* lisp/font-lock.el (font-lock-beginning-of-syntax-function): Remove

(font-lock-fontify-block): Don't let-bind it.
(font-lock-compile-keywords): Don't use it.
(font-lock-set-defaults): Don't set it.  Allow the variable alist to
start one slot earlier, instead.

* lisp/emacs-lisp/syntax.el (font-lock-beginning-of-syntax-function):
Don't declare.
(syntax-ppss): Don't use it either.

* lisp/font-core.el (font-lock-defaults): Remove SYNTAX-BEGIN
from docstring.

* doc/emacs/display.texi (Font Lock): Don't mention
font-lock-beginning-of-syntax-function.

* doc/lispref/modes.texi (Font Lock Basics): Update description of
font-lock-defaults.
(Syntactic Font Lock): Remove font-lock-beginning-of-syntax-function.

* lisp/loadhist.el (unload-feature-special-hooks):
Remove font-lock-beginning-of-syntax-function.

* lisp/obsolete/lazy-lock.el (lazy-lock-fontify-region):
* lisp/emacs-lisp/lisp.el (beginning-of-defun-raw): Don't let-bind
font-lock-beginning-of-syntax-function.

7 files changed, 11 insertions, 60 deletions

diff --git a/lisp/emacs-lisp/lisp.el b/lisp/emacs-lisp/lisp.el
index 7b7b48c66de..ca977db4b1d 100644
--- a/lisp/emacs-lisp/lisp.el
+++ b/lisp/emacs-lisp/lisp.el
@@ -364,8 +364,7 @@ is called as a function to find the defun's beginning."
 	  (arg-+ve (> arg 0)))
       (save-restriction
 	(widen)
-	(let ((ppss (let (syntax-begin-function
-			  font-lock-beginning-of-syntax-function)
+	(let ((ppss (let (syntax-begin-function)
 		      (syntax-ppss)))
 	      ;; position of least enclosing paren, or nil.
 	      encl-pos)
diff --git a/lisp/emacs-lisp/syntax.el b/lisp/emacs-lisp/syntax.el
index 51019254943..fee62149b38 100644
--- a/lisp/emacs-lisp/syntax.el
+++ b/lisp/emacs-lisp/syntax.el
@@ -43,8 +43,6 @@
 
 (eval-when-compile (require 'cl-lib))
 
-(defvar font-lock-beginning-of-syntax-function)
-
 ;;; Applying syntax-table properties where needed.
 
 (defvar syntax-propertize-function nil
@@ -503,11 +501,6 @@ running the hook."
 	      ;; - The function might be slow.
 	      ;; - If this function almost always finds a safe nearby spot,
 	      ;;   the cache won't be populated, so consulting it is cheap.
-	      (when (and (not syntax-begin-function)
-			 (boundp 'font-lock-beginning-of-syntax-function)
-			 font-lock-beginning-of-syntax-function)
-		(set (make-local-variable 'syntax-begin-function)
-		     font-lock-beginning-of-syntax-function))
 	      (when (and syntax-begin-function
 			 (progn (goto-char pos)
 				(funcall syntax-begin-function)
diff --git a/lisp/font-core.el b/lisp/font-core.el
index 6d8588bfa33..2253204d9f7 100644
--- a/lisp/font-core.el
+++ b/lisp/font-core.el
@@ -30,7 +30,7 @@
   "Defaults for Font Lock mode specified by the major mode.
 Defaults should be of the form:
 
- (KEYWORDS [KEYWORDS-ONLY [CASE-FOLD [SYNTAX-ALIST [SYNTAX-BEGIN ...]]]])
+ (KEYWORDS [KEYWORDS-ONLY [CASE-FOLD [SYNTAX-ALIST ...]]])
 
 KEYWORDS may be a symbol (a variable or function whose value is the keywords
 to use for fontification) or a list of symbols (specifying different levels
@@ -45,20 +45,9 @@ If SYNTAX-ALIST is non-nil, it should be a list of cons pairs of the form
 \(CHAR-OR-STRING . STRING) used to set the local Font Lock syntax table, for
 keyword and syntactic fontification (see `modify-syntax-entry').
 
-If SYNTAX-BEGIN is non-nil, it should be a function with no args used to move
-backwards outside any enclosing syntactic block, for syntactic fontification.
-Typical values are `beginning-of-line' (i.e., the start of the line is known to
-be outside a syntactic block), or `beginning-of-defun' for programming modes or
-`backward-paragraph' for textual modes (i.e., the mode-dependent function is
-known to move outside a syntactic block).  If nil, the beginning of the buffer
-is used as a position outside of a syntactic block, in the worst case.
-
-\(See also Info node `(elisp)Font Lock Basics'.)
-
 These item elements are used by Font Lock mode to set the variables
 `font-lock-keywords', `font-lock-keywords-only',
-`font-lock-keywords-case-fold-search', `font-lock-syntax-table' and
-`font-lock-beginning-of-syntax-function', respectively.
+`font-lock-keywords-case-fold-search', `font-lock-syntax-table'.
 
 Further item elements are alists of the form (VARIABLE . VALUE) and are in no
 particular order.  Each VARIABLE is made buffer-local before set to VALUE.
diff --git a/lisp/font-lock.el b/lisp/font-lock.el
index cec95bf259c..d93cf7184ca 100644
--- a/lisp/font-lock.el
+++ b/lisp/font-lock.el
@@ -556,21 +556,6 @@ This is normally set via `font-lock-defaults'.")
 If this is nil, the major mode's syntax table is used.
 This is normally set via `font-lock-defaults'.")
 
