On Thu, May 28, 2020 at 08:12:26PM +0200, Eugeniu Rosca wrote: > Hi Michal, > > On Tue, May 26, 2020 at 07:14:43PM +0200, Michal Suchánek wrote: > > On Tue, May 26, 2020 at 08:21:25AM -0700, Junio C Hamano wrote: > > > Eugeniu Rosca <erosca@xxxxxxxxxxxxxx> writes: > > > > > > > So, the two approaches lead to different results. If you see any false > > > > assumption or mistaken belief, could you please pinpoint that? TIA. > > > > > > Perhaps the assumption/belief that the set of commits in a history > > > can be totally ordered is the issue? When multiple people work > > > together on a project, especially in a project where "pull --no-ff" > > > is not enforced, there can exist only partial order among them? > > > > > As in if you have history with two branches > > > > D > > / \ > > B C > > \ / > > A > > > > commits B and C are not comparable. They are both between A and D but > > the order of B and C is arbitrary. Different renderings of the history > > may choose different order of B and C. This is a simle example. Linux > > history is a spaghetti of tens of branches. > > While in theory 'B' and 'C' might look equivalent, IMHO in practice > there is a clear distinction between the two. It's commonly known that > Git refers to 'B' as the 'first parent' of 'D'. Git also provides means > to identify such first parents via 'git log --first-parent'. > > A fun fact about first parents is that, unless Linus is on vacation > and hands over his responsibilities to GKH, you will be quite > confident that 'git log --first-parent linux/master' will list > stuff committed by Linus himself. That's why (I bet) in the minds > of people involved in Linux development, the diagram looks like: > > D > | \ > B C > | / > A And that's not the case. Commits B and C will typically com from different subsystems, and are truly interchangeable. These subsystems, again, will have number of separate branches that are merged together before they are submitted to Linus. Often a feature requires cross-merge between different subsystems which further complicates the history. Even if B is a commit authored by Linus and you can infer from that it's on the master branch it says nothing about order of B and C. They are still not comparable. And you may still need to reconcile the changes in B and C in D and whatever order you choose for backporting them you will need to reflect D in both B and C in the conflicting case. HTH Michal
