bug#70495: 29.3.50; M-x lsp leads to assertion failed: pdl->kind == SPECPDL_BACKTRACE

[andrei.elkin--- via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

That's awesome Eli!

>> Cc: 70495@debbugs.gnu.org
>> Date: Sun, 21 Apr 2024 14:33:39 +0300
>> From: Eli Zaretskii <eliz@gnu.org>
>> 
>> > Cc: 70495@debbugs.gnu.org
>> > Date: Sun, 21 Apr 2024 13:52:30 +0300
>> > From: Eli Zaretskii <eliz@gnu.org>
>> > 
>> > Sorry, I cannot afford installing lsp-mode and lsp-ui (which in this
>> > case will need to also install clang for the LSP server, right?), and
>> > I don't know how to use it anyway.  So I need you to tell me what's in
>> > the buffer at that position when this happens: how does
>> > lsp-mode/lsp-ui set the line-prefix or wrap-prefix, etc.  If you can
>> > come up with a Lisp recipe that doesn't need lsp-* to be installed and
>> > still reproduces the problem, this would be the best, as I could debug
>> > this on my machine.
>> 
>> Never mind, I've succeeded in reproducing this on my system.  No lsp-*
>> packages are needed at all, it's very simple to reproduce.
>> 
>> Stay tuned.
>
> FTR: to reproduce the problem, it's enough to evaluate this in "emacs -Q":
>
>   (setq line-prefix '(space :width 1))
>
> I guess no one tried to do this since Emacs 29 was released...
>
> Anyway, should be fixed now on the emacs-29 branch.

Thank you!

Andrei

PS. I'll reconsider -O3 - was not aware of its fragility.