changeset 31219:dd2364f5180a

localrepo: handle rename with hardlinks properly

In "aftertrans", we rename "journal.*" to "undo.*". We expect "journal.*"
files to disappear after renaming.

However, if "journal.foo" and "undo.foo" refer to a same file (hardlink),
rename may be a no-op, leaving both files on disk, according to Linux
manpage [1]:

    If oldpath and newpath are existing hard links referring to the same
    file, then rename() does nothing, and returns  a  suc‐ cess status.

The POSIX specification [2] is not very clear about what to do.

To be safe, remove "undo.*" before the rename so "journal.*" cannot be left
on disk.

[1]: http://man7.org/linux/man-pages/man2/rename.2.html
[2]: http://pubs.opengroup.org/onlinepubs/9699919799/

--- a/mercurial/localrepo.py	Wed Mar 01 18:21:06 2017 -0800
+++ b/mercurial/localrepo.py	Thu Mar 02 21:49:30 2017 -0800
@@ -2012,6 +2012,14 @@
     def a():
         for vfs, src, dest in renamefiles:
             try:
+                # if src and dest refer to a same file, vfs.rename is a no-op,
+                # leaving both src and dest on disk. delete dest to make sure
+                # the rename couldn't be such a no-op.
+                vfs.unlink(dest)
+            except OSError as ex:
+                if ex.errno != errno.ENOENT:
+                    raise
+            try:
                 vfs.rename(src, dest)
             except OSError: # journal file does not yet exist
                 pass