return in LEAVE misses handler in directly surounding scope

[patrickbkr]

sub s() {
    LEAVE return 5;
    return 7;
}
s()

gives

Attempt to return outside of any Routine
in sub s at leave-bug.raku line 2
in block at leave-bug.raku line 5

I've dug into this a bit.
From what I've understood, the return 7 starts an unwind. The exit handler of s() is found and called via MVM_frame_dispatch_from_c. That in turn sets cur_frame->return_address to *(tc->interp_cur_op) which still points to someplace in &return. The return 5 then searches for an applicable handler in the call stack, but misses the one of s() because cur_frame->return_address is then usually outside of the handlers corresponding area.

The best idea I could come up with to fix this is setting a sane cur_frame->return_address before calling the exit handler. But I don't know what a sane value could be. The value will not be used to return to (we already have a handler we are unwinding to), but needs to meet pc >= fh->start_offset && pc <= fh->end_offset (that's in exceptions.c search_frame_handlers_lex). I think the LEAVE doesn't even have a representation in the bytecode.

Hm. It's hacky, but something like the following could do the trick:

if (cur_frame == fh->frame) {
    cur_frame->return_address = fh->start_offset;
}

I do hope for a better idea though.

[lizmat]

Is this PR obsolete now?

[patrickbkr]

@lizmat This is an issue, not a PR. ;-)

[lizmat]

Duh :-)