ast.js

/***********************************************************************

  A JavaScript tokenizer / parser / beautifier / compressor.
  https://github.com/mishoo/UglifyJS2

  -------------------------------- (C) ---------------------------------

                           Author: Mihai Bazon
                         <mihai.bazon@gmail.com>
                       http://mihai.bazon.net/blog

  Distributed under the BSD license:

    Copyright 2012 (c) Mihai Bazon <mihai.bazon@gmail.com>

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

        * Redistributions of source code must retain the above
          copyright notice, this list of conditions and the following
          disclaimer.

        * Redistributions in binary form must reproduce the above
          copyright notice, this list of conditions and the following
          disclaimer in the documentation and/or other materials
          provided with the distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER “AS IS” AND ANY
    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
    PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE
    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
    TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
    THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
    SUCH DAMAGE.

 ***********************************************************************/

import {
    HOP,
    MAP,
    noop
} from "./utils/index.js";
import { parse } from "./parse.js";

function DEFNODE(type, props, methods, base = AST_Node) {
    if (!props) props = [];
    else props = props.split(/\s+/);
    var self_props = props;
    if (base && base.PROPS)
        props = props.concat(base.PROPS);
    var code = "return function AST_" + type + "(props){ if (props) { ";
    for (var i = props.length; --i >= 0;) {
        code += "this." + props[i] + " = props." + props[i] + ";";
    }
    const proto = base && Object.create(base.prototype);
    if (proto && proto.initialize || (methods && methods.initialize))
        code += "this.initialize();";
    code += "}";
    code += "this.flags = 0;";
    code += "}";
    var ctor = new Function(code)();
    if (proto) {
        ctor.prototype = proto;
        ctor.BASE = base;
    }
    if (base) base.SUBCLASSES.push(ctor);
    ctor.prototype.CTOR = ctor;
    ctor.prototype.constructor = ctor;
    ctor.PROPS = props || null;
    ctor.SELF_PROPS = self_props;
    ctor.SUBCLASSES = [];
    if (type) {
        ctor.prototype.TYPE = ctor.TYPE = type;
    }
    if (methods) for (i in methods) if (HOP(methods, i)) {
        if (i[0] === "$") {
            ctor[i.substr(1)] = methods[i];
        } else {
            ctor.prototype[i] = methods[i];
        }
    }
    ctor.DEFMETHOD = function(name, method) {
        this.prototype[name] = method;
    };
    return ctor;
}

const has_tok_flag = (tok, flag) => Boolean(tok.flags & flag);
const set_tok_flag = (tok, flag, truth) => {
    if (truth) {
        tok.flags |= flag;
    } else {
        tok.flags &= ~flag;
    }
};

const TOK_FLAG_NLB          = 0b0001;
const TOK_FLAG_QUOTE_SINGLE = 0b0010;
const TOK_FLAG_QUOTE_EXISTS = 0b0100;

class AST_Token {
    constructor(type, value, line, col, pos, nlb, comments_before, comments_after, file) {
        this.flags = (nlb ? 1 : 0);

        this.type = type;
        this.value = value;
        this.line = line;
        this.col = col;
        this.pos = pos;
        this.comments_before = comments_before;
        this.comments_after = comments_after;
        this.file = file;

        Object.seal(this);
    }

    get nlb() {
        return has_tok_flag(this, TOK_FLAG_NLB);
    }

    set nlb(new_nlb) {
        set_tok_flag(this, TOK_FLAG_NLB, new_nlb);
    }

    get quote() {
        return !has_tok_flag(this, TOK_FLAG_QUOTE_EXISTS)
            ? ""
            : (has_tok_flag(this, TOK_FLAG_QUOTE_SINGLE) ? "'" : '"');
    }

    set quote(quote_type) {
        set_tok_flag(this, TOK_FLAG_QUOTE_SINGLE, quote_type === "'");
        set_tok_flag(this, TOK_FLAG_QUOTE_EXISTS, !!quote_type);
    }
}

var AST_Node = DEFNODE("Node", "start end", {
    _clone: function(deep) {
        if (deep) {
            var self = this.clone();
            return self.transform(new TreeTransformer(function(node) {
                if (node !== self) {
                    return node.clone(true);
                }
            }));
        }
        return new this.CTOR(this);
    },
    clone: function(deep) {
        return this._clone(deep);
    },
    $documentation: "Base class of all AST nodes",
    $propdoc: {
        start: "[AST_Token] The first token of this node",
        end: "[AST_Token] The last token of this node"
    },
    _walk: function(visitor) {
        return visitor._visit(this);
    },
    walk: function(visitor) {
        return this._walk(visitor); // not sure the indirection will be any help
    },
    _children_backwards: () => {}
}, null);

/* -----[ statements ]----- */

var AST_Statement = DEFNODE("Statement", null, {
    $documentation: "Base class of all statements",
});

var AST_Debugger = DEFNODE("Debugger", null, {
    $documentation: "Represents a debugger statement",
}, AST_Statement);

var AST_Directive = DEFNODE("Directive", "value quote", {
    $documentation: "Represents a directive, like \"use strict\";",
    $propdoc: {
        value: "[string] The value of this directive as a plain string (it's not an AST_String!)",
        quote: "[string] the original quote character"
    },
}, AST_Statement);

var AST_SimpleStatement = DEFNODE("SimpleStatement", "body", {
    $documentation: "A statement consisting of an expression, i.e. a = 1 + 2",
    $propdoc: {
        body: "[AST_Node] an expression node (should not be instanceof AST_Statement)"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.body._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.body);
    }
}, AST_Statement);

function walk_body(node, visitor) {
    const body = node.body;
    for (var i = 0, len = body.length; i < len; i++) {
        body[i]._walk(visitor);
    }
}

function clone_block_scope(deep) {
    var clone = this._clone(deep);
    if (this.block_scope) {
        clone.block_scope = this.block_scope.clone();
    }
    return clone;
}

var AST_Block = DEFNODE("Block", "body block_scope", {
    $documentation: "A body of statements (usually braced)",
    $propdoc: {
        body: "[AST_Statement*] an array of statements",
        block_scope: "[AST_Scope] the block scope"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            walk_body(this, visitor);
        });
    },
    _children_backwards(push) {
        let i = this.body.length;
        while (i--) push(this.body[i]);
    },
    clone: clone_block_scope
}, AST_Statement);

var AST_BlockStatement = DEFNODE("BlockStatement", null, {
    $documentation: "A block statement",
}, AST_Block);

var AST_EmptyStatement = DEFNODE("EmptyStatement", null, {
    $documentation: "The empty statement (empty block or simply a semicolon)"
}, AST_Statement);

