// 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.

// ignore_for_file: omit_local_variable_types, unnecessary_breaks

import 'characters.dart' as char_codes;
import 'nodes.dart';
import 'precedence.dart';

class JavaScriptPrintingOptions {
  final bool shouldCompressOutput;
  final bool minifyLocalVariables;
  final bool preferSemicolonToNewlineInMinifiedOutput;
  final bool allowSingleLineIfStatements;

  /// True to allow keywords in properties, such as `obj.var` or `obj.function`
  /// Modern JS engines support this.
  final bool allowKeywordsInProperties;

  JavaScriptPrintingOptions({
    this.shouldCompressOutput = false,
    this.minifyLocalVariables = false,
    this.preferSemicolonToNewlineInMinifiedOutput = false,
    this.allowKeywordsInProperties = false,
    this.allowSingleLineIfStatements = false,
  });
}

/// An environment in which JavaScript printing is done.  Provides emitting of
/// text and pre- and post-visit callbacks.
abstract class JavaScriptPrintingContext {
  /// Signals an error.  This should happen only for serious internal errors.
  void error(String message) {
    throw message;
  }

  /// Adds [string] to the output.
  void emit(String string);

  /// Callback immediately before printing [node].  Whitespace may be printed
  /// after this callback before the first non-whitespace character for [node].
  void enterNode(Node node) {}

  /// Callback after printing the last character representing [node].
  void exitNode(Node node) {}

  // Callback before branching the flow of code in an expression.
  void expressionBranch() {}

  // Callback after returning to the original flow of code in an expression.
  void expressionJoin() {}

  late Printer printer;
}

/// A simple implementation of [JavaScriptPrintingContext] suitable for tests.
class SimpleJavaScriptPrintingContext extends JavaScriptPrintingContext {
  final StringBuffer buffer = StringBuffer();

  @override
  void emit(String string) {
    buffer.write(string);
  }

  String getText() => buffer.toString();
}

// TODO(ochafik): Inline the body of [TypeScriptTypePrinter] here if/when it no
// longer needs to share utils with [ClosureTypePrinter].
class Printer implements NodeVisitor {
  final JavaScriptPrintingOptions options;
  final JavaScriptPrintingContext context;
  final bool shouldCompressOutput;
  final DanglingElseVisitor danglingElseVisitor;
  final LocalNamer localNamer;

  bool inForInit = false;
  bool atStatementBegin = false;
  bool inNewTarget = false;
  bool pendingSemicolon = false;
  bool pendingSpace = false;

  // The current indentation level.
  int _indentLevel = 0;
  // A cache of all indentation strings used so far.
  final List<String> _indentList = [''];

  /// Whether the next call to [indent] should just be a no-op.
  bool _skipNextIndent = false;

  static final identifierCharacterRegExp = RegExp(r'^[a-zA-Z_0-9$]');
  static final expressionContinuationRegExp = RegExp(r'^[-+([]');

  Printer(this.options, this.context, {LocalNamer? localNamer})
    : shouldCompressOutput = options.shouldCompressOutput,
      danglingElseVisitor = DanglingElseVisitor(context),
      localNamer = determineRenamer(localNamer, options) {
    context.printer = this;
  }

  static LocalNamer determineRenamer(
    LocalNamer? localNamer,
    JavaScriptPrintingOptions options,
  ) {
    if (localNamer != null) return localNamer;
    return (options.shouldCompressOutput && options.minifyLocalVariables)
        ? MinifyRenamer()
        : IdentityNamer();
  }

  // The current indentation string.
  String get indentation {
    // Lazily add new indentation strings as required.
    while (_indentList.length <= _indentLevel) {
      _indentList.add('${_indentList.last}  ');
    }
    return _indentList[_indentLevel];
  }

  void indentMore() {
    _indentLevel++;
  }

  void indentLess() {
    _indentLevel--;
  }

  /// Always emit a newline, even under `enableMinification`.
  void forceLine() {
    out('\n');
  }

  /// Emits a newline for readability.
  void lineOut() {
    if (!shouldCompressOutput) forceLine();
  }

  void spaceOut() {
    if (!shouldCompressOutput) out(' ');
  }

  String lastAddedString = '\u0000';

  int get lastCharCode {
    assert(lastAddedString.isNotEmpty);
    return lastAddedString.codeUnitAt(lastAddedString.length - 1);
  }

  void out(String str) {
    if (str != '') {
      if (pendingSemicolon) {
        if (!shouldCompressOutput) {
          context.emit(';');
        } else if (str != '}') {
          // We want to output newline instead of semicolon because it makes
          // the raw stack traces much easier to read and it also makes line-
          // based tools like diff work much better.  JavaScript will
          // automatically insert the semicolon at the newline if it means a
          // parsing error is avoided, so we can only do this trick if the
          // next line is not something that can be glued onto a valid
          // expression to make a new valid expression.

          // If we're using the new emitter where most pretty printed code
          // is escaped in strings, it is a lot easier to deal with semicolons
          // than newlines because the former doesn't need escaping.
          if (options.preferSemicolonToNewlineInMinifiedOutput ||
              expressionContinuationRegExp.hasMatch(str)) {
            context.emit(';');
          } else {
            context.emit('\n');
          }
        }
      }
      if (pendingSpace &&
          (!shouldCompressOutput || identifierCharacterRegExp.hasMatch(str))) {
        context.emit(' ');
      }
      pendingSpace = false;
      pendingSemicolon = false;
      context.emit(str);
      lastAddedString = str;
    }
  }

  void outLn(String str) {
    out(str);
    lineOut();
  }

  void outSemicolonLn() {
    if (shouldCompressOutput) {
      pendingSemicolon = true;
    } else {
      out(';');
      forceLine();
    }
  }

  void outIndent(String str) {
    indent();
    out(str);
  }

  void outIndentLn(String str) {
    indent();
    outLn(str);
  }

  void skipNextIndent() {
    _skipNextIndent = true;
  }

  void indent() {
    if (_skipNextIndent) {
      _skipNextIndent = false;
      return;
    }
    if (!shouldCompressOutput) {
      out(indentation);
    }
  }

  void visit(Node node) {
    context.enterNode(node);
    node.accept(this);
    context.exitNode(node);
  }

  void visitCommaSeparated(
    List<Expression> nodes,
    int hasRequiredType, {
    required bool newInForInit,
    required bool newAtStatementBegin,
  }) {
    for (int i = 0; i < nodes.length; i++) {
      if (i != 0) {
        atStatementBegin = false;
        out(',');
        spaceOut();
      }
      visitNestedExpression(
        nodes[i],
        hasRequiredType,
        newInForInit: newInForInit,
        newAtStatementBegin: newAtStatementBegin,
      );
    }
  }

