ispell-multi.el -- multiple ispell processes and languages

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ispell-multi.el -- multiple ispell processes and languages

Peter Heslin
;; ispell-multi.el -- multiple ispell processes and multiple flyspell languages
;;
;; Copyright (C) 2005 P J Heslin
;;
;; Author: Peter Heslin <[hidden email]>
;; URL: http://www.dur.ac.uk/p.j.heslin/emacs/download/ispell-multi.el
;; Version: 1.1
;;
;; This program 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 2, or (at your option)
;; any later version.
;;
;; This program 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.
;;
;; If you do not have a copy of the GNU General Public License, you
;; can obtain one by writing to the Free Software Foundation, Inc., 59
;; Temple Place - Suite 330, Boston, MA 02111-1307, USA.

;;; Overview:
;;
;; ispell-multi.el enables Emacs to keep a number of ispell processes
;; alive in order to spell-check text efficiently in multiple
;; languages, and it provides a hook that tells flyspell to switch
;; languages depending on the value of a particular text property.
;;
;; Normally, ispell.el only ever keeps one ispell/aspell process
;; alive.  So if you have one buffer in which an English local
;; dictionary is used and another in which a German dictionary is
;; used, the ispell process will be killed and restarted every time
;; you run ispell in the other buffer.  This is not really a problem,
;; since doing a spellcheck is infrequent and slow anyway.  If you are
;; using flyspell-mode, however, the ispell process will be restarted
;; every time you switch buffers.  Even this may not matter too much
;; to many people, since switching buffers is also a somewhat slow
;; operation.
;;
;; Where the need for multiple ispell processes becomes really acute
;; is in buffers that have multiple languages in them and a way of
;; telling flyspell to switch local dictionaries depending on where
;; point is.  In this case, the starting and stopping of ispell
;; processes very visibly impedes the fluid movement of the cursor.
;;
;; I have written two packages that provide this sort of behavior.
;; One is flyspell-xml-lang.el, which tells flyspell what the local
;; language is in xml files depending on xml:lang attributes, and
;; another is flyspell-babel.el, which does the same with Babel
;; commands in LaTeX files.
;;
;; The present package modifies ispell.el (via defadvice) so that
;; multiple ispell processes are kept alive to check different
;; languages.  It requires version 3.6 of ispell, so users of Emacs
;; 21.3 and earlier will have to upgrade.  This has only been tested
;; with GNU Emacs.
;;
;; To install this package, just put it somewhere in your load-path
;; and put a (require 'ispell-multi) statement in your .emacs file.

;;; Using ispell-multi
;;
;; If all you want to do is to change the behavior of ispell so that
;; it uses multiple ispell processes, then (require 'ispell-multi) is
;; all you need to do.  The rest of this section is for those who want
;; to modify flyspell to switch languages within a buffer, based on
;; some criteria.  See flyspell-xml-lang.el and flyspell-babel.el for
;; examples of the usage of all of the facilities described below.
;;
;; Flyspell-mode provides a hook that runs before checking each word;
;; this allows you to change the value of ispell-local-dictionary to a
;; different language, depending on the context.  If you have a
;; package that parses a buffer and figures out what languages are in
;; it and where they are, you can tell flyspell about it by setting
;; the text property `ispell-multi-lang' to the correct ispell
;; language (this can be any value that ispell-change-dictionary
;; accepts).  Your package should set the value of the buffer-local
;; variable `flyspell-generic-check-word-p' to the symbol
;; `ispell-multi-verify'; do this *after* you have turned on
;; flyspell-mode.

;; If you the set the buffer-local variable
;; `ispell-multi-flyspell-callback' to a symbol, the associated
;; function will be called every time flyspell is called to check a
;; word, and the `ispell-multi-lang' text property returns nil.  This
;; function can be used to parse the buffer incrementally and set the
;; text-property lazily as the user moves through the buffer.
;;
;; Since the parser callback is only invoked when the text-property is
;; nil, there is a possibility that the already-set text-property and
;; the changed contents of the buffer will get out of sync.  To fix
;; this you will probably also want to arrange for the parser to be
;; run by an idle-timer.  You can arrange for this by calling the
;; function `ispell-multi-idler-setup' with a single argument, giving
;; the delay.
;;
;; If you want to indicate that some text should not be spell-checked,
;; set the `ispell-multi-lang' text property to the string "void".  To
;; indicate a reversion to the default ispell dictionary, use the
;; string "default".

