Re: please review new branch feature/byte-unwind-protect

[Stefan Monnier]

> I have one feature request that is related to unwind-protect, filed as
> issue #23963:

While we're here I have another related feature request: make it
possible to provide a "rewind".  Currently the C code has a few
hard-coded rewinds (basically: those for let bindings and those for
save-excursion, IIRC), but doesn't offer any way to provide one's own.

The rewinds are used in the backtrace debugger when the user evaluates
an expression with `e` (which evaluates the expression in the specific
stack frame at point, so it first unwinds up to that stack frame so that
the evaluation has access to the same variables in the same buffer, and
afterwards rewinds back down to the stack frame where the error
occurred).


        Stefan