'fail' exit from a constructor should be exempt from 'field is never initialized

[gwillen]

class foo {
    let x: ();
    new() {
        fail;
    }
}

This shouldn't error with 'field is never initialized'.

The real use case for this is of the form:

new() {
    res = some_operation();
    if res.is_err() {
        fail "This is a specific and helpful error message about the failure of some_operation().";
    } else {
        some_local = res.get();
    }
}

This can be worked around by initializing some_local to a placeholder value, but the type of some_local may not provide a convenient one. It can also be worked around in this specific case by not casing, and just setting some_local = res.get(), at the cost of a less useful error message.

[catamorphism]

Yes. Relabeling as "wrong" rather than "enhancement"... since the current behavior is wrong.

[Dretch]

I think this can now be closed, since the inline constructor syntax no longer works, and the new struct initialization syntax does not have this problem.

[brson]

Yes.