fix #29346, ensure all nodes are implemented by DDC's code generator

pkg/dev_compiler/lib/src/js_ast/nodes.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.
 
 part of js_ast;
 
 abstract class NodeVisitor<T> implements TypeRefVisitor<T> {
   T visitProgram(Program node);
 
   T visitBlock(Block node);
@@ skipping 1425 matching lines @@
 }
 
 // TODO(jmesserly): parser does not support this yet.
 class TemplateString extends Expression {
   /**
    * The parts of this template string: a sequence of [String]s and
    * [Expression]s. Strings and expressions will alternate, for example:
    *
    *     `foo${1 + 2} bar ${'hi'}`
    *
-   * would be represented by:
+   * would be represented by [strings]:
    *
-   *     ['foo', new JS.Binary('+', js.number(1), js.number(2)),
-   *      ' bar ', new JS.LiteralString("'hi'")]
+   *     ['foo', ' bar ', '']
+   *
+   * and [interpolations]:
+   *
+   *     [new JS.Binary('+', js.number(1), js.number(2)),
+   *      new JS.LiteralString("'hi'")]
+   *
+   * There should be exactly one more string than interpolation expression.
    */
-  final List elements;
-  TemplateString(this.elements);
+  final List<String> strings;
+  final List<Expression> interpolations;
+
+  TemplateString(this.strings, this.interpolations) {
+    assert(strings.length == interpolations.length + 1);
+  }
 
   accept(NodeVisitor visitor) => visitor.visitTemplateString(this);
 
   void visitChildren(NodeVisitor visitor) {
-    for (var element in elements) {
-      if (element is Expression) element.accept(visitor);
+    for (var element in interpolations) {
+      element.accept(visitor);
     }
   }
 
-  TemplateString _clone() => new TemplateString(elements);
+  TemplateString _clone() => new TemplateString(strings, interpolations);
 
   int get precedenceLevel => PRIMARY;
 }
 
 // TODO(jmesserly): parser does not support this yet.
 class TaggedTemplate extends Expression {
   final Expression tag;
   final TemplateString template;
 
   TaggedTemplate(this.tag, this.template);
@@ skipping 430 matching lines @@
   final List<ModuleItem> body;
   Module(this.body, {this.name});
 
   accept(NodeVisitor visitor) => visitor.visitModule(this);
   void visitChildren(NodeVisitor visitor) {
     for (ModuleItem item in body) item.accept(visitor);
   }
 
   Module _clone() => new Module(body);
 }