Refactor implementation to address review comments and API design suggestions from Luke.

pkg/fletchc/lib/dart2js_bridge.dart

 // Copyright (c) 2015, the Fletch 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.md file.
 
-import 'dart:io' show
-    File,
-    Platform;
+library fletchc.dart2js_bridge;
 
-import 'package:compiler/compiler.dart' as api;
-
-import 'package:sharedfrontend/elements.dart' as elements;
-
-import 'package:compiler/src/apiimpl.dart' as apiimpl;
-
-import 'package:compiler/src/dart2jslib.dart' as dart2js;
-
-import 'package:compiler/src/source_file_provider.dart' show
-    FormattingDiagnosticHandler;
-
-import 'package:dart2js_incremental/compiler.dart' show
-    OutputProvider;
-
-import 'package:compiler/src/filenames.dart' show
-    appendSlash;
-
-import 'package:semantic_visitor/semantic_visitor.dart' show
-    SemanticVisitor;
-
-import 'package:compiler/src/elements/elements.dart';
-import 'package:compiler/src/resolution/resolution.dart';
-import 'package:compiler/src/tree/tree.dart';
-import 'package:compiler/src/universe/universe.dart';
-import 'package:compiler/src/util/util.dart' show Spannable;
-import 'package:compiler/src/dart_types.dart';
-
-import 'bytecodes.dart';
+import 'compiler.dart' show
+    FletchCompiler;
 
