Fix block comment indent and filling for c-ts-mode (bug#59763)

Now indent and filling works like in c-mode.  The only noticeable
missing piece is that the "*/" is not attached to the last sentence
when filling.  c-mode does it by replacing whitespaces between the
"*/" and the end of the last sentence with xxx, fill it, then change
the xxx back. I don't know if we should do that in c-ts-mode's filling.

* doc/lispref/modes.texi (Parser-based Indentation): Add new preset.
* lisp/progmodes/c-ts-mode.el (c-ts-mode--indent-styles): Add new
indent rule.
(c-ts-mode--fill-paragraph): New function.
(c-ts-base-mode): Setup paragraph-start, adaptive-fill, etc.
* lisp/treesit.el (treesit-simple-indent-presets): Add new preset.

1 files changed, 8 insertions, 0 deletions

diff --git a/doc/lispref/modes.texi b/doc/lispref/modes.texi
index c44938f3929..736c2d6841f 100644
--- a/doc/lispref/modes.texi
+++ b/doc/lispref/modes.texi
@@ -5024,6 +5024,14 @@ comment-start token.  Comment-start tokens are defined by regular
 expression @code{comment-start-skip}.  This function assumes
 @var{parent} is the comment node.
 
+@item prev-adaptive-prefix
+This anchor is a function that is called with 3 arguments: @var{node},
+@var{parent}, and @var{bol}.  It tries to go to the beginning of the
+previous non-empty line, and matches @code{adaptive-fill-regexp}.  If
+there is a match, this function returns the end of the match,
+otherwise it returns nil.  This anchor is useful for a
+@code{indent-relative}-like indent behavior for block comments.
+
 @end ftable
 @end defvar