bug#62621: 29.0.60; uniquify can't make buffers unique based on things other than filename

[Spencer Baugh <sbaugh@janestreet.com>]

Dmitry Gutov <dmitry@gutov.dev> writes:

> On 14/07/2023 15:46, Spencer Baugh wrote:
>>>>> If the symbolic values are specific to project, simply let-bind
>>>>> uniquify-dirname-transform to the value of the appropriate project.el
>>>>> defcustom when project.el calls uniquify.
>>>> These customizations are in effect all the time, not just when the user
>>>> is calling a project.el command.  e.g. rename-buffer triggers uniquify.
>>> Then you can set the buffer-local value of uniquify-dirname-transform
>>> in the project.el buffers.  Would that solve the problem?
>> The buffers it should affect are all file-visiting buffers.  project.el
>> doesn't currently have any code which runs for every new buffer.  I
>> guess we've considered adding that, but I'm not sure this is a good
>> reason...
>
> I'm not sure every project.el user will want this particular behavior
> anyway. project-switch-buffer is handy, but personally, I still most
> often use 'C-x b'.
>
> But there definitely is demand for this option, as evidenced by the
> previously mentioned bug#59502, as well as this (unexpectedly,
> years-old) thread:
> https://lists.gnu.org/archive/html/emacs-devel/2021-03/msg00083.html
>
> Speaking of those, do you think it would be feasible to also offer
> these tweaks (as options, or for particular buffers):
>
> - Make the presence of the buffer name mandatory. As shown in the
>   examples in bug#59502, it could be useful to always see in buffers
>   like *eshell* produced by project-eshell. Or project-vc-dir, for
>  example.

(I assume you mean "make the presence of the project name mandatory")

I think there is a good solution to this which was not mentioned in
bug#59502 only add the project name (or dirname or whatever) to the
buffer when that's necessary to give the buffer a unique name.  That
reduces overhead when working only with one project, and neatly fits in
to how uniquify already works for file-visiting buffers.

To do this, I think we'd need to change commands to use a function other
than get-buffer-create when accessing e.g. *xref* or *eshell*, which
like create-file-buffer gets a chance to uniquify the buffer name.

It's a bit tricky though: we want commands to access and reuse existing
a project-specific buffer if there is one, but commands doesn't know the
name of that buffer so can't find it that way.  find-file has solved
this same problem ages ago, of reusing an existing buffer if we
find-file a buffer-file-name which is already open.  I think we may need
something similar for non-file-visiting buffers.

Maybe some kind of mechanism to find a buffer with basename "*eshell*"
whose default-directory contains our current default-directory?  Kind of
a "locate-dominating-buffer"?

> - Hide the parent directory from the uniquification logic (only
>   keeping the project name). So that, for example, if I call 'M-x
>   project-eshell' and then 'C-u M-x project-eshell', the generated
>   buffer names would not try to use the parent segment to uniquify,
>   and just stay as <project-name>/*eshell* and
>   <project-name>/*eshell-2*. There is currently some bespoke logic for
>   naming these particular buffers, but if we could move to uniquify
>   (and obey its custom vars), that would probably be an improvement.

Hm, so if two *eshell* buffers are in the same project, they should
first be uniquified from other *eshell* buffers by adding the project
name, and then uniquified from each other by adding numbers to the end
of the buffer name.

I think I can implement this pretty easily in uniquify.el: if a set of
conflicting buffers all have the same dirname, then resolve the conflict
by adding numbers to the end.

(Actually I was a bit surprised to realize that uniquify wasn't doing
this already, but I guess it's because it previously has only worked for
file-visiting buffers, which as I mentioned above are kept unique by
buffer-file-name, so there can't be conflicts between two buffer names
if you include their entire buffer-file-name in the buffer name.)


---

Incidentally, another feature which I've been thinking about at the
intersection of project.el and uniquify.el: We could rerun uniquify on
project-buffers in a mode where it just outputs sufficiently unique
names without actually renaming the buffers, and then use that in
project-switch-to-buffer.  So then when picking the buffer, you are
picking from buffer names which are unique *in that specific project*.
It's otherwise kind of annoying to me that project-switch-to-buffer
includes a bunch of long disambiguating paths in the buffer names even
though the buffer names aren't actually ambiguous in that command.

Does that sound interesting?  I, like you, usually use C-x b.  But I
think this feature would make C-x p b much nicer and competitive with
C-x b.