client_apps: use script/build

Each client_app is now expected to provide a runnable script at
/client_apps/app_name/script/build that builds its JS assets.

Also, `npm install` will only be run if an npm `package.json` file
exists, so the app is free not to use npm if it doesn't need to.

Closes CNVS-15445

TEST PLAN
---- ----

  - run `bundle exec rake canvas:compile_assets` and make sure it works

Change-Id: I635c79234dbb2c890e73cd9889fac86bd68fdf53
Reviewed-on: https://gerrit.instructure.com/41195
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Ryan Florence <ryanf@instructure.com>
Product-Review: Ahmad Amireh <ahmad@instructure.com>
QA-Review: Ahmad Amireh <ahmad@instructure.com>

client_apps/canvas_quiz_statistics/package.json

@@ -21,9 +21,9 @@
     "url": "https://github.com/amireh/canvas_quiz_statistics/issues"
   },
   "scripts": {
-    "start": "./node_modules/.bin/grunt",
-    "test": "./node_modules/.bin/grunt test",
-    "build": "./node_modules/.bin/grunt compile_js"
+    "start": "./node_modules/grunt-cli/bin/grunt",
+    "test": "./node_modules/grunt-cli/bin/grunt test",
+    "build": "./node_modules/grunt-cli/bin/grunt compile_js"
   },
   "devDependencies": {
     "node-sass": "^0.9.3",

client_apps/canvas_quiz_statistics/script/build

@@ -0,0 +1,17 @@
+#!/usr/bin/env node
+
+var path = require('path');
+var root = path.join(__dirname, '..');
+var grunt;
+
+// Use the app root as the CWD so that grunt can read the Gruntfile there:
+process.chdir(root);
+
+// Make sure we load the development tasks (override any CLI flags):
+process.env.production = false;
+process.env.NODE_ENV = 'development';
+
+// Run the "compile_js" grunt task; no need to use the full "build" task as
+// Canvas will not use the compiled SCSS anyway:
+grunt = require(path.join(root, 'node_modules', 'grunt', 'lib', 'grunt'));
+grunt.tasks('compile_js');

lib/tasks/js.rake

@@ -148,7 +148,7 @@ namespace :js do
       Dir.chdir(app_dir) do
         puts "Building client app '#{app_name}'"
 
-        begin
+        if File.exists?('./package.json')
           puts "\tRunning 'npm install'..."
           output = `npm install`
           unless $?.exitstatus == 0
@@ -165,7 +165,7 @@ namespace :js do
 
         begin
           puts "\tRunning 'npm run build'..."
-          output = `npm run build`
+          output = `./script/build`
           unless $?.exitstatus == 0
             puts <<-MESSAGE
             -------------------------------------------------------------------