bug#67687: Feature request: automatic tags management

[Dmitry Gutov <dmitry@gutov.dev>]

On 01/01/2024 18:50, Eli Zaretskii wrote:
>> Date: Mon, 1 Jan 2024 17:47:09 +0200
>> Cc: stefankangas@gmail.com, eskinjp@gmail.com, 67687@debbugs.gnu.org,
>>   michael.albinus@gmx.de
>> From: Dmitry Gutov <dmitry@gutov.dev>
>>
>>> 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.
>>
>> OK, added a paragraph to the mode's docstring.
>> [...]
>> +
>> +The exception is made when the user has already selected a tags
>> +table manually (for example, using \\[visit-tags-table]).  Then
>> +this mode doesn't do anything.  Reset the visited tags tables
>> +using \\[tags-reset-tags-tables]."
> 
> The above is only true for the project whose TAGS was manually
> visited, right?  IOW, it's not that once the use invokes
> visit-tags-table once, this mode will be effectively disabled for the
> entire session, right?

No, it's the latter. It's off for the whole session, just like a visited 
TAGS file is active for the whole session (not limited to any specific 
project).

The current choice is optimized for making it possible to flip 
etags-regen-mode on globally while not interrupting the workflows of 
most (hopefully all) people who currently use etags.

> If so, I suggest to make it clear:
> 
>    If you select a tags table manually (for example, using
>    \\[visit-tags-table]), then this mode will be effectively disabled
>    for the project or the directory tree from which the tags table was
>    visited (the mode will still auto-regenerate tags tables for other
>    projects and directory trees).  Use \\[tags-reset-tags-tables] to
>    countermand the effect of a previous \\[visit-tags-table].
> 
> Otherwise, this LGTM, thanks.

We could do something like this too, but a tags file, in general, can't 
always be attributed to a specific project. At least we won't always be 
able to do that correctly for custom-made tag files. For example, the 
user could have that file include another tags file from a different 
directory on the same level, just like we here do with directories 'src' 
and 'lisp'. If 'src' and 'lisp' were configured to be separate projects, 
a visited src/TAGS would be attributed to the 'src' project only, while 
in fact it covers both. So the simplest solution is not to try.