Store reference to TaskLayout in TaskVTable for increased debuggability.

[michaelwoerister]

This enables debuggers to reliably decode tasks from raw memory blobs. Being able to decode raw task memory in debuggers is a prerequisite for eventually implementing logical stack traces.

[notgull]

I always imagined that the layout functions would compile down to a constant value after all the functions. I guess not.

I have to wonder, since the TaskLayout will never change for a given S, F and T, if it could be somehow const-evaluated at compile time and if the Header or VTable could just contain a pointer to that constant. I'm not sure if that's possible without advancing the MSRV past the previously established hard limit of 1.46, but I think it would be the best of both worlds in this case.

[michaelwoerister]

Yes, I theory that should be possible and pushing the data into the TaskVTable would be ideal. But as far as I can tell, const eval support is not quite there yet (not even on nightly) -- at least I couldn't get it to work. Feel free to give it a try though. I'd be very interested in how that looks :)

[michaelwoerister]

Blocked on a decision about #30 (comment).

[michaelwoerister]

I've updated this now that #30 has been merged. It's much simpler now.

[taiki-e]

Thanks!

[taiki-e]

Published this and #30 in 4.3.0.