When looking for the module associated with one of our magical builtin headers, speculatively load module maps.

The "magical" builtin headers are the headers we provide as part of
the C standard library, which typically comes from /usr/include. We
essentially merge our headers into that location (due to cyclic
dependencies). This change makes sure that, when header search finds
one of our builtin headers, we figure out which module it actually
lives in. This case is fairly rare; one ends up having to include one
of the few built-in C headers we provide before including anything
from /usr/include to trigger it. Fixes <rdar://problem/13787184>.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@180934 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Lex/ModuleMap.cpp b/lib/Lex/ModuleMap.cpp
index 0c03201..1458a73 100644
--- a/lib/Lex/ModuleMap.cpp
+++ b/lib/Lex/ModuleMap.cpp
@@ -149,6 +149,24 @@
   return Name;
 }
 
+/// \brief Determine whether the given file name is the name of a builtin
+/// header, supplied by Clang to replace, override, or augment existing system
+/// headers.
+static bool isBuiltinHeader(StringRef FileName) {
+  return llvm::StringSwitch<bool>(FileName)
+           .Case("float.h", true)
+           .Case("iso646.h", true)
+           .Case("limits.h", true)
+           .Case("stdalign.h", true)
+           .Case("stdarg.h", true)
+           .Case("stdbool.h", true)
+           .Case("stddef.h", true)
+           .Case("stdint.h", true)
+           .Case("tgmath.h", true)
+           .Case("unwind.h", true)
+           .Default(false);
+}
+
 Module *ModuleMap::findModuleForHeader(const FileEntry *File) {
   HeadersMap::iterator Known = Headers.find(File);
   if (Known != Headers.end()) {
@@ -158,6 +176,25 @@
 
     return Known->second.getModule();
   }
+
+  // If we've found a builtin header within Clang's builtin include directory,
+  // load all of the module maps to see if it will get associated with a
+  // specific module (e.g., in /usr/include).
+  if (File->getDir() == BuiltinIncludeDir &&
+      isBuiltinHeader(llvm::sys::path::filename(File->getName()))) {
+    SmallVector<Module *, 4> AllModules;
+    HeaderInfo.collectAllModules(AllModules);
+
+    // Check again.
+    Known = Headers.find(File);
+    if (Known != Headers.end()) {
+      // If a header is not available, don't report that it maps to anything.
+      if (!Known->second.isAvailable())
+        return 0;
+
+      return Known->second.getModule();
+    }
+  }
   
   const DirectoryEntry *Dir = File->getDir();
   SmallVector<const DirectoryEntry *, 2> SkippedDirs;
@@ -1266,24 +1303,6 @@
   }
 }
 
-/// \brief Determine whether the given file name is the name of a builtin
-/// header, supplied by Clang to replace, override, or augment existing system
-/// headers.
-static bool isBuiltinHeader(StringRef FileName) {
-  return llvm::StringSwitch<bool>(FileName)
-      .Case("float.h", true)
-      .Case("iso646.h", true)
-      .Case("limits.h", true)
-      .Case("stdalign.h", true)
-      .Case("stdarg.h", true)
-      .Case("stdbool.h", true)
-      .Case("stddef.h", true)
-      .Case("stdint.h", true)
-      .Case("tgmath.h", true)
-      .Case("unwind.h", true)
-      .Default(false);
-}
-
 /// \brief Parse a header declaration.
 ///
 ///   header-declaration: