emacs/lisp/electric.el

;;; electric.el --- window maker and Command loop for `electric' modes

;; Copyright (C) 1985-1986, 1995, 2001-2014 Free Software Foundation,
;; Inc.

;; Author: K. Shane Hartman
;; Maintainer: emacs-devel@gnu.org
;; Keywords: extensions

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; "Electric" has been used in Emacs to refer to different things.
;; Among them:
;;
;; - electric modes and buffers: modes that typically pop-up in a modal kind of
;;   way a transient buffer that automatically disappears as soon as the user
;;   is done with it.
;;
;; - electric keys: self inserting keys which additionally perform some side
;;   operation which happens to be often convenient at that time.  Examples of
;;   such side operations are: reindenting code, inserting a newline,
;;   ... auto-fill-mode and abbrev-mode can be considered as built-in forms of
;;   electric key behavior.

;;; Code:

;; This loop is the guts for non-standard modes which retain control
;; until some event occurs.  It is a `do-forever', the only way out is
;; to throw.  It assumes that you have set up the keymap, window, and
;; everything else: all it does is read commands and execute them -
;; providing error messages should one occur (if there is no loop
;; function - which see).  The required argument is a tag which should
;; expect a value of nil if the user decides to punt. The second
;; argument is the prompt to be used: if nil, use "->", if 'noprompt,
;; don't use a prompt, if a string, use that string as prompt, and if
;; a function of no variable, it will be evaluated in every iteration
;; of the loop and its return value, which can be nil, 'noprompt or a
;; string, will be used as prompt.  Given third argument non-nil, it
;; INHIBITS quitting unless the user types C-g at toplevel.  This is
;; so user can do things like C-u C-g and not get thrown out.  Fourth
;; argument, if non-nil, should be a function of two arguments which
;; is called after every command is executed.  The fifth argument, if
;; provided, is the state variable for the function.  If the
;; loop-function gets an error, the loop will abort WITHOUT throwing
;; (moral: use unwind-protect around call to this function for any
;; critical stuff).  The second argument for the loop function is the
;; conditions for any error that occurred or nil if none.

(defun Electric-command-loop (return-tag
			      &optional prompt inhibit-quitting
					loop-function loop-state)

  (let (cmd
        (err nil)
        (inhibit-quit inhibit-quitting)
        (prompt-string prompt))
    (while t
      (if (functionp prompt)
          (setq prompt-string (funcall prompt)))
      (if (not (stringp prompt-string))
          (setq prompt-string (unless (eq prompt-string 'noprompt) "->")))
      (setq cmd (read-key-sequence prompt-string))
      (setq last-command-event (aref cmd (1- (length cmd)))
	    this-command (key-binding cmd t)
	    cmd this-command)
      (if (or (prog1 quit-flag (setq quit-flag nil))
	      (eq last-input-event ?\C-g))
	  (progn (setq unread-command-events nil
		       prefix-arg nil)
		 ;; If it wasn't canceling a prefix character, then quit.
		 (if (or (= (length (this-command-keys)) 1)
			 (not inhibit-quit)) ; safety
		     (progn (ding)
			    (message "Quit")
			    (throw return-tag nil))
		   (setq cmd nil))))
      (setq current-prefix-arg prefix-arg)
      (if cmd
	  (condition-case conditions
	      (progn (command-execute cmd)
		     (setq last-command this-command)
		     (if (or (prog1 quit-flag (setq quit-flag nil))
			     (eq last-input-event ?\C-g))
			 (progn (setq unread-command-events nil)
				(if (not inhibit-quit)
				    (progn (ding)
					   (message "Quit")
					   (throw return-tag nil))
				  (ding)))))
	    (buffer-read-only (if loop-function
				  (setq err conditions)
				(ding)
				(message "Buffer is read-only")
				(sit-for 2)))
	    (beginning-of-buffer (if loop-function
				     (setq err conditions)
				   (ding)
				   (message "Beginning of Buffer")
				   (sit-for 2)))
	    (end-of-buffer (if loop-function
			       (setq err conditions)
			     (ding)
			     (message "End of Buffer")
			     (sit-for 2)))
	    (error (if loop-function
		       (setq err conditions)
		     (ding)
		     (message "Error: %s"
			      (if (eq (car conditions) 'error)
				  (car (cdr conditions))
				(prin1-to-string conditions)))
		     (sit-for 2))))
	(ding))
      (if loop-function (funcall loop-function loop-state err))))
  (ding)
  (throw return-tag nil))

;; This function is like pop-to-buffer, sort of.
;; The algorithm is
;; If there is a window displaying buffer
;; 	Select it
;; Else if there is only one window
;; 	Split it, selecting the window on the bottom with height being
;; 	the lesser of max-height (if non-nil) and the number of lines in
;;      the buffer to be displayed subject to window-min-height constraint.
;; Else
;; 	Switch to buffer in the current window.
;;
;; Then if max-height is nil, and not all of the lines in the buffer
;; are displayed, grab the whole frame.
;;
;; Returns selected window on buffer positioned at point-min.

