Split analyzer2dart code into multiple source files

pkg/analyzer2dart/lib/src/tree_shaker.dart

+// Copyright (c) 2014, 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 analyzer2dart.treeShaker;
+
+import 'package:analyzer/analyzer.dart';
+import 'package:analyzer/src/generated/element.dart';
+import 'package:analyzer/src/generated/engine.dart';
+
+import 'closed_world.dart';
+
+class TreeShaker {
+  List<Element> _queue = <Element>[];
+  Set<Element> _alreadyEnqueued = new Set<Element>();
+  ClosedWorld _world = new ClosedWorld();
+
+  void add(Element e) {
+    if (!_alreadyEnqueued.contains(e)) {
+      _queue.add(e);
+      _alreadyEnqueued.add(e);
+    }
+  }
+
+  ClosedWorld shake(AnalysisContext context) {
+    while (_queue.isNotEmpty) {
+      Element e = _queue.removeAt(0);
+      print('Tree shaker handling $e');
+      CompilationUnit compilationUnit =
+          context.getResolvedCompilationUnit(e.source, e.library);
+      AstNode identifier =
+          new NodeLocator.con1(e.nameOffset).searchWithin(compilationUnit);
+      FunctionDeclaration declaration =
+          identifier.getAncestor((node) => node is FunctionDeclaration);
+      _world.elements[e] = declaration;
+      declaration.accept(new TreeShakingVisitor(this));
+    }
+    print('Tree shaking done');
+    return _world;
+  }
+}
+
+class TreeShakingVisitor extends RecursiveAstVisitor {
+  final TreeShaker treeShaker;
+
+  TreeShakingVisitor(this.treeShaker);
+
+  @override
+  void visitFunctionDeclaration(FunctionDeclaration node) {
+    print('Visiting function ${node.name.name}');
+    super.visitFunctionDeclaration(node);
+  }
+
+  @override
+  void visitMethodInvocation(MethodInvocation node) {
+    print('Visiting invocation of ${node.methodName.name}');
+    Element staticElement = node.methodName.staticElement;
+    if (staticElement != null) {
+      // TODO(paulberry): deal with the case where staticElement is
+      // not necessarily the exact target.  (Dart2js calls this a
+      // "dynamic invocation").  We need a notion of "selector".  Maybe
+      // we can use Dart2js selectors.
+      treeShaker.add(staticElement);
+    } else {
+      // TODO(paulberry): deal with this case.
+    }
+    super.visitMethodInvocation(node);
+  }
+
+}
+