From: Philip Oakley Date: Sun, 22 Apr 2018 14:15:27 GMT Subject: Re: [PATCH v8 09/16] rebase: introduce the --rebase-merges option Message-ID: In-Reply-To: <0c92bdd1829328544269722cbbd3edcd169bb148.1524306547.git.johannes.schindelin@gmx.de> From: "Johannes Schindelin" > Once upon a time, this here developer thought: wouldn't it be nice if, > say, Git for Windows' patches on top of core Git could be represented as > a thicket of branches, and be rebased on top of core Git in order to > maintain a cherry-pick'able set of patch series? > > The original attempt to answer this was: git rebase --preserve-merges. > > However, that experiment was never intended as an interactive option, > and it only piggy-backed on git rebase --interactive because that > command's implementation looked already very, very familiar: it was > designed by the same person who designed --preserve-merges: yours truly. > > Some time later, some other developer (I am looking at you, Andreas! > ;-)) decided that it would be a good idea to allow --preserve-merges to > be combined with --interactive (with caveats!) and the Git maintainer > (well, the interim Git maintainer during Junio's absence, that is) > agreed, and that is when the glamor of the --preserve-merges design > started to fall apart rather quickly and unglamorously. > > The reason? In --preserve-merges mode, the parents of a merge commit (or > for that matter, of *any* commit) were not stated explicitly, but were > *implied* by the commit name passed to the `pick` command. > > This made it impossible, for example, to reorder commits. Not to mention > to flatten the branch topology or, deity forbid, to split topic branches Aside: The idea of a "flattened" topology is, to my mind, not actually defined though may be understood by devs working in the area. Hopefully it's going away as a term, though the new 'cousins' will need clarification (there's no dot notation for that area of topology). > into two. > > Alas, these shortcomings also prevented that mode (whose original > purpose was to serve Git for Windows' needs, with the additional hope > that it may be useful to others, too) from serving Git for Windows' > needs. > > Five years later, when it became really untenable to have one unwieldy, > big hodge-podge patch series of partly related, partly unrelated patches > in Git for Windows that was rebased onto core Git's tags from time to > time (earning the undeserved wrath of the developer of the ill-fated > git-remote-hg series that first obsoleted Git for Windows' competing > approach, only to be abandoned without maintainer later) was really > untenable, the "Git garden shears" were born [*1*/*2*]: a script, > piggy-backing on top of the interactive rebase, that would first > determine the branch topology of the patches to be rebased, create a > pseudo todo list for further editing, transform the result into a real > todo list (making heavy use of the `exec` command to "implement" the > missing todo list commands) and finally recreate the patch series on > top of the new base commit. > > That was in 2013. And it took about three weeks to come up with the > design and implement it as an out-of-tree script. Needless to say, the > implementation needed quite a few years to stabilize, all the while the > design itself proved itself sound. > > With this patch, the goodness of the Git garden shears comes to `git > rebase -i` itself. Passing the `--rebase-merges` option will generate > a todo list that can be understood readily, and where it is obvious > how to reorder commits. New branches can be introduced by inserting > `label` commands and calling `merge