From 558382b5c712431f0a19262c6e1fb67fdedd908b Mon Sep 17 00:00:00 2001
From: Theodor Thornhill <theo@thornhill.no>
Date: Sun, 8 Jan 2023 20:28:02 +0100
Subject: [PATCH] Add forward-sentence with tree sitter support (bug#60623)

* etc/NEWS: Mention the new changes.
* lisp/textmodes/paragraphs.el (forward-sentence-default-function):
Move old implementation to its own function.
(forward-sentence-function): New defvar defaulting to old behavior.
(forward-sentence): Use the variable in this function unconditionally.
* lisp/treesit.el (treesit-sentence-type-regexp): New defvar.
(treesit-forward-sentence): New defun.
(treesit-major-mode-setup): Conditionally set
forward-sentence-function.
---
 etc/NEWS                     | 16 ++++++++++++++++
 lisp/textmodes/paragraphs.el | 15 +++++++++++++--
 lisp/treesit.el              | 28 ++++++++++++++++++++++++++++
 3 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/etc/NEWS b/etc/NEWS
index 690e9c3faa9..a0b2de056d8 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -57,6 +57,22 @@ treesit.el now unconditionally sets 'transpose-sexps-function' for all
 Tree-sitter modes.  This functionality utilizes the new
 'transpose-sexps-function'.
 
+** New defvar forward-sentence-function.
+Emacs now can set this variable to customize the behavior of the
+'forward-sentence' function.
+
+** New defun forward-sentence-default-function.
+The previous implementation of 'forward-sentence' is moved into its
+own function, to be bound by 'forward-sentence-function'.
+
+** New defvar-local 'treesit-sentence-type-regexp.
+Similarly to 'treesit-defun-type-regexp', this variable is used to
+navigate sentences in Tree-sitter enabled modes.
+
+** New function 'treesit-forward-sentence'.
+treesit.el now conditionally sets 'forward-sentence-function' for all
+Tree-sitter modes that sets 'treesit-sentence-type-regexp'.
+
 
 * Changes in Specialized Modes and Packages in Emacs 30.1
 ---
diff --git a/lisp/textmodes/paragraphs.el b/lisp/textmodes/paragraphs.el
index 73abb155aaa..fd2d83eeebf 100644
--- a/lisp/textmodes/paragraphs.el
+++ b/lisp/textmodes/paragraphs.el
@@ -441,13 +441,12 @@ end-of-paragraph-text
 	  (if (< (point) (point-max))
 	      (end-of-paragraph-text))))))
 
-(defun forward-sentence (&optional arg)
+(defun forward-sentence-default-function (&optional arg)
   "Move forward to next end of sentence.  With argument, repeat.
 When ARG is negative, move backward repeatedly to start of sentence.
 
 The variable `sentence-end' is a regular expression that matches ends of
 sentences.  Also, every paragraph boundary terminates sentences as well."
-  (interactive "^p")
   (or arg (setq arg 1))
   (let ((opoint (point))
         (sentence-end (sentence-end)))
@@ -480,6 +479,18 @@ forward-sentence
     (let ((npoint (constrain-to-field nil opoint t)))
       (not (= npoint opoint)))))
 
+(defvar forward-sentence-function #'forward-sentence-default-function
+  "Function to be used to calculate sentence movements.
+See `forward-sentence' for a description of its behavior.")
+
+(defun forward-sentence (&optional arg)
+  "Move forward to next end of sentence.  With argument, repeat.
+When ARG is negative, move backward repeatedly to start of sentence.
+Delegates its work to `forward-sentence-function'."
+  (interactive "^p")
+  (or arg (setq arg 1))
+  (funcall forward-sentence-function arg))
+
 (defun count-sentences (start end)
   "Count sentences in current buffer from START to END."
   (let ((sentences 0)
diff --git a/lisp/treesit.el b/lisp/treesit.el
index a7f453a8899..0681e758b37 100644
--- a/lisp/treesit.el
+++ b/lisp/treesit.el
@@ -1783,6 +1783,32 @@ treesit-end-of-defun
     (when treesit-defun-skipper
       (funcall treesit-defun-skipper))))
 
+(defvar-local treesit-sentence-type-regexp ""
+  "A regexp that matches the node type of sentence nodes.
+
+A sentence node is a node that is bigger than a sexp, and
+delimits larger statements in the source code.  It is, however,
+smaller in scope than defuns.  This is used by
+`treesit-forward-sentence' and friends.")
+
+(defun treesit-forward-sentence (&optional arg)
+  "Tree-sitter `forward-sentence-function' function.
+
+ARG is the same as in `forward-sentence-function'.
+
+If inside comment or other nodes described in
+`treesit-sentence-type-regexp', use
+`forward-sentence-default-function', else move across nodes as
+described by `treesit-sentence-type-regexp'."
+
+  (if (string-match-p
+       treesit-text-type-regexp
+       (treesit-node-type (treesit-node-at (point))))
+      (funcall #'forward-sentence-default-function arg)
+    (funcall
+     (if (> arg 0) #'treesit-end-of-thing #'treesit-beginning-of-thing)
+     treesit-sentence-type-regexp (abs arg))))
+
 (defvar-local treesit-text-type-regexp "\\`comment\\'"
   "A regexp that matches the node type of textual nodes.
 
@@ -2256,6 +2282,8 @@ treesit-major-mode-setup
                 #'treesit-add-log-current-defun))
 
   (setq-local transpose-sexps-function #'treesit-transpose-sexps)
+  (when treesit-sentence-type-regexp
+    (setq-local forward-sentence-function #'treesit-forward-sentence))
 
   ;; Imenu.
   (when treesit-simple-imenu-settings
-- 
2.34.1