Enable app/node_modules caching, make postinstall check its Electron version

.travis.yml

@@ -3,7 +3,7 @@ sudo: false
 language: node_js
 
 node_js:
-- '6.9'
+- '7.10'
 
 addons:
   apt:
@@ -43,7 +43,7 @@ before_install:
 - source app/build/resources/certs/mac/set_unix_env.sh;
 
 script:
-- npm run build && npm run upload
+- npm run build
 
 deploy:
 - provider: s3
@@ -62,3 +62,4 @@ deploy:
 cache:
   directories:
   - node_modules
+  - app/node_modules

appveyor.yml

@@ -32,7 +32,7 @@ deploy_script:
 
 environment:
   matrix:
-  - NODE_VERSION: 6.9
+  - NODE_VERSION: 7.10
   global:
     DEBUG: "electron-windows-installer:*,electron-packager:*"
     SIGN_BUILD: true

package.json

@@ -60,5 +60,8 @@
   "engines": {
     "node": "6.9.1",
     "npm": "3.10.8"
+  },
+  "dependencies": {
+    "rimraf": "^2.6.1"
   }
 }

scripts/postinstall.js

@@ -2,12 +2,15 @@
 /* eslint global-require: 0 */
 /* eslint quote-props: 0 */
 const path = require('path');
+const fs = require('fs');
+const rimraf = require('rimraf');
 const safeExec = require('./utils/child-process-wrapper.js').safeExec;
 
+const npmElectronTarget = require('../app/package.json').dependencies.electron;
 const npmEnvs = {
   system: process.env,
   electron: Object.assign({}, process.env, {
-    'npm_config_target': require('../app/package.json').dependencies.electron,
+    'npm_config_target': npmElectronTarget,
     'npm_config_arch': process.arch,
     'npm_config_target_arch': process.arch,
     'npm_config_disturl': 'https://atom.io/download/atom-shell',
@@ -31,5 +34,26 @@ function npm(cmd, options) {
   });
 }
 
-npm('install', {cwd: './app', env: 'electron'})
-.then(() => npm('dedupe', {cwd: './app', env: 'electron'}))
+async function go() {
+  // For speed, we cache app/node_modules. However, we need to
+  // be sure to do a full rebuild of native node modules when the
+  // Electron version changes. To do this we check a marker file.
+  const cacheVersionPath = './app/node_modules/.postinstall-target-version';
+  const cacheElectronTarget = fs.existsSync(cacheVersionPath) && fs.readFileSync(cacheVersionPath).toString();
+
+  if (cacheElectronTarget !== npmElectronTarget) {
+    console.log(`\n-- Clearing app/node_modules --`)
+    rimraf.sync(path.resolve(__dirname, '..', 'app', 'node_modules'));
+  }
+
+  // run `npm install` in ./app with Electron NPM config
+  await npm('install', {cwd: './app', env: 'electron'});
+
+  // run `npm dedupe` in ./app with Electron NPM config
+  await npm('dedupe', {cwd: './app', env: 'electron'});
+
+  // write the marker with the electron version
+  fs.writeFileSync(cacheVersionPath, npmElectronTarget);
+}
+
+go();