Re: The tab-line "All" group

[Juri Linkov <juri@linkov.net>]

> The behavior of `tab-line-tabs-buffer-group-function' when returning
> nil, according to its docstring, is that the "buffer should be filtered
> out".  I found it not really elucidative, though.  The actual behavior
> is to display a group called "All" (currently, a hardcoded value) and
> don't display any tab (for the buffers that belongs to this group, i.e.,
> for cases when (funcall tab-line-tabs-buffer-group-function buffer)
> returns nil).
>
> What are the actual use-cases where the behavior of "filtering out" tabs
> (i.e. to don't display) for the "All" group is useful? (i.e., to hide
> tabs *only* in the "All" group when the user has explicitly enabled the
> tab-line mode to actually see tabs).

Sorry for the delay.  Some string is needed to display to not leave
the tab-line completely empty.

> Personally, I find it somewhat confusing, especially because the name
> "All" might led the user to think that this group contains all tabs,
> which is not true.  The name "Others"/"Rest"/etc would make more sense
> in this context.  If I had to choose, I would demand
> `tab-line-tabs-buffer-group-function' to always return a valid (non-nil)
> group name.

You are right, the "All" group is too confusing.  A proper name would be
"No group" or "Ungrouped".  "No group" is shorter, so let's use it.

> If an "All" group is really useful, we can properly
> implement it, i.e., to have a group that *actually* contains all tabs.

No need to implement an "All" group explicitly since a customized
tab-line-tabs-buffer-group-function can return the string "All"
for all ungrouped buffers.

> At last, when `tab-line-tabs-buffer-group-function' returns an empty
> string, it adds the opposite (undocumented and unintended, I guess)
> "feature": to display tabs but not the group name.  The tabs are
> actually added to a group named "", but the tab name is not displayed,
> since it's an empty string.  Not sure if this info is useful or if we
> need to change something here, but I thought it would be nice to share.

Thanks for sharing.  Maybe someone might need to show no group name
for some "default group".

> Here is a simple snippet to play with tab-line groups:
>
> #+begin_src emacs-lisp
> (progn
>   (defvar my-tab-line-group-default-value nil)
>
>   (defun my-tab-line-group-function (buffer)
>     "Group tab-line tabs by project."
>     (with-current-buffer buffer
>       (if-let ((project (project-current)))
>           (project-root project)
>         my-tab-line-group-default-value)))
>
>   (setopt tab-line-tabs-function 'tab-line-tabs-buffer-groups
>           tab-line-tabs-buffer-group-function #'my-tab-line-group-function)
>
>   (global-tab-line-mode 1))
> #+end_src

Thanks for suggesting a group by project name.  This will be added now
as a new option to 'tab-line-tabs-buffer-group-function'.

PS: maybe also will add a new option 'prev-buffers'
to 'tab-line-tabs-buffer-group-sort-function'
to sort buffers by the fixed order of their
appearance in the window using information
from window prev/next buffers.