Fix scoped symlink module resolution (#1482)

Summary:
Fixes https://github.com/facebook/flipper/issues/1481

## Changelog

Fix symlinked scoped module resolving to outer directory

Pull Request resolved: https://github.com/facebook/flipper/pull/1482

Test Plan:
Added one more case to the existing test case for `getWatchFolders.ts`

```
❯ yarn run test:debug getWatchFolders
yarn run v1.22.4
$ yarn build:pkg && node --inspect node_modules/.bin/jest --runInBand getWatchFolders
$ cd pkg && yarn build
$ tsc -b
Debugger listening on ws://127.0.0.1:9229/41e16e0b-8a44-42fe-93ac-9dd9d06e418d
For help, see: https://nodejs.org/en/docs/inspector
 PASS  pkg-lib/src/__tests__/getWatchFolders.node.ts
  getWatchFolders
    ✓ getWatchFolders correctly resolves symlinked packages (12 ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   1 passed, 1 total
Time:        2.358 s
Ran all test suites matching /getWatchFolders/i.
{emoji:2728}  Done in 8.60s.
```

Reviewed By: mweststrate

Differential Revision: D23293357

Pulled By: nikoant

fbshipit-source-id: de2a506693727489238c6f6ec62d07526f8f0c69

desktop/pkg-lib/src/__tests__/getWatchFolders.node.ts

@@ -44,6 +44,11 @@ describe('getWatchFolders', () => {
           fb_plugin_module_2: mockfs.symlink({
             path: '../plugins/fb/fb_plugin_module_2',
           }),
+          '@scoped': {
+            local_module_3: mockfs.symlink({
+              path: '../../local_module_3',
+            }),
+          },
         },
         local_module_1: {
           'package.json': '{"dependencies": {"installed_module_1": "1.0.0"}}',
@@ -52,9 +57,13 @@ describe('getWatchFolders', () => {
           'package.json':
             '{"dependencies": {"fb_plugin_module_1": "1.0.0", "plugin_module_1": "1.0.0"}}',
         },
+        local_module_3: {
+          'package.json': '{"dependencies": {"installed_module_1": "1.0.0"}}',
+        },
         plugins: {
           plugin_module_1: {
-            'package.json': '{"dependencies": {"local_module_2": "1.0.0"}}',
+            'package.json':
+              '{"dependencies": {"local_module_2": "1.0.0", "@scoped/local_module_3": "1.0.0"}}',
           },
           plugin_module_2: {
             'package.json': '{"dependencies": {"fb_plugin_module_1": "1.0.0"}}',
@@ -102,6 +111,7 @@ describe('getWatchFolders', () => {
           "/test/root/plugins/fb/node_modules",
           "/test/root/plugins/plugin_module_1",
           "/test/root/plugins/plugin_module_2",
+          "/test/root/local_module_3",
         ]
       `);
     } finally {

desktop/pkg-lib/src/getWatchFolders.ts

@@ -36,15 +36,23 @@ export default async (packageDir: string): Promise<string[]> => {
       if (await fs.pathExists(nodeModulesDir)) {
         watchDirs.add(nodeModulesDir);
         for (const moduleName of dependenciesSet) {
+          const isModuleNameScoped = moduleName.includes('/');
           const fullModulePath = path.join(nodeModulesDir, moduleName);
           if (await fs.pathExists(fullModulePath)) {
             dependenciesSet.delete(moduleName);
             const stat = await fs.lstat(fullModulePath);
             if (stat.isSymbolicLink()) {
               const targetDir = await fs.readlink(fullModulePath);
-              const absoluteTargetDir = path.isAbsolute(targetDir)
-                ? targetDir
-                : path.resolve(nodeModulesDir, targetDir);
+              let absoluteTargetDir;
+              if (path.isAbsolute(targetDir)) {
+                absoluteTargetDir = targetDir;
+              } else if (isModuleNameScoped) {
+                const scope = moduleName.split('/')[0];
+                const scopeDir = path.join(nodeModulesDir, scope);
+                absoluteTargetDir = path.resolve(scopeDir, targetDir);
+              } else {
+                absoluteTargetDir = path.resolve(nodeModulesDir, targetDir);
+              }
               if (!processedPackages.has(absoluteTargetDir)) {
                 packagesToProcess.push(absoluteTargetDir);
                 processedPackages.add(absoluteTargetDir);