packager: add preprocess for buck worker

Summary: For the Buck integration (work-in-progress), we want to add the ability to do some custom preprocessing similar to the packager server. The signature is different so I prefer to have a separate function for that. Also we don't need the transform options right now, I suggest we don't add them for now and add them later if necessary.

Reviewed By: davidaurelio

Differential Revision: D5094632

fbshipit-source-id: 1775ddef90b331deabc5be3e57a67436bce06c82

packager/src/ModuleGraph/ModuleGraph.js

@@ -22,6 +22,7 @@ import type {
   GraphFn,
   GraphResult,
   Module,
+  PostProcessModules,
 } from './types.flow';
 
 type BuildFn = (
@@ -37,6 +38,7 @@ type BuildOptions = {|
 
 exports.createBuildSetup = (
   graph: GraphFn,
+  postProcessModules: PostProcessModules,
   translateDefaultsPath: string => string = x => x,
 ): BuildFn =>
   (entryPoints, options, callback) => {
@@ -51,10 +53,16 @@ exports.createBuildSetup = (
     const graphOnlyModules = seq(graphWithOptions, getModules);
 
     parallel({
-      graph: cb => graphWithOptions(
-        entryPoints,
-        cb,
-      ),
+      graph: cb => graphWithOptions(entryPoints, (error, result) => {
+        if (error) {
+          cb(error);
+          return;
+        }
+        /* $FlowFixMe: not undefined if there is no error */
+        const {modules, entryModules} = result;
+        const prModules = postProcessModules(modules, [...entryPoints]);
+        cb(null, {modules: prModules, entryModules});
+      }),
       moduleSystem: cb => graphOnlyModules(
         [translateDefaultsPath(defaults.moduleSystem)],
         cb,