Cleanup proxy/defer code

pkg/dev_compiler/lib/js/legacy/dart_library.js

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /* This file defines the module loader for the dart runtime.
 */
 var dart_library;
 if (!dart_library) {
 dart_library =
   typeof module != "undefined" && module.exports || {};
@@ skipping 13 matching lines @@
   dart_library.libraryImports = libraryImports;
 
   // Module support.  This is a simplified module system for Dart.
   // Longer term, we can easily migrate to an existing JS module system:
   // ES6, AMD, RequireJS, ....
 
   // Returns a proxy that delegates to the underlying loader.
   // This defers loading of a module until a library is actually used.
   const loadedModule = Symbol('loadedModule');
   dart_library.defer = function(module, name, patch) {
-    var revocable = Proxy.revocable(module, {
+    let done = false;
+    function loadDeferred() {
+      done = true;
+      var mod = module[loadedModule];
+      var lib = mod[name];
+      // Install unproxied module and library in caller's context.
+      patch(mod, lib);
+    }
+    // The deferred library object.  Note, the only legal operations on a Dart
+    // library object should be get (to read a top-level variable, method, or
+    // Class) or set (to write a top-level variable).

[vsm, 2017/02/17 15:16:17]

A couple notes:
(1) I'm no longer revoking the proxy - dev tools isn't fond of that.

(2) The lack of 'set' caused some tests to break - e.g., if a library sets a
top-level variable in another library and that's the first access to that other
library, this wasn't handling that.

+    return new Proxy({}, {
       get: function(o, p) {
-        var mod = o[loadedModule];
-        var lib = mod[name];
-        // Install unproxied module and library in caller's context.
-        patch(mod, lib);
-        // Ensure proxy is only used on first access.
-        revocable.revoke();
-        return lib[p];
-      }
+        if (!done) loadDeferred();
+        return module[name][p];
+      },
+      set: function(o, p, value) {
+        if (!done) loadDeferred();
+        module[name][p] = value;
+        return true;
+      },
     });
-    return revocable.proxy;
   };
 
   class LibraryLoader {
 
     constructor(name, defaultValue, imports, loader) {
       this._name = name;
       this._library = defaultValue ? defaultValue : {};
       this._imports = imports;
       this._loader = loader;
 
@@ skipping 22 matching lines @@
         return this._library;
       }
       this._state = LibraryLoader.LOADING;
 
       // Handle imports
       let args = this.loadImports();
 
       // Load the library
       let loader = this;
       let library = this._library;
+      library[dartLibraryName] = this._name;
+      library[libraryImports] = this._imports;

[vsm, 2017/02/17 15:16:17]

Note: these were getting set on the proxy instead of the library object.

       library[loadedModule] = library;
       args.unshift(library);
 
       if (this._name == 'dart_sdk') {
         // Eagerly load the SDK.
         this._loader.apply(null, args);
         loader._loader = null;
       } else {
         // Load / parse other modules on demand.
         let done = false;
-        this._library = new Proxy(args, {
+        this._library = new Proxy(library, {

[vsm, 2017/02/17 15:16:17]

Note, this is the module object, not the library object.

I'll make a separate pass to cleanup the nomenclature.

           get: function(o, name) {
-            if (done) {
-              return library[name];
+            if (!done) {
+              done = true;
+              loader._loader.apply(null, args);
+              loader._loader = null;
             }
-            done = true;
-            loader._loader.apply(null, o);
-            loader._loader = null;
-            return library[name];
+            return o[name];
           }
         });
       }
 
       this._state = LibraryLoader.READY;
-      this._library[dartLibraryName] = this._name;
-      this._library[libraryImports] = this._imports;
       return this._library;
     }
 
     stub() {
       return this._library;
     }
   }
   LibraryLoader.NOT_LOADED = 0;
   LibraryLoader.LOADING = 1;
   LibraryLoader.READY = 2;
@@ skipping 57 matching lines @@
     // Force import of core.
     var dart_sdk = import_('dart_sdk');
 
     // This import is only needed for chrome debugging. We should provide an
     // option to compile without it.
     dart_sdk._debugger.registerDevtoolsFormatter();
   }
 
 })(dart_library);
 }