  void visitAll(List<Node> nodes) {
    nodes.forEach(visit);
  }

  @override
  void visitProgram(Program program) {
    if (program.scriptTag != null) {
      out('#!${program.scriptTag}\n');
    }
    visitAll(program.body);
  }

  bool blockBody(
    Node body, {
    required bool needsSeparation,
    required bool needsNewline,
  }) {
    if (body is Block) {
      spaceOut();
      blockOut(body, shouldIndent: false, needsNewline: needsNewline);
      return true;
    }
    if (shouldCompressOutput && needsSeparation) {
      // If [shouldCompressOutput] is false, then the 'lineOut' will insert
      // the separation.
      out(' ');
    } else {
      lineOut();
    }
    indentMore();
    visit(body);
    indentLess();
    return false;
  }

  void blockOutWithoutBraces(Node node) {
    if (node is Block && !node.isScope) {
      context.enterNode(node);
      Block block = node;
      block.statements.forEach(blockOutWithoutBraces);
      context.exitNode(node);
    } else {
      visit(node);
    }
  }

  void blockOut(
    Block node, {
    required bool shouldIndent,
    required bool needsNewline,
  }) {
    if (shouldIndent) indent();
    context.enterNode(node);
    out('{');
    lineOut();
    indentMore();
    node.statements.forEach(blockOutWithoutBraces);
    indentLess();
    indent();
    out('}');
    context.exitNode(node);
    if (needsNewline) lineOut();
  }

  @override
  void visitBlock(Block block) {
    blockOut(block, shouldIndent: true, needsNewline: true);
  }

  @override
  void visitDebuggerStatement(node) {
    outIndentLn('debugger;');
  }

  @override
  void visitExpressionStatement(ExpressionStatement node) {
    indent();
    visitNestedExpression(
      node.expression,
      EXPRESSION,
      newInForInit: false,
      newAtStatementBegin: true,
    );
    outSemicolonLn();
  }

  @override
  void visitEmptyStatement(EmptyStatement node) {
    outIndentLn(';');
  }

  void ifOut(If node, bool shouldIndent) {
    var then = node.then;
    var elsePart = node.otherwise;
    bool hasElse = node.hasElse;

    // Handle dangling elses and a workaround for Android 4.0 stock browser.
    // Android 4.0 requires braces for a single do-while in the `then` branch.
    // See issue 10923.
    if (hasElse) {
      bool needsBraces = node.then.accept(danglingElseVisitor) || then is Do;
      if (needsBraces) {
        then = Block(<Statement>[then]);
      }
    }
    if (shouldIndent) indent();
    out('if');
    spaceOut();
    out('(');
    visitNestedExpression(
      node.condition,
      EXPRESSION,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    out(')');
    bool thenWasBlock;
    if (options.allowSingleLineIfStatements && !hasElse && then is! Block) {
      thenWasBlock = false;
      spaceOut();
      skipNextIndent();
      visit(then);
    } else {
      thenWasBlock = blockBody(
        then,
        needsSeparation: false,
        needsNewline: !hasElse,
      );
    }
    if (hasElse) {
      if (thenWasBlock) {
        spaceOut();
      } else {
        indent();
      }
      out('else');
      if (elsePart is If) {
        pendingSpace = true;
        context.enterNode(elsePart);
        ifOut(elsePart, false);
        context.exitNode(elsePart);
      } else {
        blockBody(elsePart, needsSeparation: true, needsNewline: true);
      }
    }
  }

  @override
  void visitIf(If node) {
    ifOut(node, true);
  }

  @override
  void visitFor(For loop) {
    outIndent('for');
    spaceOut();
    out('(');
    if (loop.init != null) {
      visitNestedExpression(
        loop.init!,
        EXPRESSION,
        newInForInit: true,
        newAtStatementBegin: false,
      );
    }
    out(';');
    if (loop.condition != null) {
      spaceOut();
      visitNestedExpression(
        loop.condition!,
        EXPRESSION,
        newInForInit: false,
        newAtStatementBegin: false,
      );
    }
    out(';');
    if (loop.update != null) {
      spaceOut();
      visitNestedExpression(
        loop.update!,
        EXPRESSION,
        newInForInit: false,
        newAtStatementBegin: false,
      );
    }
    out(')');
    blockBody(loop.body, needsSeparation: false, needsNewline: true);
  }

  @override
  void visitForIn(ForIn loop) {
    outIndent('for');
    spaceOut();
    out('(');
    visitNestedExpression(
      loop.leftHandSide,
      EXPRESSION,
      newInForInit: true,
      newAtStatementBegin: false,
    );
    out(' in');
    pendingSpace = true;
    visitNestedExpression(
      loop.object,
      EXPRESSION,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    out(')');
    blockBody(loop.body, needsSeparation: false, needsNewline: true);
  }

  @override
  void visitForOf(ForOf loop) {
    outIndent('for');
    spaceOut();
    out('(');
    visitNestedExpression(
      loop.leftHandSide,
      EXPRESSION,
      newInForInit: true,
      newAtStatementBegin: false,
    );
    out(' of');
    pendingSpace = true;
    visitNestedExpression(
      loop.iterable,
      ASSIGNMENT,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    out(')');
    blockBody(loop.body, needsSeparation: false, needsNewline: true);
  }

  @override
  void visitWhile(While loop) {
    outIndent('while');
    spaceOut();
    out('(');
    visitNestedExpression(
      loop.condition,
      EXPRESSION,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    out(')');
    blockBody(loop.body, needsSeparation: false, needsNewline: true);
  }

  @override
  void visitDo(Do loop) {
    outIndent('do');
    if (blockBody(loop.body, needsSeparation: true, needsNewline: false)) {
      spaceOut();
    } else {
      indent();
    }
    out('while');
    spaceOut();
    out('(');
    visitNestedExpression(
      loop.condition,
      EXPRESSION,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    out(')');
    outSemicolonLn();
  }

  @override
  void visitContinue(Continue node) {
    if (node.targetLabel == null) {
      outIndent('continue');
    } else {
      outIndent('continue ${node.targetLabel}');
    }
    outSemicolonLn();
  }

  @override
  void visitBreak(Break node) {
    if (node.targetLabel == null) {
      outIndent('break');
    } else {
      outIndent('break ${node.targetLabel}');
    }
    outSemicolonLn();
  }

