Add 'forward-sexp-default-function' to be used by 'treesit-forward-sexp'

* lisp/emacs-lisp/lisp.el (forward-sexp-default-function):
New function with body from 'forward-sexp' (bug#68993).
(forward-sexp-function): Change the default value from nil to
'forward-sexp-default-function'.
(forward-sexp): Use either 'forward-sexp-function' or
'forward-sexp-default-function'.

* lisp/treesit.el (treesit-forward-sexp): In nodes of type 'text'
fall back to 'forward-sexp-default-function'.  Improve docstring.

* doc/lispref/positions.texi (List Motion): Fix pxref.

1 files changed, 9 insertions, 5 deletions

diff --git a/lisp/emacs-lisp/lisp.el b/lisp/emacs-lisp/lisp.el
index c57b1357f63..bd0b38db7ea 100644
--- a/lisp/emacs-lisp/lisp.el
+++ b/lisp/emacs-lisp/lisp.el
@@ -45,7 +45,12 @@ This affects `insert-parentheses' and `insert-pair'."
   :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 @@ report errors as appropriate for this kind of usage."
                                     "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).