var AST_StatementWithBody = DEFNODE("StatementWithBody", "body", {
    $documentation: "Base class for all statements that contain one nested body: `For`, `ForIn`, `Do`, `While`, `With`",
    $propdoc: {
        body: "[AST_Statement] the body; this should always be present, even if it's an AST_EmptyStatement"
    }
}, AST_Statement);

var AST_LabeledStatement = DEFNODE("LabeledStatement", "label", {
    $documentation: "Statement with a label",
    $propdoc: {
        label: "[AST_Label] a label definition"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.label._walk(visitor);
            this.body._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.body);
        push(this.label);
    },
    clone: function(deep) {
        var node = this._clone(deep);
        if (deep) {
            var label = node.label;
            var def = this.label;
            node.walk(new TreeWalker(function(node) {
                if (node instanceof AST_LoopControl
                    && node.label && node.label.thedef === def) {
                    node.label.thedef = label;
                    label.references.push(node);
                }
            }));
        }
        return node;
    }
}, AST_StatementWithBody);

var AST_IterationStatement = DEFNODE("IterationStatement", "block_scope", {
    $documentation: "Internal class.  All loops inherit from it.",
    $propdoc: {
        block_scope: "[AST_Scope] the block scope for this iteration statement."
    },
    clone: clone_block_scope
}, AST_StatementWithBody);

var AST_DWLoop = DEFNODE("DWLoop", "condition", {
    $documentation: "Base class for do/while statements",
    $propdoc: {
        condition: "[AST_Node] the loop condition.  Should not be instanceof AST_Statement"
    }
}, AST_IterationStatement);

var AST_Do = DEFNODE("Do", null, {
    $documentation: "A `do` statement",
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.body._walk(visitor);
            this.condition._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.condition);
        push(this.body);
    }
}, AST_DWLoop);

var AST_While = DEFNODE("While", null, {
    $documentation: "A `while` statement",
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.condition._walk(visitor);
            this.body._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.body);
        push(this.condition);
    },
}, AST_DWLoop);

var AST_For = DEFNODE("For", "init condition step", {
    $documentation: "A `for` statement",
    $propdoc: {
        init: "[AST_Node?] the `for` initialization code, or null if empty",
        condition: "[AST_Node?] the `for` termination clause, or null if empty",
        step: "[AST_Node?] the `for` update clause, or null if empty"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            if (this.init) this.init._walk(visitor);
            if (this.condition) this.condition._walk(visitor);
            if (this.step) this.step._walk(visitor);
            this.body._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.body);
        if (this.step) push(this.step);
        if (this.condition) push(this.condition);
        if (this.init) push(this.init);
    },
}, AST_IterationStatement);

var AST_ForIn = DEFNODE("ForIn", "init object", {
    $documentation: "A `for ... in` statement",
    $propdoc: {
        init: "[AST_Node] the `for/in` initialization code",
        object: "[AST_Node] the object that we're looping through"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.init._walk(visitor);
            this.object._walk(visitor);
            this.body._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.body);
        if (this.object) push(this.object);
        if (this.init) push(this.init);
    },
}, AST_IterationStatement);

var AST_ForOf = DEFNODE("ForOf", "await", {
    $documentation: "A `for ... of` statement",
}, AST_ForIn);

var AST_With = DEFNODE("With", "expression", {
    $documentation: "A `with` statement",
    $propdoc: {
        expression: "[AST_Node] the `with` expression"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.expression._walk(visitor);
            this.body._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.body);
        push(this.expression);
    },
}, AST_StatementWithBody);

/* -----[ scope and functions ]----- */

var AST_Scope = DEFNODE("Scope", "variables functions uses_with uses_eval parent_scope enclosed cname", {
    $documentation: "Base class for all statements introducing a lexical scope",
    $propdoc: {
        variables: "[Map/S] a map of name -> SymbolDef for all variables/functions defined in this scope",
        uses_with: "[boolean/S] tells whether this scope uses the `with` statement",
        uses_eval: "[boolean/S] tells whether this scope contains a direct call to the global `eval`",
        parent_scope: "[AST_Scope?/S] link to the parent scope",
        enclosed: "[SymbolDef*/S] a list of all symbol definitions that are accessed from this scope or any subscopes",
        cname: "[integer/S] current index for mangling variables (used internally by the mangler)",
    },
    get_defun_scope: function() {
        var self = this;
        while (self.is_block_scope()) {
            self = self.parent_scope;
        }
        return self;
    },
    clone: function(deep, toplevel) {
        var node = this._clone(deep);
        if (deep && this.variables && toplevel && !this._block_scope) {
            node.figure_out_scope({}, {
                toplevel: toplevel,
                parent_scope: this.parent_scope
            });
        } else {
            if (this.variables) node.variables = new Map(this.variables);
            if (this.enclosed) node.enclosed = this.enclosed.slice();
            if (this._block_scope) node._block_scope = this._block_scope;
        }
        return node;
    },
    pinned: function() {
        return this.uses_eval || this.uses_with;
    }
}, AST_Block);

var AST_Toplevel = DEFNODE("Toplevel", "globals", {
    $documentation: "The toplevel scope",
    $propdoc: {
        globals: "[Map/S] a map of name -> SymbolDef for all undeclared names",
    },
    wrap_commonjs: function(name) {
        var body = this.body;
        var wrapped_tl = "(function(exports){'$ORIG';})(typeof " + name + "=='undefined'?(" + name + "={}):" + name + ");";
        wrapped_tl = parse(wrapped_tl);
        wrapped_tl = wrapped_tl.transform(new TreeTransformer(function(node) {
            if (node instanceof AST_Directive && node.value == "$ORIG") {
                return MAP.splice(body);
            }
        }));
        return wrapped_tl;
    },
    wrap_enclose: function(args_values) {
        if (typeof args_values != "string") args_values = "";
        var index = args_values.indexOf(":");
        if (index < 0) index = args_values.length;
        var body = this.body;
        return parse([
            "(function(",
            args_values.slice(0, index),
            '){"$ORIG"})(',
            args_values.slice(index + 1),
            ")"
        ].join("")).transform(new TreeTransformer(function(node) {
            if (node instanceof AST_Directive && node.value == "$ORIG") {
                return MAP.splice(body);
            }
        }));
    }
}, AST_Scope);

var AST_Expansion = DEFNODE("Expansion", "expression", {
    $documentation: "An expandible argument, such as ...rest, a splat, such as [1,2,...all], or an expansion in a variable declaration, such as var [first, ...rest] = list",
    $propdoc: {
        expression: "[AST_Node] the thing to be expanded"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.expression.walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.expression);
    },
});

