bug#69305: outline-minor-mode for tabulated-list-mode

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@linkov.net>
> Cc: 69305@debbugs.gnu.org
> Date: Tue, 27 Feb 2024 19:40:10 +0200
> 
> >> But tabulated-list-groups is not a defcustom.
> >> There are no defcustoms here.
> >
> > Buffer-menu-group-by _is_ a defcustom, and it is documented thusly:
> >
> >   +  "If non-nil, buffers are grouped by function.
> >   +This function takes one argument: a list of entries in the same format
> >   +as in `tabulated-list-entries', and should return a list in the format
> >   +suitable for `tabulated-list-groups'.
> >
> > So you are inviting users to write functions that return values of a
> > certain format, but the format's documentation IMO doesn't make it
> > clear how to specify a grouping, and for its important part alludes to
> > another variable (tabulated-list-entries), whose documentation is
> > suitable for different kind of uses, not for grouping of entries.
> 
> The format 'tabulated-list-entries' is input.
> The format 'tabulated-list-groups' is output.

Yes, I'm well aware of that.

> > Since tabulated-list-groups is such an important part of the
> > documentation of Buffer-menu-group-by, the doc string of
> > tabulated-list-groups is in effect part of the doc string of
> > Buffer-menu-group-by, and should IMO be worded as appropriate for user
> > options.
> 
> The docstring of 'tabulated-list-groups' already
> sufficiently documents the format:

No, it doesn't document it sufficiently.  As I already said several
times.

>   (defvar-local tabulated-list-groups nil
>     "Groups displayed in the current Tabulated List buffer.
>   This should be either a function, or a list.
>   If a list, each element has the form (GROUP-NAME ENTRIES),
>   where:
> 
>    - GROUP-NAME is a group name as a string, which is displayed
>      at the top line of each group.
> 
>    - ENTRIES is a list described in `tabulated-list-entries'.
> 
> There is no need to duplicate the description of linked
> 'tabulated-list-entries'.

This is not about duplication.  This is about adding information that
currently isn't there.

> And here it's clear that the function should add GROUP-NAME to
> groups from 'tabulated-list-entries'.

Which doesn't clarify the issue at hand even a single bit.