bug#28520: 26.0.50; Dired recursive copy of directory fails

[adam plaice <plaice.adam+lists@gmail.com>]

Copying a directory recursively, with dired ("C"), fails.

To reproduce:

mkdir test_dired_copy/a1/b -p
cd test_dired_copy
emacs -Q --eval '(dired ".")'

In dired, execute `dired-do-copy' (kbd "C") on the `a1' directory,
select `a2' (within the same parent directory) as the destination, and
answer `yes' to (`Recursive copies of ...?').

*Dired log* contains (in my specific case):


Copy ‘/home/adam/test_dired_copy/a1’ to ‘/home/adam/test_dired_copy/a2’ failed:
(file-already-exists File exists /home/adam/test_dired_copy/a2)

Copy failed for 1 of 1 file


The result is that the directory `a2' is created, but the subdirectory
`b' is not created within it. (For repeated testing, `a2' has to be
deleted each time.)



I think (though I'm not completely sure) that the problem can be
traced to copy-directory, since the following elisp fails as well:

(copy-directory "/home/adam/test_dired_copy/a1" "/home/adam/test_dired_copy/a2")

or equivalently (if already within the directory):

(copy-directory "a1" "a2")


The regression occurred in the commit range
52739ffe773eb403f58a6223b7ef64175df58dd7..e22794867d878d53675fcc91d2ef1ad2494a2ff2
(I have not had time to rebuild emacs sufficiently many times and
check which exact commit is responsible).

The bug is present in the heads of both the emacs-26
(4bef92e9e02d074de1d92e30dc5ef4dd62558c80) and master
(b1f83c10df7d1bbb16f4e13d18119ad4aa1a2137) branches.


Thank you,
Adam


In GNU Emacs 26.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2017-09-13 built on adam
Repository revision: 4bef92e9e02d074de1d92e30dc5ef4dd62558c80
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
System Description:    Ubuntu 16.04.3 LTS

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --with-modules --without-pop'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 MODULES LIBSYSTEMD LCMS2

Important settings:
  value of $LANG: en_GB.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Dired by name

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message subr-x puny cl-macs seq byte-opt
gv bytecomp byte-compile cconv format-spec rfc822 mml easymenu mml-sec
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mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils
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custom widget hashtable-print-readable backquote dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting move-toolbar gtk
x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 100826 7691)
 (symbols 48 20537 1)
 (miscs 40 52 193)
 (strings 32 28786 1222)
 (string-bytes 1 745696)
 (vectors 16 15163)
 (vector-slots 8 497313 9957)
 (floats 8 48 124)
 (intervals 56 824 11)
 (buffers 992 15)
 (heap 1024 24906 1131))