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+;;; guix-prettify.el --- Prettify Guix store file names
+
+;; Copyright © 2014 Alex Kost <alezost@gmail.com>
+
+;; This file is part of GNU Guix.
+
+;; GNU Guix 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 Guix 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This package provides minor-mode for prettifying Guix store file
+;; names — i.e., after enabling `guix-prettify-mode',
+;; '/gnu/store/72f54nfp6g1hz873w8z3gfcah0h4nl9p-foo-0.1' names will be
+;; replaced with '/gnu/store/…-foo-0.1' in the current buffer.  There is
+;; also `global-guix-prettify-mode' for global prettifying.
+
+;; To install, add the following to your emacs init file:
+;;
+;;   (add-to-list 'load-path "/path/to/dir-with-guix-prettify")
+;;   (autoload 'guix-prettify-mode "guix-prettify" nil t)
+;;   (autoload 'global-guix-prettify-mode "guix-prettify" nil t)
+
+;; If you want to enable/disable composition after "M-x font-lock-mode",
+;; use the following setting:
+;;
+;;   (setq font-lock-extra-managed-props
+;;         (cons 'composition font-lock-extra-managed-props))
+
+;; Credits:
+;;
+;; Thanks to Ludovic Courtès for the idea of this package.
+;;
+;; Thanks to the authors of `prettify-symbols-mode' (part of Emacs 24.4)
+;; and "pretty-symbols.el" <http://github.com/drothlis/pretty-symbols>
+;; for the code.  It helped to write this package.
+
+;;; Code:
+
+(defgroup guix-prettify nil
+  "Prettify Guix store file names."
+  :prefix "guix-prettify-"
+  :group 'font-lock
+  :group 'convenience)
+
+(defcustom guix-prettify-char ?…
+  "Character used for prettifying."
+  :type 'character
+  :group 'guix-prettify)
+
+(defcustom guix-prettify-decompose-force nil
+  "If non-nil, remove any composition.
+
+By default, after disabling `guix-prettify-mode',
+compositions (prettifying names with `guix-prettify-char') are
+removed only from strings matching `guix-prettify-regexp', so
+that compositions created by other modes are left untouched.
+
+Set this variable to non-nil, if you want to remove any
+composition unconditionally (like `prettify-symbols-mode' does).
+Most likely it will do no harm and will make the process of
+disabling `guix-prettify-mode' a little faster."
+  :type 'boolean
+  :group 'guix-prettify)
+
+(defcustom guix-prettify-regexp
+  (rx "/"
+      (or "nix" "gnu")
+      "/store/"
+      ;; Hash-parts do not include "e", "o", "u" and "t".  See base32Chars
+      ;; at <https://github.com/NixOS/nix/blob/master/src/libutil/hash.cc>
+      (group (= 32 (any "0-9" "a-d" "f-n" "p-s" "v-z"))))
+  "Regexp matching file names for prettifying.
+
+Disable `guix-prettify-mode' before modifying this variable and
+make sure to modify `guix-prettify-regexp-group' if needed.
+
+Example of a \"deeper\" prettifying:
+
+  (setq guix-prettify-regexp \"store/[[:alnum:]]\\\\\\={32\\\\}\"
+        guix-prettify-regexp-group 0)
+
+This will transform
+'/gnu/store/72f54nfp6g1hz873w8z3gfcah0h4nl9p-foo-0.1' into
+'/gnu/…-foo-0.1'"
+  :type 'regexp
+  :group 'guix-prettify)
+
+(defcustom guix-prettify-regexp-group 1
+  "Regexp group in `guix-prettify-regexp' for prettifying."
+  :type 'integer
+  :group 'guix-prettify)
+
+(defvar guix-prettify-special-modes
+  '(guix-info-mode ibuffer-mode)
+  "List of special modes that support font-locking.
