boolean-`if` on optional invalidly allowed at `comptime`

[rohlem]

Zig Version

0.14.0-dev.1924+bdd3bc056

Steps to Reproduce and Observed Behavior

fn b(arg: ?bool) bool {
    return if (arg) true else false;
}
fn u(arg: ?u0) bool {
    return if (arg) true else false;
}
test {
    _ = comptime b(true); //passes (yields false)
    _ = comptime u(0); //passes (yields false)
    //_ = b(true); //correctly issues compile error `expected type 'bool', found '?bool'`
    //_ = u(0); //correctly issues compile error `expected type 'bool', found '?u0'`
}

Expected Behavior

Optional-unwrapping if should always require a capture, as it does in runtime code.
IMO this should count as a miscompilation, since invalid code (where the intent is not clear) is processed (and yields an unintuitive result).

[mlugg]

This will be solved by #21422, which I will be able to merge soon.

[rohlem]

duplicate of #21405 (which has a less specific title, but I think the first is still the one kept open usually? Although I prefer better titles. Anyway now I've clicked the button already.)