When we added git branch support, there were a few patches that used grit. Might be useful to dig though that code and see if there is anything we can use.
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I was rather planning on making a "clean" adapter, but I'll sure have a look :-)
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This would be interesting if you can pull it off, although the few minutes I spent poking at Grit (and redmine.git) recently doesn't fill me with confidence. It went something like this...
<pre>
$ irb
ruby-1.8.7-p249 > require 'grit'
=> true

ruby-1.8.7-p249 > repo_path = '/home/michael/rails/redmine'
=> "/home/michael/rails/redmine"

ruby-1.8.7-p249 > grit = Grit::Repo.new(repo_path)
=> #<Grit::Repo "/home/michael/rails/redmine/.git">

ruby-1.8.7-p249 > recent_list = grit.commits_since(start = 'master', since = '2010-10-10', extra_options = {})
SystemStackError: stack level too deep
## full traceback omitted ...

ruby-1.8.7-p249 > recent_list_alt = `cd #{repo_path}; git log --since='2010-10-10' --format='%H'`.split
## succeeded. full array of results omitted ...

ruby-1.8.7-p249 > recent_list_alt.count
=> 81

ruby-1.8.7-p249 > Grit.version
=> "2.3.0"
</pre>

Digging a little deeper revealed that Grit attempts to load every commit in the repo, and then handle your constraints (since = DATE, etc.) by filtering the complete list in ruby before returning it to you. Apparently redmine.git is a little too large for that approach to work (not even taking performance into account).
Hopefully I'm just doing it wrong and you'll have better luck with it. :)

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Removing it from the Unplanned features since it doesn't seem to be usable and is no longer updated (last release is 2 years old).
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Not saying it works, but last release was just yesterday (2.4.1) https://github.com/mojombo/grit/ so it certainly is being actively developed.
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Right. I was looking at rubyforge :/
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Assigned issue with no assignee back to New status.
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Please change this issue to "Covert the git adapter to rugged". Rugged is the oficial ruby library with ruby bindings for libgit2. You can find more about it here: https://github.com/libgit2/rugged
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I haven't found a way to make searches by date without having to walk over all commits, but found some useful ways of walking over the commit trees (to get for example from x to y hashes, that is probably what's going to be used to get latest commits:

<pre>
<code>
1.9.3-p327 > require 'rugged'
=> true

1.9.3-p327 > repo_path = '/path/to/redmine'
=> "/path/to/redmine"

1.9.3-p327 > repo = Rugged::Repository.new(repo_path)
=> #<Rugged::Repository:0x007fa208972820>

1.9.3-p327 > walker = Rugged::Walker.new(repo)
=> #<Rugged::Walker:0x007f8092965d38>

1.9.3-p327 > walker.push("301d7e7cb13a09854a7c87aecedfcbfd27eb98d3")
1.9.3-p327 > walker.hide("c31f498ba6a21fd3e5ce7b9ba2f3b3cdc1b2e05b")

1.9.3-p327 > result = walker.to_a
=> [#<Rugged::Commit:0x007f8092977560>, #<Rugged::Commit:0x007f8092977538>, #<Rugged::Commit:0x007f8092977510>]

or you can just iterate over for a more memory friendly operation:

1.9.3-p327 > walker.push("301d7e7cb13a09854a7c87aecedfcbfd27eb98d3")
1.9.3-p327 > walker.hide("c31f498ba6a21fd3e5ce7b9ba2f3b3cdc1b2e05b")

1.9.3-p327 > walker.each {|c| puts c.inspect}
#<Rugged::Commit:0x007f809295d2f0>
#<Rugged::Commit:0x007f809295d2a0>
#<Rugged::Commit:0x007f809295d250>
</code>
</pre>

A commit object have the following methods:

=> [:message, :time, :committer, :author, :tree, :parents, :to_hash,..., :oid, :type,...]

<pre>
1.9.3-p327 > c.to_hash
=> {:message=>"German translation updated by Daniel Felix (#10191)\n\ngit-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@10998 e93f8b46-1217-0410-a6f0-8f06a7374b81\n", :committer=>{:name=>"Toshi MARUYAMA", :email=>"marutosijp2@yahoo.co.jp", :time=>2012-12-14 14:47:46 UTC}, :author=>{:name=>"Toshi MARUYAMA", :email=>"marutosijp2@yahoo.co.jp", :time=>2012-12-14 14:47:46 UTC}, :tree=>#<Rugged::Tree:0x007f8091100130>, :parents=>[#<Rugged::Commit:0x007f80911006d0>]}

1.9.3-p327 > c.oid
=> "301d7e7cb13a09854a7c87aecedfcbfd27eb98d3"

1.9.3-p327 > c.type
=> "commit"

1.9.3-p327 > Rugged::Version
=> "0.16.0"
</pre>
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Gabriel Mazetto wrote:
> Please change this issue to "Covert the git adapter to rugged".
Done.
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Typo
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I decided to try making the conversion... and have some questions:
Do I have to use "AbstractAdapter"? It was designed to be used with command line in mind, which is not the case with rugged. Should I try to create a lean "AbstractAdapter" with libraries in mind? I saw another issue talking about libsvn for example, that could be the potential for this new abstract library, with only the "SCM actions" in mind.
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https://github.com/brodock/redmine/commit/457322722a1e73ec3f13eec12afc311dc6b2f810

Branches and Tags
(tests OK)
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relates,Closed,7146,Git adapter lost commits before 7 days from database latest changeset
relates,Closed,6013,git tab,browsing, very slow -- even after first time
relates,New,5357,Git: SCM revisions ordered by date/time (should be reverse commit order)