[clang] add -fmodule-file-home-is-cwd

This diff adds a new frontend flag `-fmodule-file-home-is-cwd`.
The behavior of this flag is similar to
`-fmodule-map-file-home-is-cwd` but does not require the module
map files to be modified to have inputs relative to the cwd.
Instead the output modules will have their `BaseDirectory` set
to the cwd and will try and resolve paths relative to that.

The motiviation for this change is to support relocatable pcm
files that are built on different machines with different paths
without having to alter module map files, which is sometimes not
possible as they are provided by 3rd parties.

Reviewed By: urnathan

Differential Revision: https://reviews.llvm.org/D124874

Author: rmaz

clang/include/clang/Driver/Options.td

@@ -5619,6 +5619,10 @@ def fmodule_map_file_home_is_cwd : Flag<["-"], "fmodule-map-file-home-is-cwd">,
   HelpText<"Use the current working directory as the home directory of "
            "module maps specified by -fmodule-map-file=<FILE>">,
   MarshallingInfoFlag<HeaderSearchOpts<"ModuleMapFileHomeIsCwd">>;
+def fmodule_file_home_is_cwd : Flag<["-"], "fmodule-file-home-is-cwd">,
+  HelpText<"Use the current working directory as the base directory of "
+           "compiled module files.">,
+  MarshallingInfoFlag<HeaderSearchOpts<"ModuleFileHomeIsCwd">>;
 def fmodule_feature : Separate<["-"], "fmodule-feature">,
   MetaVarName<"<feature>">,
   HelpText<"Enable <feature> in module map requires declarations">,

clang/include/clang/Lex/HeaderSearchOptions.h

@@ -143,6 +143,12 @@ class HeaderSearchOptions {
   /// file.
   unsigned ModuleMapFileHomeIsCwd : 1;
 
+  /// Set the base path of a built module file to be the current working
+  /// directory. This is useful for sharing module files across machines
+  /// that build with different paths without having to rewrite all
+  /// modulemap files to have working directory relative paths.
+  unsigned ModuleFileHomeIsCwd : 1;
+
   /// Also search for prebuilt implicit modules in the prebuilt module cache
   /// path.
   unsigned EnablePrebuiltImplicitModules : 1;
@@ -222,9 +228,9 @@ class HeaderSearchOptions {
   HeaderSearchOptions(StringRef _Sysroot = "/")
       : Sysroot(_Sysroot), ModuleFormat("raw"), DisableModuleHash(false),
         ImplicitModuleMaps(false), ModuleMapFileHomeIsCwd(false),
-        EnablePrebuiltImplicitModules(false), UseBuiltinIncludes(true),
-        UseStandardSystemIncludes(true), UseStandardCXXIncludes(true),
-        UseLibcxx(false), Verbose(false),
+        ModuleFileHomeIsCwd(false), EnablePrebuiltImplicitModules(false),
+        UseBuiltinIncludes(true), UseStandardSystemIncludes(true),
+        UseStandardCXXIncludes(true), UseLibcxx(false), Verbose(false),
         ModulesValidateOncePerBuildSession(false),
         ModulesValidateSystemHeaders(false),
         ValidateASTInputFilesContent(false), UseDebugInfo(false),

clang/lib/Serialization/ASTWriter.cpp

@@ -1224,15 +1224,24 @@ void ASTWriter::WriteControlBlock(Preprocessor &PP, ASTContext &Context,
   }
 
   if (WritingModule && WritingModule->Directory) {
-    SmallString<128> BaseDir(WritingModule->Directory->getName());
+    SmallString<128> BaseDir;
+    if (PP.getHeaderSearchInfo().getHeaderSearchOpts().ModuleFileHomeIsCwd) {
+      // Use the current working directory as the base path for all inputs.
+      auto *CWD =
+          Context.getSourceManager().getFileManager().getDirectory(".").get();
+      BaseDir.assign(CWD->getName());
+    } else {
+      BaseDir.assign(WritingModule->Directory->getName());
+    }
     cleanPathForOutput(Context.getSourceManager().getFileManager(), BaseDir);
 
     // If the home of the module is the current working directory, then we
     // want to pick up the cwd of the build process loading the module, not
     // our cwd, when we load this module.
-    if (!PP.getHeaderSearchInfo()
-             .getHeaderSearchOpts()
-             .ModuleMapFileHomeIsCwd ||
+    if (!(PP.getHeaderSearchInfo()
+              .getHeaderSearchOpts()
+              .ModuleMapFileHomeIsCwd ||
+          PP.getHeaderSearchInfo().getHeaderSearchOpts().ModuleFileHomeIsCwd) ||
         WritingModule->Directory->getName() != StringRef(".")) {
       // Module directory.
       auto Abbrev = std::make_shared<BitCodeAbbrev>();

clang/test/Modules/module-file-home-is-cwd.m

@@ -0,0 +1,8 @@
+// RUN: cd %S
+// RUN: %clang_cc1 -fmodules -fno-implicit-modules -fmodule-file-home-is-cwd -fmodule-name=libA -emit-module Inputs/normal-module-map/module.map -o %t/mod.pcm
+// RUN: llvm-bcanalyzer --dump --disable-histogram %t/mod.pcm | FileCheck %s
+
+// CHECK: <INPUT_FILE {{.*}}/> blob data = 'Inputs{{/|\\}}normal-module-map{{/|\\}}a1.h'
+// CHECK: <INPUT_FILE {{.*}}/> blob data = 'Inputs{{/|\\}}normal-module-map{{/|\\}}a2.h'
+// CHECK: <INPUT_FILE {{.*}}/> blob data = 'Inputs{{/|\\}}normal-module-map{{/|\\}}module.map'
+// CHECK-NOT: MODULE_DIRECTORY