Bug: used Variable removed

[gyandeeps]

Source code

function* idMaker() {
    let cnt = 0;
    while (true) { // eslint-disable-line no-constant-condition
        yield `id-${++cnt}`;
    }
}

0.0.10 output

function idMaker() {
    return regeneratorRuntime.wrap(function (c) {
        for (; ; )
            switch (c.prev = c.next) {
            case 0:
                a = 0;
            case 1:
                return c.next = 4,
                "id-" + ++a;
            case 4:
                c.next = 1;
                break;
            case 6:
            case "end":
                return c.stop()
            }
    }, _marked[0], this)
}

0.0.9 output

function idMaker() {
    var a;
    return regeneratorRuntime.wrap(function (c) {
        for (; ; )
            switch (c.prev = c.next) {
            case 0:
                a = 0;
            case 1:
                return c.next = 4,
                "id-" + ++a;
            case 4:
                c.next = 1;
                break;
            case 6:
            case "end":
                return c.stop()
            }
    }, _marked[0], this)
}

Issue

On line 2, var a; is removed with 0.0.10

Babel: latest

I want to help with this bug if anyone can point me in the right direction. (I have never done babel stuff before)

[boopathi]

This is an issue with mangler. Try with presets: [ [ "babili", { deadcode: false } ], "es2015"] and the variable cnt is not mangled, but its references are mangled. Might be the binding/scope issue with babel.