+
+By default, \\[global-guix-prettify-mode] enables prettifying in
+all buffers except the ones where `font-lock-defaults' is
+nil (see Info node `(elisp) Font Lock Basics'), because it may
+break the existing highlighting.
+
+Modes from this list and all derived modes are exceptions
+\(`global-guix-prettify-mode' enables prettifying there).")
+
+(defvar guix-prettify-flush-function
+  (cond ((fboundp 'font-lock-flush) #'font-lock-flush)
+        ((fboundp 'jit-lock-refontify) #'jit-lock-refontify))
+  "Function used to refontify buffer.
+This function is called without arguments after
+enabling/disabling `guix-prettify-mode'.  If nil, do nothing.")
+
+(defun guix-prettify-compose ()
+  "Compose matching region in the current buffer."
+  (let ((beg (match-beginning guix-prettify-regexp-group))
+        (end (match-end       guix-prettify-regexp-group)))
+    (compose-region beg end guix-prettify-char 'decompose-region))
+  ;; Return nil because we're not adding any face property.
+  nil)
+
+(defun guix-prettify-decompose-buffer ()
+  "Remove file names compositions from the current buffer."
+  (with-silent-modifications
+    (let ((inhibit-read-only t))
+      (if guix-prettify-decompose-force
+          (remove-text-properties (point-min)
+                                  (point-max)
+                                  '(composition nil))
+        (save-excursion
+          (goto-char (point-min))
+          (while (re-search-forward guix-prettify-regexp nil t)
+            (remove-text-properties
+             (match-beginning guix-prettify-regexp-group)
+             (match-end       guix-prettify-regexp-group)
+             '(composition nil))))))))
+
+;;;###autoload
+(define-minor-mode guix-prettify-mode
+  "Toggle Guix Prettify mode.
+
+With a prefix argument ARG, enable Guix Prettify mode if ARG is
+positive, and disable it otherwise.  If called from Lisp, enable
+the mode if ARG is omitted or nil.
+
+When Guix Prettify mode is enabled, hash-parts of the Guix store
+file names (see `guix-prettify-regexp') are prettified,
+i.e. displayed as `guix-prettify-char' character.  This mode can
+be enabled programmatically using hooks:
+
+  (add-hook 'shell-mode-hook 'guix-prettify-mode)
+
+It is possible to enable the mode in any buffer, however not any
+buffer's highlighting may survive after adding new elements to
+`font-lock-keywords' (see `guix-prettify-special-modes' for
+details).
+
+Also you can use `global-guix-prettify-mode' to enable Guix
+Prettify mode for all modes that support font-locking."
+  :init-value nil
+  :lighter " …"
+  (let ((keywords `((,guix-prettify-regexp
+                     (,guix-prettify-regexp-group
+                      (guix-prettify-compose))))))
+    (if guix-prettify-mode
+        ;; Turn on.
+        (font-lock-add-keywords nil keywords)
+      ;; Turn off.
+      (font-lock-remove-keywords nil keywords)
+      (guix-prettify-decompose-buffer))
+    (and guix-prettify-flush-function
+         (funcall guix-prettify-flush-function))))
+
+(defun guix-prettify-supported-p ()
+  "Return non-nil, if the mode can be harmlessly enabled in current buffer."
+  (or font-lock-defaults
+      (apply #'derived-mode-p guix-prettify-special-modes)))
+
+(defun guix-prettify-turn-on ()
+  "Enable `guix-prettify-mode' in the current buffer if needed.
+See `guix-prettify-special-modes' for details."
+  (and (not guix-prettify-mode)
+       (guix-prettify-supported-p)
+       (guix-prettify-mode)))
+
+;;;###autoload
+(define-globalized-minor-mode global-guix-prettify-mode
+  guix-prettify-mode guix-prettify-turn-on)
+
+;;;###autoload
+(defalias 'guix-prettify-global-mode 'global-guix-prettify-mode)
+
+(provide 'guix-prettify)
+
+;;; guix-prettify.el ends here