Lars Ingebrigtsen [2021-08-21 15:24 +0200] wrote:

> Alan Mackenzie <acm@muc.de> writes:
>
>> Emacs-28, emacs started with site-start.el and .emacs.
>>
>> On calling
>>
>>     (parse-partial-sexp 19 18 nil nil s)
>>
>> Emacs surely ought to signal an error, since 18 < 19.  It doesn't,
>> though.  It leaves point at a random position and returns
>>
>>     (0 nil nil nil nil nil 0 nil nil nil nil)
>>
>> This is a bug.
>
> I've now made this change (and the doc string clarification discussed).
> There are no test failures after the change, and I'm not getting any
> errors when running it normally, either.

Found one :).

0. emacs -Q
1. M-x toggle-debug-on-error RET
2. M-x ielm RET RET

Debugger entered--Lisp error:
    (error "End position should be larger than start position.")
  parse-partial-sexp(#<marker at 64 in *ielm*> 64)
  ielm-return()
  funcall-interactively(ielm-return)
  call-interactively(ielm-return nil nil)
  command-execute(ielm-return)

One option is to replace XFIXNUM with fix_position, which is what the
subsequent validate_region also does.  Another option is to
CHECK_FIXNUM_COERCE_MARKER before the comparison.  Any preference?