Re: Please do not deprecate perl-mode in favour of cperl-mode

["Harald Jörg" <haj@posteo.de>]

"Paul W. Rankin" via "Emacs development discussions."
<emacs-devel@gnu.org> writes:

> On 2023-12-03 17:07, Eli Zaretskii wrote:
>>> C Perl Mode has several quirks that make it behave unlike a normal
>>> Emacs
>>> Major mode, including:
>>> - unorthodox code indentation
>>> - behaviour of TAB on region does not perform indent-region
>>> - use of specific faces instead of font-lock-* faces
>> What if CPerl mode would optionally support the above as well?
>> Would
>> it be acceptable then for you to switch?
>
> I would love to take advantage of whatever CPerl Mode advantages exist
> if CPerl Mode could do the things that Perl Mode does. And I think it 
> should be easy and clear to the user how to set these options.
>
> Here's a minimal example of perl code that indents in a way I find
> unexpected in CPerl Mode (e.g. the trailing paren should line up with 
> the start of the statement):
>
>     $r->get(
>         '/test'
>        );

This is how Perl mode indents it, isn't it?

CPerl mode has several predefined indentation styles, a recent addition
is to indent according to Damian Conway's "Perl Best Practices".  This
can be activated with (cperl-set-style "PBP").  It _should_ be the
default these days, but it isn't for compatibility reasons.  in PBP
style, indentation is like this:

    $r->get(
        '/test'
    );

> I also found weird behaviour with Electric Pair Mode; when point is at
> `|' here and `{' is inserted, I get `{|}}', which seems incorrect 
> because it unbalances the braces (Perl Mode inserts `{|}'):
>
>     $r->get(
>         '/test',
>         sub {
>             |
>         }
>     );

This would indeed be a bug.  Unfortunately, I can not reproduce it.  If
you have a recipe to demonstrate the bug, then a bug report would be
welcome!

> One more thing...
>
> CPerl Mode has a feature the applies the `underline' face to leading
> whitespace before point and there doesn't appear to be an option to
> disable this. It's not a huge thing, but Whitespace Mode provides this
> feature and it's just a weird addition to hardcode and not use
> something called `cperl-leading-whitespace-face'.

This seems to have been fixed already by Stefan Kangas.  It used to be
the customizable face `cperl-invalid-face' but is gone now, in favor of
the option `show-trailing-whitespace'.

>>> I don't wish to dampen the enthusiasm of the originator of this
>>> Perl->C
>>> Perl idea, but I would implore you to please first address C Perl
>>> Mode's
>>> shortcoming as a 1:1 replacement for Perl Mode before the
>>> baby/bathwater? C Perl Mode should at least work as well as Perl Mode
>>> before deprecation is considered.
>> Deprecation doesn't mean removal.  Even obsolete packages are still
>> available, and some of them will not be removed.  So if you insist on
>> using Perl mode, you will be able to do so for the years to come, even
>> if we deprecate and obsolete it.
>
> This is cool. My opinion is that CPerl Mode is (currently) too weird
> and idiosyncratic to be Emacs's default mode for perl (e.g. what the
> heck is `cperl-hairy' or `cperl-fontify-m-as-s'?) and will likely lead
> to more confusion than productivity/joy. But maybe if someone wants to
> take a hard look at CPerl Mode from a user friendliness perspective?

I find the documentation of `cperl-hairy' and its customization
interface not too bad - but I am the wrong person to ask.

Anyways: CPerl mode has accumulated lots of options over the years.
Many of them, for example `cperl-fontify-m-as-s', can be safely ignored
and left at their defaults.

We will have more options to allow CPerl mode to look like Perl mode.
`cperl-fontify-trailer' is the first of the new options, to account for
the different treatment of text after __END__ or __DATA__ tokens.
-- 
Cheers,
haj