rainbow-delimiters-mode, syntax-begin-function and font-lock-beginning-of-syntax-function

[fatiparty]

Jan 23, 2022, 19:58 by help-gnu-emacs@gnu.org:

Would sections [1] and [2] still be relevant in this code? 

It includes the claim  of not using `syntax-begin-function' and
that `font-lock-beginning-of-syntax-function' could be obsolete.

Have looked for `font-lock-beginning-of-syntax-function' but
could not find information of possible obsolescence.
(define-minor-mode rainbow-delimiters-minor-mode
  "Colour Brace Marks according to their depth."
  nil
  ""   ; exclude modeline indicator
  nil 
  
  (font-lock-remove-keywords nil my-font-lock)

  (when rainbow-delimiters-minor-mode
    (font-lock-add-keywords nil rainbow-delimiters-font-lock 'append)
    (set (make-local-variable 'jit-lock-contextually) t)

    ;; flush-cache to avoid old values when modifying `syntax-begin-function'
    (when (or (bound-and-true-p syntax-begin-function)
              (bound-and-true-p font-lock-beginning-of-syntax-function))
      (syntax-ppss-flush-cache 0))

    ;; [1] Don't use `syntax-begin-function', as it may break the
    ;; assumption that `syntax-ppss' is equivalent to
    ;; `parse-partial-sexp' from `point-min'.

    (when (boundp 'syntax-begin-function)
      (set (make-local-variable 'syntax-begin-function) nil))

    ;; [2] Obsolete equivalent of `syntax-begin-function'.
    (when (boundp 'font-lock-beginning-of-syntax-function)
      (set (make-local-variable
            'font-lock-beginning-of-syntax-function) nil)) )

  (when font-lock-mode
    (if (fboundp 'font-lock-flush)
        (font-lock-flush)
      (with-no-warnings (font-lock-fontify-buffer)))))