list_concat.affine

// SPDX-License-Identifier: PMPL-1.0-or-later
// SPDX-FileCopyrightText: 2026 hyperpolymath
//
// Regression for the `++` list-concat codegen defect. `OpConcat` was a
// placeholder `I32Add` (it summed the two list *pointers*), so every
// `a ++ b` produced a garbage/zero-length list. Like #255's loop bug
// this had ZERO coverage — no asserted fixture exercised `++`. Covers
// the three real shapes: literal++literal, mut-accumulate append in a
// loop, and prepend in a loop.

fn sum(xs: [Int]) -> Int {
  let mut s = 0;
  for x in xs {
    s = s + x;
  }
  s
}

fn main() -> Int {
  let a = [10, 20] ++ [30, 40, 50];      // -> [10,20,30,40,50], sum 150

  let mut b = [];
  let mut i = 1;
  while i <= 4 {
    b = b ++ [i];                        // append: [1,2,3,4], sum 10
    i = i + 1;
  }

  let mut c = [];
  let mut j = 1;
  while j <= 3 {
    c = [j] ++ c;                        // prepend: [3,2,1], sum 6
    j = j + 1;
  }

  sum(a) + sum(b) + sum(c)               // 150 + 10 + 6 = 166
}