  @override
  void visitReturn(Return node) {
    final value = node.value;
    if (value == null) {
      outIndent('return');
    } else {
      outIndent('return');
      pendingSpace = true;
      visitNestedExpression(
        value,
        EXPRESSION,
        newInForInit: false,
        newAtStatementBegin: false,
      );
    }
    outSemicolonLn();
  }

  @override
  void visitDartYield(DartYield node) {
    if (node.hasStar) {
      outIndent('yield*');
    } else {
      outIndent('yield');
    }
    pendingSpace = true;
    visitNestedExpression(
      node.expression,
      EXPRESSION,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    outSemicolonLn();
  }

  @override
  void visitThrow(Throw node) {
    outIndent('throw');
    pendingSpace = true;
    visitNestedExpression(
      node.expression,
      EXPRESSION,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    outSemicolonLn();
  }

  @override
  void visitTry(Try node) {
    outIndent('try');
    blockBody(node.body, needsSeparation: true, needsNewline: false);
    if (node.catchPart != null) {
      visit(node.catchPart!);
    }
    if (node.finallyPart != null) {
      spaceOut();
      out('finally');
      blockBody(node.finallyPart!, needsSeparation: true, needsNewline: true);
    } else {
      lineOut();
    }
  }

  @override
  void visitCatch(Catch node) {
    spaceOut();
    out('catch');
    spaceOut();
    out('(');
    visitNestedExpression(
      node.declaration,
      EXPRESSION,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    out(')');
    blockBody(node.body, needsSeparation: false, needsNewline: false);
  }

  @override
  void visitSwitch(Switch node) {
    outIndent('switch');
    spaceOut();
    out('(');
    visitNestedExpression(
      node.key,
      EXPRESSION,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    out(')');
    spaceOut();
    outLn('{');
    indentMore();
    visitAll(node.cases);
    indentLess();
    outIndentLn('}');
  }

  @override
  void visitCase(Case node) {
    outIndent('case');
    pendingSpace = true;
    visitNestedExpression(
      node.expression,
      EXPRESSION,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    outLn(':');
    if (node.body.statements.isNotEmpty) {
      indentMore();
      blockOutWithoutBraces(node.body);
      indentLess();
    }
  }

  @override
  void visitDefault(Default node) {
    outIndentLn('default:');
    if (node.body.statements.isNotEmpty) {
      indentMore();
      blockOutWithoutBraces(node.body);
      indentLess();
    }
  }

  @override
  void visitLabeledStatement(LabeledStatement node) {
    outIndent('${node.label}:');
    blockBody(node.body, needsSeparation: false, needsNewline: true);
  }

  void functionOut(Fun fun, Identifier? name) {
    out('function');
    if (fun.isGenerator) out('*');
    if (name != null) {
      out(' ');
      // Name must be a [Decl]. Therefore only test for primary expressions.
      visitNestedExpression(
        name,
        PRIMARY,
        newInForInit: false,
        newAtStatementBegin: false,
      );
    }
    localNamer.enterScope(fun);
    out('(');
    visitCommaSeparated(
      fun.params,
      PRIMARY,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    out(')');

    // When pattern support is enabled, case clauses like `case
    // AsyncModifier.sync()` will be re-interpreted as object patterns (which
    // won't be valid, since object patterns can't refer to named constructors).
    // To preserve the intended behavior, we need to extract these as named
    // constants.  TODO(paulberry): once pattern support is enabled, inline
    // these constants back into the switch statement.
    const sync_ = AsyncModifier.sync;
    const async_ = AsyncModifier.async;
    const syncStar = AsyncModifier.syncStar;
    const asyncStar = AsyncModifier.asyncStar;

    switch (fun.asyncModifier) {
      case sync_:
        break;
      case async_:
        out(' async');
        break;
      case syncStar:
        out(' sync*');
        break;
      case asyncStar:
        out(' async*');
        break;
    }
    blockBody(fun.body, needsSeparation: false, needsNewline: false);
    localNamer.leaveScope();
  }

  @override
  void visitFunctionDeclaration(FunctionDeclaration declaration) {
    indent();
    var f = declaration.function;
    context.enterNode(f);
    functionOut(f, declaration.name);
    context.exitNode(f);
    lineOut();
  }

  void visitNestedExpression(
    Expression node,
    int requiredPrecedence, {
    required bool newInForInit,
    required bool newAtStatementBegin,
  }) {
    int precedenceLevel = node.precedenceLevel;
    bool needsParentheses =
        // a - (b + c).
        (requiredPrecedence != EXPRESSION &&
            precedenceLevel < requiredPrecedence) ||
        // for (a = (x in o); ... ; ... ) { ... }
        (newInForInit && node is Binary && node.op == 'in') ||
        // (function() { ... })().
        // ({a: 2, b: 3}.toString()).
        (newAtStatementBegin &&
            (node is NamedFunction ||
                node is FunctionExpression ||
                node is ObjectInitializer));
    if (needsParentheses) {
      inForInit = false;
      atStatementBegin = false;
      inNewTarget = false;
      out('(');
      visit(node);
      out(')');
    } else {
      inForInit = newInForInit;
      atStatementBegin = newAtStatementBegin;
      visit(node);
    }
  }

  @override
  void visitVariableDeclarationList(VariableDeclarationList list) {
    // Note: keyword can be null for non-static field declarations.
    if (list.keyword != null) {
      out(list.keyword!);
      out(' ');
    }
    visitCommaSeparated(
      list.declarations,
      ASSIGNMENT,
      newInForInit: inForInit,
      newAtStatementBegin: false,
    );
  }

  @override
  void visitArrayBindingPattern(ArrayBindingPattern node) {
    out('[');
    visitCommaSeparated(
      node.variables,
      EXPRESSION,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    out(']');
  }

  @override
  void visitObjectBindingPattern(ObjectBindingPattern node) {
    out('{');
    visitCommaSeparated(
      node.variables,
      EXPRESSION,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    out('}');
  }

  @override
  void visitDestructuredVariable(DestructuredVariable node) {
    var name = node.name;
    var property = node.property;
    visit(name);
    if (property != null) {
      out('[');
      visit(property);
      out(']');
    }
    var structure = node.structure;
    if (structure != null) {
      if (property != null) {
        out(':');
        spaceOut();
      }
      visit(structure);
    }
    var defaultValue = node.defaultValue;
    if (defaultValue != null) {
      spaceOut();
      out('=');
      spaceOut();
      visitNestedExpression(
        defaultValue,
        EXPRESSION,
        newInForInit: false,
        newAtStatementBegin: false,
      );
    }
  }

