add 'npm run watch-gui', similar to build-gui

Author: Christopher Willis-Ford

README.md

@@ -23,7 +23,8 @@ that repository's main development line. For now, though, there's a separate bra
 
 If you have run `npm link scratch-gui` (or equivalent) in the `scratch-desktop` working directory, you may be able to
 accomplish the above by running `npm run build-gui` in the `scratch-desktop` directory instead of using the manual
-steps listed above.
+steps listed above. For active development iteration, try `npm run watch-gui` which will watch for changes and rebuild
+`scratch-gui` incrementally when necessary.
 
 ### Prepare media library assets
 

package.json

@@ -7,7 +7,8 @@
   "license": "BSD-3-Clause",
   "scripts": {
     "start": "electron-webpack dev --bail --display-error-details --env.minify=false",
-    "build-gui": "node ./scripts/build-gui.js",
+    "build-gui": "node ./scripts/run-in-gui.js build",
+    "watch-gui": "node ./scripts/run-in-gui.js watch",
     "clean": "rimraf ./dist/ ./static/assets/",
     "compile": "rimraf ./dist/ && electron-webpack --bail --display-error-details --env.minify=false",
     "fetch": "rimraf ./static/assets/ && mkdirp ./static/assets/ && node ./scripts/fetchMediaLibraryAssets.js",

scripts/build-gui.js

@@ -0,0 +1,27 @@
+const childProcess = require('child_process');
+const path = require('path');
+
+// process.argv: ['node', 'run-in-gui.js', 'foo', ...]
+const args = process.argv.slice(2);
+args.unshift('run');
+// args: ['run', 'foo', ...]
+
+// copy environment (including PATH) then add or replace BUILD_MODE and STATIC_PATH
+const env = {
+    ...process.env,
+    BUILD_MODE: 'dist',
+    STATIC_PATH: 'static'
+};
+
+const child = childProcess.spawnSync(
+    'npm', args,
+    {
+        cwd: path.join('node_modules', 'scratch-gui'),
+        env,
+        shell: true,
+        stdio: 'inherit'
+    }
+);
+
+if (child.error) throw child.error;
+process.exit(child.status);