var AST_Lambda = DEFNODE("Lambda", "name argnames uses_arguments is_generator async", {
    $documentation: "Base class for functions",
    $propdoc: {
        name: "[AST_SymbolDeclaration?] the name of this function",
        argnames: "[AST_SymbolFunarg|AST_Destructuring|AST_Expansion|AST_DefaultAssign*] array of function arguments, destructurings, or expanding arguments",
        uses_arguments: "[boolean/S] tells whether this function accesses the arguments array",
        is_generator: "[boolean] is this a generator method",
        async: "[boolean] is this method async",
    },
    args_as_names: function () {
        var out = [];
        for (var i = 0; i < this.argnames.length; i++) {
            if (this.argnames[i] instanceof AST_Destructuring) {
                out.push(...this.argnames[i].all_symbols());
            } else {
                out.push(this.argnames[i]);
            }
        }
        return out;
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            if (this.name) this.name._walk(visitor);
            var argnames = this.argnames;
            for (var i = 0, len = argnames.length; i < len; i++) {
                argnames[i]._walk(visitor);
            }
            walk_body(this, visitor);
        });
    },
    _children_backwards(push) {
        let i = this.body.length;
        while (i--) push(this.body[i]);

        i = this.argnames.length;
        while (i--) push(this.argnames[i]);

        if (this.name) push(this.name);
    },
    is_braceless() {
        return this.body[0] instanceof AST_Return && this.body[0].value;
    },
    // Default args and expansion don't count, so .argnames.length doesn't cut it
    length_property() {
        let length = 0;

        for (const arg of this.argnames) {
            if (arg instanceof AST_SymbolFunarg || arg instanceof AST_Destructuring) {
                length++;
            }
        }

        return length;
    }
}, AST_Scope);

var AST_Accessor = DEFNODE("Accessor", null, {
    $documentation: "A setter/getter function.  The `name` property is always null."
}, AST_Lambda);

var AST_Function = DEFNODE("Function", null, {
    $documentation: "A function expression"
}, AST_Lambda);

var AST_Arrow = DEFNODE("Arrow", null, {
    $documentation: "An ES6 Arrow function ((a) => b)"
}, AST_Lambda);

var AST_Defun = DEFNODE("Defun", null, {
    $documentation: "A function definition"
}, AST_Lambda);

/* -----[ DESTRUCTURING ]----- */
var AST_Destructuring = DEFNODE("Destructuring", "names is_array", {
    $documentation: "A destructuring of several names. Used in destructuring assignment and with destructuring function argument names",
    $propdoc: {
        "names": "[AST_Node*] Array of properties or elements",
        "is_array": "[Boolean] Whether the destructuring represents an object or array"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.names.forEach(function(name) {
                name._walk(visitor);
            });
        });
    },
    _children_backwards(push) {
        let i = this.names.length;
        while (i--) push(this.names[i]);
    },
    all_symbols: function() {
        var out = [];
        this.walk(new TreeWalker(function (node) {
            if (node instanceof AST_Symbol) {
                out.push(node);
            }
        }));
        return out;
    }
});

var AST_PrefixedTemplateString = DEFNODE("PrefixedTemplateString", "template_string prefix", {
    $documentation: "A templatestring with a prefix, such as String.raw`foobarbaz`",
    $propdoc: {
        template_string: "[AST_TemplateString] The template string",
        prefix: "[AST_Node] The prefix, which will get called."
    },
    _walk: function(visitor) {
        return visitor._visit(this, function () {
            this.prefix._walk(visitor);
            this.template_string._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.template_string);
        push(this.prefix);
    },
});

var AST_TemplateString = DEFNODE("TemplateString", "segments", {
    $documentation: "A template string literal",
    $propdoc: {
        segments: "[AST_Node*] One or more segments, starting with AST_TemplateSegment. AST_Node may follow AST_TemplateSegment, but each AST_Node must be followed by AST_TemplateSegment."
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.segments.forEach(function(seg) {
                seg._walk(visitor);
            });
        });
    },
    _children_backwards(push) {
        let i = this.segments.length;
        while (i--) push(this.segments[i]);
    }
});

var AST_TemplateSegment = DEFNODE("TemplateSegment", "value raw", {
    $documentation: "A segment of a template string literal",
    $propdoc: {
        value: "Content of the segment",
        raw: "Raw source of the segment",
    }
});

/* -----[ JUMPS ]----- */

var AST_Jump = DEFNODE("Jump", null, {
    $documentation: "Base class for “jumps” (for now that's `return`, `throw`, `break` and `continue`)"
}, AST_Statement);

var AST_Exit = DEFNODE("Exit", "value", {
    $documentation: "Base class for “exits” (`return` and `throw`)",
    $propdoc: {
        value: "[AST_Node?] the value returned or thrown by this statement; could be null for AST_Return"
    },
    _walk: function(visitor) {
        return visitor._visit(this, this.value && function() {
            this.value._walk(visitor);
        });
    },
    _children_backwards(push) {
        if (this.value) push(this.value);
    },
}, AST_Jump);

var AST_Return = DEFNODE("Return", null, {
    $documentation: "A `return` statement"
}, AST_Exit);

var AST_Throw = DEFNODE("Throw", null, {
    $documentation: "A `throw` statement"
}, AST_Exit);

var AST_LoopControl = DEFNODE("LoopControl", "label", {
    $documentation: "Base class for loop control statements (`break` and `continue`)",
    $propdoc: {
        label: "[AST_LabelRef?] the label, or null if none",
    },
    _walk: function(visitor) {
        return visitor._visit(this, this.label && function() {
            this.label._walk(visitor);
        });
    },
    _children_backwards(push) {
        if (this.label) push(this.label);
    },
}, AST_Jump);

var AST_Break = DEFNODE("Break", null, {
    $documentation: "A `break` statement"
}, AST_LoopControl);

var AST_Continue = DEFNODE("Continue", null, {
    $documentation: "A `continue` statement"
}, AST_LoopControl);

var AST_Await = DEFNODE("Await", "expression", {
    $documentation: "An `await` statement",
    $propdoc: {
        expression: "[AST_Node] the mandatory expression being awaited",
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.expression._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.expression);
    },
});

var AST_Yield = DEFNODE("Yield", "expression is_star", {
    $documentation: "A `yield` statement",
    $propdoc: {
        expression: "[AST_Node?] the value returned or thrown by this statement; could be null (representing undefined) but only when is_star is set to false",
        is_star: "[Boolean] Whether this is a yield or yield* statement"
    },
    _walk: function(visitor) {
        return visitor._visit(this, this.expression && function() {
            this.expression._walk(visitor);
        });
    },
    _children_backwards(push) {
        if (this.expression) push(this.expression);
    }
});

