Copy Rasta visitor to dart2js.

pkg/compiler/lib/src/kernel/fall_through_visitor.dart

+// Copyright (c) 2016, 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.md file.
+
+import 'package:kernel/ast.dart'
+    show
+        AssertStatement,
+        Block,
+        BreakStatement,
+        Catch,
+        ContinueSwitchStatement,
+        DoStatement,
+        EmptyStatement,
+        ExpressionStatement,
+        ForInStatement,
+        ForStatement,
+        FunctionDeclaration,
+        IfStatement,
+        InvalidStatement,
+        LabeledStatement,
+        ReturnStatement,
+        Statement,
+        StatementVisitor,
+        SwitchStatement,
+        Throw,
+        TryCatch,
+        TryFinally,
+        VariableDeclaration,
+        WhileStatement,
+        YieldStatement;
+
+/// Returns true if [node] would let execution reach the next node (aka
+/// fall-through in switch cases).
+bool fallsThrough(Statement node) => node.accept(const FallThroughVisitor());
+
+/// Visitor implementing [computeFallThrough].
+class FallThroughVisitor implements StatementVisitor<bool> {
+  const FallThroughVisitor();
+
+  bool defaultStatement(Statement node) => throw "Not implemented.";
+
+  bool visitInvalidStatement(InvalidStatement node) => false;
+
+  bool visitExpressionStatement(ExpressionStatement node) {
+    return node.expression is! Throw;
+  }
+
+  bool visitBlock(Block node) {
+    for (Statement statement in node.statements) {
+      if (!statement.accept(this)) return false;
+    }
+    return true;
+  }
+
+  bool visitEmptyStatement(EmptyStatement node) => true;
+
+  bool visitAssertStatement(AssertStatement node) => true;
+
+  bool visitLabeledStatement(LabeledStatement node) => true;
+
+  bool visitBreakStatement(BreakStatement node) => false;
+
+  bool visitWhileStatement(WhileStatement node) => true;
+
+  bool visitDoStatement(DoStatement node) => node.body.accept(this);
+
+  bool visitForStatement(ForStatement node) => true;
+
+  bool visitForInStatement(ForInStatement node) => true;
+
+  bool visitSwitchStatement(SwitchStatement node) => true;
+
+  bool visitContinueSwitchStatement(ContinueSwitchStatement node) => false;
+
+  bool visitIfStatement(IfStatement node) {
+    if (node.then == null || node.otherwise == null) return true;
+    return node.then.accept(this) || node.otherwise.accept(this);
+  }
+
+  bool visitReturnStatement(ReturnStatement node) => false;
+
+  bool visitTryCatch(TryCatch node) {
+    if (node.body.accept(this)) return true;
+    for (Catch catchNode in node.catches) {
+      if (catchNode.body.accept(this)) return true;
+    }
+    return false;
+  }
+
+  bool visitTryFinally(TryFinally node) {
+    return node.body.accept(this) && node.finalizer.accept(this);
+  }
+
+  bool visitYieldStatement(YieldStatement node) => true;
+
+  bool visitVariableDeclaration(VariableDeclaration node) => true;
+
+  bool visitFunctionDeclaration(FunctionDeclaration node) => true;
+}