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Re: file-name-shadow-mode

From: Stefan Monnier
Subject: Re: file-name-shadow-mode
Date: Wed, 23 Mar 2005 17:55:28 -0500
User-agent: Gnus/5.11 (Gnus v5.11) Emacs/22.0.50 (gnu/linux)

> How 'bout the patch below which makes no assumption (that I know of) about
> substitute-in-file-name, and will thus work correctly even with weird
> magic file name handlers.

Regarding performance of my code: I just bumped into a performance problem.
The problem is that substitute-in-file-name can take a non-negligible amount
of time to execute when there's a "~user" in the file name, because it calls
getpwnam to figure out whether "user" actually exists or not.

At least here with 8K users in our YP database, my code causes
file-name-shadow-mode to take around 0.5-1s to refresh the screen after each
key stroke if there's a ~user in the file name I'm editing.

So I've tweaked my code to streamline the common case where the shadow
doesn't need to be moved.  I also fixed the problem where a file name like
"/home/foo/bar/:toto//tata" was sometimes shadowed as "r/:toto//tata"
instead of just "/tata".


--- orig/lisp/rfn-eshadow.el
+++ mod/lisp/rfn-eshadow.el
@@ -97,7 +97,7 @@
   '(face file-name-shadow field shadow)
   "Properties given to the `shadowed' part of a filename in the minibuffer.
 Only used when `file-name-shadow-mode' is active.
-If emacs is not running under a window system,
+If Emacs is not running under a window system,
 `file-name-shadow-tty-properties' is used instead."
   :type file-name-shadow-properties-custom-type
   :group 'minibuffer)
@@ -123,20 +123,6 @@
 ;;; Internal variables
-;; Regexp to locate dividing point between shadow and real pathname
-(defconst rfn-eshadow-regexp
-  (cond ((memq system-type '(ms-dos windows-nt))
-        ;; This horrible regexp considers the following patterns as
-        ;; starting an absolute pathname, when following a `/' or an `\':
-        ;;   L:  /  //  ~  $  \\  \\\\
-       (t
-        ;; default is for unix-style filenames
-        "\\(.*/\\)\\([/~]\\|$[^$]\\|$\\'\\)"))
-  "Regular expression used to match shadowed filenames.
-There should be at least one regexp group; the end of the first one
-is used as the end of the shadowed portion of the filename.")
 ;; A list of minibuffers to which we've added a post-command-hook.
 (defvar rfn-eshadow-frobbed-minibufs nil)
@@ -170,31 +156,54 @@
     (add-to-list 'rfn-eshadow-frobbed-minibufs (current-buffer))
     (add-hook 'post-command-hook #'rfn-eshadow-update-overlay nil t)))
+(defsubst rfn-eshadow-sifn-equal (goal pos)
+  (equal goal (buffer-substring-no-properties pos (point-max))))
 ;; post-command-hook to update overlay
 (defun rfn-eshadow-update-overlay ()
   "Update `rfn-eshadow-overlay' to cover shadowed part of minibuffer input.
 This is intended to be used as a minibuffer post-command-hook for
 `file-name-shadow-mode'; the minibuffer should have already
 been set up by `rfn-eshadow-setup-minibuffer'."
-  ;; This is not really a correct implementation; it won't always do the
-  ;; right thing in the presence of environment variables that
-  ;; substitute-in-file-name would expand; currently it just assumes any
-  ;; environment variable contains an absolute filename.
-  (save-excursion
-    (let ((inhibit-point-motion-hooks t))
-      (goto-char (minibuffer-prompt-end))
-      ;; Update the overlay (which will evaporate if it's empty).
-      (move-overlay rfn-eshadow-overlay
-                   (point)
-                   (if (looking-at rfn-eshadow-regexp)
-                       (match-end 1)
-                     (point))))))
+  ;; This code usually is instantaneous, but if the file name includes
+  ;; a "~<user>", substitute-in-file-name will lookup your system's list of
+  ;; users to see whether "<user>" is an actual user or not, and that
+  ;; can sometimes take a while, so we wrap this in `while-no-input'.
+  (while-no-input
+    (condition-case nil
+       (let ((goal (substitute-in-file-name (minibuffer-contents)))
+             (mid (overlay-end rfn-eshadow-overlay))
+             (start (minibuffer-prompt-end))
+             (end (point-max)))
+         (unless
+             ;; Catch the common case where the shadow does not need to move.
+             (and mid
+                  (or (eq mid end)
+                      (not (rfn-eshadow-sifn-equal goal (1+ mid))))
+                  (or (eq mid start)
+                      (rfn-eshadow-sifn-equal goal mid)))
+           ;; Binary search for the greatest position still equivalent to
+           ;; the whole.
+           (while (or (< (1+ start) end)
+                      (if (and (< (1+ end) (point-max))
+                               (rfn-eshadow-sifn-equal goal (1+ end)))
+                          ;; (SIFN end) != goal, but (SIFN (1+end)) == goal,
+                          ;; We've reached a discontinuity: this can happen
+                          ;; e.g. if `end' point to "/:...".
+                          (setq start (1+ end) end (point-max))))
+             (setq mid (/ (+ start end) 2))
+             (if (equal (condition-case nil
+                            (rfn-eshadow-sifn-equal goal mid)
+                          (error nil))
+                        goal)
+                 (setq start mid)
+               (setq end mid)))
+           (move-overlay rfn-eshadow-overlay (minibuffer-prompt-end) start)))
+      ;; `substitute-in-file-name' can fail on partial input.
+      ;; (error nil)
+      )))
-;;; Note this definition must be at the end of the file, because
-;;; `define-minor-mode' actually calls the mode-function if the
-;;; associated variable is non-nil, which requires that all needed
-;;; functions be already defined.  [This is arguably a bug in d-m-m]
 (define-minor-mode file-name-shadow-mode
   "Toggle File-Name Shadow mode.
@@ -222,5 +231,5 @@
 (provide 'rfn-eshadow)
-;;; arch-tag: dcf70a52-0115-4ec2-b1e3-4f8d3541a888
+;; arch-tag: dcf70a52-0115-4ec2-b1e3-4f8d3541a888
 ;;; rfn-eshadow.el ends here

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