Hi Philip, On Thu, 18 Jan 2018, Philip Oakley wrote: > From: "Johannes Schindelin" <johannes.schindelin@xxxxxx> > > This one is a bit tricky to explain, so let's try with a diagram: > > > > C > > / \ > > A - B - E - F > > \ / > > D > > > > To illustrate what this new mode is all about, let's consider what > > happens upon `git rebase -i --recreate-merges B`, in particular to > > the commit `D`. In the default mode, the new branch structure is: > > > > --- C' -- > > / \ > > A - B ------ E' - F' > > \ / > > D' > > > > This is not really preserving the branch topology from before! The > > reason is that the commit `D` does not have `B` as ancestor, and > > therefore it gets rebased onto `B`. > > > > However, when recreating branch structure, there are legitimate use > > cases where one might want to preserve the branch points of commits that > > do not descend from the <upstream> commit that was passed to the rebase > > command, e.g. when a branch from core Git's `next` was merged into Git > > for Windows' master we will not want to rebase those commits on top of a > > Windows-specific commit. In the example above, the desired outcome would > > look like this: > > > > --- C' -- > > / \ > > A - B ------ E' - F' > > \ / > > -- D' -- > > I'm not understanding this. I see that D properly starts from A, but > don't see why it is now D'. Surely it's unchanged. It is not necessarily unchanged, because this is an *interactive* rebase. If you mark `D` for `reword`, for example, it may be changed. I use the label D' in the mathematical sense, to indicate that D' is derived from D. It may even be identical to D, but the point is that it is in the todo list of the interactive rebase, so it can be changed. As opposed to, say, A and B. Those cannot be changed in this interactive rebase. > Maybe it's the arc/node confusion. Maybe even spell out that the rebased > commits from the command are B..HEAD, but that includes D, which may not > be what folk had expected. (not even sure if the reflog comes into > determining merge-bases here..) > > I do think an exact definition is needed (e.g. via --ancestry-path or > its equivalent?). I don't find "ancestry path" any more intuitive a term than the mathematically correct "uncomparable". If you have a better way to explain this (without devolving into mathematical terminology), please let's hear it. Don't get me wrong, as a mathematician I am comfortable with very precise descriptions involving plenty of Greek symbols. But this documentation, and these commit messages do not target myself. I know perfectly well what I am talking about here. The target audience are software developers who may not have a background in mathematics, who do not even want to fully understand what the heck constitutes a Directed Acyclic Graph. So what we need here is plain English. And I had thought that the analogy with the family tree would be intuitive enough for even math haters to understand easily and quickly... Ciao, Dscho
