Am 07.03.2013 19:59, schrieb Heiko Voigt: > On Thu, Mar 07, 2013 at 10:49:09AM +0100, Daniel Bratell wrote: >> Den 2013-03-06 19:12:05 skrev Heiko Voigt <hvo...@hvoigt.net>: >> >>> On Mon, Feb 25, 2013 at 05:44:05PM +0100, Daniel Bratell wrote: >>>> A submodule change can be merged, but only if the merge is a >>>> "fast-forward" which I think is a fair demand, but currently it >>>> checks if >>>> it's a fast-forward from a commit that might not be very interesting >>>> anymore. >>>> >>>> If two branches A and B split at a point when they used submodule commit >>>> S1 (based on S), and both then switched to S2 (also based on S) >>>> and B then >>>> switched to S21, then it's today not possible to merge B into A, despite >>>> S21 being a descendant of S2 and you get a conflict and this warning: >>>> >>>> warning: Failed to merge submodule S (commits don't follow merge-base) >>>> >>>> (attempt at ASCII gfx: >>>> >>>> Submodule tree: >>>> >>>> S ---- S1 >>>> \ >>>> \ - S2 -- S21 >>>> >>>> Main tree: >>>> >>>> A' (uses S1) --- A (uses S2) >>>> \ >>>> \ --- B' (uses S2) -- B (uses S21) >>>> >>>> >>>> I would like it to end up as: >>>> >>>> A' (uses S1) --- A (uses S2) ------------ A+ (uses S21) >>>> \ / >>>> \ --- B' (uses S2) -- B (uses S21)- / >>>> >>>> And that should be legal since S21 is a descendant of S2. >>> >>> So to summarize what you are requesting: You want a submodule merge be >>> two way in the view of the superproject and calculate the merge base >>> in the submodule from the two commits that are going to be merged? >>> >>> It currently sounds logical but I have to think about it further and >>> whether that might break other use cases. >> >> Maybe both could be legal even. The current code can't be all wrong, >> and this case also seems to be straightforward. > > Ok I have thought about it further and I did not come up with a simple > (and stable) enough strategy that would allow your use case to merge > cleanly without user interaction. > > The problem is that your are actually doing a rewind from base to both > tips. The fact that a rewind is there makes git suspicious and we simply > give up. IMO, thats the right thing to do in such a situation. > > What should a merge strategy do? It infers from two changes what the > final intention might be. For submodules we can do that when the changes > on both sides point forward. Since thats the typical progress of > development. If not there is some reason for it we do not know about. So > the merge gives up. > > Please see this post about why we need to forbid rewinds from the > initial design discussion: > > http://article.gmane.org/gmane.comp.version-control.git/149003
I agree that rewinds are a very good reason not merge two branches using a fast-forward strategy, but I believe Daniel's use case is a (and maybe the only) valid exception to that rule: both branches contain *exactly* the same rewind. In that case I don't see any problem to just do a fast forward to S21, as both agree on the commits to rewind. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html