mojo: Add a externs_js_library target for js_libraries that type check

Some interfaces depend on many other interfaces. Before this patch users
would have to manually add externs for every interface used.

This CL introduces a new target that js_libraries can use to include
all the necessary externs to use an interface.

Bug: 849993
Change-Id: I97acb7bbbd604e7ebeb1cb5fe814e4afecefe2d6
Reviewed-on: https://chromium-review.googlesource.com/c/1369485Reviewed-by: Ken Rockot <rockot@google.com>
Reviewed-by: calamity <calamity@chromium.org>
Commit-Queue: Giovanni Ortuño Urquidi <ortuno@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615441}

chrome/browser/resources/app_management/BUILD.gn

@@ -25,8 +25,8 @@ if (!is_android) {
 
   js_library("browser_proxy") {
     deps = [
-      ":externs",
       ":fake_page_handler",
+      "//chrome/browser/ui/webui/app_management:mojo_bindings_js_externs",
       "//ui/webui/resources/js:cr",
     ]
   }
@@ -34,26 +34,9 @@ if (!is_android) {
   js_library("constants") {
   }
 
-  js_library("externs") {
-    sources = []
-    extra_deps = [ "//chrome/browser/ui/webui/app_management:mojo_bindings_js" ]
-
-    # TODO(calamity): This list should be built by the mojo_bindings_js target
-    # above.
-    externs_list = [
-      "$externs_path/mojo.js",
-      "$root_gen_dir/chrome/browser/ui/webui/app_management/app_management.mojom-lite.externs.js",
-      "$root_gen_dir/chrome/services/app_service/public/mojom/types.mojom-lite.externs.js",
-      "$root_gen_dir/mojo/public/mojom/base/big_buffer.mojom-lite.externs.js",
-      "$root_gen_dir/skia/public/interfaces/bitmap.mojom-lite.externs.js",
-      "$root_gen_dir/skia/public/interfaces/image_info.mojom-lite.externs.js",
-      "$root_gen_dir/ui/gfx/image/mojo/image.mojom-lite.externs.js",
-    ]
-  }
-
   js_library("fake_page_handler") {
     deps = [
-      ":externs",
+      "//chrome/browser/ui/webui/app_management:mojo_bindings_js_externs",
       "//ui/webui/resources/js:cr",
     ]
   }

chrome/browser/resources/md_downloads/BUILD.gn

@@ -25,7 +25,6 @@ js_type_check("closure_compile") {
     ":browser_proxy",
     ":constants",
     ":downloads",
-    ":externs",
     ":item",
     ":manager",
     ":search_service",
@@ -35,9 +34,10 @@ js_type_check("closure_compile") {
 
 js_library("browser_proxy") {
   deps = [
-    ":externs",
+    "//chrome/browser/ui/webui/md_downloads:mojo_bindings_js_externs",
     "//ui/webui/resources/js:cr",
   ]
+  externs_list = [ "externs.js" ]
 }
 
 js_library("constants") {
@@ -53,14 +53,6 @@ js_library("downloads") {
   ]
 }
 
-js_library("externs") {
-  extra_deps = [ "//chrome/browser/ui/webui/md_downloads:mojo_bindings_js" ]
-  externs_list = [
-    "$root_gen_dir/chrome/browser/ui/webui/md_downloads/md_downloads.mojom-lite.externs.js",
-    "$externs_path/mojo.js",
-  ]
-}
-
 js_library("icon_loader") {
   deps = [
     "//ui/webui/resources/js:assert",
@@ -73,7 +65,6 @@ js_library("item") {
   deps = [
     ":browser_proxy",
     ":constants",
-    ":externs",
     ":icon_loader",
     "//third_party/polymer/v1_0/components-chromium/paper-behaviors:paper-inky-focus-behavior-extracted",
     "//ui/webui/resources/js:cr",
@@ -85,7 +76,6 @@ js_library("item") {
 js_library("manager") {
   deps = [
     ":browser_proxy",
-    ":externs",
     ":item",
     ":search_service",
     ":toolbar",
@@ -102,7 +92,6 @@ js_library("manager") {
 js_library("search_service") {
   deps = [
     ":browser_proxy",
-    ":externs",
     "//ui/webui/resources/js:cr",
     "//ui/webui/resources/js:load_time_data",
   ]

mojo/public/tools/bindings/mojom.gni

@@ -1286,6 +1286,28 @@ template("mojom") {
         }
       }
     }
+
+    js_externs_target_suffix = "_js_externs"
+    js_externs_target_name = "${target_name}${js_externs_target_suffix}"
+    if (defined(invoker.sources)) {
+      js_library(js_externs_target_name) {
+        sources = []
+        extra_public_deps = [ ":$generator_js_target_name" ]
+        externs_list = [ "${externs_path}/mojo.js" ]
+        externs_list += process_file_template(
+                invoker.sources,
+                [ "{{source_gen_dir}}/{{source_name_part}}.mojom-lite.externs.js" ])
+
+        deps = []
+        foreach(d, all_deps) {
+          full_name = get_label_info(d, "label_no_toolchain")
+          deps += [ "${full_name}${js_externs_target_suffix}" ]
+        }
+      }
+    } else {
+      group(js_externs_target_name) {
+      }
+    }
   }
 }