lisp/font-core.el

   1 ;;; font-core.el --- Core interface to font-lock
   2
   3 ;; Copyright (C) 1992-2018 Free Software Foundation, Inc.
   4
   5 ;; Maintainer: emacs-devel@gnu.org
   6 ;; Keywords: languages, faces
   7 ;; Package: emacs
   8
   9 ;; This file is part of GNU Emacs.
  10
  11 ;; GNU Emacs is free software: you can redistribute it and/or modify
  12 ;; it under the terms of the GNU General Public License as published by
  13 ;; the Free Software Foundation, either version 3 of the License, or
  14 ;; (at your option) any later version.
  15
  16 ;; GNU Emacs is distributed in the hope that it will be useful,
  17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19 ;; GNU General Public License for more details.
  20
  21 ;; You should have received a copy of the GNU General Public License
  22 ;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
  23
  24 ;;; Code:
  25
  26 ;; This variable is used by mode packages that support Font Lock mode by
  27 ;; defining their own keywords to use for `font-lock-keywords'.  (The mode
  28 ;; command should make it buffer-local and set it to provide the set up.)
  29 (defvar font-lock-defaults nil
  30   "Defaults for Font Lock mode specified by the major mode.
  31 Defaults should be of the form:
  32
  33  (KEYWORDS [KEYWORDS-ONLY [CASE-FOLD [SYNTAX-ALIST ...]]])
  34
  35 KEYWORDS may be a symbol (a variable or function whose value is the keywords
  36 to use for fontification) or a list of symbols (specifying different levels
  37 of fontification).
  38
  39 If KEYWORDS-ONLY is non-nil, syntactic fontification (strings and
  40 comments) is not performed.
  41
  42 If CASE-FOLD is non-nil, the case of the keywords is ignored when fontifying.
  43
  44 If SYNTAX-ALIST is non-nil, it should be a list of cons pairs of the form
  45 \(CHAR-OR-STRING . STRING) used to set the local Font Lock syntax table, for
  46 keyword and syntactic fontification (see `modify-syntax-entry').
  47
  48 These item elements are used by Font Lock mode to set the variables
  49 `font-lock-keywords', `font-lock-keywords-only',
  50 `font-lock-keywords-case-fold-search', `font-lock-syntax-table'.
  51
  52 Further item elements are alists of the form (VARIABLE . VALUE) and are in no
  53 particular order.  Each VARIABLE is made buffer-local before set to VALUE.
  54
  55 Currently, appropriate variables include `font-lock-mark-block-function'.
  56 If this is non-nil, it should be a function with no args used to mark any
  57 enclosing block of text, for fontification via \\[font-lock-fontify-block].
  58 Typical values are `mark-defun' for programming modes or `mark-paragraph' for
  59 textual modes (i.e., the mode-dependent function is known to put point and mark
  60 around a text block relevant to that mode).
  61
  62 Other variables include that for syntactic keyword fontification,
  63 `font-lock-syntactic-keywords' and those for buffer-specialized fontification
  64 functions, `font-lock-fontify-buffer-function',
  65 `font-lock-unfontify-buffer-function', `font-lock-fontify-region-function',
  66 `font-lock-unfontify-region-function', and `font-lock-inhibit-thing-lock'.")
  67 ;;;###autoload
  68 (put 'font-lock-defaults 'risky-local-variable t)
  69 (make-variable-buffer-local 'font-lock-defaults)
  70
  71 (defvar font-lock-function 'font-lock-default-function
  72   "A function which is called when `font-lock-mode' is toggled.
  73 It will be passed one argument, which is the current value of
  74 `font-lock-mode'.")
  75
  76 ;; The mode for which font-lock was initialized, or nil if none.
  77 (defvar font-lock-major-mode)
  78
  79 (define-minor-mode font-lock-mode
  80   "Toggle syntax highlighting in this buffer (Font Lock mode).
  81 With a prefix argument ARG, enable Font Lock mode if ARG is
  82 positive, and disable it otherwise.  If called from Lisp, enable
  83 the mode if ARG is omitted or nil.
  84
  85 When Font Lock mode is enabled, text is fontified as you type it:
  86
  87  - Comments are displayed in `font-lock-comment-face';
  88  - Strings are displayed in `font-lock-string-face';
  89  - Certain other expressions are displayed in other faces
  90    according to the value of the variable `font-lock-keywords'.
  91
  92 To customize the faces (colors, fonts, etc.) used by Font Lock for
  93 fontifying different parts of buffer text, use \\[customize-face].
