7 files changed, 44 insertions, 10 deletions
diff --git a/clang/docs/Modules.rst b/clang/docs/Modules.rst
index 02393d7ba9f..912cdafc8c3 100644
--- a/clang/docs/Modules.rst
+++ b/clang/docs/Modules.rst
@@ -194,6 +194,9 @@ Command-line parameters
 ``-fmodule-name=module-id``
   Consider a source file as a part of the given module.
 
+``-fmodule-map-file=<file>``
+  Load the given module map file if a header from its directory or one of its subdirectories is loaded.
+
 Module Map Language
 ===================
 
diff --git a/clang/include/clang/Driver/CC1Options.td b/clang/include/clang/Driver/CC1Options.td
index d5a8b775d74..1b96ef38c10 100644
--- a/clang/include/clang/Driver/CC1Options.td
+++ b/clang/include/clang/Driver/CC1Options.td
@@ -483,9 +483,12 @@ def fno_deprecated_macro : Flag<["-"], "fno-deprecated-macro">,
 
 def nostdsysteminc : Flag<["-"], "nostdsysteminc">,
   HelpText<"Disable standard system #include directories">;
-def fmodule_name : Joined<["-"], "fmodule-name=">, 
+def fmodule_name : Joined<["-"], "fmodule-name=">,
   MetaVarName<"<name>">,
-  HelpText<"Specify the name of the module to build">;           
+  HelpText<"Specify the name of the module to build">;
+def fmodule_map_file : Joined<["-"], "fmodule-map-file=">,
+  MetaVarName<"<file>">,
+  HelpText<"Load this module map file">;
 def fdisable_module_hash : Flag<["-"], "fdisable-module-hash">,
   HelpText<"Disable the module hash">;
 def c_isystem : JoinedOrSeparate<["-"], "c-isystem">, MetaVarName<"<directory>">,
diff --git a/clang/include/clang/Lex/HeaderSearchOptions.h b/clang/include/clang/Lex/HeaderSearchOptions.h
index 830f48dce8b..0b21c0dd349 100644
--- a/clang/include/clang/Lex/HeaderSearchOptions.h
+++ b/clang/include/clang/Lex/HeaderSearchOptions.h
@@ -120,6 +120,9 @@ public:
   /// of computing the module hash.
   llvm::SetVector<std::string> ModulesIgnoreMacros;
 
+  /// \brief The set of user-provided module-map-files.
+  llvm::SetVector<std::string> ModuleMapFiles;
+
   /// Include the compiler builtin includes.
   unsigned UseBuiltinIncludes : 1;
 
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index c8c676899c5..afba109453d 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -896,6 +896,9 @@ static void ParseHeaderSearchArgs(HeaderSearchOptions &Opts, ArgList &Args) {
     StringRef MacroDef = (*it)->getValue();
     Opts.ModulesIgnoreMacros.insert(MacroDef.split('=').first);
   }
+  std::vector<std::string> ModuleMapFiles =
+      Args.getAllArgValues(OPT_fmodule_map_file);
+  Opts.ModuleMapFiles.insert(ModuleMapFiles.begin(), ModuleMapFiles.end());
 
   // Add -I..., -F..., and -index-header-map options in order.
   bool IsIndexHeaderMap = false;
diff --git a/clang/lib/Lex/HeaderSearch.cpp b/clang/lib/Lex/HeaderSearch.cpp
index ec84bb16d60..5bcc4ea0441 100644
--- a/clang/lib/Lex/HeaderSearch.cpp
+++ b/clang/lib/Lex/HeaderSearch.cpp
@@ -941,26 +941,48 @@ bool HeaderSearch::hasModuleMap(StringRef FileName,
     DirName = llvm::sys::path::parent_path(DirName);
     if (DirName.empty())
       return false;
-    
+
     // Determine whether this directory exists.
     const DirectoryEntry *Dir = FileMgr.getDirectory(DirName);
     if (!Dir)
       return false;
     
-    // Try to load the module map file in this directory.
+    // Load user-specified module map files in 'Dir'.
+    bool ModuleMapFound = false;
+    for (llvm::SetVector<std::string>::iterator
+             I = HSOpts->ModuleMapFiles.begin(),
+             E = HSOpts->ModuleMapFiles.end();
+         I != E; ++I) {
+      StringRef ModuleMapFileDir = llvm::sys::path::parent_path(*I);
+      if (!llvm::sys::fs::equivalent(ModuleMapFileDir, DirName))
+        continue;
+
+      const FileEntry *File = FileMgr.getFile(*I);
+      if (!File)
+        continue;
+
+      loadModuleMapFile(File, /*IsSystem=*/false);
+      ModuleMapFound = true;
+    }
+
+    // Try to load the "module.map" file in this directory.
     switch (loadModuleMapFile(Dir, IsSystem)) {
     case LMM_NewlyLoaded:
     case LMM_AlreadyLoaded:
+      ModuleMapFound = true;
+      break;
+
+    case LMM_NoDirectory:
+    case LMM_InvalidModuleMap:
+      break;
+    }
+
+    if (ModuleMapFound) {
       // Success. All of the directories we stepped through inherit this module
       // map file.
       for (unsigned I = 0, N = FixUpDirectories.size(); I != N; ++I)
         DirectoryHasModuleMap[FixUpDirectories[I]] = true;
-      
       return true;
-
-    case LMM_NoDirectory:
-    case LMM_InvalidModuleMap:
-      break;
     }
 
     // If we hit the top of our search, we're done.
diff --git a/clang/test/Modules/Inputs/modular_maps/module.map b/clang/test/Modules/Inputs/modular_maps/modulea.map
index 7018c413042..7018c413042 100644
--- a/clang/test/Modules/Inputs/modular_maps/module.map
+++ b/clang/test/Modules/Inputs/modular_maps/modulea.map
diff --git a/clang/test/Modules/modular_maps.cpp b/clang/test/Modules/modular_maps.cpp
index c521fb28f72..5070f7d5bf9 100644
--- a/clang/test/Modules/modular_maps.cpp
+++ b/clang/test/Modules/modular_maps.cpp
@@ -1,5 +1,5 @@
 // RUN: rm -rf %t
-// RUN: %clang_cc1 -x objective-c++ -fmodules-cache-path=%t -fmodules -I %S/Inputs/modular_maps %s -verify
+// RUN: %clang_cc1 -x objective-c++ -fmodules-cache-path=%t -fmodules -fmodule-map-file=%S/Inputs/modular_maps/modulea.map -I %S/Inputs/modular_maps %s -verify
 
 #include "a.h"
 #include "b.h" // expected-error {{private header}}