Allow modules in bundles to resolve modules outside of bundle (#11)

index.js

@@ -767,22 +767,16 @@ Module._extensions['.bundle'] = function (module, source, referrer) {
   module._resolutions = bundle.resolutions
 
   module._protocol = protocol.extend({
-    preresolve (context, specifier) {
-      return specifier
-    },
-
     postresolve (context, url) {
-      return url
+      return bundle.exists(url.href) ? url : context.postresolve(url)
     },
 
-    * resolve () {},
-
     exists (context, url) {
-      return bundle.exists(url.href)
+      return bundle.exists(url.href) || context.exists(url)
     },
 
     read (context, url) {
-      return bundle.read(url.href)
+      return bundle.read(url.href) || context.read(url)
     }
   })
 

test.js

@@ -2831,6 +2831,30 @@ test('load .bundle with asset import, resolutions map', (t) => {
   t.is(Module.load(new URL(root + '/app.bundle'), bundle.toBuffer()).exports, isWindows ? 'c:\\app.bundle\\baz.txt' : '/app.bundle/baz.txt')
 })
 
+test('load .bundle with asset import, resolutions map pointing outside .bundle', (t) => {
+  t.teardown(onteardown)
+
+  const protocol = new Module.Protocol({
+    exists (url) {
+      return url.href === root + '/bar.txt'
+    }
+  })
+
+  const bundle = new Module.Bundle()
+    .write('/foo.js', 'module.exports = require.asset(\'./bar.txt\')', { main: true })
+    .write('/baz.txt', 'hello world', { asset: true })
+
+  bundle.resolutions = {
+    '/foo.js': {
+      './bar.txt': {
+        asset: root + '/bar.txt'
+      }
+    }
+  }
+
+  t.is(Module.load(new URL(root + '/app.bundle'), bundle.toBuffer(), { protocol }).exports, isWindows ? 'c:\\bar.txt' : '/bar.txt')
+})
+
 function onteardown () {
   // TODO Provide a public API for clearing the cache.
   Module._cache = Object.create(null)