/* -----[ IF ]----- */

var AST_If = DEFNODE("If", "condition alternative", {
    $documentation: "A `if` statement",
    $propdoc: {
        condition: "[AST_Node] the `if` condition",
        alternative: "[AST_Statement?] the `else` part, or null if not present"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.condition._walk(visitor);
            this.body._walk(visitor);
            if (this.alternative) this.alternative._walk(visitor);
        });
    },
    _children_backwards(push) {
        if (this.alternative) {
            push(this.alternative);
        }
        push(this.body);
        push(this.condition);
    }
}, AST_StatementWithBody);

/* -----[ SWITCH ]----- */

var AST_Switch = DEFNODE("Switch", "expression", {
    $documentation: "A `switch` statement",
    $propdoc: {
        expression: "[AST_Node] the `switch` “discriminant”"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.expression._walk(visitor);
            walk_body(this, visitor);
        });
    },
    _children_backwards(push) {
        let i = this.body.length;
        while (i--) push(this.body[i]);
        push(this.expression);
    }
}, AST_Block);

var AST_SwitchBranch = DEFNODE("SwitchBranch", null, {
    $documentation: "Base class for `switch` branches",
}, AST_Block);

var AST_Default = DEFNODE("Default", null, {
    $documentation: "A `default` switch branch",
}, AST_SwitchBranch);

var AST_Case = DEFNODE("Case", "expression", {
    $documentation: "A `case` switch branch",
    $propdoc: {
        expression: "[AST_Node] the `case` expression"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.expression._walk(visitor);
            walk_body(this, visitor);
        });
    },
    _children_backwards(push) {
        let i = this.body.length;
        while (i--) push(this.body[i]);
        push(this.expression);
    },
}, AST_SwitchBranch);

/* -----[ EXCEPTIONS ]----- */

var AST_Try = DEFNODE("Try", "bcatch bfinally", {
    $documentation: "A `try` statement",
    $propdoc: {
        bcatch: "[AST_Catch?] the catch block, or null if not present",
        bfinally: "[AST_Finally?] the finally block, or null if not present"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            walk_body(this, visitor);
            if (this.bcatch) this.bcatch._walk(visitor);
            if (this.bfinally) this.bfinally._walk(visitor);
        });
    },
    _children_backwards(push) {
        if (this.bfinally) push(this.bfinally);
        if (this.bcatch) push(this.bcatch);
        let i = this.body.length;
        while (i--) push(this.body[i]);
    },
}, AST_Block);

var AST_Catch = DEFNODE("Catch", "argname", {
    $documentation: "A `catch` node; only makes sense as part of a `try` statement",
    $propdoc: {
        argname: "[AST_SymbolCatch|AST_Destructuring|AST_Expansion|AST_DefaultAssign] symbol for the exception"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            if (this.argname) this.argname._walk(visitor);
            walk_body(this, visitor);
        });
    },
    _children_backwards(push) {
        let i = this.body.length;
        while (i--) push(this.body[i]);
        if (this.argname) push(this.argname);
    },
}, AST_Block);

var AST_Finally = DEFNODE("Finally", null, {
    $documentation: "A `finally` node; only makes sense as part of a `try` statement"
}, AST_Block);

/* -----[ VAR/CONST ]----- */

var AST_Definitions = DEFNODE("Definitions", "definitions", {
    $documentation: "Base class for `var` or `const` nodes (variable declarations/initializations)",
    $propdoc: {
        definitions: "[AST_VarDef*] array of variable definitions"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            var definitions = this.definitions;
            for (var i = 0, len = definitions.length; i < len; i++) {
                definitions[i]._walk(visitor);
            }
        });
    },
    _children_backwards(push) {
        let i = this.definitions.length;
        while (i--) push(this.definitions[i]);
    },
}, AST_Statement);

var AST_Var = DEFNODE("Var", null, {
    $documentation: "A `var` statement"
}, AST_Definitions);

var AST_Let = DEFNODE("Let", null, {
    $documentation: "A `let` statement"
}, AST_Definitions);

var AST_Const = DEFNODE("Const", null, {
    $documentation: "A `const` statement"
}, AST_Definitions);

var AST_VarDef = DEFNODE("VarDef", "name value", {
    $documentation: "A variable declaration; only appears in a AST_Definitions node",
    $propdoc: {
        name: "[AST_Destructuring|AST_SymbolConst|AST_SymbolLet|AST_SymbolVar] name of the variable",
        value: "[AST_Node?] initializer, or null of there's no initializer"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.name._walk(visitor);
            if (this.value) this.value._walk(visitor);
        });
    },
    _children_backwards(push) {
        if (this.value) push(this.value);
        push(this.name);
    },
});

var AST_NameMapping = DEFNODE("NameMapping", "foreign_name name", {
    $documentation: "The part of the export/import statement that declare names from a module.",
    $propdoc: {
        foreign_name: "[AST_SymbolExportForeign|AST_SymbolImportForeign] The name being exported/imported (as specified in the module)",
        name: "[AST_SymbolExport|AST_SymbolImport] The name as it is visible to this module."
    },
    _walk: function (visitor) {
        return visitor._visit(this, function() {
            this.foreign_name._walk(visitor);
            this.name._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.name);
        push(this.foreign_name);
    },
});

var AST_Import = DEFNODE("Import", "imported_name imported_names module_name assert_clause", {
    $documentation: "An `import` statement",
    $propdoc: {
        imported_name: "[AST_SymbolImport] The name of the variable holding the module's default export.",
        imported_names: "[AST_NameMapping*] The names of non-default imported variables",
        module_name: "[AST_String] String literal describing where this module came from",
        assert_clause: "[AST_Object?] The import assertion"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            if (this.imported_name) {
                this.imported_name._walk(visitor);
            }
            if (this.imported_names) {
                this.imported_names.forEach(function(name_import) {
                    name_import._walk(visitor);
                });
            }
            this.module_name._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.module_name);
        if (this.imported_names) {
            let i = this.imported_names.length;
            while (i--) push(this.imported_names[i]);
        }
        if (this.imported_name) push(this.imported_name);
    },
});

var AST_ImportMeta = DEFNODE("ImportMeta", null, {
    $documentation: "A reference to import.meta",
});

