[clang] Always allow including builtin headers in [no_undeclared_headers] modules.

Previously, this would fail if the builtin headers had been "claimed" by
a different module that wraps these builtin headers. libc++ does this,
for example.

This change adds a test demonstrating this situation; the test fails
without the fix.

1 files changed, 20 insertions, 11 deletions

diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index 3ac1df1..1df28cc 100644
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -1276,14 +1276,12 @@ bool HeaderSearch::ShouldEnterIncludeFile(Preprocessor &PP,
     //
     // It's common that libc++ and system modules will both define such
     // submodules. Make sure cached results for a builtin header won't
-    // prevent other builtin modules to potentially enter the builtin header.
-    // Note that builtins are header guarded and the decision to actually
-    // enter them is postponed to the controlling macros logic below.
+    // prevent other builtin modules from potentially entering the builtin
+    // header. Note that builtins are header guarded and the decision to
+    // actually enter them is postponed to the controlling macros logic below.
     bool TryEnterHdr = false;
     if (FileInfo.isCompilingModuleHeader && FileInfo.isModuleHeader)
-      TryEnterHdr = File->getDir() == ModMap.getBuiltinDir() &&
-                    ModuleMap::isBuiltinHeader(
-                        llvm::sys::path::filename(File->getName()));
+      TryEnterHdr = ModMap.isBuiltinHeader(File);
 
     // Textual headers can be #imported from different modules. Since ObjC
     // headers find in the wild might rely only on #import and do not contain
@@ -1416,20 +1414,31 @@ static bool suggestModule(HeaderSearch &HS, const FileEntry *File,
                           ModuleMap::KnownHeader *SuggestedModule) {
   ModuleMap::KnownHeader Module =
       HS.findModuleForHeader(File, /*AllowTextual*/true);
-  if (SuggestedModule)
-    *SuggestedModule = (Module.getRole() & ModuleMap::TextualHeader)
-                           ? ModuleMap::KnownHeader()
-                           : Module;
 
   // If this module specifies [no_undeclared_includes], we cannot find any
   // file that's in a non-dependency module.
   if (RequestingModule && Module && RequestingModule->NoUndeclaredIncludes) {
-    HS.getModuleMap().resolveUses(RequestingModule, /*Complain*/false);
+    HS.getModuleMap().resolveUses(RequestingModule, /*Complain*/ false);
     if (!RequestingModule->directlyUses(Module.getModule())) {
+      // Builtin headers are a special case. Multiple modules can use the same
+      // builtin as a modular header (see also comment in
+      // ShouldEnterIncludeFile()), so the builtin header may have been
+      // "claimed" by an unrelated module. This shouldn't prevent us from
+      // including the builtin header textually in this module.
+      if (HS.getModuleMap().isBuiltinHeader(File)) {
+        if (SuggestedModule)
+          *SuggestedModule = ModuleMap::KnownHeader();
+        return true;
+      }
       return false;
     }
   }
 
+  if (SuggestedModule)
+    *SuggestedModule = (Module.getRole() & ModuleMap::TextualHeader)
+                           ? ModuleMap::KnownHeader()
+                           : Module;
+
   return true;
 }