Merge non-initialized var declarations more aggessively

[nicolo-ribaudo]

Bug report or Feature request?

Sub-optimal output

Version (complete output of terser -V or specific git commit)

Whatever is on https://try.terser.org/ as of 2023-09-15

Complete CLI command or minify() options used

{
  module: true,
  compress: {},
  mangle: {},
  output: {},
  parse: {},
  rename: {},
}

terser input

export function next() {
  var r;
  while (r = stack.pop()) {
    var p = r.d.call(r.v);
    p(p);
  }
}

terser output or error

(note: run through Prettier to make it more readable)

export function next() {
  for (var a; a = stack.pop(); ) {
    var o = a.d.call(a.v);
    o(o);
  }
}

Expected result

export function next() {
  for (; a = stack.pop(); ) {
    var a, o = a.d.call(a.v);
    o(o);
  }
}

[fabiosantoscode]

This is interesting. Var can indeed be moved anywhere on a function to improve code size, not just here.