var assert = require("assert");
var types = require("./types");
var n = types.namedTypes;
var b = types.builders;
var isObject = types.builtInTypes.object;
var isArray = types.builtInTypes.array;
var isFunction = types.builtInTypes.function;
var Patcher = require("./patcher").Patcher;
var normalizeOptions = require("./options").normalize;
var fromString = require("./lines").fromString;
var attachComments = require("./comments").attach;
var util = require("./util");

exports.parse = function parse(source, options) {
    options = normalizeOptions(options);

    var lines = fromString(source, options);

    var sourceWithoutTabs = lines.toString({
        tabWidth: options.tabWidth,
        reuseWhitespace: false,
        useTabs: false
    });

    var program = options.esprima.parse(sourceWithoutTabs, {
        loc: true,
        range: options.range,
        comment: true,
        tolerant: options.tolerant,
        sourceType: 'module'
    });

    // Expand the Program node's .loc to include all comments, since
    // typically its .loc.start and .loc.end will coincide with those of
    // the first and last statements, respectively, excluding any comments
    // that fall outside that region.
    program.loc = util.getTrueLoc(program);

    var comments = program.comments;
    delete program.comments;

    // In order to ensure we reprint leading and trailing program
    // comments, wrap the original Program node with a File node.
    var file = b.file(program);
    file.loc = {
        lines: lines,
        indent: 0,
        start: lines.firstPos(),
        end: lines.lastPos()
    };

    // Passing file.program here instead of just file means that initial
    // comments will be attached to program.body[0] instead of program.
    attachComments(comments, file.program, lines);

    // Return a copy of the original AST so that any changes made may be
    // compared to the original.
    return new TreeCopier(lines).copy(file);
};

function TreeCopier(lines) {
    assert.ok(this instanceof TreeCopier);
    this.lines = lines;
    this.indent = 0;
}

var TCp = TreeCopier.prototype;

TCp.copy = function(node) {
    if (isArray.check(node)) {
        return node.map(this.copy, this);
    }

    if (!isObject.check(node)) {
        return node;
    }

    util.fixFaultyLocations(node);

    var copy = Object.create(Object.getPrototypeOf(node), {
        original: { // Provide a link from the copy to the original.
            value: node,
            configurable: false,
            enumerable: false,
            writable: true
        }
    });

    var loc = node.loc;
    var oldIndent = this.indent;
    var newIndent = oldIndent;

    if (loc) {
        // When node is a comment, we set node.loc.indent to
        // node.loc.start.column so that, when/if we print the comment by
        // itself, we can strip that much whitespace from the left margin
        // of the comment. This only really matters for multiline Block
        // comments, but it doesn't hurt for Line comments.
        if (node.type === "Block" || node.type === "Line" ||
            this.lines.isPrecededOnlyByWhitespace(loc.start)) {
            newIndent = this.indent = loc.start.column;
        }

        loc.lines = this.lines;
        loc.indent = newIndent;
    }

    var keys = Object.keys(node);
    var keyCount = keys.length;
    for (var i = 0; i < keyCount; ++i) {
        var key = keys[i];
        if (key === "loc") {
            copy[key] = node[key];
        } else {
            copy[key] = this.copy(node[key]);
        }
    }

    this.indent = oldIndent;

    return copy;
};

@@ -1781,37 +1781,96 @@
 nts(
-comments, file.program,
+%0A        comments,%0A        program.body.length ? file.program : file,%0A       
  lines
+%0A    
 );%0A%0A

Allow programs that contain only comments.