(defun Electric-pop-up-window (buffer &optional max-height)
  (let* ((win (or (get-buffer-window buffer) (selected-window)))
	 (buf (get-buffer buffer))
	 (one-window (one-window-p t))
	 (pop-up-windows t)
	 (pop-up-frames nil))
    (if (not buf)
	(error "Buffer %s does not exist" buffer)
      (cond ((and (eq (window-buffer win) buf))
	     (select-window win))
	    (one-window
	     (pop-to-buffer buffer)
	     (setq win (selected-window)))
	    (t
	     (switch-to-buffer buf)))
      ;; Don't shrink the window, but expand it if necessary.
      (goto-char (point-min))
      (unless (= (point-max) (window-end win t))
	(fit-window-to-buffer win max-height))
      win)))

;;; Electric keys.

(defgroup electricity ()
  "Electric behavior for self inserting keys."
  :group 'editing)

(defun electric--after-char-pos ()
  "Return the position after the char we just inserted.
Returns nil when we can't find this char."
  (let ((pos (point)))
    (when (or (eq (char-before) last-command-event) ;; Sanity check.
              (save-excursion
                (or (progn (skip-chars-backward " \t")
                           (setq pos (point))
                           (eq (char-before) last-command-event))
                    (progn (skip-chars-backward " \n\t")
                           (setq pos (point))
                           (eq (char-before) last-command-event)))))
      pos)))

(defun electric--sort-post-self-insertion-hook ()
  "Ensure order of electric functions in `post-self-insertion-hook'.

Hooks in this variable interact in non-trivial ways, so a
relative order must be maintained within it."
  (setq-default post-self-insert-hook
                (sort (default-value 'post-self-insert-hook)
                      #'(lambda (fn1 fn2)
                          (< (or (get fn1 'priority) 0)
                             (or (get fn2 'priority) 0))))))

;;; Electric indentation.

;; Autoloading variables is generally undesirable, but major modes
;; should usually set this variable by adding elements to the default
;; value, which only works well if the variable is preloaded.
;;;###autoload
(defvar electric-indent-chars '(?\n)
  "Characters that should cause automatic reindentation.")

(defvar electric-indent-functions nil
  "Special hook run to decide whether to auto-indent.
Each function is called with one argument (the inserted char), with
point right after that char, and it should return t to cause indentation,
`no-indent' to prevent indentation or nil to let other functions decide.")

(defvar-local electric-indent-inhibit nil
  "If non-nil, reindentation is not appropriate for this buffer.
This should be set by major modes such as `python-mode' since
Python does not lend itself to fully automatic indentation.")

(defvar electric-indent-functions-without-reindent
  '(indent-relative indent-to-left-margin indent-relative-maybe
    py-indent-line coffee-indent-line org-indent-line yaml-indent-line
    haskell-indentation-indent-line haskell-indent-cycle haskell-simple-indent)
  "List of indent functions that can't reindent.
If `line-indent-function' is one of those, then `electric-indent-mode' will
not try to reindent lines.  It is normally better to make the major
mode set `electric-indent-inhibit', but this can be used as a workaround.")

(defun electric-indent-post-self-insert-function ()
  ;; FIXME: This reindents the current line, but what we really want instead is
  ;; to reindent the whole affected text.  That's the current line for simple
  ;; cases, but not all cases.  We do take care of the newline case in an
  ;; ad-hoc fashion, but there are still missing cases such as the case of
  ;; electric-pair-mode wrapping a region with a pair of parens.
  ;; There might be a way to get it working by analyzing buffer-undo-list, but
  ;; it looks challenging.
  (let (pos)
    (when (and
           electric-indent-mode
           ;; Don't reindent while inserting spaces at beginning of line.
           (or (not (memq last-command-event '(?\s ?\t)))
               (save-excursion (skip-chars-backward " \t") (not (bolp))))
           (setq pos (electric--after-char-pos))
           (save-excursion
             (goto-char pos)
             (let ((act (or (run-hook-with-args-until-success
                             'electric-indent-functions
                             last-command-event)
                            (memq last-command-event electric-indent-chars))))
               (not
                (or (memq act '(nil no-indent))
                    ;; In a string or comment.
                    (unless (eq act 'do-indent) (nth 8 (syntax-ppss))))))))
      ;; For newline, we want to reindent both lines and basically behave like
      ;; reindent-then-newline-and-indent (whose code we hence copied).
      (when (<= pos (line-beginning-position))
        (let ((before (copy-marker (1- pos) t)))
          (save-excursion
            (unless (or (memq indent-line-function
                              electric-indent-functions-without-reindent)
                        electric-indent-inhibit)
              ;; Don't reindent the previous line if the indentation function
              ;; is not a real one.
              (goto-char before)
              (indent-according-to-mode))
            ;; We are at EOL before the call to indent-according-to-mode, and
            ;; after it we usually are as well, but not always.  We tried to
            ;; address it with `save-excursion' but that uses a normal marker
            ;; whereas we need `move after insertion', so we do the
            ;; save/restore by hand.
            (goto-char before)
	    (when (eolp)
	      ;; Remove the trailing whitespace after indentation because
	      ;; indentation may (re)introduce the whitespace.
	      (delete-horizontal-space t)))))
      (unless (and electric-indent-inhibit
                   (> pos (line-beginning-position)))
        (indent-according-to-mode)))))

