On Thu, Feb 25, 2021 at 10:34 AM Michal Suchánek <msuchanek@xxxxxxx> wrote: > > On Thu, Feb 25, 2021 at 02:40:59AM +0000, brian m. carlson wrote: > > On 2021-02-24 at 17:58:34, Michal Suchánek wrote: > > > Hello, > > > > > > I find the results of git merge-base A B quite useless. > > > > > > Suppose you have a repository with file sets > > > > > > S and T > > > > > > where S are sources which are developed in mainline and number of stable > > > versions, and feature branches, and T are build tools (such as autoconf > > > tests or whatever) that are largely independent of the source version. > > > > > > Because of the independence of T from S T are developed in a separate > > > branch t which is merged into all branches developing S as needed. > > > > > > Fixes to S may affect more than one version, and depending on the > > > situation it might be useful to apply fixes to S to mutiple > > > stable/feature branche at once. For that one would need a merge base of > > > the branches in question. > > > > > > However, merge-base almost always give a commit on branch t which is the > > > merge base of files in set T and does not contain files in set S at all. > > > In other words it is merge base only for files from set T and not set S. > > > Can I get merge base that is merge base for all files that have common > > > history between two branches? > > > > The merge base is determined by the history. In your case, I imagine > > you have a history like this: > > > > A -- B -- C -- D -- E -- F -- G (S) > > _/ _/ _/ > > H -- I -- J -- K -- L -- M -- N (T) > > > > Here, the merge base of N and G is M, and the merge base of F and M is > > K. Those are the most recent common ancestors, which are typically > > chosen as the merge base. > > > > In your case, you probably want to cherry-pick a commit, or maybe rebase > > a small set of commits onto another set. That would probably work > > better than trying to merge. It's possible that there's something about > > this case that I'm missing where it wouldn't work properly, but it's > > definitely the approach I would try. > > It's like this > > T > ----o----o----o----o----o----o----o----o----o----o----o----o---(t)---o----o---- > \ \ \ \\\ > \ \ \ \\\ > \ \ \ \\\ > \ o----o----o\̶---o---(s)---o----o----o----o----o----o\̶\̶-(a) > \ / \ / \\ > S+T o----o----o----o----o----o----o----o----o----o----o----o----o----o\̶--(b) > / / \ > ---o----o----o----o----o----o----o----o----o----o----o----o----o----o----o---(m) > > So (t) is common ancestor for (a) and (b) that merge-base reports but it is > only ancestor for files in set T, and does not have files from set S at all. > The common ancestor I am insterested in is (s) which is merge base for both > sets of files. >From git-merge-base(1): "When the history involves criss-cross merges, there can be more than one best common ancestor for two commits...When the --all option is not given, it is unspecified which best one is output." Perhaps you want to specify --all to git merge-base, and then perform additional checks on the output to select one yourself?
