bug#38024: 27.0.50; icomplete sometimes fails to show completions after backward-killing words

["João Távora" <joaotavora@gmail.com>]

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Kevin, you're on the right track. The redisplay thing is not the right fix,
indeed. Stefan has a fix for this, which he sent me, but I can't find it
now.

Anyway, it has to do with avoiding the 'select' event in while-no-input.

In case you want to try that before Stefan drops by.

João

On Fri, Nov 1, 2019, 21:40 Kévin Le Gouguec <kevin.legouguec@gmail.com>
wrote:

> Hello,
>
> tl;dr unless I'm mistaken, sometimes `while-no-input' returns t despite
> no input having arrived; this prevents `icomplete-exhibit' from
> displaying completion candidates.
>
> In more details:
>
> This is a bit of a heisenbug; hopefully someone out there will know what
> knobs to tweak to find more information about this.
>
> From emacs -Q:
>
>     M-x icomplete-mode RET
>     ;; Find a way to set `default-directory' to some long-ish path,
>     ;; e.g. with:
>     M-x find-library RET icomplete RET
>     C-x C-f
>     ;; icomplete should show a bunch of completions.
>     M-DEL
>     M-DEL
>     …
>
> After each `backward-kill-word', icomplete usually displays new
> completion candidates with no further user input; sometimes however, no
> candidates show up until the user does something (e.g. press TAB or
> start typing).
>
> Commit 5860fd3 (Make icomplete-exhibit actually work when navigating up
> directories) tried to fix this, but AFAICT it merely reduces the odds of
> the bug happening: I can still reproduce it, although less often.  Also,
> this new call to `redisplay' causes some noticeable flickering when
> typing characters: the completions blink in and out as I fill in the
> prompt.
>
> I've tinkered with icomplete.el (commenting out the call to `redisplay'
> since it makes the bug harder to trigger); the closest I got to
> pin-pointing the cause for this issue was while goofing around in
> `icomplete-exhibit', specifically with the `while-no-input' part:
>
>           (let* (…
>                  (text (while-no-input
>                          (icomplete-completions
>                           …)))
>                  …)
>             ;; Do nothing if while-no-input was aborted.
>             (when (stringp text)
>               update overlay…))
>
> I replaced (when (stringp text) …) with (if (stringp text) (progn …)
> (message "text is %s" text)): it seems that text is t when icomplete
> fails to show updated candidates, which according to `while-no-input'
> means that some input arrived…
>
> However, when I tried to debug `while-no-input', I got stumped: I tried
> to do some more printf-debugging[1], but all I observe is that
> sometimes, the code seems to be interrupted between
>
>          (let ((throw-on-input ',catch-sym)
>                val)
> and
>            (setq val (or (input-pending-p)
>                          (progn ,@body)))
>
> I tried to find where exactly the code gets interrupted, but I could not
> get a consistent answer; sometimes it seems to be before executing body,
> sometimes it seems to be somewhere inside `icomplete-completions'…
>
> What would be the best way to investigate this further?
>
> Thank you for your time.
>
>
> [1] With this patch:
>
>
> When the bug happens, I get the following messages:
>
>     after with-local-quit
>     after catch and let
>     text is t
>
>
> PS: It just occured to me that I should search debbugs for
>     "while-no-input" in addition to "icomplete".  I just did that;
>     bug#15042 looks like it could maybe be related?
>
>
> In GNU Emacs 27.0.50 (build 6, i686-pc-linux-gnu, GTK+ Version 3.24.5,
> cairo version 1.16.0)
>  of 2019-10-21 built on little-buster
> Repository revision: 61fb5214816ef3d57e676d900e499ffcd079a1f9
> Repository branch: master
> Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
> System Description: Debian GNU/Linux 10 (buster)
>
> Configured using:
>  'configure --with-xwidgets --with-cairo'
>
> Configured features:
> XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND GPM DBUS GSETTINGS GLIB NOTIFY
> INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF
> ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS XWIDGETS
> LIBSYSTEMD JSON PDUMPER LCMS2 GMP
>
> Important settings:
>   value of $LANG: en_US.UTF-8
>   locale-coding-system: utf-8-unix
>

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