Link shared libs to allow re-using them in both in public and fb-internal plugins

Summary:
Link plugin shared libraries to the "plugins/node_modules" dir so they can be used as peer dependencies by both public and fb-internal plugins.

```
plugins
- node_modules
-- fb_shared_lib (symlink pointing to "plugins/fb/fb_shared_lib")
-- public_shared_lib (symlink pointing to "plugins/public/public_shared_lib")
- fb
-- fb_shared_lib
-- fb_plugin (can now use both fb_shared_lib and public_shared_lib as peer dependencies)
- public
-- public_shared_lib
-- public_plugin (can now use both public_shared_lib and fb_shared_lib (optionally if it's an fb-internal repo) as peer dependencies)
```

Reviewed By: passy

Differential Revision: D27034936

fbshipit-source-id: 68ee5312060ff57649ae061dd7dd14f8beb6d4a1

desktop/plugins/postinstall.ts

@@ -10,6 +10,7 @@
 import {execSync} from 'child_process';
 import path from 'path';
 import fs from 'fs-extra';
+import pmap from 'p-map';
 
 async function postinstall() {
   const publicPluginsDir = path.join(__dirname, 'public');
@@ -24,6 +25,42 @@ async function postinstall() {
       stdio: 'inherit',
     });
   }
+  const [publicPackages, fbPackages] = await Promise.all([
+    fs.readdir(publicPluginsDir),
+    fs.readdir(fbPluginsDir).catch(() => [] as string[]),
+  ]);
+  const packages = [
+    ...publicPackages.map((p) => path.join(publicPluginsDir, p)),
+    ...fbPackages.map((p) => path.join(fbPluginsDir, p)),
+  ];
+  const modulesDir = path.join(__dirname, 'node_modules');
+  await pmap(packages, async (packageDir) => {
+    const packageJsonPath = path.join(packageDir, 'package.json');
+    if (!(await fs.pathExists(packageJsonPath))) {
+      return;
+    }
+    const packageJson = await fs.readJson(
+      path.join(packageDir, 'package.json'),
+    );
+    if (
+      packageJson.keywords &&
+      packageJson.keywords.includes('flipper-plugin')
+    ) {
+      return;
+    }
+    const destPath = path.join(modulesDir, packageJson.name);
+    console.log(
+      `linking ${path.relative(__dirname, destPath)} to ${path.relative(
+        __dirname,
+        packageDir,
+      )}`,
+    );
+    if (await fs.pathExists(destPath)) {
+      return;
+    }
+    await fs.ensureDir(path.dirname(destPath));
+    await fs.symlink(packageDir, destPath, 'junction');
+  });
 }
 
 postinstall()