Use destructuring assignments for named parameters (#180)

lib/src/js/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> {
   T visitProgram(Program node);
 
   T visitBlock(Block node);
@@ skipping 70 matching lines @@
   T visitComment(Comment node);
   T visitCommentExpression(CommentExpression node);
 
   T visitInterpolatedExpression(InterpolatedExpression node);
   T visitInterpolatedLiteral(InterpolatedLiteral node);
   T visitInterpolatedParameter(InterpolatedParameter node);
   T visitInterpolatedSelector(InterpolatedSelector node);
   T visitInterpolatedStatement(InterpolatedStatement node);
   T visitInterpolatedMethod(InterpolatedMethod node);
   T visitInterpolatedIdentifier(InterpolatedIdentifier node);
+
+  T visitArrayBindingPattern(ArrayBindingPattern node);
+  T visitObjectBindingPattern(ObjectBindingPattern node);
+  T visitDestructuredVariable(DestructuredVariable node);
 }
 
 class BaseVisitor<T> implements NodeVisitor<T> {
   T visitNode(Node node) {
     node.visitChildren(this);
     return null;
   }
 
   T visitProgram(Program node) => visitNode(node);
 
@@ skipping 102 matching lines @@
       => visitInterpolatedNode(node);
   T visitInterpolatedIdentifier(InterpolatedIdentifier node)
       => visitInterpolatedNode(node);
 
   // Ignore comments by default.
   T visitComment(Comment node) => null;
   T visitCommentExpression(CommentExpression node) => null;
 
   T visitAwait(Await node) => visitExpression(node);
   T visitDartYield(DartYield node) => visitStatement(node);
+
+  T visitBindingPattern(BindingPattern node) => visitNode(node);
+  T visitArrayBindingPattern(ArrayBindingPattern node)
+      => visitBindingPattern(node);
+  T visitObjectBindingPattern(ObjectBindingPattern node)
+      => visitBindingPattern(node);
+  T visitDestructuredVariable(DestructuredVariable node) => visitNode(node);
 }
 
 abstract class Node {
   /// Sets the source location of this node. For performance reasons, we allow
   /// setting this after construction.
   Object sourceInformation;
 
   ClosureAnnotation _closureAnnotation;
   /// Closure annotation of this node.
   ClosureAnnotation get closureAnnotation => _closureAnnotation;
 
   accept(NodeVisitor visitor);
   void visitChildren(NodeVisitor visitor);
 
   // Shallow clone of node.  Does not clone positions since the only use of this
   // private method is create a copy with a new position.
   Node _clone();
 
   withClosureAnnotation(ClosureAnnotation closureAnnotation) {
     if (this.closureAnnotation == closureAnnotation) return this;
-    
+
     return _clone()
         ..sourceInformation = sourceInformation
         .._closureAnnotation = closureAnnotation;
   }
   // Returns a node equivalent to [this], but with new source position and end
   // source position.
   Node withSourceInformation(sourceInformation) {
     if (sourceInformation == this.sourceInformation) {
       return this;
     }
@@ skipping 500 matching lines @@
     leftHandSide.accept(visitor);
     if (value != null) value.accept(visitor);
   }
 
   Assignment _clone() =>
       new Assignment.compound(leftHandSide, op, value);
 }
 
 class VariableInitialization extends Assignment {
   /** [value] may be null. */
-  VariableInitialization(Identifier declaration, Expression value)
+  VariableInitialization(VariableBinding declaration, Expression value)
       : super(declaration, value);
 
-  Identifier get declaration => leftHandSide;
+  VariableBinding get declaration => leftHandSide;
 
   accept(NodeVisitor visitor) => visitor.visitVariableInitialization(this);
 
   VariableInitialization _clone() =>
       new VariableInitialization(declaration, value);
 }
 
