Steps towards making dart2js JS AST templates an indepentent library.

pkg/compiler/lib/src/js/js.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 js;
 
 import 'precedence.dart';
-import '../util/characters.dart' as charCodes;
-import '../util/util.dart';
-import '../io/code_output.dart' show CodeBuffer;
-import '../io/source_information.dart' show SourceInformation;
-import '../js_emitter/js_emitter.dart' show USE_NEW_EMITTER;
+import '../util/characters.dart' as charCodes;    // TODO(sra): Local copy of used constants.
+import '../io/code_output.dart' show CodeBuffer;  // TODO(sra): Remove.
+import '../io/source_information.dart' show SourceInformation; // TODO(sra): Remove.
+import '../js_emitter/js_emitter.dart' show USE_NEW_EMITTER;  // TODO(sra): Turn into an option.
 
 // TODO(floitsch): remove this dependency (currently necessary for the
 // CodeBuffer).
-import '../dart2jslib.dart' as leg;
+import '../dart2jslib.dart' as leg;  // TODO(sra): Remove.
 
-import '../dump_info.dart';
+import '../dump_info.dart' show DumpInfoTask;  // TODO(sra): Remove.
 
 part 'nodes.dart';
 part 'builder.dart';
 part 'printer.dart';
 part 'template.dart';
+
+
+// The following code will be moved out of this library into js_backend.  When
+// this happens, most of the imports can be removed.
+
+CodeBuffer prettyPrint(Node node, leg.Compiler compiler,
+                       {DumpInfoTask monitor,
+                        bool allowVariableMinification: true}) {
+  JavaScriptPrintingOptions options = new JavaScriptPrintingOptions(
+      shouldCompressOutput: compiler.enableMinification,
+      minifyLocalVariables: allowVariableMinification);
+  Dart2JSJavaScriptPrintingContext context =
+      new Dart2JSJavaScriptPrintingContext(compiler, monitor);
+  Printer printer = new Printer(options, context);
+  printer.visit(node);
+  return context.outBuffer;
+}
+
+class Dart2JSJavaScriptPrintingContext extends JavaScriptPrintingContext {
+  final leg.Compiler compiler;
+  final DumpInfoTask monitor;
+  final CodeBuffer outBuffer = new CodeBuffer();
+
+  Dart2JSJavaScriptPrintingContext(leg.Compiler this.compiler,
+      DumpInfoTask this.monitor);
+
+  void error(String message) {
+    compiler.internalError(NO_LOCATION_SPANNABLE, message);
+  }
+
+  void emit(String string) {
+    outBuffer.add(string);
+  }
+
+  void enterNode(Node node) {
+    if (node.sourceInformation != null) {
+      node.sourceInformation.beginMapping(outBuffer);
+    }
+    if (monitor != null) monitor.enteringAst(node, outBuffer.length);
+  }
+
+  void exitNode(Node node) {
+    if (monitor != null) monitor.exitingAst(node, outBuffer.length);
+    if (node.sourceInformation != null) {
+      node.sourceInformation.endMapping(outBuffer);
+    }
+  }
+}