Re: Emacs Lisp code formatting

[Campbell Barton]

On 11/4/21 10:59, Lars Ingebrigtsen wrote:
> Campbell Barton <ideasman42@gmail.com> writes:
>
> > There are a handful of 3rd party lisp formatting tools [0], though, YMMV.
> >
> > [0]: https://emacs.stackexchange.com/a/55759/2418
>
> Thanks.  I had a look at them, but they seem to have the problem of
> being 1) too dependent on the rest of a larger package or 2) having
> special code for known constructs (meaning that there'd be a maintenance
> burden over the years).
>
> I wonder how far one can get by using the symbol properties (i.e.,
> edebug-form-spec/lisp-indent-function/doc-string-elt).  Has anybody
> looked into that?  If not, I think I'll take a whack at implementing
> something simple based on that -- it seems like it should be possible to
> make something general based on that.

You could get quite far, an issue I ran into is function introspection 
such as `func-arity' depend on the code being loaded into emacs.

You could scan external `require' calls, but this means parsing many 
files to extract the information you need.
If you're OK with loading the code for the purpose of introspection - 
you could spawn an emacs instance for that purpose.
If speed is important (such as running this whenever saving a file) the 
information could be cached (with a file list to detect when the cache 
needs to be regenerated).

This is the main sticking point for me, something that would need to be 
resolved before auto-formatting could be recommended for general use.

Note that I use auto-format on save for all my packages (full 
auto-formatting, not just auto-indent), and personally find it great, 
but as far as I know I'm the only person doing this.