Capture C++ modules compilation commands in compile_commands.json

This change ensures that .modulemap files are included in the exported
compilation database. It also implements the {{cc_module_name}}
substitution to correctly generate -fmodule-name flags in the compile
commands.

Modified compile_commands_writer_unittest.cc to verify that module
compilation commands are correctly generated and included.

This is to fix https://crbug.com/475763034#comment9

Bug: 475763034
Change-Id: I3693cb555a30df9082f611aa690e561d1427d4ff
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/21320
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@google.com>

src/gn/compile_commands_writer.cc

diff --git a/src/gn/compile_commands_writer.cc b/src/gn/compile_commands_writer.cc
index 29d2a5a..bef0287 100644
--- a/src/gn/compile_commands_writer.cc
+++ b/src/gn/compile_commands_writer.cc
@@ -229,6 +229,8 @@
     } else if (range.type == &CSubstitutionCFlagsObjCc) {
       if (source_type == SourceFile::SOURCE_MM)
         out << flags.cflags_objcc;
+    } else if (range.type == &CSubstitutionModuleName) {
+      EscapeStringToStream(out, target->module_name(), opts);
     } else if (range.type == &SubstitutionLabel ||
                range.type == &SubstitutionLabelName ||
                range.type == &SubstitutionLabelNoToolchain ||
@@ -295,7 +297,8 @@
       if (source_type != SourceFile::SOURCE_CPP &&
           source_type != SourceFile::SOURCE_C &&
           source_type != SourceFile::SOURCE_M &&
-          source_type != SourceFile::SOURCE_MM)
+          source_type != SourceFile::SOURCE_MM &&
+          source_type != SourceFile::SOURCE_MODULEMAP)
         continue;
 
       const char* tool_name = Tool::kToolNone;

src/gn/compile_commands_writer_unittest.cc

diff --git a/src/gn/compile_commands_writer_unittest.cc b/src/gn/compile_commands_writer_unittest.cc
index 9dff19d..d7fcad0 100644
--- a/src/gn/compile_commands_writer_unittest.cc
+++ b/src/gn/compile_commands_writer_unittest.cc
@@ -626,8 +626,8 @@
       Tool::CreateTool(CTool::kCToolCxxModule);
   TestWithScope::SetCommandForTool(
       "c++ {{source}} {{cflags}} {{cflags_cc}} {{module_deps_no_self}} "
-      "{{defines}} {{include_dirs}} -fmodule-name={{label}} -c -x c++ "
-      "-Xclang -emit-module -o {{output}}",
+      "{{defines}} {{include_dirs}} -fmodule-name={{cc_module_name}} -c "
+      "-x c++ -Xclang -emit-module -o {{output}}",
       cxx_module_tool.get());
   cxx_module_tool->set_outputs(SubstitutionList::MakeForTest(
       "{{source_out_dir}}/{{target_output_name}}.{{source_name_part}}.pcm"));
@@ -663,6 +663,13 @@
   const char expected[] =
       "[\r\n"
       "  {\r\n"
+      "    \"file\": \"../../foo/foo.modulemap\",\r\n"
+      "    \"directory\": \"out/Debug\",\r\n"
+      "    \"command\": \"c++ ../../foo/foo.modulemap      "
+      "-fmodule-name=module -c -x c++ -Xclang -emit-module -o  "
+      "withmodules/obj/foo/module.foo.pcm\"\r\n"
+      "  },\r\n"
+      "  {\r\n"
       "    \"file\": \"../../foo/dep.cc\",\r\n"
       "    \"directory\": \"out/Debug\",\r\n"
       "    \"command\": \"c++ ../../foo/dep.cc    "
@@ -674,6 +681,13 @@
   const char expected[] =
       "[\n"
       "  {\n"
+      "    \"file\": \"../../foo/foo.modulemap\",\n"
+      "    \"directory\": \"out/Debug\",\n"
+      "    \"command\": \"c++ ../../foo/foo.modulemap      "
+      "-fmodule-name=module -c -x c++ -Xclang -emit-module -o  "
+      "withmodules/obj/foo/module.foo.pcm\"\n"
+      "  },\n"
+      "  {\n"
       "    \"file\": \"../../foo/dep.cc\",\n"
       "    \"directory\": \"out/Debug\",\n"
       "    \"command\": \"c++ ../../foo/dep.cc    "