(put 'electric-indent-post-self-insert-function 'priority  60)

(defun electric-indent-just-newline (arg)
  "Insert just a newline, without any auto-indentation."
  (interactive "*P")
  (let ((electric-indent-mode nil))
    (newline arg 'interactive)))


;;;###autoload
(define-minor-mode electric-indent-mode
  "Toggle on-the-fly reindentation (Electric Indent mode).
With a prefix argument ARG, enable Electric Indent mode if ARG is
positive, and disable it otherwise.  If called from Lisp, enable
the mode if ARG is omitted or nil.

This is a global minor mode.  When enabled, it reindents whenever
the hook `electric-indent-functions' returns non-nil, or you
insert a character from `electric-indent-chars'."
  :global t :group 'electricity
  :initialize 'custom-initialize-delay
  :init-value t
  (if (not electric-indent-mode)
      (progn
        (when (eq (lookup-key global-map [?\C-j])
                  'electric-indent-just-newline)
          (define-key global-map [?\C-j] 'newline-and-indent))
        (remove-hook 'post-self-insert-hook
                     #'electric-indent-post-self-insert-function))
    (when (eq (lookup-key global-map [?\C-j]) 'newline-and-indent)
      (define-key global-map [?\C-j] 'electric-indent-just-newline))
    (add-hook 'post-self-insert-hook
              #'electric-indent-post-self-insert-function)
    (electric--sort-post-self-insertion-hook)))

;;;###autoload
(define-minor-mode electric-indent-local-mode
  "Toggle `electric-indent-mode' only in this buffer."
  :variable (buffer-local-value 'electric-indent-mode (current-buffer))
  (cond
   ((eq electric-indent-mode (default-value 'electric-indent-mode))
    (kill-local-variable 'electric-indent-mode))
   ((not (default-value 'electric-indent-mode))
    ;; Locally enabled, but globally disabled.
    (electric-indent-mode 1)                ; Setup the hooks.
    (setq-default electric-indent-mode nil) ; But keep it globally disabled.
    )))

;;; Electric newlines after/before/around some chars.

(defvar electric-layout-rules nil
  "List of rules saying where to automatically insert newlines.

Each rule has the form (CHAR . WHERE) where CHAR is the char that
was just inserted and WHERE specifies where to insert newlines
and can be: nil, `before', `after', `around', `after-stay', or a
function of no arguments that returns one of those symbols.

The symbols specify where in relation to CHAR the newline
character(s) should be inserted. `after-stay' means insert a
newline after CHAR but stay in the same place.")

(defun electric-layout-post-self-insert-function ()
  (let* ((rule (cdr (assq last-command-event electric-layout-rules)))
         pos)
    (when (and rule
               (setq pos (electric--after-char-pos))
               ;; Not in a string or comment.
               (not (nth 8 (save-excursion (syntax-ppss pos)))))
      (let ((end (copy-marker (point)))
            (sym (if (functionp rule) (funcall rule) rule)))
        (set-marker-insertion-type end (not (eq sym 'after-stay)))
        (goto-char pos)
        (pcase sym
          ;; FIXME: we used `newline' down here which called
          ;; self-insert-command and ran post-self-insert-hook recursively.
          ;; It happened to make electric-indent-mode work automatically with
          ;; electric-layout-mode (at the cost of re-indenting lines
          ;; multiple times), but I'm not sure it's what we want.
          ;;
          ;; FIXME: check eolp before inserting \n?
          (`before (goto-char (1- pos)) (skip-chars-backward " \t")
                   (unless (bolp) (insert "\n")))
          (`after  (insert "\n"))
          (`after-stay (save-excursion
                         (let ((electric-layout-rules nil))
                           (newline 1 t))))
          (`around (save-excursion
                     (goto-char (1- pos)) (skip-chars-backward " \t")
                     (unless (bolp) (insert "\n")))
                   (insert "\n")))      ; FIXME: check eolp before inserting \n?
        (goto-char end)))))

(put 'electric-layout-post-self-insert-function 'priority  40)

;;;###autoload
(define-minor-mode electric-layout-mode
  "Automatically insert newlines around some chars.
With a prefix argument ARG, enable Electric Layout mode if ARG is
positive, and disable it otherwise.  If called from Lisp, enable
the mode if ARG is omitted or nil.
The variable `electric-layout-rules' says when and how to insert newlines."
  :global t :group 'electricity
  (cond (electric-layout-mode
         (add-hook 'post-self-insert-hook
                   #'electric-layout-post-self-insert-function)
         (electric--sort-post-self-insertion-hook))
        (t
         (remove-hook 'post-self-insert-hook
                      #'electric-layout-post-self-insert-function))))

(provide 'electric)

;;; electric.el ends here