Re: Debugging a seldom seen bug (C-g with Ido)

[Vasilii Kolobkov]

NB: Resending to the list.

Stefan, thank you so much!

Although i skimmed though the [[info:elisp#Quitting]], i'm still
confused about some parts and might be naming things wrong.

Stefan Monnier via Users list for the GNU Emacs text editor
<help-gnu-emacs@gnu.org> writes:

> It's probably timing-dependent.  My guess is that it happens when you it
> `C-g` while Emacs is running some ELisp code and it processes the `C-g` as
> a (signal 'quit), like what happens when you hit `C-g` to interrupt
> execution of ELisp code, rather than by looking it up in the keymaps.

This seem to explain it.

> Feel free to send the resulting backtrace here (along with
> a description of what you were doing and what you remember seeing on
> screen shortly before the problem).

I managed to reliably reproduce it now: calling describe-function with
icomplete-mode enabled takes plenty time to produce a list of completion
candidates.

Now if i hit C-g before the candidates are shown, i'm seeing a "[Quit]"
appended to the minibuffer, without other effects, and after a while,
i'd get a list of candidates.  When doing it with debug-on-quit set, i
see just one other redisplay_internal call at the top most of the time.

  Debugger entered--Lisp error: (quit)
    redisplay_internal\ \(C\ function\)()
    read-from-minibuffer("Describe function: " ...)
    completing-read-default("Describe function: " ...)
    completing-read("Describe function: " ...)
    byte-code(...)
    call-interactively(describe-function nil nil)
    command-execute(describe-function)

When the candidates are already  present, hitting C-g aborts out of
minibuffer.  In case of debug-on-quit, it happens here:

  Debugger entered--Lisp error: (quit)
    read-from-minibuffer("Describe function: " ...)
    completing-read-default("Describe function: " ...)
    completing-read("Describe function: " ...)
    byte-code(...)
    call-interactively(describe-function nil nil)
    command-execute(describe-function)

I don't think there is anything wrong here, other than my flawed
expectations :)