  94
  95 You can enable Font Lock mode in any major mode automatically by
  96 turning on in the major mode's hook.  For example, put in your
  97 ~/.emacs:
  98
  99  (add-hook \\='c-mode-hook \\='turn-on-font-lock)
 100
 101 Alternatively, you can use Global Font Lock mode to automagically
 102 turn on Font Lock mode in buffers whose major mode supports it
 103 and whose major mode is one of `font-lock-global-modes'.  For
 104 example, put in your ~/.emacs:
 105
 106  (global-font-lock-mode t)
 107
 108 Where major modes support different levels of fontification, you
 109 can use the variable `font-lock-maximum-decoration' to specify
 110 which level you generally prefer.  When you turn Font Lock mode
 111 on/off the buffer is fontified/defontified, though fontification
 112 occurs only if the buffer is less than `font-lock-maximum-size'.
 113
 114 To add your own highlighting for some major mode, and modify the
 115 highlighting selected automatically via the variable
 116 `font-lock-maximum-decoration', you can use
 117 `font-lock-add-keywords'.
 118
 119 To fontify a buffer, without turning on Font Lock mode and
 120 regardless of buffer size, you can use \\[font-lock-fontify-buffer].
 121
 122 To fontify a block (the function or paragraph containing point,
 123 or a number of lines around point), perhaps because modification
 124 on the current line caused syntactic change on other lines, you
 125 can use \\[font-lock-fontify-block].
 126
 127 You can set your own default settings for some mode, by setting a
 128 buffer local value for `font-lock-defaults', via its mode hook.
 129
 130 The above is the default behavior of `font-lock-mode'; you may
 131 specify your own function which is called when `font-lock-mode'
 132 is toggled via `font-lock-function'. "
 133   nil nil nil
 134   :after-hook (font-lock-initial-fontify)
 135   ;; Don't turn on Font Lock mode if we don't have a display (we're running a
 136   ;; batch job) or if the buffer is invisible (the name starts with a space).
 137   (when (or noninteractive (eq (aref (buffer-name) 0) ?\s))
 138     (setq font-lock-mode nil))
 139   (funcall font-lock-function font-lock-mode)
 140   ;; Arrange to unfontify this buffer if we change major mode later.
 141   (if font-lock-mode
 142       (add-hook 'change-major-mode-hook 'font-lock-change-mode nil t)
 143     (remove-hook 'change-major-mode-hook 'font-lock-change-mode t)))
 144
 145 ;; Get rid of fontification for the old major mode.
 146 ;; We do this when changing major modes.
 147 (defun font-lock-change-mode ()
 148   (font-lock-mode -1))
 149
 150 (defun font-lock-defontify ()
 151   "Clear out all `font-lock-face' properties in current buffer.
 152 A major mode that uses `font-lock-face' properties might want to put
 153 this function onto `change-major-mode-hook'."
 154   (let ((modp (buffer-modified-p))
 155         (inhibit-read-only t))
 156     (save-restriction
 157       (widen)
 158       (remove-list-of-text-properties (point-min) (point-max)
 159                                       '(font-lock-face)))
 160     (restore-buffer-modified-p modp)))
 161
 162 (defvar font-lock-set-defaults)
 163 (defun font-lock-default-function (mode)
 164   ;; Turn on Font Lock mode.
 165   (when mode
 166     (set (make-local-variable 'char-property-alias-alist)
 167          (copy-tree char-property-alias-alist))
 168     ;; Add `font-lock-face' as an alias for the `face' property.
 169     (let ((elt (assq 'face char-property-alias-alist)))
 170       (if elt
 171           (unless (memq 'font-lock-face (cdr elt))
 172             (setcdr elt (nconc (cdr elt) (list 'font-lock-face))))
 173         (push (list 'face 'font-lock-face) char-property-alias-alist))))
 174   ;; Turn off Font Lock mode.
 175   (unless mode
 176     ;; Remove `font-lock-face' as an alias for the `face' property.
 177     (set (make-local-variable 'char-property-alias-alist)
 178          (copy-tree char-property-alias-alist))
 179     (let ((elt (assq 'face char-property-alias-alist)))
 180       (when elt
 181         (setcdr elt (remq 'font-lock-face (cdr elt)))
 182         (when (null (cdr elt))
 183           (setq char-property-alias-alist
 184                 (delq elt char-property-alias-alist))))))
 185
 186   ;; Only do hard work if the mode has specified stuff in
 187   ;; `font-lock-defaults'.
 188   (when (font-lock-specified-p mode)
 189     (font-lock-mode-internal mode)))
 190
 191 (defun turn-on-font-lock ()
 192   "Turn on Font Lock mode (only if the terminal can display it)."
 193   (unless font-lock-mode
 194     (font-lock-mode)))
 195
 196 ;;; Global Font Lock mode.
