To record my own opinion: I think it's a fine idea that users in that situation should be able to do that sort of thing but I don't think that functionality belongs in "svn" as I think it's an uncommon use case and can't be cleanly and generally supported -- it's rather a hack. If we supported third-party client-side plug-ins that's where it would belong ... but we don't have any plans to do so.
- Julian I (Julian Foad) wrote: > I want to share with you an idea that came to me from a customer. I'm > not at all proposing that anybody should do this, I'm just curious what > you think. > > Imagine, if you will, that we are coders working in a Subversion > repository that has grown very large and that for IT reasons a decision > has been made to freeze the repository -- make it read-only -- and a new > repository has been created, taking a snapshot of the old HEAD and > importing that as the new r1. We are to continue our development work > in the new repository. > > Those of you who are "old" enough svn devs, think back to when > Subversion became self-hosting, starting with a snapshow of the head of > the CVS repository. All the prior history was back before r1, > inaccessible via Subversion. Was that a big problem? No, it wasn't, > and I know that the snapshot approach is often recommended as a > pragmatic and perfectly reasonable way to migrate from one VCS to > another. But maybe this time there will be hundreds of developers > working in dozens of projects[1]. > > As Subversion devs today we might like to say "no, don't do that, let's > find a better solution to whatever problem was forcing us to re-start > with an imported snapshot". But imagine that's already been discussed > and this is the best way forward and now we simply have to get on with > using the new repository. > > Q: What simple modifications could "we" (anybody) make to our > Subversion clients that would help us to work more effectively in this > scenario? The customer I got this idea from is more interested in > TortoiseSVN than in "svn" and asked me a somewhat different question, > but I think this is the general idea that's of wider interest. > > A: What do you think? > > Maybe one of the most useful things we could do is teach "svn > log" (when running in the usual 'backwards' direction) to run a > follow-on log in the old repo if and when reaching r1. Perhaps we'd set > a revprop on (new) r0 or r1 pointing to the old repo URL so that this > info is configured in a single place. The two sets of revision numbers > in the output would be confusing so we may want to consider tagging the > old and/or the new revnums with some marker as well as inserting an "And > now from the old repository:" message. > > I think teaching "svn blame" to view the old repo would be harder: > it would require more intrusive code changes in svn_client_blame(). > It's not theoretically difficult to do, of course, but perhaps the > code-to-value ratio would not be worth having in libsvn_client ... hmm, > unless we re-architect the blame code so that it's fed diffs from the > client layer instead of fetching them itself, then it could be done > really cleanly. The output format would just need a minor tweak to > distinguish old from new revs. > > I think teaching "svn diff" to do general cross-repo diffs would not > be feasible with the current diff implementation. However, one of my > goals is to generalize the diff code further so it could support such > things (cross-repo, unversioned local tree, etc.). That would be useful > in theory, but in practice I can't see it really being used very often > in this start-again scenario. But any single-rev diff is easily > supported because the cut-over revision is present in both repos. (We > can assume that the tree in old@OLD_HEAD is identical to new@1.) So > maybe we'd want to make single-rev diffs and all same-repo diffs easier > by tweaking "svn diff" to follow the specified path back into a revision > in the old repo, a bit like what I said above for "svn log", if some > special switch is specified. > > Any other commands or work flows that might be really useful? I > wouldn't dream of trying to make "svn up" go back to the old repo, that > would certainly be over the top. And I wouldn't expect "svn cat", "svn > proplist" etc. to be worth bothering with, unless all such simple > read-only commands get the same functionality "for free". > > > Mad or genius? (And I know it wouldn't be worth bothering in a small > repository; let's assume it's a big and busy project with lots of > interesting history.) > > - Julian > > > [1] I'm just making up numbers here; I don't know what sort of numbers > the customer that brought up this idea has. > >
