Item12821: Create FoswikirefsPlugin to map svn revisions to git hashrefs

Part of the git migration strategy. Intention is to map old svn revision numbers to git hashrefs.

A svn rev will point to the foswiki account, core or extension repo, and the corresponding hash. However svn cross-branch commits are 1:n, so there is no way to map a single svn changeset to a single git commit. Possible solution, default to the "more important" branch.

-- GeorgeClark - 24 Mar 2014

Discovered some issues after the first implementation.

• SVN cross-branch commits result in two or more git commits each with a unique commit hash, one for each target branch.
• The commit hash identifiers from a locally generated git-svn clone seem to differ, particularly for the two hash id's generated with the cross-branch commit. The way to ensure they are correct is to issue a git clone from github and extract the information from that log, not the git-svn log.

The following command generates a reasonably processable results, The SVN ID followed by some noise on one line, and the git hash and abbreviated hash on the next.

 git log --format=tformat:"SVN: %<(44>,ltrunc)%B GIT: %H  %h "

SVN: ..@17445 0b4bb1d4-4e5a-0410-9cc4-b2b747904278
 GIT: a6f16a15f91b3b5ca7170818030ae1ed2e555ecd  a6f16a1 
SVN: ..@17444 0b4bb1d4-4e5a-0410-9cc4-b2b747904278
 GIT: 87cb1ef41f3f0b794c9c3542147809f1aacdae06  87cb1ef 

-- GeorgeClark - 25 Mar 2014

Another small tidbit, the default abbreviation for a hash is 7 characters, but git will automatically extend it to prevent collisions. In our current repo, we have 1 commit that required 10 digits, 35 require 8, the rest are all 7 digits.

git rev-list --all --abbrev=0 --abbrev-commit | grep -E '.{10,}'
b27684b179

-- GeorgeClark - 25 Mar 2014

Most of the updates for this task were checked in under Item11267. Extension now installed on foswiki.org.

-- GeorgeClark - 20 Aug 2014

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