  @override
  void visitSimpleBindingPattern(SimpleBindingPattern node) {
    visit(node.name);
  }

  @override
  void visitAssignment(Assignment assignment) {
    visitNestedExpression(
      assignment.leftHandSide,
      LEFT_HAND_SIDE,
      newInForInit: inForInit,
      newAtStatementBegin: atStatementBegin,
    );
    spaceOut();
    String? op = assignment.op;
    if (op != null) out(op);
    out('=');
    spaceOut();
    visitNestedExpression(
      assignment.value,
      ASSIGNMENT,
      newInForInit: inForInit,
      newAtStatementBegin: false,
    );
  }

  @override
  void visitVariableInitialization(VariableInitialization initialization) {
    visitNestedExpression(
      initialization.declaration,
      LEFT_HAND_SIDE,
      newInForInit: inForInit,
      newAtStatementBegin: atStatementBegin,
    );
    if (initialization.value != null) {
      spaceOut();
      out('=');
      spaceOut();
      visitNestedExpression(
        initialization.value!,
        ASSIGNMENT,
        newInForInit: inForInit,
        newAtStatementBegin: false,
      );
    }
  }

  @override
  void visitConditional(Conditional cond) {
    visitNestedExpression(
      cond.condition,
      LOGICAL_OR,
      newInForInit: inForInit,
      newAtStatementBegin: atStatementBegin,
    );
    spaceOut();
    out('?');
    spaceOut();
    // The then part is allowed to have an 'in'.
    visitNestedExpression(
      cond.then,
      ASSIGNMENT,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    context.expressionBranch();
    spaceOut();
    out(':');
    spaceOut();
    visitNestedExpression(
      cond.otherwise,
      ASSIGNMENT,
      newInForInit: inForInit,
      newAtStatementBegin: false,
    );
    context.expressionJoin();
  }

  @override
  void visitNew(New node) {
    out('new ');
    inNewTarget = true;
    visitNestedExpression(
      node.target,
      ACCESS,
      newInForInit: inForInit,
      newAtStatementBegin: false,
    );
    inNewTarget = false;
    out('(');
    visitCommaSeparated(
      node.arguments,
      SPREAD,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    out(')');
  }

  @override
  void visitCall(Call call) {
    visitNestedExpression(
      call.target,
      LEFT_HAND_SIDE,
      newInForInit: inForInit,
      newAtStatementBegin: atStatementBegin,
    );
    out('(');
    visitCommaSeparated(
      call.arguments,
      SPREAD,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    out(')');
  }

  @override
  void visitBinary(Binary binary) {
    Expression left = binary.left;
    Expression right = binary.right;
    String op = binary.op;
    int leftPrecedenceRequirement;
    int rightPrecedenceRequirement;
    bool leftSpace = true; // left<HERE>op right
    switch (op) {
      case ',':
        //  x, (y, z) <=> (x, y), z.
        leftPrecedenceRequirement = EXPRESSION;
        rightPrecedenceRequirement = EXPRESSION;
        leftSpace = false;
        break;
      case '||':
        leftPrecedenceRequirement = LOGICAL_OR;
        // x || (y || z) <=> (x || y) || z.
        rightPrecedenceRequirement = LOGICAL_OR;
        break;
      case '&&':
        leftPrecedenceRequirement = LOGICAL_AND;
        // x && (y && z) <=> (x && y) && z.
        rightPrecedenceRequirement = LOGICAL_AND;
        break;
      case '|':
        leftPrecedenceRequirement = BIT_OR;
        // x | (y | z) <=> (x | y) | z.
        rightPrecedenceRequirement = BIT_OR;
        break;
      case '^':
        leftPrecedenceRequirement = BIT_XOR;
        // x ^ (y ^ z) <=> (x ^ y) ^ z.
        rightPrecedenceRequirement = BIT_XOR;
        break;
      case '&':
        leftPrecedenceRequirement = BIT_AND;
        // x & (y & z) <=> (x & y) & z.
        rightPrecedenceRequirement = BIT_AND;
        break;
      case '==':
      case '!=':
      case '===':
      case '!==':
        leftPrecedenceRequirement = EQUALITY;
        rightPrecedenceRequirement = RELATIONAL;
        break;
      case '<':
      case '>':
      case '<=':
      case '>=':
      case 'instanceof':
      case 'in':
        leftPrecedenceRequirement = RELATIONAL;
        rightPrecedenceRequirement = SHIFT;
        break;
      case '>>':
      case '<<':
      case '>>>':
        leftPrecedenceRequirement = SHIFT;
        rightPrecedenceRequirement = ADDITIVE;
        break;
      case '+':
      case '-':
        leftPrecedenceRequirement = ADDITIVE;
        // We cannot remove parenthesis for "+" because
        //   x + (y + z) <!=> (x + y) + z:
        // Example:
        //   "a" + (1 + 2) => "a3";
        //   ("a" + 1) + 2 => "a12";
        rightPrecedenceRequirement = MULTIPLICATIVE;
        break;
      case '*':
      case '/':
      case '%':
        leftPrecedenceRequirement = MULTIPLICATIVE;
        // We cannot remove parenthesis for "*" because of precision issues.
        rightPrecedenceRequirement = UNARY;
        break;
      case '**':
        // 'a ** b ** c' parses as 'a ** (b ** c)', so the left must have higher
        // precedence.
        leftPrecedenceRequirement = UNARY;
        rightPrecedenceRequirement = EXPONENTIATION;
        break;
      default:
        leftPrecedenceRequirement = EXPRESSION;
        rightPrecedenceRequirement = EXPRESSION;
        context.error('Forgot operator: $op');
    }

    visitNestedExpression(
      left,
      leftPrecedenceRequirement,
      newInForInit: inForInit,
      newAtStatementBegin: atStatementBegin,
    );

    if (op == 'in' || op == 'instanceof') {
      // There are cases where the space is not required but without further
      // analysis we cannot know.
      out(' ');
      out(op);
      out(' ');
    } else {
      if (leftSpace) spaceOut();
      out(op);
      spaceOut();
    }
    visitNestedExpression(
      right,
      rightPrecedenceRequirement,
      newInForInit: inForInit,
      newAtStatementBegin: false,
    );
  }

