bug#55414: 29.0.50; Byte compilation error for the modus-themes

[Alan Mackenzie]

Hello, Lars.

On Thu, May 26, 2022 at 13:57:09 +0200, Lars Ingebrigtsen wrote:
> Eli Zaretskii <eliz@gnu.org> writes:

> > Lars, is it just me, or are you also concerned by a large increase in
> > the default values of these variables?

> I'm not really that concerned in general, but in this case, the entire
> problem ....

Which problem would that be, exactly?  If it's the failure of
modus-themes to compile without causing a stack overflow error, then ...

> .... is apparently due to one function --
> byte-compile--first-symbol-with-pos -- that's very recursive.

No, no, no, no.  byte-compile--first-symbol-with-pos is NOT the cause of
the stack overflow - it's part of the handling of that stack overflow,
and unfortunately causes a second stack overflow.  Having examined
Prot's backtraces (around 16th May), I explained this in my post of
2022-05-16 as follows:

#########################################################################
Looking a bit more carefully at the backtrace, it's evident there were
two lisp eval depth overflows.  The first was in the compilation of the
library, where a condition-case was used to discard the diagnostic data
(I hate it when this is done).  This was in the macro
displaying-byte-compile-warnings in .../lisp/emacs-lisp/bytecomp.el.
This failure then called the byte compiler error routines, which caused
the second overflow, in byte-compile--first-symbol-with-pos.

This second overflow is "only just" happening - another few spare slots,
and it would have succeeded; at least on this particular part of the
program structure.
#########################################################################

> It could be rewritten to not be recursive, and these problems would go
> away (which we've seen in many contexts now), if I understand
> correctly.

You're saying byte-compile--first-symbol-with-pos could be reformulated
to be non-recursive, I think.  I don't understand that.  It is a
function working on an arbitrary tree structure.  Such functions are
always coded using recursion, aren't they?  What am I missing here?

> -- 
> (domestic pets only, the antidote for overdose, milk.)
>    bloggy blog: http://lars.ingebrigtsen.no

-- 
Alan Mackenzie (Nuremberg, Germany).