Re: About org-sort -> org-sort-list with custom sort function

[Kyle Meyer <kyle@kyleam.com>]

Zhitao Gong <zhitaao.gong@gmail.com> writes:

> I think there is a bug in org-sort or org-sort-list function.
>
> If you call org-sort (C-c ^) on list items, this function will call
> org-sort-list.  However, org-sort calls org-sort-list with only one
> argument, i.e., the with-case (see the code below)
>
> #+BEGIN_SRC emacs-lisp
> ((org-at-item-p) (org-call-with-arg 'org-sort-list with-case))
> #+END_SRC emacs-lisp

org-sort actually isn't calling org-sort-list with one argument; it's
calling it interactively, while let-binding current-prefix-arg:

    (defsubst org-call-with-arg (command arg)
      "Call COMMAND interactively, but pretend prefix arg was ARG."
      (let ((current-prefix-arg arg)) (call-interactively command)))

I'm a bit confused about why org-call-with-arg is necessary because I
think call-interactively already propagates the current prefix argument,
but perhaps I'm missing some subtlety here.  Either way ...

> The problem is that if you choose ?f (sorting with custom key function),
> then org-sort-list expects another argument, the compare-func, which is
> not passed to it.
>
> IMHO, there are two ways to solve this
>
> 1. Ask for the compare-func in org-sort-list, as it does for the
>    getkey-func.  A default value could be provided for compare-func,
>    e.g., string<, <, etc.  Or
> 2. Restrict the return type to a string (or integer) so that we could
>    fix the compare-func

I see it as a documentation issue.  org-sort-list's docstring doesn't
make it clear which part of the description applies to an interactive
caller versus a Lisp caller.  An interactive caller can choose the ?f
sorting type, but they can't specify the compare-func.  Entries are
compared using sort-subr's default comparison behavior (see its
docstring), and getkey-func has to return a value that's compatible with
this behavior.

And I think it's OK to not expose compare-func to the interactive
caller.  In cases where sort-subr's default behavior won't do and a user
wants to supply a value for compare-func, they can create their own
command that wraps a non-interactive org-sort-list call.

What do you think?

-- 
Kyle