  @override
  void visitPrefix(Prefix unary) {
    String op = unary.op;
    switch (op) {
      case 'delete':
      case 'void':
      case 'typeof':
        // There are cases where the space is not required but without further
        // analysis we cannot know.
        out(op);
        out(' ');
        break;
      case '+':
      case '++':
        if (lastCharCode == char_codes.$PLUS) out(' ');
        out(op);
        break;
      case '-':
      case '--':
        if (lastCharCode == char_codes.$MINUS) out(' ');
        out(op);
        break;
      default:
        out(op);
    }
    visitNestedExpression(
      unary.argument,
      unary.precedenceLevel,
      newInForInit: inForInit,
      newAtStatementBegin: false,
    );
  }

  @override
  void visitSpread(Spread unary) => visitPrefix(unary);

  @override
  void visitYield(Yield yield) {
    out(yield.star ? 'yield*' : 'yield');
    if (yield.value == null) return;
    out(' ');
    visitNestedExpression(
      yield.value!,
      yield.precedenceLevel,
      newInForInit: inForInit,
      newAtStatementBegin: false,
    );
  }

  @override
  void visitPostfix(Postfix postfix) {
    visitNestedExpression(
      postfix.argument,
      LEFT_HAND_SIDE,
      newInForInit: inForInit,
      newAtStatementBegin: atStatementBegin,
    );
    out(postfix.op);
  }

  @override
  void visitThis(This node) {
    out('this');
  }

  @override
  void visitSuper(Super node) {
    out('super');
  }

  @override
  void visitIdentifier(Identifier node) {
    out(localNamer.getName(node));
  }

  @override
  void visitRestParameter(RestParameter node) {
    out('...');
    visitIdentifier(node.parameter);
  }

  bool isDigit(int charCode) {
    return char_codes.$0 <= charCode && charCode <= char_codes.$9;
  }

  bool isValidJavaScriptId(String field) {
    if (field.length < 3) return false;
    // Ignore the leading and trailing string-delimiter.
    for (int i = 1; i < field.length - 1; i++) {
      // TODO(floitsch): allow more characters.
      int charCode = field.codeUnitAt(i);
      if (!(char_codes.$a <= charCode && charCode <= char_codes.$z ||
          char_codes.$A <= charCode && charCode <= char_codes.$Z ||
          charCode == char_codes.$$ ||
          charCode == char_codes.$_ ||
          i != 1 && isDigit(charCode))) {
        return false;
      }
    }
    // TODO(floitsch): normally we should also check that the field is not a
    // reserved word.  We don't generate fields with reserved word names except
    // for 'super'.
    return options.allowKeywordsInProperties || field != '"super"';
  }

  @override
  void visitAccess(PropertyAccess access) {
    /// Normally we can omit parens on the receiver if it is a Call, even though
    /// Call expressions have lower precedence.
    ///
    /// However this optimization doesn't work inside New expressions:
    ///
    ///     new obj.foo().bar()
    ///
    /// This will be parsed as:
    ///
    ///     (new obj.foo()).bar()
    ///
    /// Which is incorrect. So we must have parenthesis in this case:
    ///
    ///     new (obj.foo()).bar()
    ///
    int precedence = inNewTarget ? ACCESS : CALL;

    visitNestedExpression(
      access.receiver,
      precedence,
      newInForInit: inForInit,
      newAtStatementBegin: atStatementBegin,
    );
    propertyNameOut(access.selector, inAccess: true);
  }

  @override
  void visitNamedFunction(NamedFunction namedFunction) {
    var f = namedFunction.function;
    context.enterNode(f);
    functionOut(f, namedFunction.name);
    context.exitNode(f);
  }

  @override
  void visitFun(Fun fun) {
    functionOut(fun, null);
  }

  @override
  void visitArrowFun(ArrowFun fun) {
    localNamer.enterScope(fun);
    if (fun.params.length == 1 && fun.params[0] is Identifier) {
      visitNestedExpression(
        fun.params.single,
        SPREAD,
        newInForInit: false,
        newAtStatementBegin: false,
      );
    } else {
      out('(');
      visitCommaSeparated(
        fun.params,
        SPREAD,
        newInForInit: false,
        newAtStatementBegin: false,
      );
      out(')');
    }
    spaceOut();
    out('=>');
    var body = fun.body;
    if (body is Expression) {
      spaceOut();
      // Object initializers require parentheses to disambiguate
      // AssignmentExpression from FunctionBody. See:
      // https://tc39.github.io/ecma262/#sec-arrow-function-definitions
      var needsParen = body is ObjectInitializer;
      if (needsParen) out('(');
      visitNestedExpression(
        body,
        ASSIGNMENT,
        newInForInit: false,
        newAtStatementBegin: false,
      );
      if (needsParen) out(')');
    } else {
      blockBody(body as Block, needsSeparation: false, needsNewline: false);
    }
    localNamer.leaveScope();
  }

  @override
  void visitLiteralBool(LiteralBool node) {
    out(node.value ? 'true' : 'false');
  }

  @override
  void visitLiteralString(LiteralString node) {
    out(node.value);
  }

  @override
  void visitLiteralNumber(LiteralNumber node) {
    int charCode = node.value.codeUnitAt(0);
    if (charCode == char_codes.$MINUS && lastCharCode == char_codes.$MINUS) {
      out(' ');
    }
    out(node.value);
  }

  @override
  void visitLiteralNull(LiteralNull node) {
    out('null');
  }

  @override
  void visitArrayInitializer(ArrayInitializer node) {
    out('[');
    indentMore();
    var multiline = node.multiline;
    List<Expression> elements = node.elements;
    for (int i = 0; i < elements.length; i++) {
      Expression element = elements[i];
      if (element is ArrayHole) {
        // Note that array holes must have a trailing "," even if they are
        // in last position. Otherwise `[,]` (having length 1) would become
        // equal to `[]` (the empty array)
        // and [1,,] (array with 1 and a hole) would become [1,] = [1].
        out(',');
        continue;
      }
      if (i != 0 && !multiline) spaceOut();
      if (multiline) {
        forceLine();
        indent();
      }
      visitNestedExpression(
        element,
        ASSIGNMENT,
        newInForInit: false,
        newAtStatementBegin: false,
      );
      // We can skip the trailing "," for the last element (since it's not
      // an array hole).
      if (i != elements.length - 1) out(',');
    }
    indentLess();
    if (multiline) {
      lineOut();
      indent();
    }
    out(']');
  }

