Error: local variable is not used, but in fact it is

[wolfseifert]

The transpiler emits "error: local variable is not used", but in fact it is used.

Compiling

main: () = {
  b := true;
  i := 0;
  while i < 3 && b next i++ {
    std::cout << i << std::endl;
  }
}

yields

whiles.cpp2(2,3): error: local variable b is not used; consider changing its name to '_' to make it explicitly anonymous, or removing it entirely if its side effects are not needed

This happens at least since git version 11f2dbb.

[gregmarr]

This check was added in 243d03d

[JohelEGP]

Same for the reproducer of #825.
I'm explicitly discarding them!
Even if I use them, I still get an error: https://cpp2.godbolt.org/z/ze48hqe7h.

[JohelEGP]

The reproducer of #825 has 3 similar variants:

  _ = :(copy b) _ = b;        // Doesn't move.
  for args do (copy c) _ = c; // Doesn't move.
f: (copy x) _    = x; // Moves.

Only the parameter of the function expression is diagnosed.
The parameter of both the for body and the function are equally local.
It seems inconsistent to diagnose the first one but not the other two.

[JohelEGP]

It also rejects this case, called out by the commit message.

        (copy count := 0)
        while !ret.emplace_back(get_argument(count)).empty() next count++ { }

[JohelEGP]

This case is accepted if you don't use UFCS (https://cpp2.godbolt.org/z/jYr1cEqfd):

perfects: @struct type = {
  operator(): (this, copy consume) = {
    i:=0;
    // consume(i); // Works.
    i.consume();
  }
}
main: () = { }

[JohelEGP]

Same for the reproducer of #825.
I'm explicitly discarding them!
Even if I use them, I still get an error: https://cpp2.godbolt.org/z/ze48hqe7h.

Removing copy and forward also makes them work.