Fix plugin source maps in dev mode

Summary:
Start bundling source maps together with the source code itself in the dev mode. Therefore it is no longer required to add a link to the external source map file in dev mode.
In prod mode we still ship them separately.

Reviewed By: mweststrate

Differential Revision: D39775064

fbshipit-source-id: 6c56df7a3fce084c07a8618a63dbd8ae4741348c

desktop/flipper-ui-browser/src/initializeRenderHost.tsx

@@ -82,10 +82,13 @@ export function initializeRenderHost(
     flipperServer,
     async requirePlugin(path) {
       let source = await flipperServer.exec('plugin-source', path);
+
       // append source url (to make sure a file entry shows up in the debugger)
       source += `\n//# sourceURL=file://${path}`;
-      // and source map url (to get source code if available)
-      source += `\n//# sourceMappingURL=file://${path.replace(/.js$/, '.map')}`;
+      if (isProduction()) {
+        // and source map url (to get source code if available)
+        source += `\n//# sourceMappingURL=file://${path}.map`;
+      }
 
       // Plugins are compiled as typical CJS modules, referring to the global
       // 'module', which we'll make available by loading the source into a closure that captures 'module'.

desktop/pkg-lib/src/runBuild.tsx

@@ -66,7 +66,7 @@ async function runBuild({
       // It is an optional dependency for rollup that we use in react-devtools
       'fsevents',
     ],
-    sourcemap: 'external',
+    sourcemap: dev ? 'inline' : 'external',
     minify: !dev,
     plugins: intern ? [resolveFbStubsToFbPlugin] : undefined,
   });