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

[Juri Linkov]

>> >> >> +@defvar tabulated-list-groups
>> >> >> +This buffer-local variable specifies the groups of entries displayed 
>> >> >> in
>> >> >> +the Tabulated List buffer.  Its value should be either a list, or a
>> >> >> +function.
>> >> >> +
>> >> >> +If the value is a list, each list element corresponds to one group, 
>> >> >> and
>> >> >> +should have the form @w{@code{(@var{group-name} @var{entries})}}, 
>> >> >> where
>> >> >> +@var{group-name} is a string inserted before all group entries, and
>> >> >> +@var{entries} have the same format as @code{tabulated-list-entries}
>> >> >> +(see above).
>> >> >> +
>> >> >> +Otherwise, the value should be a function which returns a list of the
>> >> >> +above form when called with no arguments.
>> >> >> +@end defvar
>> >> >
>> >> > I think the way to specify ENTRIES for this customization should be
>> >> > described in more detail.  Reading the above description, even the
>> >> > idea of using ENTRIES for specifying grouping is unclear, since
>> >> > tabulated-list-entries is basically just a list of column descriptors.
>> >>
>> >> But ENTRIES are described in 'tabulated-list-entries'.  Here ENTRIES
>> >> are no different from 'tabulated-list-entries' that are just
>> >> column descriptors.
>> >
>> > My point is that it isn't obvious how to describe grouping in terms of
>> > column descriptors.  I think the manual should tell in more detail how
>> > to use column descriptors to specify how entries should be grouped.
>> > Maybe an example or two is all that it takes to do that.
>>
>> Sorry, I don't understand what is unclear here:
>>
>>   If the value is a list, each list element corresponds to one group, and
>>   should have the form @w{@code{(@var{group-name} @var{entries})}}, where
>>   @var{group-name} is a string inserted before all group entries, and
>>   @var{entries} have the same format as @code{tabulated-list-entries}
>>   (see above).
>>
>> Basically this says that the format is (group-name entries) where
>> entries are described in tabulated-list-entries as having the format
>> (id contents).  There is no need to duplicate the description of entries.
>
> Maybe I'm missing something here.  To put it more concretely, can you
> show a value of tabulated-list-groups that will cause the buffers in
> buffer list grouped by major mode using the above form?

Data structure for `tabulated-list-groups' is a list of elements,
each element should of the form

  (GROUP-NAME (ID . CONTENTS) (ID . CONTENTS) ...)

where GROUP-NAME is the name of the group, ID is a Lisp object that
identifies the entry and CONTENTS is a vector with the same number of
elements as `tabulated-list-format'.  When buffers grouped by major mode:

  (("* Lisp Interaction" (#<buffer *scratch*> ["." " " "*" #("*scratch*" 0 9 
...) "225" "Lisp Interaction" ""]) ...))

>> >> >> +(ert-deftest tabulated-list-groups ()
>> >> >> +  (with-temp-buffer
>> >> >> +    (tabulated-list-mode)
>> >> >> +    (setq tabulated-list-groups
>> >> >> +          (reverse
>> >> >> +           (seq-group-by (lambda (b) (concat "* " (aref (cadr b) 3)))
>> >> >> +                         tabulated-list--test-entries)))
>> >> >> +    (setq tabulated-list-format tabulated-list--test-format)
>> >> >> +    (setq tabulated-list-padding 7)
>> >> >> +    (tabulated-list-init-header)
>> >> >> +    (tabulated-list-print)
>> >> >
>> >> > This seems to test only the function value of tabulated-list-groups?
>> >> > What about the other form of the value?
>> >>
>> >> The other forms have no functional difference.
>> >
>> > Sorry, I don't follow.  Shouldn't we test the capability of specifying
>> > grouping by the method other than by providing a function?
>>
>> Actually there are no other methods.
>
> The doc string says the "value can be either a list or a function".  I
> see only one value here, so I'm asking what about a value of the other
> form.  Or what am I missing here?

Another form is a function.  But there is no need to test this.
It's just a copy from tabulated-list-entries that is unused.