 main(List<String> arguments) {
-  FormattingDiagnosticHandler handler = new FormattingDiagnosticHandler()
-      ..throwOnError = false;
-
-  OutputProvider outputProvider = new OutputProvider();
-
-  Uri myLocation = Uri.base.resolveUri(Platform.script);
-  if (myLocation.scheme == 'package') {
-    Uri runtimePackageRoot =
-        Uri.base.resolve(appendSlash(Platform.packageRoot));
-    myLocation =
-        new Uri.file(
-            new File.fromUri(runtimePackageRoot.resolve(myLocation.path))
-                .resolveSymbolicLinksSync());
-  }
-
   Uri script = Uri.base.resolve(arguments.single);
-
-  Uri libraryRoot = myLocation.resolve('../../../../dart/sdk/');
-
   Uri packageRoot = script.resolve('packages/');
-
-  List<String> options = <String>[];
-
-  Map<String, dynamic> environment = <String, dynamic>{};
-
   FletchCompiler compiler = new FletchCompiler(
-      handler.provider,
-      outputProvider,
-      handler,
-      libraryRoot,
-      packageRoot,
-      options,
-      environment);
-
+      packageRoot: packageRoot,
+      options: ['--verbose']);
   compiler.run(script);
 }
-
-abstract class FletchCompilerHack extends apiimpl.Compiler {
-  FletchCompilerHack(
-      api.CompilerInputProvider provider,
-      api.CompilerOutputProvider outputProvider,
-      api.DiagnosticHandler handler,
-      Uri libraryRoot,
-      Uri packageRoot,
-      List<String> options,
-      Map<String, dynamic> environment)
-      : super(provider, outputProvider, handler, libraryRoot, packageRoot,
-              options, environment) {
-    switchBackendHack();
-  }
-
-  void switchBackendHack() {
-    // TODO(ahe): Modify dart2js to support a custom backend directly, and
-    // remove this method.
-    int backendTaskCount = backend.tasks.length;
-    int apiimplTaskCount = 2;
-    int baseTaskCount = tasks.length - backendTaskCount - apiimplTaskCount;
-
-    tasks.removeRange(baseTaskCount, baseTaskCount + backendTaskCount);
-
-    backend = new FletchBackend(this);
-    tasks.addAll(backend.tasks);
-  }
-}
-
-class FletchCompiler extends FletchCompilerHack {
-  FletchCompiler(
-      api.CompilerInputProvider provider,
-      api.CompilerOutputProvider outputProvider,
-      api.DiagnosticHandler handler,
-      Uri libraryRoot,
-      Uri packageRoot,
-      List<String> options,
-      Map<String, dynamic> environment)
-      : super(provider, outputProvider, handler, libraryRoot, packageRoot,
-              ['--output-type=dart']..addAll(options), environment);
-
-  void computeMain() {
-    if (mainApp == null) return;
-
-    mainFunction = mainApp.findLocal("_entry");
-  }
-
-  void onLibraryCreated(elements.LibraryElement library) {
-    // TODO(ahe): Remove this.
-    library.canUseNative = true;
-    super.onLibraryCreated(library);
-  }
-}
-
-class FletchBackend extends dart2js.Backend {
-  final FletchResolutionCallbacks resolutionCallbacks =
-      new FletchResolutionCallbacks();
-
-  FletchBackend(dart2js.Compiler compiler)
-      : super(compiler);
-
-  List<CompilerTask> get tasks => <CompilerTask>[];
-
-  dart2js.ConstantSystem get constantSystem {
-    throw new UnsupportedError("get constantSystem");
-  }
-
-  dart2js.BackendConstantEnvironment get constants {
-    throw new UnsupportedError("get constants");
-  }
-
-  dart2js.ConstantCompilerTask get constantCompilerTask {
-    throw new UnsupportedError("get constantCompilerTask");
-  }
-
-  void enqueueHelpers(dart2js.ResolutionEnqueuer world, dart2js.Registry registry) {
-  }
-
-  void codegen(dart2js.CodegenWorkItem work) {
-  }
-
-  bool get canHandleCompilationFailed => true;
-
-  int assembleProgram() {
-    compiler.reportHint(
-        compiler.mainFunction,
-        dart2js.MessageKind.GENERIC,
-        {'text': 'Compiling ${compiler.mainFunction.name}'});
-
-    FletchVisitor visitor = new FletchVisitor(compiler.mainFunction);
-    compiler.mainFunction.node.accept(visitor);
-    print("Constants");
-    visitor.constants.forEach((constant, int index) {
-      print("  #$index: $constant");
-    });
-
-    print("Bytecodes:");
-    int offset = 0;
-    for (Bytecode bytecode in visitor.bytecodes) {
-      print("  $offset: $bytecode");
-      offset += bytecode.size;
-    }
-  }
-}
-
-class FletchResolutionCallbacks extends dart2js.ResolutionCallbacks {
-}
-
-class FletchVisitor extends SemanticVisitor {
-  final List<Bytecode> bytecodes = <Bytecode>[];
-
-  final Map<dynamic, int> constants = <dynamic, int>{};
-
-  FletchVisitor(element)
-      : super(element.resolvedAst.elements);
-
-  void visitStaticMethodInvocation(
-      Send node,
-      /* MethodElement */ element,
-      NodeList arguments,
-      Selector selector) {
-    arguments.accept(this);
-    int id = constants.putIfAbsent(element, () => constants.length);
-    bytecodes.add(new InvokeStaticUnfold(id));
-    bytecodes.add(const Pop());
-  }
-
-  void visitLiteralString(LiteralString node) {
-    int id = constants.putIfAbsent(
-        node.dartString.slowToString(), () => constants.length);
-    bytecodes.add(new LoadConstUnfold(id));
-  }
-
-  void visitLiteralInt(LiteralInt node) {
-    int id = constants.putIfAbsent(node.value, () => constants.length);
-    bytecodes.add(new LoadConstUnfold(id));
-  }
-
-
-  void visitLiteral(Literal node) {
-    print("literal ${node}");
-  }
-
-  void visitFunctionExpression(FunctionExpression node) {
-    node.body.accept(this);
-  }
-
