bug#19701: 24.3; directory-files platform-dependent behaviour when directory doesn't exist

["Vida Gábor" <vidagabor@gmail.com>]

> This was never a problem, though.  What exactly does Gnus do that this
> subtlety gets in the way?

I'm migrating from Windows to GNU/Linux, and while I'm doing this Gnus didn't start
properly with my old configuration. I use %F in gnus-group-line-format, which ends up
calling gnus-total-fetched-for. This function calculates the total amount of disk
space used by cache and agent. I use Gnus agent but don't use cache (gnus-use-cache
is nil).

Later, gnus-cache-update-file-total-fetched-for iterates over the files that belong
to the cahe of the group. This list in nil on Windows, so I had no problem, but on
GNU/Linux, it raises an error, because I have no cache directory.

I replaced some parts of the call stack below with ellipsis.

Debugger entered--Lisp error: (file-error "Opening directory" "no such file or directory" "/home/evidgbo/config/emacs.d/gnus-cache/nntp+gmane:gmane.announce")
  directory-files("/home/evidgbo/config/emacs.d/gnus-cache/nntp+gmane:gmane.announce" t nil t)
  gnus-cache-update-file-total-fetched-for("nntp+gmane:gmane.announce" nil)
  gnus-cache-total-fetched-for("nntp+gmane:gmane.announce")
  gnus-total-fetched-for("nntp+gmane:gmane.announce")
  (format " %5s U, %3d T, %3d D,  %s  L:%d  %s  %s\n" gnus-tmp-number-of-unread (gnus-range-length (cdr (assq (quote tick) gnus-tmp-marked))) (gnus-range-length (cdr (assq (quote dormant) gnus-tmp-marked))) (gnus-total-fetched-for gnus-tmp-group) gnus-tmp-level (gnus-user-format-function-t gnus-tmp-header) (if (boundp (quote gnus-tmp-decoded-group)) gnus-tmp-decoded-group gnus-tmp-group))
  (insert (format " %5s U, %3d T, %3d D,  %s  L:%d  %s  %s\n" gnus-tmp-number-of-unread (gnus-range-length (cdr (assq (quote tick) gnus-tmp-marked))) (gnus-range-length (cdr (assq (quote dormant) gnus-tmp-marked))) (gnus-total-fetched-for gnus-tmp-group) gnus-tmp-level (gnus-user-format-function-t gnus-tmp-header) (if (boundp (quote gnus-tmp-decoded-group)) gnus-tmp-decoded-group gnus-tmp-group)))
  (let (gnus-position) (insert (format "%c%s %c%c %5s " gnus-tmp-process-marked gnus-group-indentation gnus-tmp-summary-live (gnus-group-new-mail gnus-tmp-group) (if (gnus-active gnus-tmp-group) (gnus-number-of-unseen-articles-in-group gnus-tmp-group) "*"))) (setq gnus-position (point)) (gnus-put-text-property (point) (progn (insert gnus-tmp-qualified-group) (point)) gnus-mouse-face-prop gnus-mouse-face) (if (> (current-column) 35) (let ((end (point))) (if (= (move-to-column 35) 35) (delete-region (point) end) (delete-region (1- (point)) end) (insert " "))) (insert-char 32 (max (- 35 (current-column)) 0))) (insert (format " %5s U, %3d T, %3d D,  %s  L:%d  %s  %s\n" gnus-tmp-number-of-unread (gnus-range-length (cdr (assq (quote tick) gnus-tmp-marked))) (gnus-range-length (cdr (assq (quote dormant) gnus-tmp-marked))) (gnus-total-fetched-for gnus-tmp-group) gnus-tmp-level (gnus-user-format-function-t gnus-tmp-header) (if (boundp (quote gnus-tmp-decoded-group)) gnus-tmp-decoded-group gnus-tmp-group))) (if gnus-position (gnus-put-text-property gnus-position (1+ gnus-position) (quote gnus-position) t)))
  eval((let (gnus-position) (insert (format "%c%s %c%c %5s " gnus-tmp-process-marked gnus-group-indentation gnus-tmp-summary-live (gnus-group-new-mail gnus-tmp-group) (if (gnus-active gnus-tmp-group) (gnus-number-of-unseen-articles-in-group gnus-tmp-group) "*"))) (setq gnus-position (point)) (gnus-put-text-property (point) (progn (insert gnus-tmp-qualified-group) (point)) gnus-mouse-face-prop gnus-mouse-face) (if (> (current-column) 35) (let ((end (point))) (if (= (move-to-column 35) 35) (delete-region (point) end) (delete-region (1- (point)) end) (insert " "))) (insert-char 32 (max (- 35 (current-column)) 0))) (insert (format " %5s U, %3d T, %3d D,  %s  L:%d  %s  %s\n" gnus-tmp-number-of-unread (gnus-range-length (cdr (assq (quote tick) gnus-tmp-marked))) (gnus-range-length (cdr (assq (quote dormant) gnus-tmp-marked))) (gnus-total-fetched-for gnus-tmp-group) gnus-tmp-level (gnus-user-format-function-t gnus-tmp-header) (if (boundp (quote gnus-tmp-decoded-group)) gnus-tmp-decoded-group gnus-tmp-group))) (if gnus-position (gnus-put-text-property gnus-position (1+ gnus-position) (quote gnus-position) t))))
  gnus-group-insert-group-line("nntp+gmane:gmane.announce" 3 ((seen (1 . 18742) (18916 . 19115))) 3948 "nntp:gmane")
  gnus-topic-prepare-topic((("announcements" visible nil nil)) 2 5 nil nil 1 nil)
  gnus-topic-prepare-topic((("gmane" visible nil ((subscribe . "^nntp\\+gmane:") (gcc-self . "nnimap+nedu:incoming") (agent-predicate and (not my-article-old-p)))) (("announcements" visible nil nil))) 1 5 nil nil 1 nil)
  gnus-topic-prepare-topic(...)
  gnus-group-prepare-topics(5 nil nil)
  gnus-group-list-groups(nil)
  byte-code("..." [dont-connect did-connect gnus-startup-file gnus-current-startup-file gnus-slave gnus-use-dribble-file gnus-group-quit gnus-run-hooks gnus-startup-hook gnus-make-newsrc-file gnus-dribble-read-file gnus-setup-news nil gnus-setup-news-hook gnus-request-create-group "queue" (nndraft "") gnus-start-draft-setup gnus-group-list-groups gnus-group-first-unread-group gnus-configure-windows group gnus-group-set-mode-line gnus-started-hook level gnus-agent] 4)
  gnus-1(nil nil nil)
  gnus(nil)
  call-interactively(gnus record nil)
  command-execute(gnus record)
  execute-extended-command(nil "gnus")
  call-interactively(execute-extended-command nil nil)

But I had no time so far to do a clean reproduction. As a workaround, I removed %F
from gnus-group-line-format temporary.