
                       const TargetInfo &Target);
 
   /// \brief Mark this module and all of its submodules as unavailable.
-  void markUnavailable();
+  void markUnavailable(bool MissingRequirement = false);
 
   /// \brief Find the submodule with the given name.
   ///

clang/lib/Basic/Module.cpp

@@ -39,6 +39,7 @@ Module::Module(StringRef Name, SourceLocation DefinitionLoc, Module *Parent,
       IsSystem = true;
     if (Parent->IsExternC)
       IsExternC = true;
+    IsMissingRequirement = Parent->IsMissingRequirement;
     
     Parent->SubModuleIndex[Name] = Parent->SubModules.size();
     Parent->SubModules.push_back(this);
@@ -160,11 +161,10 @@ void Module::addRequirement(StringRef Feature, bool RequiredState,
   if (hasFeature(Feature, LangOpts, Target) == RequiredState)
     return;
 
-  IsMissingRequirement = true;
-  markUnavailable();
+  markUnavailable(/*MissingRequirement*/true);
 }
 
-void Module::markUnavailable() {
+void Module::markUnavailable(bool MissingRequirement) {
   if (!IsAvailable)
     return;
 
@@ -178,6 +178,7 @@ void Module::markUnavailable() {
       continue;
 
     Current->IsAvailable = false;
+    Current->IsMissingRequirement |= MissingRequirement;
     for (submodule_iterator Sub = Current->submodule_begin(),
                          SubEnd = Current->submodule_end();
          Sub != SubEnd; ++Sub) {

clang/test/Modules/Inputs/submodules/module.map

@@ -20,6 +20,7 @@ module missing_unavailable_headers {
   module missing {
     requires !objc
     header "missing.h"
+    module also_missing { header "also_missing.h" }
   }
   module not_missing { }
 }