var AST_Export = DEFNODE("Export", "exported_definition exported_value is_default exported_names module_name assert_clause", {
    $documentation: "An `export` statement",
    $propdoc: {
        exported_definition: "[AST_Defun|AST_Definitions|AST_DefClass?] An exported definition",
        exported_value: "[AST_Node?] An exported value",
        exported_names: "[AST_NameMapping*?] List of exported names",
        module_name: "[AST_String?] Name of the file to load exports from",
        is_default: "[Boolean] Whether this is the default exported value of this module",
        assert_clause: "[AST_Object?] The import assertion"
    },
    _walk: function (visitor) {
        return visitor._visit(this, function () {
            if (this.exported_definition) {
                this.exported_definition._walk(visitor);
            }
            if (this.exported_value) {
                this.exported_value._walk(visitor);
            }
            if (this.exported_names) {
                this.exported_names.forEach(function(name_export) {
                    name_export._walk(visitor);
                });
            }
            if (this.module_name) {
                this.module_name._walk(visitor);
            }
        });
    },
    _children_backwards(push) {
        if (this.module_name) push(this.module_name);
        if (this.exported_names) {
            let i = this.exported_names.length;
            while (i--) push(this.exported_names[i]);
        }
        if (this.exported_value) push(this.exported_value);
        if (this.exported_definition) push(this.exported_definition);
    }
}, AST_Statement);

/* -----[ OTHER ]----- */

var AST_Call = DEFNODE("Call", "expression args optional _annotations", {
    $documentation: "A function call expression",
    $propdoc: {
        expression: "[AST_Node] expression to invoke as function",
        args: "[AST_Node*] array of arguments",
        optional: "[boolean] whether this is an optional call (IE ?.() )",
        _annotations: "[number] bitfield containing information about the call"
    },
    initialize() {
        if (this._annotations == null) this._annotations = 0;
    },
    _walk(visitor) {
        return visitor._visit(this, function() {
            var args = this.args;
            for (var i = 0, len = args.length; i < len; i++) {
                args[i]._walk(visitor);
            }
            this.expression._walk(visitor);  // TODO why do we need to crawl this last?
        });
    },
    _children_backwards(push) {
        let i = this.args.length;
        while (i--) push(this.args[i]);
        push(this.expression);
    },
});

var AST_New = DEFNODE("New", null, {
    $documentation: "An object instantiation.  Derives from a function call since it has exactly the same properties"
}, AST_Call);

var AST_Sequence = DEFNODE("Sequence", "expressions", {
    $documentation: "A sequence expression (comma-separated expressions)",
    $propdoc: {
        expressions: "[AST_Node*] array of expressions (at least two)"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.expressions.forEach(function(node) {
                node._walk(visitor);
            });
        });
    },
    _children_backwards(push) {
        let i = this.expressions.length;
        while (i--) push(this.expressions[i]);
    },
});

var AST_PropAccess = DEFNODE("PropAccess", "expression property optional", {
    $documentation: "Base class for property access expressions, i.e. `a.foo` or `a[\"foo\"]`",
    $propdoc: {
        expression: "[AST_Node] the “container” expression",
        property: "[AST_Node|string] the property to access.  For AST_Dot & AST_DotHash this is always a plain string, while for AST_Sub it's an arbitrary AST_Node",

        optional: "[boolean] whether this is an optional property access (IE ?.)"
    }
});

var AST_Dot = DEFNODE("Dot", "quote", {
    $documentation: "A dotted property access expression",
    $propdoc: {
        quote: "[string] the original quote character when transformed from AST_Sub",
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.expression._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.expression);
    },
}, AST_PropAccess);

var AST_DotHash = DEFNODE("DotHash", "", {
    $documentation: "A dotted property access to a private property",
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.expression._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.expression);
    },
}, AST_PropAccess);

var AST_Sub = DEFNODE("Sub", null, {
    $documentation: "Index-style property access, i.e. `a[\"foo\"]`",
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.expression._walk(visitor);
            this.property._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.property);
        push(this.expression);
    },
}, AST_PropAccess);

var AST_Chain = DEFNODE("Chain", "expression", {
    $documentation: "A chain expression like a?.b?.(c)?.[d]",
    $propdoc: {
        expression: "[AST_Call|AST_Dot|AST_DotHash|AST_Sub] chain element."
    },
    _walk: function (visitor) {
        return visitor._visit(this, function() {
            this.expression._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.expression);
    },
});

var AST_Unary = DEFNODE("Unary", "operator expression", {
    $documentation: "Base class for unary expressions",
    $propdoc: {
        operator: "[string] the operator",
        expression: "[AST_Node] expression that this unary operator applies to"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.expression._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.expression);
    },
});

var AST_UnaryPrefix = DEFNODE("UnaryPrefix", null, {
    $documentation: "Unary prefix expression, i.e. `typeof i` or `++i`"
}, AST_Unary);

var AST_UnaryPostfix = DEFNODE("UnaryPostfix", null, {
    $documentation: "Unary postfix expression, i.e. `i++`"
}, AST_Unary);

var AST_Binary = DEFNODE("Binary", "operator left right", {
    $documentation: "Binary expression, i.e. `a + b`",
    $propdoc: {
        left: "[AST_Node] left-hand side expression",
        operator: "[string] the operator",
        right: "[AST_Node] right-hand side expression"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.left._walk(visitor);
            this.right._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.right);
        push(this.left);
    },
});

var AST_Conditional = DEFNODE("Conditional", "condition consequent alternative", {
    $documentation: "Conditional expression using the ternary operator, i.e. `a ? b : c`",
    $propdoc: {
        condition: "[AST_Node]",
        consequent: "[AST_Node]",
        alternative: "[AST_Node]"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            this.condition._walk(visitor);
            this.consequent._walk(visitor);
            this.alternative._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.alternative);
        push(this.consequent);
        push(this.condition);
    },
});

var AST_Assign = DEFNODE("Assign", "logical", {
    $documentation: "An assignment expression — `a = b + 5`",
    $propdoc: {
        logical: "Whether it's a logical assignment"
    }
}, AST_Binary);

var AST_DefaultAssign = DEFNODE("DefaultAssign", null, {
    $documentation: "A default assignment expression like in `(a = 3) => a`"
}, AST_Binary);

