A conservative algorithm to minimally rename the sweetjs hygienified variables at file scope.

rename_sweet.js

// Takes a file produced by sweet.js and minimally renames
// all the identifiers that have been hygienified by the macro
// expansion. Run using -
//    node /path/to/rename_sweet.js file1.js > fileout.js
var fs = require('fs');

var code = fs.readFileSync(process.argv[2], 'utf8');

var idRE = /[A-Za-z_][A-Za-z0-9_\$]*/g;

function findIDs(code, ids) {
    var id;
    while (id = idRE.exec(code)) {
        ids.push({index: id.index, match: id[0]});
    }
    return ids;
}

function rename(code) {

    var ids = findIDs(code, []);

    var uniqs = {};

    // Find the unique set of ids.
    ids.forEach(function (id) {
        uniqs['$'+id.match] = true;
    });

    // Get the unique list, strip out the leading '$' character.
    var uniqids = Object.keys(uniqs).map(function (s) { return s.substring(1); });

    //console.log(ids);
    //console.log(ids.length);

    var idmap = {};

    // idmap['*'+id] keeps track of a count of the number of times
    // that id occurs so that we can add an appropriate suffix to
    // unique ids.
    uniqids.forEach(function (id) {
        idmap['$'+id] = id;
        idmap['*'+id] = 1;
    });

    var sweetidRE = /^([A-Za-z_][A-Za-z0-9_\$]*)\$([0-9]+)$/;

    // Prepare a rename map that is minimal.
    uniqids.forEach(function (id) {
        var x = sweetidRE.exec(id);
        if (x) {
            var root = x[1];
            var suffix = x[2];
            if (idmap['*'+root]) {
                // The root is already used. Increment the number and use it.
                idmap['*'+root] += 1;
                idmap['$'+id] = root + '_' + idmap['*'+root];
            } else {
                // The root is unused. Use it for the first time.
                idmap['*'+root] = 1;
                idmap['$'+id] = root;
            }
        }
    });

    // Assemble the result.
    var result = [], pos = 0;
    ids.forEach(function (id, i) {
        result.push(code.substring(pos, id.index));
        result.push(idmap['$'+id.match]);
        pos = id.index + id.match.length;
        if (i === ids.length - 1) {
            result.push(code.substring(pos));
        }
    });

    return result.join('');
}

process.stdout.write(rename(code));