Add prog-fill-reindent-defun (bug#59664)

Introduce a new command that aims to reindent code in a defun, or fill
a paragraph of text.  The command uses treesit.el when available,
otherwise falls back to using syntax-ppss and regexps.  Treesit.el
needs a new variable that is intended to be set by the major modes so
that this and other future functions can know what kind of node we are
looking at.

* doc/emacs/programs.texi: Mention the new command.
* etc/NEWS: Mention the new command.
* lisp/progmodes/c-ts-mode.el (c++-ts-mode): Add regexp for the new
variable.
* lisp/progmodes/csharp-mode.el (csharp-ts-mode): Add regexp for the
new variable.
* lisp/progmodes/java-ts-mode.el (java-ts-mode): Add regexp for the
new variable.
* lisp/progmodes/js.el (js-ts-mode): Add regexp for the new variable.
* list/progmodes/prog-mode.el (prog-mode-map): Bind the new command by
default.
(prog-fill-reindent-defun): New command.
* lisp/progmodes/sh-script.el (bash-ts-mode): Add regexp for the new
variable.
* lisp/progmodes/typescript-ts-mode.el (typescript-ts-base-mode): Add
regexp for the new variable.
* lisp/treesit.el (treesit-text-type-regexp): New variable.

doc/emacs/programs.texi

@@ -409,6 +409,9 @@ large chunks of code:
 @table @kbd
 @item C-M-q
 Reindent all the lines within one parenthetical grouping.
+@item M-q
+Fill a single paragraph in a defun, or reindent all the lines within
+that defun.
 @item C-u @key{TAB}
 Shift an entire parenthetical grouping rigidly sideways so that its
 first line is properly indented.
@@ -429,6 +432,22 @@ indentation of the line where the grouping starts).  The function that
 etc.  To correct the overall indentation as well, type @kbd{@key{TAB}}
 first.
 
+@kindex M-q
+@findex prog-fill-reindent-defun
+@vindex beginning-of-defun-function
+@vindex end-of-defun-function
+@vindex fill-paragraph-function
+  Major modes that derive from @code{prog-mode} can either fill a
+single paragraph in a defun, such as a doc-string, or a comment, or
+(re)indent the surrounding defun if point is not in a comment or a
+string by typing @kbd{M-q} or using the command @kbd{M-x
+prog-fill-reindent-defun}.  The bounds of a defun is decided by the
+variable @code{beginning-of-defun-function} and
+@code{end-of-defun-function}, and the filling mechanism is decided by
+@code{fill-paragraph-function} (@ref{List Motion,,, elisp, The Emacs
+Lisp Reference Manual}, or @ref{Filling,,, elisp, The Emacs Lisp
+Reference Manual} for more information).
+
 @kindex C-u TAB
   If you like the relative indentation within a grouping but not the
 indentation of its first line, move point to that first line and type

etc/NEWS

@@ -76,6 +76,13 @@ using this new option.  (Or set 'display-buffer-alist' directly.)
 After manually editing 'eshell-aliases-file', you can use
 'M-x eshell-read-aliases-list' to load the edited aliases.
 
+** Prog Mode
++++
+*** New command 'prog-fill-reindent-defun'
+This command either fills a single paragraph in a defun, such as a
+doc-string, or a comment, or (re)indents the surrounding defun if
+point is not in a comment or a string.  It is by default bound to
+'M-q' in 'prog-mode' and all its descendants.
 
 * New Modes and Packages in Emacs 30.1
 

lisp/progmodes/c-ts-mode.el

@@ -627,6 +627,10 @@ the subtrees."
                   (group (or (syntax comment-end)
                              (seq (+ "*") "/")))))
 
+  (setq-local treesit-text-type-regexp
+              (regexp-opt '("comment"
+                            "raw_string_literal")))
+
   (treesit-parser-create 'cpp)
 
   (setq-local treesit-simple-indent-rules

lisp/progmodes/csharp-mode.el

@@ -918,6 +918,11 @@ Key bindings:
                   (group (or (syntax comment-end)
                              (seq (+ "*") "/")))))
 
+  (setq-local treesit-text-type-regexp
+              (regexp-opt '("comment"
+                            "verbatim_string-literal"
+                            "interpolated_verbatim_string-text")))
+
   ;; Indent.
   (setq-local treesit-simple-indent-rules csharp-ts-mode--indent-rules)
 

lisp/progmodes/java-ts-mode.el

@@ -313,6 +313,11 @@ the subtrees."
                   (group (or (syntax comment-end)
                              (seq (+ "*") "/")))))
 