;;; Aspell vs. Ispell
;;
;; ispell.el and ispell-multi.el will work happily with aspell instead
;; of ispell, since the former can emulate the latter.  Aspell has
;; many advantages over ispell, including a very large selection of
;; language dictionaries, and it is much better able to suggest the
;; correct spelling (which is quite handy when using
;; flyspell-auto-correct-previous-word).  If you prefer to use aspell,
;; you can put the following into your .emacs:
;;    
;;    (setq ispell-program-name "aspell")
;;    (setq ispell-really-aspell t)
;;    (setq ispell-extra-args '("--sug-mode=fast"))
;;
;; The first two lines tell ispell.el to run aspell instead of ispell,
;; and the third line tells aspell not to use its default algorithm
;; for suggesting spellings, but to use a faster one; the default is
;; very accurate, but can be a bit slow for use with flyspell.  If
;; this is not fast enough, try "ultra" instead of "fast" (but even
;; ultra mode is still two times slower than ispell).
;;
;; If you are installing a new aspell dictionary that ispell.el does
;; not know about, you will have to add it to
;; ispell-local-dictionary-alist; see the documentation of
;; flyspell-xml-lang.el for an example.

;;; Implementation Notes
;;
;; We try to share ispell processes between buffers, so that a single
;; process can service all buffers or regions in a given language.
;; But if you put buffer-local variables that modify the behavior of
;; ispell for a given buffer (such as LocalWords), then that buffer's
;; ispell processes will not be shared.
;;
;; Each buffer is responsible for killing the ispell processes that it
;; starts.  This means that when the buffer that starts a process for
;; a given language is killed, it will kill all the processes it has
;; started, even if they are in use by another buffer.  Thus a new
;; ispell process for that language will have to be started next time
;; you switch to that other buffer.

;;; Bugs and Limitations
;;
;; If you change ispell dictionaries by using the function
;; `ispell-change-dictionary', then an ispell process will be killed,
;; where it would not have been if you had simply set
;; ispell-local-dictionary.  That's because this package just modifies
;; the way ispell deals with local variables like
;; ispell-local-dictionary; it doesn't touch the
;; ispell-change-dictionary function.  Maybe it should.  The necessary
;; ispell process will be re-started next time you need it, so this is
;; not really a bug so much as a slight performance issue.
;;
;; It would be better to keep track of all of the buffers that have
;; used a given process, so that we would refrain from killing it if
;; we know that there is another buffer that might be interested in
;; using it.  This would add complexity to the implementation,
;; however.
;;
;; It might have been nice to put in here the code to inspect a
;; text-property to find out the language of the text, so that ispell
;; in general would obey a certain property and change dictionary
;; accordingly.  This won't work, though, since ispell-region works on
;; a line-by-line basis, which would fail in the case of a mid-line
;; language-switch.  
;;
;; In the abstract, it might be nice to share ispell processes between
;; buffers that have identical buffer-local modifications to ispell's
;; behavior, but that would be very complex to implement, and I think
;; unlikely to be useful in practice.
;;
;; flyspell-large-region, which is the fast mode of flyspell that it
;; uses when checking the entirety of a large buffer, does not work at
;; all, since it depends on launching a single ispell process for this
;; purpose and so cannot cope with multiple languages.  For this
;; reason, flyspell-large-region should be disabled in buffers using
;; this package.

;;; Changes
;;
;; 1.0 Pre-release
;; 1.1 Worked around ispell-current-dictionary / ispell-dictionary
;;     inconsistency in Emacs CVS / stand-alone ispell.el

(require 'ispell)
;; For Emacs 21.3, we have to use an updated ispell.el (3.6 or from
;; Emacs CVS), and for some reason we may have to load it again to get
;; ispell-dictionary-alist set properly.
(unless (assoc "english" ispell-dictionary-alist)
  (load "ispell"))
;; For updated ispell.el with emacs < 21.3.5
(when (not (fboundp 'set-process-query-on-exit-flag))
  (defun set-process-query-on-exit-flag (one two) ()))

; In current Emacs CVS, the variable ispell-current-dictionary is used
; to indicate the dictionary associated with the current ispell
; process, while in the current, separately distributed version of
; ispell.el (3.7beta), this variable does not exist, and
; ispell-dictionary serves this purpose.
(defvar ispell-multi-current-dictionary-var
  (if (boundp 'ispell-current-dictionary)
      'ispell-current-dictionary
    'ispell-dictionary))

(defvar ispell-multi-processes nil
  "Buffer-local variable to record a list of all of the ispell
  processes started by this buffer.")
(make-variable-buffer-local 'ispell-multi-processes)

