support for outshine mode

[jave]

I like using outshine mode in clojure-mode buffers, but folding doesnt appear to work in clojure-ts mode.

https://github.com/alphapapa/outshine

[bbatsov]

Seems that's some extension of the built-in outline-mode. Probably we haven't implemented properly the support for outline, as I doubt outshine requires something special. Should be an easy task.

[rrudakov]

FYI, we need to define proper value for treesit-outline-predicate. From the documentation:

treesit-outline-predicate is a variable defined in ‘treesit.el’.

Its value is ‘treesit-outline-predicate--from-imenu’

Predicate used to find outline headings in the syntax tree.
The predicate can be a function, a regexp matching node type,
and more; see docstring of ‘treesit-thing-settings’.
It matches the nodes located on lines with outline headings.
Intended to be set by a major mode.  When nil, the predicate
is constructed from the value of ‘treesit-simple-imenu-settings’
when a major mode sets it.

[bbatsov]

Yeah, that's what I figured as well.

[rrudakov]

treesit.el sets treesit-outline-predicate automatically based on imenu settings, so if I execute M-x outline-cycle in clojure-ts-mode buffer when point is on function or var definition, it hides the content correctly:

In clojure-mode it works differently, there we set 2 buffer local variables:

(setq-local outline-regexp ";;;;* ")
(setq-local outline-level 'lisp-outline-level)

Which allows hiding buffer content based on comments starting from 4 and more semicolons. M-x outline-cycle doesn't fold def-like forms in clojure-mode.

I don't think it's possible to set treesit-outline-predicate to fold special comments, any comment in the syntax tree is just a (comment) node, no matter how many semicolons are there. To calculate outline depth treesit.el just counts how many parent nodes does the current node have, but (comment) node, which is supposed to be outline heading is always top-level.

What is the desired behavior of outline-minor-mode for clojure-ts-mode? We can leave default treesit-based settings and fold forms based on imenu, or we can just use the same settings as clojure-mode to fold comments.

[rrudakov]

We can also add a customization option, something like clojure-ts-outline-variant with 2 values, imenu or comments. WDYT?

[bbatsov]

Yeah, this seems like a reasonable approach to me.