On 31.01.2012 12:08, Julian Foad wrote: > (I'm assuming that your b@r2 in this example is a simple copy with no diff, > otherwise the first part of 'merge 3' should use a@r1 instead of b@r2 for > its base.) > > But no, merge 3 should be even simpler than that. We don't have to go and > fetch the old (b@r2:b@r4) and (b@r5:b@r6) diffs again and merge them into > (a), because that's already been done recently and stored as (b@r8). So all > we have to do is locate the youngest common ancestor of (b@r8) and (a@head), > which is (a@r7), and do a single 3-way merge: > > * merge 3: (mine=a@head, old=a@r7, yours=b@head) > diff3 a@r7 a@r7 b@r8 | patch a > > (In this case this merge is trivial because mine==old, but if there had been > a further change on (a), say in (a@r8), then it would be non-trivial.)
Yeah, you're right, I forgot that b@r8 already has all the info. I got muddled by my own example. :) Since there are no cherry-picks in a->b merges, there would of course be none in b->a merges, either. [...] > Locating the youngest common ancestor is a step that needs further > explanation; it's not trivially obvious. We mean to follow the "merge > arrows" that are shown on these graphs, as well as the basic lines of > history. Each of these "merge arrows" means that all changes in the > source branch have been merged into the target branch at that point. When > modify this algorithm to cope with cherry-picking, that is > to skip revisions that have already been cherry-picked, which we will need > to do, then we will also have another kind of merge arrow on our graphs, a > kind that doesn't mean all source changes have been merged to the target. > The algorithm will get more complex. I won't talk about that here.) Yes, it's complex. I'm almost sure that the current mergeinfo format can represent cherry-picks correctly, though, so at least you won't have to extend the format. Cherry-picking is the part that really makes this hairy. But it might be worth looking at the poor, defunct svnmerge.py, which /could/ properly handle cherry-picks, at least most of the time. :) Big cheer for grabbing this dragon by the horns, Julian. -- Brane
