bug in get_extra commuting patch

This bug is triggered if for whatever reason Darcs finds itself in a position where a patch which is shared by both repos appears to depend on a patch which is local to one of them only. Such a dependency would be absurd. We can divide this error into three known cases:

  1. Darcs thinks a patch is shared, but it’s actually local to one of the repositories
  2. The contrary: Darcs mistakenly believes a shared patch is local
  3. There is a real dependency and it indicates a deep Darcs bug (see issue1014)

There have been several real life cases of this error message. So far we have tracked them down to

  • issue1644 Non-ASCII characters in patch bundles. In some cases, mailers may decide to send utf-8-encoded patch bundles as ISO8859-1. Upon decoding, Ttis causes Darcs to be confused about the identity of patches (it mistakenly believes that one of the patches mentioned in the context is missing from your repository). A good test for this is to m5 sum the bundle on both ends. See the issue for a workaround
  • issue27 - different patches with exactly the same name/log/etc get recorded in quick succession (giving them the same timestamp), thereby creating a case of mistaken identity. Fixed with patch salt.
  • issue753 - (I’m not entirely clear on this one yet, but it seems to involve corrupted patch bundles either changing the name or the contents of a patch)
  • issue1026 - single CVS repository has had its subdirectories converted into separate darcs repositories. The problem is that CVS does not perform atomic commits, but allows the same commit log to be applied to different files. This creates another case of mistaken identity in patches when attempting to pull between unrelated repositories. This has been resolved, along with issue27, although repositories that were converted prior to Darcs 2.1 may still trigger the bug.
  • issue1014 - where due to Darcs 2 semantics wrt duplicate patches a common patch really can depend on two different local patches

So what do you do when you see an error message like this? Contact the darcs team ( so that we can try to develop a workaround together. Try also to determine if you have been bitten by one of the known cases above or if you may have found yet another way to trigger this error :-(

darcs convert fails!

The problem: Suppose you have a plain darcs 1 repository, and want to convert it to darcs 2 format, and get an error message of the following type:

darcs failed:  Error applying hunk to file foo

What are possible problems, and their solutions?

One possible cause is that you have some “corrupt hunks” within some of your patches. Old fashioned repositories used by Darcs 1 were prone to this sort of corruption. Darcs-2 uses hashed repositories that avoid this problem. See DarcsTwo for more details.

An example: Suppose in file foo contains only the line ‘abc’

A patch that deletes the first line ‘abc’ and replaces it with ‘def’ (created e.g. with diff -u) might contain something like the following

@@ -1 +1 @@

The problem now arises if you have a patch that tries to delete the first line ‘ghi’ and replace it with ‘def’. This will not work, because the first line actually reads ‘abc’, and not ‘ghi’. Such a patch might might look like this:

@@ -1 +1 @@

The original, plain darcs 1 repositories can (with some ingenuity…) be brought into a state where you have such corrupt hunks that fail to apply. This can become obvious when you try to darcs convert because the new formats try to prevent this kind of corruption.

How can you fix it?

  1. Create a new repository with darcs init --hashed
  2. Pull your patches from the dubious repository, one by one, until you identify a patch that fails. Write down the timestamp associated with the patch.
  3. Figure out why the patch fails: create a patch file manually: darcs diff -p 'thefailingpatchname' filename > fail.patch where ‘thefailingpatchname’ is a pattern that identifies the patch, filename is the name of the file for which the hunk fails to apply
  4. Try to apply the patch manually:

    patch filename fail.patch

    and see what happens. It also helps to look at the patch, and the file it is trying to patch, you can for instance see if the patch wants to change a line in the file which does not exist.
  5. Try to find a way to make the patch apply. Use darcs revert to revert the file to the original state, and then edit the patch by hand. For example, if the problem is that the patch should be replacing the line ‘abc’ with ‘def’ instead of trying to replace ‘ghi’ with ‘def’, replace ‘ghi’ with ‘abc’.
  6. Once you have a version of the patch that applies,

    1. make a temporary copy of the dubious repository (e.g. with cp -R),
    2. and change the corresponding patch in the temporary repository: The patches are in _darcs/patches, and filenames start with a number that indicates the timestamp (see step 2). 20091001104115…. is a patch that was made on the 1st of October 2009, at 10:41 and 15 seconds (GMT). To edit the patches you need to gunzip them, make the changes, and then gzip them.
  7. Repeat steps 1 and 2, pulling from the temporary copy of the dubious repository, and see whether you can now pull the fixed patch.

Repeat for any remaining failing patches.

  1. Once you have a repository with no more remaining failing patches, you can run darcs convert.

Strange conflicts

Why do my “darcs replace” patches conflict?

