Make string juxtaposition combine properly with string interpolations.

frog/leg/tree/visitors.dart

 // Copyright (c) 2011, 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.
 
 class AbstractVisitor<R> implements Visitor<R> {
+  const AbstractVisitor();
+
   abstract R visitNode(Node node);
 
   R visitBlock(Block node) => visitStatement(node);
   R visitBreakStatement(BreakStatement node) => visitGotoStatement(node);
   R visitCatchBlock(CatchBlock node) => visitNode(node);
   R visitClassNode(ClassNode node) => visitNode(node);
   R visitConditional(Conditional node) => visitExpression(node);
   R visitContinueStatement(ContinueStatement node) => visitGotoStatement(node);
   R visitDoWhile(DoWhile node) => visitLoop(node);
   R visitEmptyStatement(EmptyStatement node) => visitStatement(node);
   R visitExpression(Expression node) => visitNode(node);
   R visitExpressionStatement(ExpressionStatement node) => visitStatement(node);
   R visitFor(For node) => visitLoop(node);
   R visitForInStatement(ForInStatement node) => visitLoop(node);
   R visitFunctionDeclaration(FunctionDeclaration node) => visitStatement(node);
   R visitFunctionExpression(FunctionExpression node) => visitExpression(node);
   R visitGotoStatement(GotoStatement node) => visitStatement(node);
   R visitIdentifier(Identifier node) => visitExpression(node);
   R visitIf(If node) => visitStatement(node);
   R visitLabeledStatement(LabeledStatement node) => visitStatement(node);
   R visitLiteral(Literal node) => visitExpression(node);
   R visitLiteralBool(LiteralBool node) => visitLiteral(node);
   R visitLiteralDouble(LiteralDouble node) => visitLiteral(node);
   R visitLiteralInt(LiteralInt node) => visitLiteral(node);
   R visitLiteralList(LiteralList node) => visitExpression(node);
   R visitLiteralMap(LiteralMap node) => visitExpression(node);
   R visitLiteralMapEntry(LiteralMapEntry node) => visitNode(node);
   R visitLiteralNull(LiteralNull node) => visitLiteral(node);
   R visitLiteralString(LiteralString node) => visitLiteral(node);
-  R visitLiteralStringJuxtaposition(LiteralStringJuxtaposition node) {
-    return visitLiteralString(node);
-  }
+  R visitStringJuxtaposition(Juxtaposition node) => visitExpression(node);
   R visitLoop(Loop node) => visitStatement(node);
   R visitModifiers(Modifiers node) => visitNode(node);
   R visitNamedArgument(NamedArgument node) => visitExpression(node);
   R visitNewExpression(NewExpression node) => visitExpression(node);
   R visitNodeList(NodeList node) => visitNode(node);
   R visitOperator(Operator node) => visitIdentifier(node);
   R visitParenthesizedExpression(ParenthesizedExpression node) {
     return visitExpression(node);
   }
   R visitPostfix(Postfix node) => visitNodeList(node);
@@ skipping 25 matching lines @@
 class TraversingVisitor extends AbstractVisitor {
   final Visitor visitor;
 
   TraversingVisitor(Visitor this.visitor);
 
   visitNode(Node node) {
     node.accept(visitor);
     node.visitChildren(this);
   }
 }