Minify locale JSON files at build time

This CL adds a new build rule "minify_json" that takes a list of JSON
files, minifies them, and puts the result into then "gen/" directory.

The i18n module uses the new rule to minify the locale JSON, reducing
the raw size per locale file 10-15%.

R=tvanderlippe@chromium.org

Fixed: 1293324
Change-Id: I0aabc5cdea7957334dfe21304e117dc23a563606
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/3431345
Reviewed-by: Tim Van der Lippe <tvanderlippe@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>

front_end/core/i18n/BUILD.gn

@@ -5,6 +5,7 @@
 import("../../../scripts/build/ninja/devtools_entrypoint.gni")
 import("../../../scripts/build/ninja/devtools_module.gni")
 import("../../../scripts/build/ninja/devtools_pre_built.gni")
+import("../../../scripts/build/ninja/minify_json.gni")
 
 devtools_module("i18n") {
   sources = [
@@ -23,7 +24,7 @@ devtools_module("i18n") {
 
   public_deps = [
     ":i18n_bundled_locales",
-    ":i18n_remote_locales",
+    ":i18n_locales",
   ]
 }
 
@@ -122,20 +123,26 @@ bundled_devtools_locale_files = [
   "zh.json",
 ]
 
-copy_to_gen("i18n_remote_locales") {
+minify_json("i18n_locales") {
   sources = []
-  foreach(locale, remote_devtools_locale_files) {
+  foreach(locale,
+          remote_devtools_locale_files + bundled_devtools_locale_files) {
     sources += [ "locales/$locale" ]
   }
 }
 
-devtools_pre_built("i18n_bundled_locales") {
-  sources = []
+group("i18n_bundled_locales") {
+  public_deps = [ ":i18n_locales" ]
+
   data = []
+
   foreach(locale, bundled_devtools_locale_files) {
-    sources += [ "locales/$locale" ]
     data += [ "$target_gen_dir/locales/$locale" ]
   }
+
+  metadata = {
+    grd_files = data
+  }
 }
 
 # For locales that are only used by tests, and not in releases.

scripts/build/ninja/minify-json-files.js

@@ -0,0 +1,19 @@
+// Copyright 2022 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+const fs = require('fs');
+const path = require('path');
+const {writeIfChanged} = require('./write-if-changed.js');
+
+const [, , src, dest, files] = process.argv;
+
+for (const file of files.split(',')) {
+  const srcPath = path.join(src, file);
+  const destPath = path.join(dest, file);
+
+  // Minifying JSON is straight-forward as JSON.stringify omits whitespace.
+  const srcContents = fs.readFileSync(srcPath);
+  const destContents = JSON.stringify(JSON.parse(srcContents));
+  writeIfChanged(destPath, destContents);
+}

scripts/build/ninja/minify_json.gni

@@ -0,0 +1,28 @@
+# Copyright 2022 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("./node.gni")
+import("./vars.gni")
+
+template("minify_json") {
+  node_action(target_name) {
+    forward_variables_from(invoker, [ "sources" ])
+
+    script = "scripts/build/ninja/minify-json-files.js"
+
+    _src = rebase_path(".", root_build_dir)
+    _dest = rebase_path(target_gen_dir, root_build_dir)
+
+    args = [
+      _src,
+      _dest,
+      string_join(",", sources),
+    ]
+
+    outputs = []
+    foreach(_input, sources) {
+      outputs += [ "$target_gen_dir/$_input" ]
+    }
+  }
+}