[Modules] Add 'no_undeclared_includes' module map attribute

The 'no_undeclared_includes' attribute should be used in a module to
tell that only non-modular headers and headers from used modules are
accepted.

The main motivation behind this is to prevent dep cycles between system
libraries (such as darwin) and libc++.

Patch by Richard Smith!

llvm-svn: 284797

1 files changed, 8 insertions, 1 deletions

diff --git a/clang/lib/Basic/Module.cpp b/clang/lib/Basic/Module.cpp
index 8578947db82..80bbc24f3db 100644
--- a/clang/lib/Basic/Module.cpp
+++ b/clang/lib/Basic/Module.cpp
@@ -33,7 +33,7 @@ Module::Module(StringRef Name, SourceLocation DefinitionLoc, Module *Parent,
       IsExplicit(IsExplicit), IsSystem(false), IsExternC(false),
       IsInferred(false), InferSubmodules(false), InferExplicitSubmodules(false),
       InferExportWildcard(false), ConfigMacrosExhaustive(false),
-      NameVisibility(Hidden) {
+      NoUndeclaredIncludes(false), NameVisibility(Hidden) {
   if (Parent) {
     if (!Parent->isAvailable())
       IsAvailable = false;
@@ -41,6 +41,8 @@ Module::Module(StringRef Name, SourceLocation DefinitionLoc, Module *Parent,
       IsSystem = true;
     if (Parent->IsExternC)
       IsExternC = true;
+    if (Parent->NoUndeclaredIncludes)
+      NoUndeclaredIncludes = true;
     IsMissingRequirement = Parent->IsMissingRequirement;
     
     Parent->SubModuleIndex[Name] = Parent->SubModules.size();
@@ -181,6 +183,11 @@ bool Module::directlyUses(const Module *Requested) const {
   for (auto *Use : Top->DirectUses)
     if (Requested->isSubModuleOf(Use))
       return true;
+
+  // Anyone is allowed to use our builtin stddef.h and its accompanying module.
+  if (!Requested->Parent && Requested->Name == "_Builtin_stddef_max_align_t")
+    return true;
+
   return false;
 }