1. Summarise the issue (what were doing, what went wrong?)

$ darcs clone http://darcs.net/darcs-wiki darcs-wiki2 && cd darcs-wiki2
&& darcs pull http://hub.darcs.net/darcs/darcs-wiki --dry-run
Copying patches, to get lazy repository hit ctrl-C...
Finished cloning.                                                       
Would pull the following changes:                                      
patch 5d2b60e61db6f9919ae03ff02caf5e619cae001e
Author: rizwan1218 <alirizwan046@gmail.com>
Date:   Tue Jul 16 19:40:41 MSK 2013
  * San Diego Movers

patch 3f22f0db685809606b444204f8ffbebc07b39bbf
Author: rizwan1218 <alirizwan046@gmail.com>
Date:   Tue Jul 16 19:41:54 MSK 2013
  * San Diego Movers

patch e70ee194b0a200f08d32d4c6154f06ffe7017882
Author: SashaLenor <sashalenor@gmail.com>
Date:   Wed Aug 28 20:21:02 MSK 2013
  * *

patch c5e0c30e8b2940624b1d9b0657b3dea87f192afe
Author: SashaLenor <sashalenor@gmail.com>
Date:   Tue Sep  3 22:56:43 MSK 2013
  * *

patch d7acf6beeab97c4a0de1d9ee9691f30ebc56337c
Author: SashaLenor <sashalenor@gmail.com>
Date:   Tue Sep  3 22:57:05 MSK 2013
  * *

patch 114d02eabaf1ef7834105e356521c35b4d9a3ada
Author: SashaLenor <sashalenor@gmail.com>
Date:   Fri Sep 20 13:08:45 MSK 2013
  * *

patch dc98e9c77162d3e0d44c594f2d721d64e2c34e0c
Author: obegendi <obegendi@hotmail.com>
Date:   Sun Dec  6 04:44:12 MSK 2015
  * test

Making no changes: this is a dry run.
$ 

2. What behaviour were you expecting instead?

There are no extra patches in the mirror. The purpose of the mirror is
to serve as a base for any forks (with pull requests) at hub.darcs.net.

3. What darcs version are you using? (Try: darcs --exact-version)

$ darcs --exact-version
darcs compiled on Dec 22 2015, at 23:03:45

Context:

[TAG 2.10.2
Guillaume Hoffmann <guillaumh@gmail.com>**20151109135257
 Ignore-this: b5175dd8e51689988632b312af9611da
] 

Compiled with:

HTTP-4000.2.22
array-0.4.0.1
attoparsec-0.13.0.1
base-4.6.0.0
base16-bytestring-0.1.1.6
binary-0.5.1.1
bytestring-0.10.0.0
containers-0.5.0.0
cryptohash-0.11.6
data-ordlist-0.4.7.0
directory-1.2.0.0
filepath-1.3.0.1
hashable-1.2.3.3
haskeline-0.7.0.3
html-1.0.1.2
mmap-0.5.8
mtl-2.1.2
network-2.6.2.1
network-uri-2.6.0.3
old-locale-1.0.0.5
old-time-1.1.0.1
parsec-3.1.9
process-1.1.0.2
random-1.0.1.1
regex-applicative-0.3.2.1
regex-compat-tdfa-0.95.1.4
sandi-0.3.0.1
tar-0.4.0.1
terminfo-0.3.2.5
text-1.2.1.3
time-1.4.0.1
transformers-0.3.0.0
transformers-compat-0.4.0.3
unix-2.6.0.0
unix-compat-0.4.1.4
utf8-string-0.3.7
vector-0.10.0.1
zip-archive-0.2.3.7
zlib-0.5.4.0
$ 

4. What operating system are you running?
  GNU/*/Linux (ALTLinux) on x86_64

So, the correct way to pull someone's changes for the wiki from
hub.darcs.net would be to pull only the complement of his repo to the
mirror repo.

Example -- how not to pull the extra (spam) changes from a fork (imz's one):

[imz@ovicaa darcs-wiki2]$ darcs pull --complement
http://hub.darcs.net/imz/darcs-wiki
http://hub.darcs.net/darcs/darcs-wiki --dry-run
Would pull the following changes:
patch c6ee1c26ddc1fcbb6b6ddded99ade9a773bfea98
Author: Ivan Zakharyaschev <imz@altlinux.org>
Date:   Wed Jun 19 01:51:50 MSK 2013
  * tip: Invoking Emacs functions as external merge/diff tools.
  
  Preparing the args for an Emacs function in a shell script (as it is
done in the manual) is ugly. Here I show how do it with Elisp code.

patch 66383b0cb4abec8770687c00c1e8bd7c6dbc709f
Author: Ivan Zakharyaschev <imz@altlinux.org>
Date:   Wed Dec 23 20:40:28 MSK 2015
  * minor: correct formatting of code

Making no changes: this is a dry run.
[imz@ovicaa darcs-wiki2]$

Thanks for reporting this! I have obliterated the spam patches on the
hub.darcs.net mirror, so it is in sync with upstream again.

The mirror's cron rule currently does:

darcs pull -qa http://darcs.net/darcs-wiki

How can it also obliterate any patches which have been obliterated
upstream ? I think we'd want darcs obliterate --complement something...,
right ?

I generally use `darcs obliterate --not-in-remote` to keep an eye on 
that.

Doing such a sync for an ordinary user of hub.darcs.net would be quite
inconvenient because `ssh hub.darcs.net obliterate` doesn't accept
options -- as I learned at http://stackoverflow.com/a/29323279/94687 .

ganesh's suggestion has been implemented (thanks).

imz: I'm not sure what you mean; I think this particular issue can be
marked resolved ?

> ganesh's suggestion has been implemented (thanks).
> I think this particular issue can be marked resolved ?

I think so, too. Thanks!

> imz: I'm not sure what you mean;

I've brought up the issue that as an ordinary user of hub.darcs.net, one
is not able to do such a thing  easily (for another one's own repo), if
one wants it to be an exact mirror of something else.

Changes cannot be obliterated in an automated way through the ssh
interface. The "obliterate" command under ssh doesn't interpret any
additional options which would make it possible to select the changes
from the command line. It works interactively only.

That's not directly related to this issue, of course. Just a side-note.