Add support for the package: directive in Frog and dart2js.

lib/compiler/implementation/apiimpl.dart

 // Copyright (c) 2012, 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.
 
 #library('leg_apiimpl');
 
 #import('leg.dart', prefix: 'leg');
 #import('elements/elements.dart', prefix: 'leg');
 #import('tree/tree.dart', prefix: 'leg');
 #import('ssa/tracer.dart', prefix: 'ssa');
 // TODO(ahe): Remove dependency on frog.
 #import('../../../frog/lang.dart', prefix: 'frog');
 #import('../compiler.dart');
 #import('../../uri/uri.dart');
 #import('library_map.dart');
 
 
 class Compiler extends leg.Compiler {
   ReadUriFromString provider;
   DiagnosticHandler handler;
   Uri libraryRoot;
+  Uri packageRoot;
   List<String> options;
   bool mockableLibraryUsed = false;
 
   Compiler(this.provider, this.handler, this.libraryRoot, this.options)
     : super(tracer: new ssa.HTracer());
 
   leg.LibraryElement scanBuiltinLibrary(String path) {
     Uri uri = libraryRoot.resolve(DART2JS_LIBRARY_MAP[path]);
     leg.LibraryElement library = scanner.loadLibrary(uri, null);
     return library;
   }
 
   void log(message) {
     handler(null, null, null, message, false);
   }
 
   leg.Script readScript(Uri uri, [leg.ScriptTag node]) {
     if (uri.scheme == 'dart') {
       uri = translateDartUri(uri, node);
+    } else if (uri.scheme == 'package') {
+      uri = translatePackageUri(uri, node);
     }
     String text = "";
     try {
       // TODO(ahe): We expect the future to be complete and call value
       // directly. In effect, we don't support truly asynchronous API.
       text = provider(uri).value;
     } catch (var exception) {
       cancel("${uri}: $exception", node: node);
     }
     frog.SourceFile sourceFile = new frog.SourceFile(uri.toString(), text);
     return new leg.Script(uri, sourceFile);
   }
 
   translateDartUri(Uri uri, leg.ScriptTag node) {
     String path = DART2JS_LIBRARY_MAP[uri.path];
     if (path === null || uri.path.startsWith('_')) {
       reportError(node, 'library not found ${uri}');
       return null;
     }
     if (uri.path == 'dom' || uri.path == 'html' || uri.path == 'io') {
       // TODO(ahe): Get rid of mockableLibraryUsed when test.dart
       // supports this use case better.
       mockableLibraryUsed = true;
     }
     return libraryRoot.resolve(path);
   }
 
+  translatePackageUri(Uri uri, leg.ScriptTag node) =>

[Bob Nystrom, 2012/04/09 23:54:08]

I <3 => too, but I think a regular {} body is better when it wraps to another
line.

[nweiz, 2012/04/10 00:16:31]

I think it's fine for a single-line body, even if that body's on the next line.
This pattern is pretty common in the existing codebase. We should have John
declare it one way or the other in the style guide.

+    packageRoot.resolve(uri.path);
+
   bool run(Uri uri) {
+    packageRoot = uri.resolve('packages/');
     bool success = super.run(uri);
     for (final task in tasks) {
       log('${task.name} took ${task.timing}msec');
     }
     return success;
   }
 
   void reportDiagnostic(leg.SourceSpan span, String message, bool fatal) {
     if (span === null) {
       handler(null, null, null, message, fatal);
     } else {
       handler(span.uri, span.begin, span.end, message, fatal);
     }
   }
 
   bool get isMockCompilation() {
     return mockableLibraryUsed
       && (options.indexOf('--allow-mock-compilation') !== -1);
   }
 }