[PCH+Modules] Load -fmodule-map-file content before including PCHs

[bruno]

Summary

Consider:

1. Generate PCH with -fmodules and -fmodule-map-file
2. Use PCH with -fmodules and the same -fmodule-map-file

If we don't load -fmodule-map-file content before including PCHs, the modules that are dependencies in PCHs cannot get loaded, since there's no matching module map file when reading back the AST.

rdar://problem/40852867

[bruno]

Ping!

[benlangmuir]

LGTM

cfe/trunk/lib/Frontend/FrontendAction.cpp

else {
       SourceMgr.setMainFileID(BufferID);
     }
   }
 
   // Initialize the action.
   if (!BeginSourceFileAction(CI))
     goto failure;
 
+  // If we were asked to load any module map files, do so now.
+  for (const auto &Filename : CI.getFrontendOpts().ModuleMapFiles) {
+    if (auto *File = CI.getFileManager().getFile(Filename))
+      CI.getPreprocessor().getHeaderSearchInfo().loadModuleMapFile(
+          File, /*IsSystem*/false);
+    else
+      CI.getDiagnostics().Report(diag::err_module_map_not_found) << Filename;
+  }
+
+  // Add a module declaration scope so that modules from -fmodule-map-file
+  // arguments may shadow modules found implicitly in search paths.
+  CI.getPreprocessor()
+      .getHeaderSearchInfo()
+      .getModuleMap()
+      .finishModuleDeclarationScope();
+
   // Create the AST context and consumer unless this is a preprocessor only
   // action.
   if (!usesPreprocessorOnly()) {
     // Parsing a model file should reuse the existing ASTContext.
     if (!isModelParsingAction())
       CI.createASTContext();
 
     // For preprocessed files, check if the first line specifies the original
bool FrontendAction::BeginSourceFile(CompilerInstance &CI,
   } else {
     // FIXME: If this is a problem, recover from it by creating a multiplex
     // source.
     assert((!CI.getLangOpts().Modules || CI.getModuleManager()) &&
            "modules enabled but created an external source that "
            "doesn't support modules");
   }
 
-  // If we were asked to load any module map files, do so now.
-  for (const auto &Filename : CI.getFrontendOpts().ModuleMapFiles) {
-    if (auto *File = CI.getFileManager().getFile(Filename))
-      CI.getPreprocessor().getHeaderSearchInfo().loadModuleMapFile(
-          File, /*IsSystem*/false);
-    else
-      CI.getDiagnostics().Report(diag::err_module_map_not_found) << Filename;
-  }
-
-  // Add a module declaration scope so that modules from -fmodule-map-file
-  // arguments may shadow modules found implicitly in search paths.
-  CI.getPreprocessor()
-      .getHeaderSearchInfo()
-      .getModuleMap()
-      .finishModuleDeclarationScope();
-
   // If we were asked to load any module files, do so now.
   for (const auto &ModuleFile : CI.getFrontendOpts().ModuleFiles)
     if (!CI.loadModuleFile(ModuleFile))
       goto failure;
 
   // If there is a layout overrides file, attach an external AST source that
   // provides the layouts from that file.
   if (!CI.getFrontendOpts().OverrideRecordLayoutsFile.empty() &&

cfe/trunk/test/Modules/module-imported-by-pch-with-modulemap.m

+// RUN: rm -rf %t.dst %t.cache
+// RUN: mkdir -p %t.dst/folder-with-modulemap %t.dst/pch-folder
+// RUN: echo '#import "folder-with-modulemap/included.h"' > %t.dst/header.h
+// RUN: echo 'extern int MyModuleVersion;' > %t.dst/folder-with-modulemap/MyModule.h
+// RUN: echo '@import MyModule;' > %t.dst/folder-with-modulemap/included.h
+// RUN: echo 'module MyModule { header "MyModule.h" }' > %t.dst/folder-with-modulemap/MyModule.modulemap
+
+// RUN: %clang_cc1 -emit-pch -o %t.dst/pch-folder/header.pch -fmodule-map-file=%t.dst/folder-with-modulemap/MyModule.modulemap -x objective-c-header -fmodules-cache-path=%t.cache -fmodules -fimplicit-module-maps %t.dst/header.h
+// RUN: %clang_cc1 -fsyntax-only -fmodule-map-file=%t.dst/folder-with-modulemap/MyModule.modulemap -fmodules-cache-path=%t.cache -fmodules -fimplicit-module-maps %s -include-pch %t.dst/pch-folder/header.pch -verify
+
+// expected-no-diagnostics
+
+void test() {
+  (void)MyModuleVersion; // should be found by implicit import
+}
+