Add preinstall script to fix yarn workspaces issue on windows

yarnpkg/yarn#4564

packages/app/package.json

@@ -11,6 +11,7 @@
  },
  "main": "__generated__/AppEntry.js",
  "scripts": {
+ "preinstall": "node ./patch-yarn.js",
  "postinstall": "expo-yarn-workspaces postinstall",
  "start": "expo start",
  "ios": "expo start --ios",

packages/app/patch-yarn.js

@@ -0,0 +1,32 @@
+// Yarn has (v1.17.3) still a path lookup bug on Windows, when it looks for the binaries referenced in
+// scripts under '\gui\node_modules\node_modules' instead of '\gui\node_modules'.
+// This patch adds a junction between those two to keep that house of cards from falling apart.
+// GitHub issue: https://github.com/yarnpkg/yarn/issues/4564#issuecomment-414613939,
+// Pull Request: https://github.com/mullvad/mullvadvpn-app/pull/369
+
+const path = require('path');
+const fs = require('fs');
+
+if (process.platform !== 'win32') {
+ return;
+}
+
+const sourcePath = path.resolve(path.join(__dirname, '../../node_modules'));
+const symlinkPath = path.join(__dirname, '../../node_modules/node_modules');
+
+try {
+ console.log('Removing a symlink to node_modules/node_modules');
+ fs.unlinkSync(symlinkPath);
+} catch (error) {
+ if (error.code !== 'ENOENT') {
+ throw error;
+ }
+}
+
+try {
+ console.log('Applying yarn workspaces patch for node_modules/node_modules');
+ fs.symlinkSync(sourcePath, symlinkPath, 'junction');
+ console.log('Done');
+} catch (error) {
+ console.error('Cannot symlink node_modules/node_modules: ' + error.message);
+}