/* -----[ LITERALS ]----- */

var AST_Array = DEFNODE("Array", "elements", {
    $documentation: "An array literal",
    $propdoc: {
        elements: "[AST_Node*] array of elements"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            var elements = this.elements;
            for (var i = 0, len = elements.length; i < len; i++) {
                elements[i]._walk(visitor);
            }
        });
    },
    _children_backwards(push) {
        let i = this.elements.length;
        while (i--) push(this.elements[i]);
    },
});

var AST_Object = DEFNODE("Object", "properties", {
    $documentation: "An object literal",
    $propdoc: {
        properties: "[AST_ObjectProperty*] array of properties"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            var properties = this.properties;
            for (var i = 0, len = properties.length; i < len; i++) {
                properties[i]._walk(visitor);
            }
        });
    },
    _children_backwards(push) {
        let i = this.properties.length;
        while (i--) push(this.properties[i]);
    },
});

var AST_ObjectProperty = DEFNODE("ObjectProperty", "key value", {
    $documentation: "Base class for literal object properties",
    $propdoc: {
        key: "[string|AST_Node] property name. For ObjectKeyVal this is a string. For getters, setters and computed property this is an AST_Node.",
        value: "[AST_Node] property value.  For getters and setters this is an AST_Accessor."
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            if (this.key instanceof AST_Node)
                this.key._walk(visitor);
            this.value._walk(visitor);
        });
    },
    _children_backwards(push) {
        push(this.value);
        if (this.key instanceof AST_Node) push(this.key);
    }
});

var AST_ObjectKeyVal = DEFNODE("ObjectKeyVal", "quote", {
    $documentation: "A key: value object property",
    $propdoc: {
        quote: "[string] the original quote character"
    },
    computed_key() {
        return this.key instanceof AST_Node;
    }
}, AST_ObjectProperty);

var AST_PrivateSetter = DEFNODE("PrivateSetter", "static", {
    $propdoc: {
        static: "[boolean] whether this is a static private setter"
    },
    $documentation: "A private setter property",
    computed_key() {
        return false;
    }
}, AST_ObjectProperty);

var AST_PrivateGetter = DEFNODE("PrivateGetter", "static", {
    $propdoc: {
        static: "[boolean] whether this is a static private getter"
    },
    $documentation: "A private getter property",
    computed_key() {
        return false;
    }
}, AST_ObjectProperty);

var AST_ObjectSetter = DEFNODE("ObjectSetter", "quote static", {
    $propdoc: {
        quote: "[string|undefined] the original quote character, if any",
        static: "[boolean] whether this is a static setter (classes only)"
    },
    $documentation: "An object setter property",
    computed_key() {
        return !(this.key instanceof AST_SymbolMethod);
    }
}, AST_ObjectProperty);

var AST_ObjectGetter = DEFNODE("ObjectGetter", "quote static", {
    $propdoc: {
        quote: "[string|undefined] the original quote character, if any",
        static: "[boolean] whether this is a static getter (classes only)"
    },
    $documentation: "An object getter property",
    computed_key() {
        return !(this.key instanceof AST_SymbolMethod);
    }
}, AST_ObjectProperty);

var AST_ConciseMethod = DEFNODE("ConciseMethod", "quote static is_generator async", {
    $propdoc: {
        quote: "[string|undefined] the original quote character, if any",
        static: "[boolean] is this method static (classes only)",
        is_generator: "[boolean] is this a generator method",
        async: "[boolean] is this method async",
    },
    $documentation: "An ES6 concise method inside an object or class",
    computed_key() {
        return !(this.key instanceof AST_SymbolMethod);
    }
}, AST_ObjectProperty);

var AST_PrivateMethod = DEFNODE("PrivateMethod", "", {
    $documentation: "A private class method inside a class",
}, AST_ConciseMethod);

var AST_Class = DEFNODE("Class", "name extends properties", {
    $propdoc: {
        name: "[AST_SymbolClass|AST_SymbolDefClass?] optional class name.",
        extends: "[AST_Node]? optional parent class",
        properties: "[AST_ObjectProperty*] array of properties"
    },
    $documentation: "An ES6 class",
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            if (this.name) {
                this.name._walk(visitor);
            }
            if (this.extends) {
                this.extends._walk(visitor);
            }
            this.properties.forEach((prop) => prop._walk(visitor));
        });
    },
    _children_backwards(push) {
        let i = this.properties.length;
        while (i--) push(this.properties[i]);
        if (this.extends) push(this.extends);
        if (this.name) push(this.name);
    },
}, AST_Scope /* TODO a class might have a scope but it's not a scope */);

var AST_ClassProperty = DEFNODE("ClassProperty", "static quote", {
    $documentation: "A class property",
    $propdoc: {
        static: "[boolean] whether this is a static key",
        quote: "[string] which quote is being used"
    },
    _walk: function(visitor) {
        return visitor._visit(this, function() {
            if (this.key instanceof AST_Node)
                this.key._walk(visitor);
            if (this.value instanceof AST_Node)
                this.value._walk(visitor);
        });
    },
    _children_backwards(push) {
        if (this.value instanceof AST_Node) push(this.value);
        if (this.key instanceof AST_Node) push(this.key);
    },
    computed_key() {
        return !(this.key instanceof AST_SymbolClassProperty);
    }
}, AST_ObjectProperty);

var AST_ClassPrivateProperty = DEFNODE("ClassPrivateProperty", "", {
    $documentation: "A class property for a private property",
}, AST_ClassProperty);

var AST_DefClass = DEFNODE("DefClass", null, {
    $documentation: "A class definition",
}, AST_Class);

var AST_ClassExpression = DEFNODE("ClassExpression", null, {
    $documentation: "A class expression."
}, AST_Class);

var AST_Symbol = DEFNODE("Symbol", "scope name thedef", {
    $propdoc: {
        name: "[string] name of this symbol",
        scope: "[AST_Scope/S] the current scope (not necessarily the definition scope)",
        thedef: "[SymbolDef/S] the definition of this symbol"
    },
    $documentation: "Base class for all symbols"
});

var AST_NewTarget = DEFNODE("NewTarget", null, {
    $documentation: "A reference to new.target"
});

var AST_SymbolDeclaration = DEFNODE("SymbolDeclaration", "init", {
    $documentation: "A declaration symbol (symbol in var/const, function name or argument, symbol in catch)",
}, AST_Symbol);

var AST_SymbolVar = DEFNODE("SymbolVar", null, {
    $documentation: "Symbol defining a variable",
}, AST_SymbolDeclaration);

var AST_SymbolBlockDeclaration = DEFNODE("SymbolBlockDeclaration", null, {
    $documentation: "Base class for block-scoped declaration symbols"
}, AST_SymbolDeclaration);

var AST_SymbolConst = DEFNODE("SymbolConst", null, {
    $documentation: "A constant declaration"
}, AST_SymbolBlockDeclaration);

var AST_SymbolLet = DEFNODE("SymbolLet", null, {
    $documentation: "A block-scoped `let` declaration"
}, AST_SymbolBlockDeclaration);