  @override
  void visitArrayHole(ArrayHole node) {
    throw 'Unreachable';
  }

  @override
  void visitObjectInitializer(ObjectInitializer node) {
    List<Property> properties = node.properties;
    out('{');
    indentMore();

    var multiline = node.multiline;
    for (int i = 0; i < properties.length; i++) {
      if (i != 0) {
        out(',');
        if (!multiline) spaceOut();
      }
      if (multiline) {
        forceLine();
        indent();
      }
      visit(properties[i]);
    }
    indentLess();
    if (multiline) {
      lineOut();
      indent();
    }
    out('}');
  }

  @override
  void visitProperty(Property node) {
    if (node.isStatic) {
      out('static ');
    }
    propertyNameOut(node.name);
    if (node.isClassProperty) {
      out(' =');
    } else {
      out(':');
    }
    spaceOut();
    visitNestedExpression(
      node.value,
      ASSIGNMENT,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    if (node.isClassProperty) {
      out(';');
    }
  }

  @override
  void visitRegExpLiteral(RegExpLiteral node) {
    out(node.pattern);
  }

  @override
  void visitTemplateString(TemplateString node) {
    out('`');
    int len = node.interpolations.length;
    for (var i = 0; i < len; i++) {
      out(node.strings[i]);
      out(r'${');
      visit(node.interpolations[i]);
      out('}');
    }
    out(node.strings[len]);
    out('`');
  }

  @override
  void visitTaggedTemplate(TaggedTemplate node) {
    visit(node.tag);
    visit(node.template);
  }

  @override
  void visitClassDeclaration(ClassDeclaration node) {
    indent();
    visit(node.classExpr);
    lineOut();
  }

  @override
  void visitClassExpression(ClassExpression node) {
    localNamer.enterScope(node);
    out('class ');
    visit(node.name);
    if (node.heritage != null) {
      out(' extends ');
      visit(node.heritage!);
    }
    spaceOut();
    if (node.properties.isNotEmpty) {
      out('{');
      lineOut();
      indentMore();
      for (var property in node.properties) {
        indent();
        visit(property);
        lineOut();
      }
      indentLess();
      indent();
      out('}');
    } else {
      out('{}');
    }
    localNamer.leaveScope();
  }

  @override
  void visitMethod(Method node) {
    if (node.isStatic) {
      out('static ');
    }
    if (node.isGetter) {
      out('get ');
    } else if (node.isSetter) {
      out('set ');
    } else if (node.function.isGenerator) {
      out('*');
    }
    propertyNameOut(node.name, inMethod: true);

    var fun = node.function;
    localNamer.enterScope(fun);
    out('(');
    visitCommaSeparated(
      fun.params,
      SPREAD,
      newInForInit: false,
      newAtStatementBegin: false,
    );
    out(')');
    // TODO(jmesserly): async modifiers
    if (fun.body.statements.isEmpty) {
      spaceOut();
      out('{}');
    } else {
      spaceOut();
      blockOut(fun.body, shouldIndent: false, needsNewline: false);
    }
    localNamer.leaveScope();
  }

  void propertyNameOut(
    Expression node, {
    bool inMethod = false,
    bool inAccess = false,
  }) {
    if (node is LiteralNumber) {
      LiteralNumber nameNumber = node;
      if (inAccess) out('[');
      out(nameNumber.value);
      if (inAccess) out(']');
    } else {
      if (node is LiteralString) {
        if (isValidJavaScriptId(node.value)) {
          if (inAccess) out('.');
          out(node.valueWithoutQuotes);
        } else {
          if (inMethod || inAccess) out('[');
          out(node.value);
          if (inMethod || inAccess) out(']');
        }
      } else {
        // ComputedPropertyName
        out('[');
        visitNestedExpression(
          node,
          EXPRESSION,
          newInForInit: false,
          newAtStatementBegin: false,
        );
        out(']');
      }
    }
  }

  @override
  void visitImportDeclaration(ImportDeclaration node) {
    indent();
    out('import ');
    if (node.defaultBinding != null) {
      visit(node.defaultBinding!);
      if (node.namedImports != null) {
        out(',');
        spaceOut();
      }
    }
    if (node.namedImports != null) {
      nameSpecifierListOut(node.namedImports!, false);
    }
    fromClauseOut(node.from);
    outSemicolonLn();
  }

  @override
  void visitExportDeclaration(ExportDeclaration node) {
    indent();
    out('export ');
    if (node.isDefault) out('default ');
    // TODO(jmesserly): we need to avoid indent/newline if this is a statement.
    visit(node.exported);
    outSemicolonLn();
  }

  @override
  void visitExportClause(ExportClause node) {
    nameSpecifierListOut(node.exports, true);
    if (node.from != null) {
      fromClauseOut(node.from!);
    }
  }

  void nameSpecifierListOut(List<NameSpecifier> names, bool export) {
    if (names.length == 1 && names[0].name!.name == '*') {
      nameSpecifierOut(names[0], export);
      return;
    }

    out('{');
    spaceOut();
    for (int i = 0; i < names.length; i++) {
      if (i != 0) {
        out(',');
        spaceOut();
      }
      nameSpecifierOut(names[i], export);
    }
    spaceOut();
    out('}');
  }

  void fromClauseOut(LiteralString from) {
    out(' from');
    spaceOut();
    out("'${from.valueWithoutQuotes}.js'");
  }

  /// This is unused, see [nameSpecifierOut].
  @override
  void visitNameSpecifier(NameSpecifier node) {
    throw UnsupportedError('visitNameSpecifier');
  }

  void nameSpecifierOut(NameSpecifier node, bool export) {
    if (node.isStar) {
      out('*');
    } else {
      assert(node.name != null);
      var nodeName = node.name!;
      var localName = localNamer.getName(nodeName);
      if (node.asName == null) {
        // If our local was renamed, generate an implicit "as".
        // This is a convenience feature so imports and exports can be renamed.
        var name = nodeName.name;
        if (localName != name) {
          out(export ? localName : name);
          out(' as ');
          out(export ? name : localName);
          return;
        }
      }
      out(localName);
    }
    if (node.asName != null) {
      out(' as ');
      visitIdentifier(node.asName!);
    }
  }

  @override
  void visitLiteralExpression(LiteralExpression node) {
    out(node.template);
  }

  @override
  void visitLiteralStatement(LiteralStatement node) {
    outLn(node.code);
  }

  void visitInterpolatedNode(InterpolatedNode node) {
    out('#${node.nameOrPosition}');
  }

  @override
  void visitInterpolatedExpression(InterpolatedExpression node) =>
      visitInterpolatedNode(node);

  @override
  void visitInterpolatedLiteral(InterpolatedLiteral node) =>
      visitInterpolatedNode(node);