+  (setq-local treesit-text-type-regexp
+              (regexp-opt '("line_comment"
+                            "block_comment"
+                            "text_block")))
+
   ;; Indent.
   (setq-local treesit-simple-indent-rules java-ts-mode--indent-rules)
 

lisp/progmodes/js.el

@@ -3860,6 +3860,11 @@ Currently there are `js-mode' and `js-ts-mode'."
                     (group (or (syntax comment-end)
                                (seq (+ "*") "/")))))
     (setq-local comment-multi-line t)
+
+    (setq-local treesit-text-type-regexp
+                (regexp-opt '("comment"
+                              "template_string")))
+
     ;; Electric-indent.
     (setq-local electric-indent-chars
 	        (append "{}():;," electric-indent-chars)) ;FIXME: js2-mode adds "[]*".

lisp/progmodes/prog-mode.el

@@ -30,7 +30,11 @@
 ;;; Code:
 
 (eval-when-compile (require 'cl-lib)
-                   (require 'subr-x))
+                   (require 'subr-x)
+                   (require 'treesit))
+
+(declare-function treesit-parser-list "treesit.c")
+(declare-function treesit-node-type "treesit.c")
 
 (defgroup prog-mode nil
   "Generic programming mode, from which others derive."
@@ -102,7 +106,8 @@
 
 (defvar-keymap prog-mode-map
   :doc "Keymap used for programming modes."
-  "C-M-q" #'prog-indent-sexp)
+  "C-M-q" #'prog-indent-sexp
+  "M-q" #'prog-fill-reindent-defun)
 
 (defvar prog-indentation-context nil
   "When non-nil, provides context for indenting embedded code chunks.
@@ -140,6 +145,32 @@ instead."
 	  (end (progn (forward-sexp 1) (point))))
       (indent-region start end nil))))
 
+(defun prog-fill-reindent-defun (&optional argument)
+  "Refill or reindent the paragraph or defun that contains point.
+
+If the point is in a string or a comment, fill the paragraph that
+contains point or follows point.
+
+Otherwise, reindent the definition that contains point or follows
+point."
+  (interactive "P")
+  (save-excursion
+    (let ((treesit-text-node
+           (and (treesit-parser-list)
+                (string-match-p
+                 treesit-text-type-regexp
+                 (treesit-node-type (treesit-node-at (point)))))))
+      (if (or treesit-text-node
+              (nth 8 (syntax-ppss))
+              (re-search-forward comment-start-skip (line-end-position) t))
+          (if (memq fill-paragraph-function '(t nil))
+              (lisp-fill-paragraph argument)
+            (funcall fill-paragraph-function argument))
+        (beginning-of-defun)
+        (let ((start (point)))
+          (end-of-defun)
+          (indent-region start (point) nil))))))
+
 (defun prog-first-column ()
   "Return the indentation column normally used for top-level constructs."
   (or (car prog-indentation-context) 0))

lisp/progmodes/sh-script.el

@@ -1619,6 +1619,10 @@ not written in Bash or sh."
                   ( bracket delimiter misc-punctuation operator)))
     (setq-local treesit-font-lock-settings
                 sh-mode--treesit-settings)
+    (setq-local treesit-text-type-regexp
+                (regexp-opt '("comment"
+                              "heredoc_start"
+                              "heredoc_body")))
     (treesit-major-mode-setup)))
 
 (advice-add 'bash-ts-mode :around #'sh--redirect-bash-ts-mode

lisp/progmodes/typescript-ts-mode.el

@@ -329,6 +329,10 @@ Argument LANGUAGE is either `typescript' or `tsx'."
                   (group (or (syntax comment-end)
                              (seq (+ "*") "/")))))
 
+  (setq-local treesit-text-type-regexp
+              (regexp-opt '("comment"
+                            "template_string")))
+
   ;; Electric
   (setq-local electric-indent-chars
               (append "{}():;," electric-indent-chars))

lisp/treesit.el

@@ -1639,6 +1639,15 @@ ARG is the same as in `beginning-of-defun'."
     (when top
       (goto-char (treesit-node-end top)))))
 
+(defvar-local treesit-text-type-regexp "\\`comment\\'"
+  "A regexp that matches the node type of textual nodes.
+
+A textual node is a node that is not normal code, such as
+comments and multiline string literals.  For example,
+\"(line|block)_comment\" in the case of a comment, or
+\"text_block\" in the case of a string.  This is used by
+`prog-fill-reindent-defun' and friends.")
+
 ;;; Activating tree-sitter
 
 (defun treesit-ready-p (language &optional quiet)