ikiwiki/doc/bugs/svn_fails_to_update.mdwn

In poking around at the svn backend I found that the svn post-commit 
hook calls to svn update fail regularly with an error code of 256. 
Apparently during the post-commit hook can't update because the 
working copy is locked from the commit. Since the post-commit hook doesn't send
errors anywhere and svn update runs with --quiet anyhow, this error
isn't usually visible, but on my system:

    ethan@sundance:~/tests/webtemplates/ikiwiki3/wc$ svn commit -m "Blah.."
    Sending        index.mdwn
    Transmitting file data .
    Committed revision 3.

    #verifying output was created
    ethan@sundance:~/tests/webtemplates/ikiwiki3/wc$ less ../dest/index.html 

    ethan@sundance:~/tests/webtemplates/ikiwiki3/wc$ svn info
    Path: .
    URL: file:///home/ethan/tests/webtemplates/ikiwiki3/svn/trunk
    Repository Root: file:///home/ethan/tests/webtemplates/ikiwiki3/svn
    Repository UUID: f42bb0d6-3c1e-0410-b2d4-aeaad48dd6c4
    Revision: 2
    Node Kind: directory
    Schedule: normal
    Last Changed Author: ethan
    Last Changed Rev: 2
    Last Changed Date: 2006-09-24 21:15:55 -0400 (Sun, 24 Sep 2006)

A sample error message (obtained through file redirection) is:

    svn: Working copy '.' locked
    svn: run 'svn cleanup' to remove locks (type 'svn help cleanup' for details)

Did I do something stupid again or is this the case on your system too? 
--Ethan

Additional note: this doesn't happen when performing svn commits from another wc, 
but *does* happen when committing from the web.
--Ethan

> Yeah, this makes sense now that you bring it up. Perhaps I should make
> ikiwiki skip the update when called from the post-commit hook if the repo
> is locked, although this could mask other problems.. --[[Joey]]

>> I don't think it's (yet) a serious problem, because any commit to the repo
>> either comes from another WC, in which case, no problem, or it is committed by 
>> ikiwiki through its own WC, in which case that WC is "the newest". The only problem
>> is that ikiwiki's rcs information for web commits gets screwed up. I think the
>> correct fix is to call rcs_update from rcs_commit in svn.pm, if 
>> the commit succeeds. I'm not sure whether this ought to happen for all RCSes
>> or just svn. --Ethan

>>> You say that the rcs information for web commits is screwed up .. how? 
>>> Does this affect something that I'm not seeing? --[[Joey]]

I just meant that when you call ikiwiki.cgi?do=edit, it gets the 
"current" RCS revision, and uses that in the merges later if there
are other edits in the meantime. So I guess if you have a file a.mdwn,
and at revision X it contains the list:

    a
    b
    c
    d

And then one user edits it by removing "c" from web, and 
then starts editing it again, ikiwiki.cgi will think the edit "started"
at revision X (although it's really X+1). So if another user edits via
web in the meantime, the subsequent merge will try to remove "c" again.
To be honest I don't know what will happen in this case (svn merge fails?
conflict markers?), but I'm pretty sure it's a problem. Anyhow, I think we 
should call update manually after commit, I just don't know if this should
be RCS-specific, or whether it's safe to update after commit on all RCSes.
--Ethan

Hmm, turns out that isn't the case! svn's prepedit function calls svn info 
which gets the "right" information even when the WC isn't current. I am 
having problems merging but that probably has nothing to do with this bug. 
[This patch](http://ikidev.betacantrips.com/patches/update.patch) calls
rcs_update after commit in CGI.pm, it might be a good idea anyhow. --Ethan

> Ok, I follow you. I am unsure whether this problem effects other rcses
> besides svn. Depends on how they handle locking, etc. But calling
> rcs_update will always be safe, so I'll do that. [[bugs/done]]
> 
> That still leaves the issue that it calls svn update in the post-commit
> hook when it's locked and fails with that error message. Granted svn does
> throw that away by default, but it's still ugly and wasteful. But
> checking for a lock first is even uglier (and racey) and more wasteful,
> so I don't see a fix.. --[[Joey]]