  @override
  void visitInterpolatedParameter(InterpolatedParameter node) =>
      visitInterpolatedNode(node);

  @override
  void visitInterpolatedSelector(InterpolatedSelector node) =>
      visitInterpolatedNode(node);

  @override
  void visitInterpolatedMethod(InterpolatedMethod node) =>
      visitInterpolatedNode(node);

  @override
  void visitInterpolatedIdentifier(InterpolatedIdentifier node) =>
      visitInterpolatedNode(node);

  @override
  void visitInterpolatedStatement(InterpolatedStatement node) {
    outLn('#${node.nameOrPosition}');
  }

  @override
  void visitComment(Comment node) {
    if (shouldCompressOutput) return;
    String comment = node.comment.trim();
    if (comment.isEmpty) return;
    for (var line in comment.split('\n')) {
      if (comment.startsWith('//')) {
        outIndentLn(line.trim());
      } else {
        outIndentLn('// ${line.trim()}');
      }
    }
  }

  @override
  void visitCommentExpression(CommentExpression node) {
    if (shouldCompressOutput) return;
    String comment = node.comment.trim();
    if (comment.isEmpty) return;
    if (comment.startsWith('/*')) {
      out(comment);
    } else {
      out('/* $comment */');
    }
    visit(node.expression);
  }

  @override
  void visitAwait(Await node) {
    out('await ');
    visit(node.expression);
  }
}

// Collects all the var declarations in the function.  We need to do this in a
// separate pass because JS vars are lifted to the top of the function.
class VarCollector extends BaseVisitorVoid {
  bool nested;
  final Set<String> vars;
  final Set<String> params;

  VarCollector() : nested = false, vars = {}, params = {};

  void forEachVar(void Function(String) fn) => vars.forEach(fn);
  void forEachParam(void Function(String) fn) => params.forEach(fn);

  void collectVarsInFunction(FunctionExpression fun) {
    if (!nested) {
      nested = true;
      for (var param in fun.params) {
        // TODO(jmesserly): add ES6 support. Currently not needed because
        // dart2js does not emit ES6 rest param or destructuring.
        params.add((param as Identifier).name);
      }
      fun.body.accept(this);
      nested = false;
    }
  }

  @override
  void visitFunctionDeclaration(FunctionDeclaration declaration) {
    // Note that we don't bother collecting the name of the function.
    collectVarsInFunction(declaration.function);
  }

  @override
  void visitNamedFunction(NamedFunction namedFunction) {
    // Note that we don't bother collecting the name of the function.
    collectVarsInFunction(namedFunction.function);
  }

  @override
  void visitMethod(Method declaration) {
    collectVarsInFunction(declaration.function);
  }

  @override
  void visitFun(Fun fun) {
    collectVarsInFunction(fun);
  }

  @override
  void visitArrowFun(ArrowFun fun) {
    collectVarsInFunction(fun);
  }

  @override
  void visitClassExpression(ClassExpression node) {
    // Note that we don't bother collecting the name of the class.
    node.heritage?.accept(this);
    for (Property method in node.properties) {
      method.accept(this);
    }
  }

  @override
  void visitCatch(Catch node) {
    declareVariable(node.declaration);
    node.body.accept(this);
  }

  @override
  void visitVariableInitialization(VariableInitialization node) {
    // TODO(jmesserly): add ES6 support. Currently not needed because
    // dart2js does not emit ES6 rest param or destructuring.
    declareVariable(node.declaration as Identifier);
    node.value?.accept(this);
  }

  void declareVariable(Identifier decl) {
    if (decl.allowRename) vars.add(decl.name);
  }
}

/// Returns true, if the given node must be wrapped into braces when used
/// as then-statement in an [If] that has an else branch.
class DanglingElseVisitor extends BaseVisitor<bool> {
  JavaScriptPrintingContext context;

  DanglingElseVisitor(this.context);

  @override
  bool visitProgram(Program node) => false;

  @override
  bool visitNode(Node node) {
    context.error('Forgot node: $node');
    return true;
  }

  @override
  bool visitBlock(Block node) => false;
  @override
  bool visitComment(Comment node) => true;
  @override
  bool visitCommentExpression(CommentExpression node) => true;
  @override
  bool visitExpressionStatement(ExpressionStatement node) => false;
  @override
  bool visitEmptyStatement(EmptyStatement node) => false;
  @override
  bool visitIf(If node) {
    if (!node.hasElse) return true;
    return node.otherwise.accept(this);
  }

  @override
  bool visitFor(For node) => node.body.accept(this);
  @override
  bool visitForIn(ForIn node) => node.body.accept(this);
  @override
  bool visitForOf(ForOf node) => node.body.accept(this);
  @override
  bool visitWhile(While node) => node.body.accept(this);
  @override
  bool visitDo(Do node) => false;
  @override
  bool visitContinue(Continue node) => false;
  @override
  bool visitBreak(Break node) => false;
  @override
  bool visitReturn(Return node) => false;
  @override
  bool visitThrow(Throw node) => false;
  @override
  bool visitTry(Try node) {
    if (node.finallyPart != null) {
      return node.finallyPart!.accept(this);
    } else {
      return node.catchPart!.accept(this);
    }
  }

  @override
  bool visitCatch(Catch node) => node.body.accept(this);
  @override
  bool visitSwitch(Switch node) => false;
  @override
  bool visitCase(Case node) => false;
  @override
  bool visitDefault(Default node) => false;
  @override
  bool visitFunctionDeclaration(FunctionDeclaration node) => false;
  @override
  bool visitLabeledStatement(LabeledStatement node) => node.body.accept(this);
  @override
  bool visitLiteralStatement(LiteralStatement node) => true;
  @override
  bool visitClassDeclaration(ClassDeclaration node) => false;

  @override
  bool visitExpression(Expression node) => false;
}

abstract class LocalNamer {
  String getName(Identifier node);
  void enterScope(Node node);
  void leaveScope();
}

class IdentityNamer implements LocalNamer {
  @override
  String getName(Identifier node) => node.name;
  @override
  void enterScope(Node node) {}
  @override
  void leaveScope() {}
}

class MinifyRenamer implements LocalNamer {
  final List<Map<String, String>> maps = [];
  final List<int> parameterNumberStack = [];
  final List<int> variableNumberStack = [];
  int parameterNumber = 0;
  int variableNumber = 0;

  @override
  void enterScope(Node node) {
    var vars = VarCollector();
    node.accept(vars);
    maps.add({});
    variableNumberStack.add(variableNumber);
    parameterNumberStack.add(parameterNumber);
    vars.forEachVar(declareVariable);
    vars.forEachParam(declareParameter);
  }

