what is the git-svn-id?

Question

Here is an example git-svn-id from a local test repo.

git-svn-id: file:///tmp/svnrepo/branches/foobar@6 0f7bc949-3f51-4b04-a2a6-16f580a5904d

What is the last part? The "@6" means that it is svn revision number 6, but after that looks to be some hash. It seems to be the same on every single commit.

How is that last part generated? I am assuming it is a hash algorithm applied to the first commit of the git repo. That way the git-svn-id can also guarantee that the total ancestry of that commit is the same or different given another git-svn-id.

Answer 1

It's a subversion construct. In subversion, every repo is given a UUID. You can find a svn repo's UUID via svn info. In the example below, the "Repository UUID" line is the repo's UUID.

$ svn info
Path: .
Working Copy Root Path: /tmp/svnco
URL: file:///tmp/svnrepo
Relative URL: ^/
Repository Root: file:///tmp/svnrepo
Repository UUID: 0f7bc949-3f51-4b04-a2a6-16f580a5904d
Revision: 6
Node Kind: directory
Schedule: normal
Last Changed Author: ABird
Last Changed Rev: 6
Last Changed Date: 2015-02-23 16:54:45 -0500 (Mon, 23 Feb 2015)

Here is the git-svn code which seems to read svn info output and saves the UUID: https://github.com/git/git/blob/master/vcs-svn/svndump.c#L356

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To address some of my assumptions in the question: the UUID does not incorporate any information about the git repo's ancestry. From my understanding, someone can git svn clone the same repo, but not include the entire history of the repo. If that is the case between two git-svn repos, then the same point in the svn repo will become different sha1 hashes in the two repos.