var AST_SymbolFunarg = DEFNODE("SymbolFunarg", null, {
    $documentation: "Symbol naming a function argument",
}, AST_SymbolVar);

var AST_SymbolDefun = DEFNODE("SymbolDefun", null, {
    $documentation: "Symbol defining a function",
}, AST_SymbolDeclaration);

var AST_SymbolMethod = DEFNODE("SymbolMethod", null, {
    $documentation: "Symbol in an object defining a method",
}, AST_Symbol);

var AST_SymbolClassProperty = DEFNODE("SymbolClassProperty", null, {
    $documentation: "Symbol for a class property",
}, AST_Symbol);

var AST_SymbolLambda = DEFNODE("SymbolLambda", null, {
    $documentation: "Symbol naming a function expression",
}, AST_SymbolDeclaration);

var AST_SymbolDefClass = DEFNODE("SymbolDefClass", null, {
    $documentation: "Symbol naming a class's name in a class declaration. Lexically scoped to its containing scope, and accessible within the class."
}, AST_SymbolBlockDeclaration);

var AST_SymbolClass = DEFNODE("SymbolClass", null, {
    $documentation: "Symbol naming a class's name. Lexically scoped to the class."
}, AST_SymbolDeclaration);

var AST_SymbolCatch = DEFNODE("SymbolCatch", null, {
    $documentation: "Symbol naming the exception in catch",
}, AST_SymbolBlockDeclaration);

var AST_SymbolImport = DEFNODE("SymbolImport", null, {
    $documentation: "Symbol referring to an imported name",
}, AST_SymbolBlockDeclaration);

var AST_SymbolImportForeign = DEFNODE("SymbolImportForeign", null, {
    $documentation: "A symbol imported from a module, but it is defined in the other module, and its real name is irrelevant for this module's purposes",
}, AST_Symbol);

var AST_Label = DEFNODE("Label", "references", {
    $documentation: "Symbol naming a label (declaration)",
    $propdoc: {
        references: "[AST_LoopControl*] a list of nodes referring to this label"
    },
    initialize: function() {
        this.references = [];
        this.thedef = this;
    }
}, AST_Symbol);

var AST_SymbolRef = DEFNODE("SymbolRef", null, {
    $documentation: "Reference to some symbol (not definition/declaration)",
}, AST_Symbol);

var AST_SymbolExport = DEFNODE("SymbolExport", null, {
    $documentation: "Symbol referring to a name to export",
}, AST_SymbolRef);

var AST_SymbolExportForeign = DEFNODE("SymbolExportForeign", null, {
    $documentation: "A symbol exported from this module, but it is used in the other module, and its real name is irrelevant for this module's purposes",
}, AST_Symbol);

var AST_LabelRef = DEFNODE("LabelRef", null, {
    $documentation: "Reference to a label symbol",
}, AST_Symbol);

var AST_This = DEFNODE("This", null, {
    $documentation: "The `this` symbol",
}, AST_Symbol);

var AST_Super = DEFNODE("Super", null, {
    $documentation: "The `super` symbol",
}, AST_This);

var AST_Constant = DEFNODE("Constant", null, {
    $documentation: "Base class for all constants",
    getValue: function() {
        return this.value;
    }
});

var AST_String = DEFNODE("String", "value quote", {
    $documentation: "A string literal",
    $propdoc: {
        value: "[string] the contents of this string",
        quote: "[string] the original quote character"
    }
}, AST_Constant);

var AST_Number = DEFNODE("Number", "value raw", {
    $documentation: "A number literal",
    $propdoc: {
        value: "[number] the numeric value",
        raw: "[string] numeric value as string"
    }
}, AST_Constant);

var AST_BigInt = DEFNODE("BigInt", "value", {
    $documentation: "A big int literal",
    $propdoc: {
        value: "[string] big int value"
    }
}, AST_Constant);

var AST_RegExp = DEFNODE("RegExp", "value", {
    $documentation: "A regexp literal",
    $propdoc: {
        value: "[RegExp] the actual regexp",
    }
}, AST_Constant);

var AST_Atom = DEFNODE("Atom", null, {
    $documentation: "Base class for atoms",
}, AST_Constant);

var AST_Null = DEFNODE("Null", null, {
    $documentation: "The `null` atom",
    value: null
}, AST_Atom);

var AST_NaN = DEFNODE("NaN", null, {
    $documentation: "The impossible value",
    value: 0/0
}, AST_Atom);

var AST_Undefined = DEFNODE("Undefined", null, {
    $documentation: "The `undefined` value",
    value: (function() {}())
}, AST_Atom);

var AST_Hole = DEFNODE("Hole", null, {
    $documentation: "A hole in an array",
    value: (function() {}())
}, AST_Atom);

var AST_Infinity = DEFNODE("Infinity", null, {
    $documentation: "The `Infinity` value",
    value: 1/0
}, AST_Atom);

var AST_Boolean = DEFNODE("Boolean", null, {
    $documentation: "Base class for booleans",
}, AST_Atom);

var AST_False = DEFNODE("False", null, {
    $documentation: "The `false` atom",
    value: false
}, AST_Boolean);

var AST_True = DEFNODE("True", null, {
    $documentation: "The `true` atom",
    value: true
}, AST_Boolean);

/* -----[ Walk function ]---- */

/**
 * Walk nodes in depth-first search fashion.
 * Callback can return `walk_abort` symbol to stop iteration.
 * It can also return `true` to stop iteration just for child nodes.
 * Iteration can be stopped and continued by passing the `to_visit` argument,
 * which is given to the callback in the second argument.
 **/
function walk(node, cb, to_visit = [node]) {
    const push = to_visit.push.bind(to_visit);
    while (to_visit.length) {
        const node = to_visit.pop();
        const ret = cb(node, to_visit);

        if (ret) {
            if (ret === walk_abort) return true;
            continue;
        }

        node._children_backwards(push);
    }
    return false;
}

function walk_parent(node, cb, initial_stack) {
    const to_visit = [node];
    const push = to_visit.push.bind(to_visit);
    const stack = initial_stack ? initial_stack.slice() : [];
    const parent_pop_indices = [];

    let current;

    const info = {
        parent: (n = 0) => {
            if (n === -1) {
                return current;
            }