  @override
  void leaveScope() {
    maps.removeLast();
    variableNumber = variableNumberStack.removeLast();
    parameterNumber = parameterNumberStack.removeLast();
  }

  @override
  String getName(Identifier node) {
    String oldName = node.name;
    // Go from inner scope to outer looking for mapping of name.
    for (int i = maps.length - 1; i >= 0; i--) {
      var map = maps[i];
      var replacement = map[oldName];
      if (replacement != null) return replacement;
    }
    return oldName;
  }

  static const LOWER_CASE_LETTERS = 26;
  static const LETTERS = LOWER_CASE_LETTERS;
  static const DIGITS = 10;

  static int nthLetter(int n) {
    return (n < LOWER_CASE_LETTERS)
        ? char_codes.$a + n
        : char_codes.$A + n - LOWER_CASE_LETTERS;
  }

  // Parameters go from a to z and variables go from z to a.  This makes each
  // argument list and each top-of-function var declaration look similar and
  // helps gzip compress the file.  If we have more than 26 arguments and
  // variables then we meet somewhere in the middle of the alphabet.  After
  // that we give up trying to be nice to the compression algorithm and just
  // use the same namespace for arguments and variables, starting with A, and
  // moving on to a0, a1, etc.
  String declareVariable(String oldName) {
    if (avoidRenaming(oldName)) return oldName;
    String newName;
    if (variableNumber + parameterNumber < LOWER_CASE_LETTERS) {
      // Variables start from z and go backwards, for better gzipability.
      newName = getNameNumber(oldName, LOWER_CASE_LETTERS - 1 - variableNumber);
    } else {
      // After 26 variables and parameters we allocate them in the same order.
      newName = getNameNumber(oldName, variableNumber + parameterNumber);
    }
    variableNumber++;
    return newName;
  }

  String declareParameter(String oldName) {
    if (avoidRenaming(oldName)) return oldName;
    String newName;
    if (variableNumber + parameterNumber < LOWER_CASE_LETTERS) {
      newName = getNameNumber(oldName, parameterNumber);
    } else {
      newName = getNameNumber(oldName, variableNumber + parameterNumber);
    }
    parameterNumber++;
    return newName;
  }

  bool avoidRenaming(String oldName) {
    // Variables of this $form$ are used in pattern matching the message of JS
    // exceptions, so should not be renamed.
    // TODO(sra): Introduce a way for indicating in the JS text which variables
    // should not be renamed.
    return oldName.startsWith(r'$') && oldName.endsWith(r'$');
  }

  String getNameNumber(String oldName, int n) {
    if (maps.isEmpty) return oldName;

    String newName;
    if (n < LETTERS) {
      // Start naming variables a, b, c, ..., z, A, B, C, ..., Z.
      newName = String.fromCharCodes([nthLetter(n)]);
    } else {
      // Then name variables a0, a1, a2, ..., a9, b0, b1, ..., Z9, aa0, aa1, ...
      // For all functions with fewer than 500 locals this is just as compact
      // as using aa, ab, etc. but avoids clashes with keywords.
      n -= LETTERS;
      int digit = n % DIGITS;
      n ~/= DIGITS;
      int alphaChars = 1;
      int nameSpaceSize = LETTERS;
      // Find out whether we should use the 1-character namespace (size 52), the
      // 2-character namespace (size 52*52), etc.
      while (n >= nameSpaceSize) {
        n -= nameSpaceSize;
        alphaChars++;
        nameSpaceSize *= LETTERS;
      }
      var codes = <int>[];
      for (var i = 0; i < alphaChars; i++) {
        nameSpaceSize ~/= LETTERS;
        codes.add(nthLetter((n ~/ nameSpaceSize) % LETTERS));
      }
      codes.add(char_codes.$0 + digit);
      newName = String.fromCharCodes(codes);
    }
    assert(RegExp(r'[a-zA-Z][a-zA-Z0-9]*').hasMatch(newName));
    maps.last[oldName] = newName;
    return newName;
  }
}

/// Like [BaseVisitor], but calls [declare] for [Identifier] declarations, and
/// [visitIdentifier] otherwise.
abstract class VariableDeclarationVisitor extends BaseVisitorVoid {
  bool _inImportDeclaration = false;

  void declare(Identifier node);

  @override
  void visitFunctionExpression(FunctionExpression node) {
    node.params.forEach(_scanVariableBinding);
    node.body.accept(this);
  }

  void _scanVariableBinding(VariableBinding d) {
    if (d is Identifier) {
      declare(d);
    } else {
      d.accept(this);
    }
  }

  @override
  void visitRestParameter(RestParameter node) {
    _scanVariableBinding(node.parameter);
    super.visitRestParameter(node);
  }

  @override
  void visitDestructuredVariable(DestructuredVariable node) {
    var name = node.name;
    _scanVariableBinding(name);
    super.visitDestructuredVariable(node);
  }

  @override
  void visitSimpleBindingPattern(SimpleBindingPattern node) {
    _scanVariableBinding(node.name);
    super.visitSimpleBindingPattern(node);
  }

  @override
  void visitVariableInitialization(VariableInitialization node) {
    _scanVariableBinding(node.declaration);
    node.value?.accept(this);
  }

  @override
  void visitCatch(Catch node) {
    declare(node.declaration);
    node.body.accept(this);
  }

  @override
  void visitFunctionDeclaration(FunctionDeclaration node) {
    declare(node.name);
    node.function.accept(this);
  }

  @override
  void visitNamedFunction(NamedFunction node) {
    declare(node.name);
    node.function.accept(this);
  }

  @override
  void visitClassExpression(ClassExpression node) {
    declare(node.name);
    node.heritage?.accept(this);
    for (Property element in node.properties) {
      element.accept(this);
    }
  }

  @override
  void visitImportDeclaration(ImportDeclaration node) {
    if (node.defaultBinding != null) {
      declare(node.defaultBinding!);
    }
    if (node.namedImports != null) {
      _inImportDeclaration = true;
      for (var namedImport in node.namedImports!) {
        namedImport.accept(this);
      }
      _inImportDeclaration = false;
    }
  }

  @override
  void visitNameSpecifier(NameSpecifier node) {
    final asName = node.asName;
    // The specified 'as' name only declares a local name in the context of an
    // import.
    if (_inImportDeclaration && asName != null) {
      declare(asName);
    }
    node.name?.accept(this);
  }
}