bug#67687: Feature request: automatic tags management

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 1 Jan 2024 03:23:36 +0200
> Cc: stefankangas@gmail.com, eskinjp@gmail.com, 67687@debbugs.gnu.org,
>  michael.albinus@gmx.de
> From: Dmitry Gutov <dmitry@gutov.dev>
> 
> >> a) We won't add new files to the index, because we (apparently) can't
> >> simply use the project's list of files -- there is no guarantee that it
> >> matches the fileset that the original author of the TAGS file had in mind.
> > 
> > The user has etags-regen-ignores to control that.
> 
> etags-regen-ignores wouldn't normally include filters that already are 
> in project's ignores. But of course the user might choose to add them.
> 
> >> b) There is no way to pick up the --regex options used for generating
> >> the original TAGS, or any other options we don't know about.
> > 
> > There are defcustoms to control both of those.
> 
> If all of these options are set to the expected values, what's stopping 
> the user from calling 'M-x tags-reset-tags-tables' and having 
> etags-regen-mode create the table on its own? The extra 10 seconds of 
> waiting?
> 
> Also note that if you have an existing TAGS file in the root of the 
> project, with default configuration etags-regen-mode will pick it up to 
> visit and refresh it where necessary (when there are changed or missing 
> files).
> 
> >> Either way, we get a poorly-defined behavior with edge cases that are
> >> likely to surprise the user at different points of time. So we might
> >> indeed grow such a capability, but it'll probably stay off by default.
> > 
> > I agree that sometimes it could be against the user's expectations.
> > But I also think that other times it is according to user's
> > expectations.  Which tells me that this is a separate issue that needs
> > a separate knob; we shouldn't deterministically deduce what users want
> > in this respect from the fact that he/she loaded an existing tags
> > table.  Moreover, it is quite possible that even when the mode is
> > turned on, users might want sometimes to load tags tables manually.
> 
> I don't mind adding additional knobs.

I guess for now it will be enough to document that invoking
visit-tags-table disables the mode for that project.  AFAICT this is
not currently documented anywhere in the patch.