bug#68993: treesitter support for forward-sexp-default-function

[Juri Linkov]

> My suggestion would be for both treesit-forward-sentence and -sexp to
> use “text” for their heuristic. If someone wants more customized
> behavior, they can always write a custom forward-sentence/sexp function.

Thanks for the suggestion.  So here is the patch that implements this:

diff --git a/lisp/treesit.el b/lisp/treesit.el
index 1443162f79c..62d797513fc 100644
--- a/lisp/treesit.el
+++ b/lisp/treesit.el
@@ -2145,7 +2145,10 @@ treesit-forward-sexp
   (interactive "^p")
   (let ((arg (or arg 1))
         (pred (or treesit-sexp-type-regexp 'sexp)))
-    (or (if (> arg 0)
+    (or (when (treesit-node-match-p (treesit-node-at (point)) 'text t)
+          (funcall #'forward-sexp-default-function arg)
+          t)
+        (if (> arg 0)
             (treesit-end-of-thing pred (abs arg) 'restricted)
           (treesit-beginning-of-thing pred (abs arg) 'restricted))
         ;; If we couldn't move, we should signal an error and report
diff --git a/lisp/emacs-lisp/lisp.el b/lisp/emacs-lisp/lisp.el
index c57b1357f63..4c0f720b1a0 100644
--- a/lisp/emacs-lisp/lisp.el
+++ b/lisp/emacs-lisp/lisp.el
@@ -45,7 +45,12 @@ parens-require-spaces
   :type 'boolean
   :group 'lisp)
 
-(defvar forward-sexp-function nil
+(defun forward-sexp-default-function (&optional arg)
+  "Default function for `forward-sexp-function'."
+  (goto-char (or (scan-sexps (point) arg) (buffer-end arg)))
+  (if (< arg 0) (backward-prefix-chars)))
+
+(defvar forward-sexp-function #'forward-sexp-default-function
   ;; FIXME:
   ;; - for some uses, we may want a "sexp-only" version, which only
   ;;   jumps over a well-formed sexp, rather than some dwimish thing
@@ -74,10 +79,9 @@ forward-sexp
                                     "No next sexp"
                                   "No previous sexp"))))
     (or arg (setq arg 1))
-    (if forward-sexp-function
-        (funcall forward-sexp-function arg)
-      (goto-char (or (scan-sexps (point) arg) (buffer-end arg)))
-      (if (< arg 0) (backward-prefix-chars)))))
+    (funcall (or forward-sexp-function
+                 #'forward-sexp-default-function)
+             arg)))
 
 (defun backward-sexp (&optional arg interactive)
   "Move backward across one balanced expression (sexp).