bug#28519: 26.0.50; Dired move of directory across partition boundary fails

[adam plaice]

Moving a directory, with dired ("R"), across a partition boundary fails.

To reproduce:

mkdir test_dired_move/a -p
cd test_dired_move
emacs -Q --eval '(dired ".")'

In dired, execute `dired-do-rename' (kbd "R") on the `a' directory and
select a (writable) destination on a different partition, if such exists
(typically /media/... or /mnt/... on a unix system).

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


Move ‘/home/adam/test_dired_move/a’ to ‘/mnt/data/a’ failed:
(file-error Non-regular file Is a directory /home/adam/test_dired_move/a)

Move failed for 1 of 1 file


I think (though I'm not 100% certain) that the problem can be traced to
rename-file, since the following elisp fails as well (with the exact
same file-error):

(rename-file "/home/adam/test_dired_move/a" "/mnt/data/a")



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). Since
01c885f21f343045783eb9ad1ff5f9b83d6cd789 touches src/fileio.c I
presume that it would be this one.


Moving a directory on the same partition works as expected. Moving a
plain file to another partition also works normally.


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

Thank you for reading and spending your time on emacs!
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:
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Memory information:
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