If you have two parallel darcs replace patches that use different token char expressions, they are treated as a conflict because TODO

Performance issues

See Performance for tips on improving darcs performance.

Darcs amend-record

If amend-record is very slow or appears to hang, the problem may be complex contents in _darcs/patches/unrevert. This file acts as an optional net and can be renamed or moved to see if that helps.

Darcs unrecord

If unrecord is very slow or appears to hang, the problem may be complex contents in _darcs/patches/unrevert. This file acts as an optional net and can be renamed or moved to see if that helps.

Darcs send

Patches falsely reported as missing

Sometimes darcs will say to you:

darcs: Cannot apply this patch bundle, since we're missing:

And then print the info for a patch that you do have.

In this case, there may be an encoding issue. If the context the patch bundle is encoded in a different way than the context in the repository, and the patch info contains non-ASCII characters, the patches are not recognized as being the same. In this case the sender of the patch must probably make sure that the patch bundle is sent with the right encoding.

Very large patch bundles

Check to see if the remote repository has tagged recently.

If they have not tagged in a while, it might be a good time for them to do so. In general, a good time to tag would be when you make a new release.

If they have tagged in a while, have a look at your inventory file (_darcs/hashed_inventory). Do you see a long inventory with tag(s) in it? Try darcs optimize --reorder.

What may have happened is that you pulled the tag on top of some local patches. The optimize --reorder rearranges your repository to give you “clean” tags (tags that only follow patches they depend on), which results in much smaller bundles.

If none of this makes any sense, give us a shout on or on the IRC channel.

Problems applying patches from

This is due to an incorrect MIME parser (issue26) in Darcs. The current workaround is to either open your mailbox in an alternative client like mutt, or just save the raw message and view it with mutt -f

Darcs push (and put)


$ darcs push --all foo@bar:baz

darcs failed:  Unable to "darcs apply" here.

You need to be in a repository directory to run this command.
Apply failed!


$ ssh foo@bar               # an interactive session
foo@bar$ echo $PATH
foo@bar$ which darcs
foo@bar$ darcs --version
2.3.0 (release)
foo@bar$ exit

# non-interactive sessions
$ ssh foo@bar 'echo $PATH'
$ ssh foo@bar which darcs
$ ssh foo@bar darcs --version
1.0.9 (release)

Both Darcs 1.x and Darcs 2.x are installed on the remote host. The latter is installed in ~/.cabal/bin, which is added to $PATH by foo’s .bashrc. Because .bashrc isn’t sourced for non-interactive sessions, the local “darcs push” runs /usr/bin/darcs, which doesn’t understand darcs-2 repositories.


  • set PATH in ~/.ssh/environment (OpenSSH only);
  • switch to a pull-based workflow; or
  • install Darcs 2 in the default path (e.g. in /usr/local/bin).

Darcs push (ssh stdout problems)


$darcs push user@remote:/path/to/repo

 "darcs failed:  Not a repository: user@remote:/path/to/repo ((scp)
 failed to fetch: user@remote:/path/to/repo/_darcs/inventory."


Customized rc files (.bashrc, .zshrc) on the remote that print to the stdout when sourced interfere with the communication between the remote repository and darcs. If you use darcs push with the verbose flag:

$darcs push -v user@remote:/path/to/repo

you should see the remote computer’s stdout interfere with darcs.


Removing informative statements, such as ‘echo date’, that dump to the stdout on login should fix the issue. You could probably also script around the problem (ignore ‘x’ statements if connection is ssh).

HTTP problems

The official darcs statically linked binary doesn’t honor the http_proxy environment variable

Trying to use darcs clone over HTTP proxy results with the following error:

No proxy support for HTTP package yet (try libcurl)!

Please use the dynamically linked binary instead.

If you see something like:

darcs: error while loading shared libraries: cannot open shared object file: No such file or directory

a quick fix like creating a proper symlink in /usr/lib might help.

The dynamically linked binary can fetch data over HTTP proxies because it makes use of libcurl.

The official darcs dynamically linked binary adds garbage to output and breaks darcsweb

When the official darcs dynamically linked binary is called, it may display additional output to stderr:

darcs: /usr/lib/ no version information available (required by darcs)

This is a minor itch, but when using darcsweb (which makes darcs print XML output and parses it), this additional output breaks the XML parser.

The fix is to use a shell wrapper that silences darcs and eliminates the stderr output. Assuming that the dynamically linked darcs binary is called darcs-dynamic, you can use a wrapper shell script like this:


darcs-dynamic "$@" 2>/dev/null