bug#39075: 28.0.50; Emacs hangs on 100% CPU and grows beyond bounds in shell-mode

[Eli Zaretskii]

> From: Pieter van Oostrum <pieter-l@vanoostrum.org>
> Cc: 39075@debbugs.gnu.org
> Date: Sun, 12 Jan 2020 18:11:22 +0100
> 
> I ran it under gdb, and interrupted it several times with C-z in gdb. Most of 
> the stack traces were in the garbage collector, suggesting that it is 
> collecting like crazy. This doesn't surprise me, as it is constantly 
> allocating new memory. The rest of this stack trace doesn't have useful 
> information.
> 
> I managed to get a stack trace where it is processing. I haven't analysed 
> these yet, but I include both here.

Thanks, this was very useful.  It turns out to reproduce one must do
this at the shell's prompt, after "M-x shell":

  $ cd /some/directory/;

The /some/directory/ part should be a real directory.  Once one types
the semi-colon, Emacs hangs.  Here's the Lisp backtrace:

  "Automatic GC" (0x0)
  "looking-at" (0x766f5fc8)
  "shell--parse-pcomplete-arguments" (0x766f64f8)
  "pcomplete-parse-arguments" (0x766f6a90)
  "pcomplete-completions" (0x766f6f60)
  "pcomplete-completions-at-point" (0x766f7698)
  "run-hook-with-args-until-success" (0x766f7690)
  "comint-completion-at-point" (0x766f7b10)
  0x317f7b0 PVEC_COMPILED
  "completion-in-region--postch" (0x766f8450)

So I think shell--parse-pcomplete-arguments infloops in this case.