Re: Automatic (e)tags generation and incremental updates

[Dmitry Gutov <dgutov@yandex.ru>]

On 12.01.2021 19:55, Eli Zaretskii wrote:
>> Cc: tom@tromey.com, john@yates-sheets.org, philipk@posteo.net,
>>   emacs-devel@gnu.org
>> From: Dmitry Gutov <dgutov@yandex.ru>
>> Date: Tue, 12 Jan 2021 19:32:18 +0200
>>
>>> What about regenerating etags only if M-. etc. fail to find an
>>> identifier?
>>
>> There are downsides.
>>
>> You will have to press M-. twice sometimes with that approach.
> 
> Why twice? I thought about regenerating automatically once the search
> fails, then retrying the search with an updated tags table.

Hm, I guess we can do that.

Still, I try to navigate to unknown symbols often enough. It can be an 
unfamiliar class, I don't know if it's defined here or in some 
dependency library... If every time I did that Emacs froze for, say, a 
second, and I didn't know the reasoning for it, my opinion of the editor 
would get pretty low.

So it might be a fine approach, but you have to know what it's doing and 
why. So, off by default.

>> Completion will routinely fail to show some tags that should be present.
>> Also, if the rescan takes a while, I'm not sure you'd want to do that on
>> every 'M-.' failure.
> 
> You could also regenerate when the user switches to another branch.
> That's not a very frequent thing to do.

That can be part of it. So far the options seem to be:

- Brute-force it with project-files and 'stat', checking to see which 
files were added, which removed, and which ones have modtime more recent 
than the previous update.

- Do something clever with Git. I.e. track the current revision, see 
whether it changed and which files changed with it, and also check the 
modtimes of untracked files.

- inotify. Seems to be the most effort-intensive option. I've also seen 
the 'watchman' program (by Facebook) mentioned as pretty reliable, but 
depending on it is probably not great.

Anyway, if you have any suggestions regarding how to write the file 
quicker (and why utf-8-emacs coding didn't help), that would be great.