(defvar ispell-multi-lang-process nil
  "Alist mapping languages to ispell processes.  Only for
  processes without any buffer-local modifications")

(defvar ispell-multi-lang-process-local nil
  "As ispell-multi-lang-process, but a buffer-local alist, to use
  for processes with buffer-local modifications")
(make-variable-buffer-local 'ispell-multi-lang-process-local)

(defvar ispell-multi-flyspell-verify-default nil
  "The original value of `flyspell-generic-check-word-p', before
  it was overridden in order to invoke this package; taken from
  the the `flyspell-mode-predicate' property of the major mode
  name.")
(make-variable-buffer-local 'ispell-multi-flyspell-verify-default)

(defvar ispell-multi-flyspell-callback nil
  "Buffer local variable that indicates a function to call when
  flyspell is checking a word and the text property
  `ispell-multi-lang' is nil.  This function will normally set
  that property at point and for some of the text in the
  neighborhood")
(make-variable-buffer-local 'ispell-multi-flyspell-callback)

(defvar ispell-multi-verbose nil
  "If non-nil, print diagnostic messages about switching dictionaries")

(defvar ispell-multi-valid-dictionary-list nil
  "Cached value of ispell-valid-dictionary-list.")
(when (fboundp 'ispell-valid-dictionary-list)
  (setq ispell-multi-valid-dictionary-list
        (ispell-valid-dictionary-list)))

;; This is our hook into ispell.el.
(defadvice ispell-accept-buffer-local-defs (around ispell-multi-advice activate)
  "Advice that changes ispell to enable multiple ispell processes."
  (let* ((local-mods (ispell-multi-buffer-local-modifications-p))
         (alist (if local-mods
                    'ispell-multi-lang-process-local
                  'ispell-multi-lang-process))
         (stored-process (cdr (assoc ispell-local-dictionary (symbol-value alist)))))

    ;; Store the currently running process if we haven't already
    (when (and ispell-process
               (eq (process-status ispell-process) 'run)
               (not (rassq ispell-process (symbol-value alist))))
      (set alist (cons (cons (symbol-value ispell-multi-current-dictionary-var) ispell-process)
                       (symbol-value alist)))
      (setq ispell-multi-processes (cons ispell-process ispell-multi-processes)))

    ;; Do we already have a process for this language?
    (if (and stored-process
             (eq (process-status stored-process) 'run))
        (progn
          (setq ispell-process stored-process)
          ;; When ispell-current-dictionary / ispell-dictionary is
          ;; the same as ispell-local-dictionary, ispell.el will
          ;; refrain from killing the process
          (set ispell-multi-current-dictionary-var ispell-local-dictionary))
     
      ;; This is to fool ispell into not killing the old process when
      ;; it starts the new one.  But we don't want a new process if
      ;; the current one is correct, or if the new dict is void.
      (unless (or (equal (symbol-value ispell-multi-current-dictionary-var) ispell-local-dictionary)
                  (equal ispell-local-dictionary "void"))
        (setq ispell-process nil))
     
      ;; Possibly start a new process
      (unless (equal ispell-local-dictionary "void")  ; ensure against error
        ad-do-it))))


(defun ispell-multi-kill-processes-hook ()
  "Kill all ispell processes started by this buffer"
  (interactive)
  (while ispell-multi-processes
    (setq ispell-process (car ispell-multi-processes))
    (when (eq (process-status ispell-process) 'run)
      (ispell-kill-ispell))
    (setq ispell-multi-processes (cdr ispell-multi-processes)))
  (ispell-multi-processes-alist-cleanup))

(add-hook 'kill-buffer-hook 'ispell-multi-kill-processes-hook)

(defun ispell-multi-processes-alist-cleanup ()
  "Remove any defunct processes from the global alist"
  (let ((newlist))
    (while ispell-multi-lang-process
      (when (eq (process-status (cdar ispell-multi-lang-process)) 'run)
        (setq newlist (cons (car ispell-multi-lang-process) newlist)))
      (setq ispell-multi-lang-process (cdr ispell-multi-lang-process)))
    (setq ispell-multi-lang-process (nreverse newlist))))
 
(defvar ispell-multi-local-regexp
  (mapconcat 'regexp-quote (list ispell-dictionary-keyword
                                 ispell-pdict-keyword
                                 ispell-words-keyword) "\\|"))

(defun ispell-multi-buffer-local-modifications-p ()
  (save-excursion
    (goto-char (point-max))
    (re-search-backward ispell-multi-local-regexp nil t)))