-(defvar font-lock-beginning-of-syntax-function nil
-  "Non-nil means use this function to move back outside all constructs.
-When called with no args it should move point backward to a place which
-is not in a string or comment and not within any bracket-pairs (or else,
-a place such that any bracket-pairs outside it can be ignored for Emacs
-syntax analysis and fontification).
-
-If this is nil, Font Lock uses `syntax-begin-function' to move back
-outside of any comment, string, or sexp.  This variable is semi-obsolete;
-we recommend setting `syntax-begin-function' instead.
-
-This is normally set via `font-lock-defaults'.")
-(make-obsolete-variable 'font-lock-beginning-of-syntax-function
-                        'syntax-begin-function "23.3" 'set)
-
 (defvar font-lock-mark-block-function nil
   "Non-nil means use this function to mark a block of text.
 When called with no args it should leave point at the beginning of any
@@ -1347,7 +1332,7 @@ no ARG is given and `font-lock-mark-block-function' is nil.
 If `font-lock-mark-block-function' non-nil and no ARG is given, it is used to
 delimit the region to fontify."
   (interactive "P")
-  (let ((inhibit-point-motion-hooks t) font-lock-beginning-of-syntax-function
+  (let ((inhibit-point-motion-hooks t)
 	deactivate-mark)
     ;; Make sure we have the right `font-lock-keywords' etc.
     (if (not font-lock-mode) (font-lock-set-defaults))
@@ -1765,9 +1750,7 @@ If SYNTACTIC-KEYWORDS is non-nil, it means these keywords are used for
 	  (cons t (cons keywords
 			(mapcar #'font-lock-compile-keyword keywords))))
     (if (and (not syntactic-keywords)
-	     (let ((beg-function
-		    (or font-lock-beginning-of-syntax-function
-			syntax-begin-function)))
+	     (let ((beg-function syntax-begin-function))
 	       (or (eq beg-function 'beginning-of-defun)
 		   (get beg-function 'font-lock-syntax-paren-check)))
 	     (not beginning-of-defun-function))
@@ -1890,17 +1873,14 @@ Sets various variables using `font-lock-defaults' and
 			      (list (car selem))
 			    (mapcar 'identity (car selem))))
 	      (modify-syntax-entry char syntax font-lock-syntax-table)))))
-      ;; Syntax function for syntactic fontification?
-      (if (nth 4 defaults)
-	(set (make-local-variable 'font-lock-beginning-of-syntax-function)
-               (nth 4 defaults))
-        (kill-local-variable 'font-lock-beginning-of-syntax-function))
+      ;; (nth 4 defaults) used to hold `font-lock-beginning-of-syntax-function',
+      ;; but that was removed in 25.1, so if it's a cons cell, we assume that
+      ;; it's part of the variable alist.
       ;; Variable alist?
-      (dolist (x (nthcdr 5 defaults))
+      (dolist (x (nthcdr (if (consp (nth 4 defaults)) 4 5) defaults))
 	(set (make-local-variable (car x)) (cdr x)))
       ;; Set up `font-lock-keywords' last because its value might depend
-      ;; on other settings (e.g. font-lock-compile-keywords uses
-      ;; font-lock-beginning-of-syntax-function).
+      ;; on other settings.
       (set (make-local-variable 'font-lock-keywords)
 	   (font-lock-eval-keywords keywords))
       ;; Local fontification?
diff --git a/lisp/jit-lock.el b/lisp/jit-lock.el
index 8c798d5c4d0..4e8fa7b15cb 100644
--- a/lisp/jit-lock.el
+++ b/lisp/jit-lock.el
@@ -382,14 +382,6 @@ Defaults to the whole buffer.  END can be out of bounds."
    (save-excursion
      (unless start (setq start (point-min)))
      (setq end (if end (min end (point-max)) (point-max)))
-     ;; This did bind `font-lock-beginning-of-syntax-function' to
-     ;; nil at some point, for an unknown reason.  Don't do this; it
-     ;; can make highlighting slow due to expensive calls to
-     ;; `parse-partial-sexp' in function
-     ;; `font-lock-fontify-syntactically-region'.  Example: paging
-     ;; from the end of a buffer to its start, can do repeated
-     ;; `parse-partial-sexp' starting from `point-min', which can
-     ;; take a long time in a large buffer.
      (let ((orig-start start) next)
        (save-match-data
 	 ;; Fontify chunks beginning at START.  The end of a
diff --git a/lisp/loadhist.el b/lisp/loadhist.el
index 52fd04736f6..4ea1bcb9f50 100644
--- a/lisp/loadhist.el
+++ b/lisp/loadhist.el
@@ -123,7 +123,6 @@ from a file."
     delete-frame-functions disabled-command-function
     fill-nobreak-predicate find-directory-functions
     find-file-not-found-functions
-    font-lock-beginning-of-syntax-function
     font-lock-fontify-buffer-function
     font-lock-fontify-region-function
     font-lock-mark-block-function
diff --git a/lisp/obsolete/lazy-lock.el b/lisp/obsolete/lazy-lock.el
index 79afd80813f..d05a7d86dbc 100644
--- a/lisp/obsolete/lazy-lock.el
+++ b/lisp/obsolete/lazy-lock.el
@@ -892,8 +892,7 @@ verbosity is controlled via the variable `lazy-lock-stealth-verbose'."
       (save-excursion
 	(save-match-data
 	  (save-buffer-state
-	   ;; Ensure syntactic fontification is always correct.
-	   (font-lock-beginning-of-syntax-function next)
+	   (next)
 	   ;; Find successive unfontified regions between BEG and END.
 	   (condition-case data
 	       (do-while beg