-  void visitBlock(Block node) {
-    node.visitChildren(this);
-  }
-
-  void visitNodeList(NodeList node) {
-    node.visitChildren(this);
-  }
-
-  void visitExpressionStatement(ExpressionStatement node) {
-    node.visitChildren(this);
-  }
-
-  void visitParameterAccess(Send node, ParameterElement element);
-
-  void visitParameterAssignment(SendSet node, ParameterElement element, Node rhs);
-  void visitParameterInvocation(Send node,
-                             ParameterElement element,
-                             NodeList arguments,
-                             Selector selector);
-
-  void visitLocalVariableAccess(Send node, LocalVariableElement element);
-  void visitLocalVariableAssignment(SendSet node,
-                                 LocalVariableElement element,
-                                 Node rhs);
-  void visitLocalVariableInvocation(Send node,
-                                 LocalVariableElement element,
-                                 NodeList arguments,
-                                 Selector selector);
-
-  void visitLocalFunctionAccess(Send node, LocalFunctionElement element);
-  void visitLocalFunctionAssignment(SendSet node,
-                                 LocalFunctionElement element,
-                                 Node rhs,
-                                 Selector selector);
-  void visitLocalFunctionInvocation(Send node,
-                                 LocalFunctionElement element,
-                                 NodeList arguments,
-                                 Selector selector);
-
-  void visitDynamicAccess(Send node, Selector selector);
-  void visitDynamicAssignment(SendSet node, Selector selector, Node rhs);
-  void visitDynamicInvocation(Send node,
-                           NodeList arguments,
-                           Selector selector);
-
-  void visitStaticFieldAccess(Send node, FieldElement element);
-  void visitStaticFieldAssignment(SendSet node, FieldElement element, Node rhs);
-  void visitStaticFieldInvocation(Send node,
-                               FieldElement element,
-                               NodeList arguments,
-                               Selector selector);
-
-  void visitStaticMethodAccess(Send node, MethodElement element);
-
-  void visitStaticPropertyAccess(Send node, FunctionElement element);
-  void visitStaticPropertyAssignment(SendSet node,
-                                  FunctionElement element,
-                                  Node rhs);
-  void visitStaticPropertyInvocation(Send node,
-                                  FieldElement element,
-                                  NodeList arguments,
-                                  Selector selector);
-
-  void visitTopLevelFieldAccess(Send node, FieldElement element);
-  void visitTopLevelFieldAssignment(SendSet node, FieldElement element, Node rhs);
-  void visitTopLevelFieldInvocation(Send node,
-                               FieldElement element,
-                               NodeList arguments,
-                               Selector selector);
-
-  void visitTopLevelMethodAccess(Send node, MethodElement element);
-  void visitTopLevelMethodInvocation(Send node,
-                                  MethodElement element,
-                                  NodeList arguments,
-                                  Selector selector);
-
-  void visitTopLevelPropertyAccess(Send node, FunctionElement element);
-  void visitTopLevelPropertyAssignment(SendSet node,
-                                    FunctionElement element,
-                                    Node rhs);
-  void visitTopLevelPropertyInvocation(Send node,
-                                    FieldElement element,
-                                    NodeList arguments,
-                                    Selector selector);
-
-  void visitClassTypeLiteralAccess(Send node, ClassElement element);
-  void visitClassTypeLiteralInvocation(Send node,
-                                    ClassElement element,
-                                    NodeList arguments,
-                                    Selector selector);
-  void visitClassTypeLiteralAssignment(SendSet node,
-                                    ClassElement element,
-                                    Node rhs);
-
-  void visitTypedefTypeLiteralAccess(Send node, TypedefElement element);
-
-  void visitTypedefTypeLiteralInvocation(Send node,
-                                      TypedefElement element,
-                                      NodeList arguments,
-                                      Selector selector);
-
-  void visitTypedefTypeLiteralAssignment(SendSet node,
-                                      TypedefElement element,
-                                      Node rhs);
-
-  void visitTypeVariableTypeLiteralAccess(Send node, TypeVariableElement element);
-
-  void visitTypeVariableTypeLiteralInvocation(Send node,
-                                           TypeVariableElement element,
-                                           NodeList arguments,
-                                           Selector selector);
-
-  void visitTypeVariableTypeLiteralAssignment(SendSet node,
-                                           TypeVariableElement element,
-                                           Node rhs);
-
-  void visitDynamicTypeLiteralAccess(Send node);
-
-  void visitAssert(Send node, Node expression);
-
-  internalError(Spannable spannable, String reason);
-
-}