(defun ispell-multi-verify ()
  (unless ispell-multi-flyspell-verify-default
    (setq ispell-multi-flyspell-verify-default
          (or (get major-mode 'flyspell-mode-predicate)
              'none)))
  (let ((do-check t))
    ;; Don't switch language if we're not supposed to check this bit anyway
    (when (and ispell-multi-flyspell-verify-default
               (not (eq ispell-multi-flyspell-verify-default 'none)))
      (setq do-check (funcall ispell-multi-flyspell-verify-default)))
    (when do-check
      (let* ((current-position (point))
             (lang (get-text-property current-position 'ispell-multi-lang)))
        (when (and (not lang)
                   ispell-multi-flyspell-callback)
          (ispell-multi-message "parsing ...")
          (save-excursion
            (funcall ispell-multi-flyspell-callback))
          (ispell-multi-message "finished parsing.")
          (setq lang (get-text-property current-position 'ispell-multi-lang)))
        (when lang
          (when (string= lang "default")
            (setq lang (default-value 'ispell-local-dictionary))
            (ispell-multi-message "Using default dictionary"))
          (unless (string= ispell-local-dictionary lang)
            (cond
             ((string= lang "void")
              (setq do-check nil)
              (ispell-multi-message
               "current dictionary is void: not checking"))
             ((and ispell-multi-valid-dictionary-list
                   (member lang ispell-multi-valid-dictionary-list))
              (ispell-multi-message (concat "dictionary changing to: " lang))
              (setq ispell-local-dictionary lang)
              ;; Be paranoid, since this is called from a post-command hook
              (condition-case nil
                  (ispell-accept-buffer-local-defs)
                (error (ispell-multi-message
                        (concat "Error: ispell didn't like language" lang)))))
             (t
              (ispell-multi-message
               (concat "Warning: no dictionary installed for " lang))))))))
    do-check))

(defvar ispell-multi-ticker 0)
(defvar ispell-multi-old-point 0)
(make-variable-buffer-local 'ispell-multi-ticker)
(make-variable-buffer-local 'ispell-multi-old-point)

(defun ispell-multi-idler ()
  (when (and flyspell-mode
             (eq flyspell-generic-check-word-p 'ispell-multi-verify)
             (not (= (buffer-modified-tick) ispell-multi-ticker))
             (not (= (point) ispell-multi-old-point)))
    (let ((old-lang (get-text-property (point) 'ispell-multi-lang))
          new-lang)
      (when ispell-multi-flyspell-callback
        (ispell-multi-message "parsing (idle) ...")
        (save-excursion
          (funcall ispell-multi-flyspell-callback))
        (ispell-multi-message "finished parsing.")
        (setq new-lang (get-text-property (point) 'ispell-multi-lang))
        (unless (or (equal old-lang new-lang)
                    (equal new-lang "void"))
          (when (string= new-lang "default")
            (setq new-lang (default-value 'ispell-local-dictionary)))
          (setq ispell-local-dictionary new-lang)
          (ispell-accept-buffer-local-defs)))
      (setq ispell-multi-ticker (buffer-modified-tick))
      (setq ispell-multi-old-point (point)))))

(defvar ispell-multi-idle-timer nil)
(defun ispell-multi-idler-setup (delay)
  (unless ispell-multi-idle-timer
    (setq ispell-multi-idle-timer
          (run-with-idle-timer 5 t 'ispell-multi-idler))))

(defun ispell-multi-idler-cancel ()
    (cancel-timer ispell-multi-idle-timer)
    (setq ispell-multi-idle-timer nil))

(defun ispell-multi-unhack-flyspell-modeline ()
  "Remove the flyspell modeline entry"
  (setq minor-mode-alist
        (delq (assq 'flyspell-mode minor-mode-alist) minor-mode-alist)))
 
(defun ispell-multi-hack-flyspell-modeline ()
  "Add a modeline entry for flyspell that indicates the current
  language in parentheses."
  (ispell-multi-unhack-flyspell-modeline)
  (setq minor-mode-alist
        (cons '(flyspell-mode
                (:eval
                 (let ((lang (get-text-property (point) 'ispell-multi-lang)))
                   (concat flyspell-mode-line-string
                           (when lang
                             (concat " (" (capitalize lang) ")")))))) minor-mode-alist)))

(defun ispell-multi-message (mess &optional force)
  (when (or ispell-multi-verbose force)
    (message "ispell-multi -- %s" mess)))

(provide 'ispell-multi)

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