            // [ p1 p0 ] [ 1 0 ]
            if (initial_stack && n >= stack.length) {
                n -= stack.length;
                return initial_stack[
                    initial_stack.length - (n + 1)
                ];
            }

            return stack[stack.length - (1 + n)];
        },
    };

    while (to_visit.length) {
        current = to_visit.pop();

        while (
            parent_pop_indices.length &&
            to_visit.length == parent_pop_indices[parent_pop_indices.length - 1]
        ) {
            stack.pop();
            parent_pop_indices.pop();
        }

        const ret = cb(current, info);

        if (ret) {
            if (ret === walk_abort) return true;
            continue;
        }

        const visit_length = to_visit.length;

        current._children_backwards(push);

        // Push only if we're going to traverse the children
        if (to_visit.length > visit_length) {
            stack.push(current);
            parent_pop_indices.push(visit_length - 1);
        }
    }

    return false;
}

const walk_abort = Symbol("abort walk");

/* -----[ TreeWalker ]----- */

class TreeWalker {
    constructor(callback) {
        this.visit = callback;
        this.stack = [];
        this.directives = Object.create(null);
    }

    _visit(node, descend) {
        this.push(node);
        var ret = this.visit(node, descend ? function() {
            descend.call(node);
        } : noop);
        if (!ret && descend) {
            descend.call(node);
        }
        this.pop();
        return ret;
    }

    parent(n) {
        return this.stack[this.stack.length - 2 - (n || 0)];
    }

    push(node) {
        if (node instanceof AST_Lambda) {
            this.directives = Object.create(this.directives);
        } else if (node instanceof AST_Directive && !this.directives[node.value]) {
            this.directives[node.value] = node;
        } else if (node instanceof AST_Class) {
            this.directives = Object.create(this.directives);
            if (!this.directives["use strict"]) {
                this.directives["use strict"] = node;
            }
        }
        this.stack.push(node);
    }

    pop() {
        var node = this.stack.pop();
        if (node instanceof AST_Lambda || node instanceof AST_Class) {
            this.directives = Object.getPrototypeOf(this.directives);
        }
    }

    self() {
        return this.stack[this.stack.length - 1];
    }

    find_parent(type) {
        var stack = this.stack;
        for (var i = stack.length; --i >= 0;) {
            var x = stack[i];
            if (x instanceof type) return x;
        }
    }

    has_directive(type) {
        var dir = this.directives[type];
        if (dir) return dir;
        var node = this.stack[this.stack.length - 1];
        if (node instanceof AST_Scope && node.body) {
            for (var i = 0; i < node.body.length; ++i) {
                var st = node.body[i];
                if (!(st instanceof AST_Directive)) break;
                if (st.value == type) return st;
            }
        }
    }

    loopcontrol_target(node) {
        var stack = this.stack;
        if (node.label) for (var i = stack.length; --i >= 0;) {
            var x = stack[i];
            if (x instanceof AST_LabeledStatement && x.label.name == node.label.name)
                return x.body;
        } else for (var i = stack.length; --i >= 0;) {
            var x = stack[i];
            if (x instanceof AST_IterationStatement
                || node instanceof AST_Break && x instanceof AST_Switch)
                return x;
        }
    }
}

// Tree transformer helpers.
class TreeTransformer extends TreeWalker {
    constructor(before, after) {
        super();
        this.before = before;
        this.after = after;
    }
}

const _PURE     = 0b00000001;
const _INLINE   = 0b00000010;
const _NOINLINE = 0b00000100;

export {
    AST_Accessor,
    AST_Array,
    AST_Arrow,
    AST_Assign,
    AST_Atom,
    AST_Await,
    AST_BigInt,
    AST_Binary,
    AST_Block,
    AST_BlockStatement,
    AST_Boolean,
    AST_Break,
    AST_Call,
    AST_Case,
    AST_Catch,
    AST_Chain,
    AST_Class,
    AST_ClassExpression,
    AST_ClassPrivateProperty,
    AST_ClassProperty,
    AST_ConciseMethod,
    AST_Conditional,
    AST_Const,
    AST_Constant,
    AST_Continue,
    AST_Debugger,
    AST_Default,
    AST_DefaultAssign,
    AST_DefClass,
    AST_Definitions,
    AST_Defun,
    AST_Destructuring,
    AST_Directive,
    AST_Do,
    AST_Dot,
    AST_DotHash,
    AST_DWLoop,
    AST_EmptyStatement,
    AST_Exit,
    AST_Expansion,
    AST_Export,
    AST_False,
    AST_Finally,
    AST_For,
    AST_ForIn,
    AST_ForOf,
    AST_Function,
    AST_Hole,
    AST_If,
    AST_Import,
    AST_ImportMeta,
    AST_Infinity,
    AST_IterationStatement,
    AST_Jump,
    AST_Label,
    AST_LabeledStatement,
    AST_LabelRef,
    AST_Lambda,
    AST_Let,
    AST_LoopControl,
    AST_NameMapping,
    AST_NaN,
    AST_New,
    AST_NewTarget,
    AST_Node,
    AST_Null,
    AST_Number,
    AST_Object,
    AST_ObjectGetter,
    AST_ObjectKeyVal,
    AST_ObjectProperty,
    AST_ObjectSetter,
    AST_PrefixedTemplateString,
    AST_PrivateGetter,
    AST_PrivateMethod,
    AST_PrivateSetter,
    AST_PropAccess,
    AST_RegExp,
    AST_Return,
    AST_Scope,
    AST_Sequence,
    AST_SimpleStatement,
    AST_Statement,
    AST_StatementWithBody,
    AST_String,
    AST_Sub,
    AST_Super,
    AST_Switch,
    AST_SwitchBranch,
    AST_Symbol,
    AST_SymbolBlockDeclaration,
    AST_SymbolCatch,
    AST_SymbolClass,
    AST_SymbolClassProperty,
    AST_SymbolConst,
    AST_SymbolDeclaration,
    AST_SymbolDefClass,
    AST_SymbolDefun,
    AST_SymbolExport,
    AST_SymbolExportForeign,
    AST_SymbolFunarg,
    AST_SymbolImport,
    AST_SymbolImportForeign,
    AST_SymbolLambda,
    AST_SymbolLet,
    AST_SymbolMethod,
    AST_SymbolRef,
    AST_SymbolVar,
    AST_TemplateSegment,
    AST_TemplateString,
    AST_This,
    AST_Throw,
    AST_Token,
    AST_Toplevel,
    AST_True,
    AST_Try,
    AST_Unary,
    AST_UnaryPostfix,
    AST_UnaryPrefix,
    AST_Undefined,
    AST_Var,
    AST_VarDef,
    AST_While,
    AST_With,
    AST_Yield,

    // Walkers
    TreeTransformer,
    TreeWalker,
    walk,
    walk_abort,
    walk_body,
    walk_parent,

    // annotations
    _INLINE,
    _NOINLINE,
    _PURE,
};