Subject: bug#27647: 26.0.50; Line numbers implemented natively disappear momentarily when frame out of focus

From: Romanos Skiadas <[email-masked]>
Date: Thu, 5 Oct 2017 23:17:30 +0100

On 05/10/17 14:39, Eli Zaretskii wrote:
>> From: Eli Zaretskii <[email-masked]>
>> Cc: [email-masked], [email-masked],
>> 	[email-masked]
>>
>> It's most probably something related to some hook or timer that you
>> set up in your customizations.
> Or maybe some feature calls kill-all-local-variables, but doesn't
> restore display-line-numbers until later.
>
>
>
I have been seeing this problem for a while due to something happening 
with flycheck-pos-tip, like in the original report. I disabled the 
package, but today I started seeing it (or could it be something 
different?) again in a buffer. It's far from a recipe, but I was seeing 
this:

- In a buffer, the line numbers looked like attached screenshot (1)
- in a buffer, I pressed any combination of keys that would cause 
which-key to pop up
- I pressed C-g to close which-key. At this point, the line numbers 
would look like screenshot (2). They don't go away per se, it looks like 
something goes wrong in some calculation maybe?
- Pressing C-g restored the line numbers to state (1)

I played with adding debug-watch to a couple of variables, this was a 
few hours ago so I only remember I did it with display-line-numbers and 
nothing showed up. I also did debug-on-entry on 
kill-all-local-variables, it never gets called.

After playing with the buffer for a while, I found out that this 
behaviour goes away with git-gutter-mode disabled. I'll find some time 
to try to get something reproducible with stock Emacs within the next 
couple of days.

@Eli, I still have the buffer around and can try out things. Do you have 
any debugging hints for this?

Best,
Romanos