scriptc/tests/corpus/2038-evolving-array-js.cjs

// A function-local `const gb = []` in a JS file is tsc's EVOLVING array
// (inference starts at never[]) — never's f64 representation (the
// uninhabited stance) must not capture it, or a later dyn push
// ("expected number at $, got string") dynChecks strings into a number
// array. The empty literal routes to the JS DOM-array fallback instead:
// pushes of dyn values (JSON.parse results), strings, and numbers all
// land, and length/index/join read back through the keyed-DOM paths.
'use strict';

function viaDyn() {
  const gb = [];
  gb.push(JSON.parse('"s"'));
  gb.push(JSON.parse('2'));
  console.log('dyn:', gb.join('|'), gb.length, gb[0]);
}
viaDyn();

function viaNumbers() {
  const ns = [];
  for (let i = 0; i < 3; i++) ns.push(i * 10);
  console.log('nums:', ns.join(','), ns.length, ns[2]);
}
viaNumbers();

// An ANNOTATED empty literal keeps its slot (the contextual type wins
// over the evolving inference) — jsdoc types the binding.
function viaAnnotated() {
  /** @type {string[]} */
  const ss = [];
  ss.push('a');
  ss.push('b');
  console.log('ann:', ss.join('-'));
}
viaAnnotated();

// The mixed command tuple (test/common's pwdCommand shape): the inner
// empty literal taints the OUTER literal's own type with never[]
// ((string | never[])[]) — the whole value rides the DOM fallback
// instead of building a static (number[] | string)[] that fences at the
// union re-tag.
function viaMixedTuple() {
  const cmd = ['pwd', []];
  console.log('cmd:', cmd.length, cmd[1].length);
}
viaMixedTuple();

// The ternary form (the pwdCommand spelling): the DOM arm coerces into
// the ternary's union slot and the whole binding stays usable.
function viaTernary(win) {
  const cmd = win ? ['cmd.exe', ['/d', '/c', 'cd']] : ['pwd', []];
  console.log('tern:', cmd.length);
}
viaTernary(false);
viaTernary(true);