Merge pull request #3350 from skevy/fix-babelrc-plugin-resolution

Make Babel actually resolve plugins relative to where they were specified (via .babelrc).

packages/babel-core/src/helpers/resolve.js

@@ -1,4 +1,5 @@
 import Module from "module";
+import path from "path";
 
 let relativeModules = {};
 
@@ -10,6 +11,17 @@ export default function (loc: string, relative: string = process.cwd()): ?string
 
   if (!relativeMod) {
     relativeMod = new Module;
+
+    // We need to define an id and filename on our "fake" relative` module so that
+    // Node knows what "." means in the case of us trying to resolve a plugin
+    // such as "./myPlugins/somePlugin.js". If we don't specify id and filename here,
+    // Node presumes "." is process.cwd(), not our relative path.
+    // Since this fake module is never "loaded", we don't have to worry about mutating
+    // any global Node module cache state here.
+    let filename = path.join(relative, ".babelrc");
+    relativeMod.id = filename;
+    relativeMod.filename = filename;
+
     relativeMod.paths = Module._nodeModulePaths(relative);
     relativeModules[relative] = relativeMod;
   }