+(defun font-lock-add-keywords (mode keywords &optional how)
+ "Add highlighting KEYWORDS for MODE.
+
+MODE should be a symbol, the major mode command name, such as `c-mode'
+or nil. If nil, highlighting keywords are added for the current buffer.
+KEYWORDS should be a list; see the variable `font-lock-keywords'.
+By default they are added at the beginning of the current highlighting list.
+If optional argument HOW is `set', they are used to replace the current
+highlighting list. If HOW is any other non-nil value, they are added at the
+end of the current highlighting list.
+
+For example:
+
+ (font-lock-add-keywords 'c-mode
+ '((\"\\\\\\=<\\\\(FIXME\\\\):\" 1 font-lock-warning-face prepend)
+ (\"\\\\\\=<\\\\(and\\\\|or\\\\|not\\\\)\\\\\\=>\" . font-lock-keyword-face)))
+
+adds two fontification patterns for C mode, to fontify `FIXME:' words, even in
+comments, and to fontify `and', `or' and `not' words as keywords.
+
+The above procedure will only add the keywords for C mode, not
+for modes derived from C mode. To add them for derived modes too,
+pass nil for MODE and add the call to c-mode-hook.
+
+For example:
+
+ (add-hook 'c-mode-hook
+ (lambda ()
+ (font-lock-add-keywords nil
+ '((\"\\\\\\=<\\\\(FIXME\\\\):\" 1 font-lock-warning-face prepend)
+ (\"\\\\\\=<\\\\(and\\\\|or\\\\|not\\\\)\\\\\\=>\" .
+ font-lock-keyword-face)))))
+
+The above procedure may fail to add keywords to derived modes if
+some involved major mode does not follow the standard conventions.
+File a bug report if this happens, so the major mode can be corrected.
+
+Note that some modes have specialized support for additional patterns, e.g.,
+see the variables `c-font-lock-extra-types', `c++-font-lock-extra-types',
+`objc-font-lock-extra-types' and `java-font-lock-extra-types'."
+ (cond (mode
+ ;; If MODE is non-nil, add the KEYWORDS and HOW spec to
+ ;; `font-lock-keywords-alist' so `font-lock-set-defaults' uses them.
+ (let ((spec (cons keywords how)) cell)
+ (if (setq cell (assq mode font-lock-keywords-alist))
+ (if (eq how 'set)
+ (setcdr cell (list spec))
+ (setcdr cell (append (cdr cell) (list spec))))
+ (push (list mode spec) font-lock-keywords-alist)))
+ ;; Make sure that `font-lock-removed-keywords-alist' does not
+ ;; contain the new keywords.
+ (font-lock-update-removed-keyword-alist mode keywords how))
+ (t
+ ;; Otherwise set or add the keywords now.
+ ;; This is a no-op if it has been done already in this buffer
+ ;; for the correct major mode.
+ (font-lock-set-defaults)
+ (let ((was-compiled (eq (car font-lock-keywords) t)))
+ ;; Bring back the user-level (uncompiled) keywords.
+ (if was-compiled
+ (setq font-lock-keywords (cadr font-lock-keywords)))
+ ;; Now modify or replace them.
+ (if (eq how 'set)
+ (setq font-lock-keywords keywords)
+ (font-lock-remove-keywords nil keywords) ;to avoid duplicates
+ (let ((old (if (eq (car-safe font-lock-keywords) t)
+ (cdr font-lock-keywords)
+ font-lock-keywords)))
+ (setq font-lock-keywords (if how
+ (append old keywords)
+ (append keywords old)))))
+ ;; If the keywords were compiled before, compile them again.
+ (if was-compiled
+ (setq font-lock-keywords
+ (font-lock-compile-keywords font-lock-keywords)))))))
+
+(defun font-lock-update-removed-keyword-alist (mode keywords how)
+ "Update `font-lock-removed-keywords-alist' when adding new KEYWORDS to MODE."
+ ;; When font-lock is enabled first all keywords in the list
+ ;; `font-lock-keywords-alist' are added, then all keywords in the
+ ;; list `font-lock-removed-keywords-alist' are removed. If a
+ ;; keyword was once added, removed, and then added again it must be
+ ;; removed from the removed-keywords list. Otherwise the second add
+ ;; will not take effect.