 197
 198 ;; A few people have hassled in the past for a way to make it easier to turn on
 199 ;; Font Lock mode, without the user needing to know for which modes s/he has to
 200 ;; turn it on, perhaps the same way hilit19.el/hl319.el does.  I've always
 201 ;; balked at that way, as I see it as just re-molding the same problem in
 202 ;; another form.  That is; some person would still have to keep track of which
 203 ;; modes (which may not even be distributed with Emacs) support Font Lock mode.
 204 ;; The list would always be out of date.  And that person might have to be me.
 205
 206 ;; Implementation.
 207 ;;
 208 ;; In a previous discussion the following hack came to mind.  It is a gross
 209 ;; hack, but it generally works.  We use the convention that major modes start
 210 ;; by calling the function `kill-all-local-variables', which in turn runs
 211 ;; functions on the hook variable `change-major-mode-hook'.  We attach our
 212 ;; function `font-lock-change-major-mode' to that hook.  Of course, when this
 213 ;; hook is run, the major mode is in the process of being changed and we do not
 214 ;; know what the final major mode will be.  So, `font-lock-change-major-mode'
 215 ;; only (a) notes the name of the current buffer, and (b) adds our function
 216 ;; `turn-on-font-lock-if-desired' to the hook variables
 217 ;; `after-change-major-mode-hook' and `post-command-hook' (for modes
 218 ;; that do not yet run `after-change-major-mode-hook').  By the time
 219 ;; the functions on the first of these hooks to be run are run, the new major
 220 ;; mode is assumed to be in place.  This way we get a Font Lock function run
 221 ;; when a major mode is turned on, without knowing major modes or their hooks.
 222 ;;
 223 ;; Naturally this requires that major modes run `kill-all-local-variables'
 224 ;; and `after-change-major-mode-hook', as they are supposed to.  For modes
 225 ;; that do not run `after-change-major-mode-hook' yet, `post-command-hook'
 226 ;; takes care of things if the mode is set directly or indirectly by
 227 ;; an interactive command; however, problems can occur if the mode is
 228 ;; set by a timer or process: in that case, proper handling of Font Lock mode
 229 ;; may be delayed until the next interactive command.
 230
 231 ;; User interface.
 232 ;;
 233 ;; Although Global Font Lock mode is a pseudo-mode, I think that the user
 234 ;; interface should conform to the usual Emacs convention for modes, i.e., a
 235 ;; command to toggle the feature (`global-font-lock-mode') with a variable for
 236 ;; finer control of the mode's behavior (`font-lock-global-modes').
 237 ;;
 238 ;; The feature should not be enabled by loading font-lock.el, since other
 239 ;; mechanisms for turning on Font Lock mode, such as M-x font-lock-mode RET or
 240 ;; (add-hook 'c-mode-hook 'turn-on-font-lock), would cause Font Lock mode to be
 241 ;; turned on everywhere.  That would not be intuitive or informative because
 242 ;; loading a file tells you nothing about the feature or how to control it.  It
 243 ;; would also be contrary to the Principle of Least Surprise.  sm.
 244
 245 (defcustom font-lock-global-modes t
 246   "Modes for which Font Lock mode is automagically turned on.
 247 Global Font Lock mode is controlled by the command `global-font-lock-mode'.
 248 If nil, means no modes have Font Lock mode automatically turned on.
 249 If t, all modes that support Font Lock mode have it automatically turned on.
 250 If a list, it should be a list of `major-mode' symbol names for which Font Lock
 251 mode should be automatically turned on.  The sense of the list is negated if it
 252 begins with `not'.  For example:
 253  (c-mode c++-mode)
 254 means that Font Lock mode is turned on for buffers in C and C++ modes only."
 255   :type '(choice (const :tag "none" nil)
 256                  (const :tag "all" t)
 257                  (set :menu-tag "mode specific" :tag "modes"
 258                       :value (not)
 259                       (const :tag "Except" not)
 260                       (repeat :inline t (symbol :tag "mode"))))
 261   :group 'font-lock)
 262
 263 (defun turn-on-font-lock-if-desired ()
 264   (when (cond ((eq font-lock-global-modes t)
 265                t)
 266               ((eq (car-safe font-lock-global-modes) 'not)
 267                (not (memq major-mode (cdr font-lock-global-modes))))
 268               (t (memq major-mode font-lock-global-modes)))
 269     (let (inhibit-quit)
 270       (turn-on-font-lock))))
 271
 272 (define-globalized-minor-mode global-font-lock-mode
 273   font-lock-mode turn-on-font-lock-if-desired
 274   ;; What was this :extra-args thingy for?  --Stef
 275   ;; :extra-args (dummy)
 276   :initialize 'custom-initialize-delay
 277   :init-value (not (or noninteractive emacs-basic-display))
 278   :group 'font-lock
 279   :version "22.1")
 280
 281 ;;; End of Global Font Lock mode.
 282
 283 (provide 'font-core)
 284
 285 ;;; font-core.el ends here