bug#48724: Code collapsing and outline headings for elisp

[Christopher Dimech <dimech@gmx.com>]

> Sent: Sunday, May 30, 2021 at 9:57 AM
> From: "Juri Linkov" <juri@linkov.net>
> To: "Christopher Dimech" <dimech@gmx.com>
> Cc: 48724@debbugs.gnu.org
> Subject: Re: bug#48724: Code collapsing and outline headings for elisp
>
> > Currently, outline-minor-mode has the capability to treat "defun" constructs
> > as heading, allowing one to choose to hide some code from view by collapsing
> > the region of code.  It would be beneficial for the actual major mode itself
> > (i.e. emacs-lisp-mode) to handle the code collapsing, leaving the code highlighting
> > intact.  Code collapsing could also be extended beyond not only collapsing
> > functions and variables ((defun, defvar), but also to additional constructs that could
> > be indented (e.g. lists '(...), let, let*, pcase) and other constructs users could
> > find useful (e.g. if, when, ).
> >
> > And for outline-minor-mode, the mode could then be used to further enhance the structuring
> > of larger chunks of code (e.g. a collection of functions) using outline headings.  Outlining
> > would then be a separate capability different from code collapsing.
> 
> Currently everything is customizable in outline-minor-mode by just
> two variables: outline-regexp and outline-level.  So when necessary,
> emacs-lisp-mode could provide an option that will set different values
> of these variables, one of which could set outline-regexp to a regexp
> that matches: lists, '(...), let, let*, pcase, if, when, etc…

The general impression is that outline-minor-mode is a general mode
for customisable headings that are then handled by the respective
major mode.

General settings could be better, because some variables are not customizable.

Serious problem is that the two important variables: `outline-regexp' and
`outline-heading-alist' are not customizable by using "M-x customize-group".

Additionally both of them should be customizable per mode.  Don't you think so?

There has been a discussion today about outline-minor-mode settings for fortran
(both fixed and free form).  Have had a go at using "!" and "!!", but "Hide Body"
did not hide the body.

There could be some default headings for fortran when outline-minor-mode is enabled.
One could follow the current setup for emacs-lisp-mode, for fortran.

!! for heading level 1
!!! for subheading level 2
!!!! for subsubheading level 3

Together with "Hide Body" for lines beginning with "subroutine" and "function".