+ (let ((cell (assq mode font-lock-removed-keywords-alist)))
+ (if cell
+ (if (eq how 'set)
+ ;; A new set of keywords is defined. Forget all about
+ ;; our old keywords that should be removed.
+ (setq font-lock-removed-keywords-alist
+ (delq cell font-lock-removed-keywords-alist))
+ ;; Delete all previously removed keywords.
+ (dolist (kword keywords)
+ (setcdr cell (delete kword (cdr cell))))
+ ;; Delete the mode cell if empty.
+ (if (null (cdr cell))
+ (setq font-lock-removed-keywords-alist
+ (delq cell font-lock-removed-keywords-alist)))))))
+
+;; Written by Anders Lindgren <andersl@andersl.com>.
+;;
+;; Case study:
+;; (I) The keywords are removed from a major mode.
+;; In this case the keyword could be local (i.e. added earlier by
+;; `font-lock-add-keywords'), global, or both.
+;;
+;; (a) In the local case we remove the keywords from the variable
+;; `font-lock-keywords-alist'.
+;;
+;; (b) The actual global keywords are not known at this time.
+;; All keywords are added to `font-lock-removed-keywords-alist',
+;; when font-lock is enabled those keywords are removed.
+;;
+;; Note that added keywords are taken out of the list of removed
+;; keywords. This ensure correct operation when the same keyword
+;; is added and removed several times.
+;;
+;; (II) The keywords are removed from the current buffer.
+(defun font-lock-remove-keywords (mode keywords)
+ "Remove highlighting KEYWORDS for MODE.
+
+MODE should be a symbol, the major mode command name, such as `c-mode'
+or nil. If nil, highlighting keywords are removed for the current buffer.
+
+To make the removal apply to modes derived from MODE as well,
+pass nil for MODE and add the call to MODE-hook. This may fail
+for some derived modes if some involved major mode does not
+follow the standard conventions. File a bug report if this
+happens, so the major mode can be corrected."
+ (cond (mode
+ ;; Remove one keyword at the time.
+ (dolist (keyword keywords)
+ (let ((top-cell (assq mode font-lock-keywords-alist)))
+ ;; If MODE is non-nil, remove the KEYWORD from
+ ;; `font-lock-keywords-alist'.
+ (when top-cell
+ (dolist (keyword-list-how-pair (cdr top-cell))
+ ;; `keywords-list-how-pair' is a cons with a list of
+ ;; keywords in the car top-cell and the original how
+ ;; argument in the cdr top-cell.
+ (setcar keyword-list-how-pair
+ (delete keyword (car keyword-list-how-pair))))
+ ;; Remove keyword list/how pair when the keyword list
+ ;; is empty and how doesn't specify `set'. (If it
+ ;; should be deleted then previously deleted keywords
+ ;; would appear again.)
+ (let ((cell top-cell))
+ (while (cdr cell)
+ (if (and (null (car (car (cdr cell))))
+ (not (eq (cdr (car (cdr cell))) 'set)))
+ (setcdr cell (cdr (cdr cell)))
+ (setq cell (cdr cell)))))
+ ;; Final cleanup, remove major mode cell if last keyword
+ ;; was deleted.
+ (if (null (cdr top-cell))
+ (setq font-lock-keywords-alist
+ (delq top-cell font-lock-keywords-alist))))
+ ;; Remember the keyword in case it is not local.
+ (let ((cell (assq mode font-lock-removed-keywords-alist)))
+ (if cell
+ (unless (member keyword (cdr cell))
+ (nconc cell (list keyword)))
+ (push (cons mode (list keyword))
+ font-lock-removed-keywords-alist))))))
+ (t
+ ;; Otherwise remove it immediately.
+ (font-lock-set-defaults)
+ (let ((was-compiled (eq (car font-lock-keywords) t)))
+ ;; Bring back the user-level (uncompiled) keywords.
+ (if was-compiled
+ (setq font-lock-keywords (cadr font-lock-keywords)))
+
+ ;; Edit them.
+ (setq font-lock-keywords (copy-sequence font-lock-keywords))
+ (dolist (keyword keywords)
+ (setq font-lock-keywords
+ (delete keyword font-lock-keywords)))
+
+ ;; If the keywords were compiled before, compile them again.
+ (if was-compiled
+ (setq font-lock-keywords
+ (font-lock-compile-keywords font-lock-keywords)))))))