+abstract class VariableBinding extends Expression {
+}
+
+class DestructuredVariable extends Expression implements Parameter {
+  final Identifier name;
+  final BindingPattern structure;
+  final Expression defaultValue;
+  DestructuredVariable({this.name, this.structure, this.defaultValue}) {
+    assert(name != null || structure != null);
+  }
+
+  accept(NodeVisitor visitor) => visitor.visitDestructuredVariable(this);
+  void visitChildren(NodeVisitor visitor) {
+    name?.accept(visitor);
+    structure?.accept(visitor);
+    defaultValue?.accept(visitor);
+  }
+
+  /// Avoid parenthesis when pretty-printing.
+  @override int get precedenceLevel => PRIMARY;
+  @override Node _clone() =>
+      new DestructuredVariable(
+          name: name, structure: structure, defaultValue: defaultValue);
+}
+
+abstract class BindingPattern extends Expression implements VariableBinding {
+  final List<DestructuredVariable> variables;
+  BindingPattern(this.variables);
+
+  void visitChildren(NodeVisitor visitor) {
+    for (DestructuredVariable v in variables) v.accept(visitor);
+  }
+}
+
+class ObjectBindingPattern extends BindingPattern {
+  ObjectBindingPattern(List<DestructuredVariable> variables)
+      : super(variables);
+  accept(NodeVisitor visitor) => visitor.visitObjectBindingPattern(this);
+
+  /// Avoid parenthesis when pretty-printing.
+  @override int get precedenceLevel => PRIMARY;
+  @override Node _clone() => new ObjectBindingPattern(variables);
+}
+
+class ArrayBindingPattern extends BindingPattern {
+  ArrayBindingPattern(List<DestructuredVariable> variables)
+      : super(variables);
+  accept(NodeVisitor visitor) => visitor.visitArrayBindingPattern(this);
+
+  /// Avoid parenthesis when pretty-printing.
+  @override int get precedenceLevel => PRIMARY;
+  @override Node _clone() => new ObjectBindingPattern(variables);
+}
+
 class Conditional extends Expression {
   final Expression condition;
   final Expression then;
   final Expression otherwise;
 
   Conditional(this.condition, this.then, this.otherwise);
 
   accept(NodeVisitor visitor) => visitor.visitConditional(this);
 
   void visitChildren(NodeVisitor visitor) {
@@ skipping 148 matching lines @@
   Prefix _clone() => new Prefix(op, argument);
 
   void visitChildren(NodeVisitor visitor) {
     argument.accept(visitor);
   }
 
   int get precedenceLevel => UNARY;
 }
 
 // SpreadElement isn't really a prefix expression, as it can only appear in
-// certain places such as ArgumentList and destructuring, but we pretend
+// certain places such as ArgumentList and BindingPattern, but we pretend
 // it is for simplicity's sake.
 class Spread extends Prefix {
   Spread(Expression operand) : super('...', operand);
   int get precedenceLevel => SPREAD;
 
   accept(NodeVisitor visitor) => visitor.visitSpread(this);
   Spread _clone() => new Spread(argument);
 }
 
 class Postfix extends Expression {
   final String op;
   final Expression argument;
 
   Postfix(this.op, this.argument);
 
   accept(NodeVisitor visitor) => visitor.visitPostfix(this);
 
   Postfix _clone() => new Postfix(op, argument);
 
   void visitChildren(NodeVisitor visitor) {
     argument.accept(visitor);
   }
 
   int get precedenceLevel => UNARY;
 }
 
-abstract class Parameter implements Expression {}
+abstract class Parameter implements Expression, VariableBinding {}
 
-class Identifier extends Expression implements Parameter {
+class Identifier extends Expression implements Parameter, VariableBinding {
   final String name;
   final bool allowRename;
 
   Identifier(this.name, {this.allowRename: true}) {
     assert(_identifierRE.hasMatch(name));
   }
   static RegExp _identifierRE = new RegExp(r'^[A-Za-z_$][A-Za-z_$0-9]*$');
 
   Identifier _clone() =>
       new Identifier(name, allowRename: allowRename);
@@ skipping 725 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);
 }