On Wed, May 24, 2023 at 2:06 AM Junio C Hamano <gitster@xxxxxxxxx> wrote: > > Tao Klerks <tao@xxxxxxxxxx> writes: > > > The current implementation of this patch is far too restrictive. It > > doesn't break any tests (and maybe I should add one now that I know), > > but it's doing the wrong thing. > > I am ambivalent. What do we want to see in a multi-pick sequence > that is different from rebase? I would argue there are primarily three things that are different: 1. The checkout of the new base (and checkout of the original in an "--abort") 2. The support for and/or more-common expectation of "messing" with commits as you go, eg squash, edit 3. The (partial) support for rebasing/recreating merge commits I'm not sure to what extent any of these justify having tighter restrictions on when we allow a rebase to start, though. > A single-step cherry-pick can fail > safely before it touches the index or the working tree files, but if > two-step cherry-pick, whose first step succeeds, finds that it > cannot safely carry out its second step without clobbering the local > changes made to the working tree files, what should happen? Are we > OK if we stopped in the state just after the first step has already > been done? This is the current behavior: it stops before the specific pick that is going to affect local unstaged changes, or if there are *any* staged changes (in which case it stops as it's about to do the first pick - the first time this check runs). The reasoning for this behavior, as I understand it, is that the "--abort" strategy, intending to "undo whatever I started doing here, including a conflict resolution", resets the index. So as long as there is nothing you want to keep in the index, and as long as we know that any previous picks haven't impacted any files with unstaged changes, we're good. The bug that I want to fix is that we only end up checking whether there are changes in the index *after* we've already committed to resetting the index upon later "--abort". It's a kind of catch-22: we've detected that aborting would destroy your work, so we leave you in a state where the most obvious thing to do is abort, so we destroy your work... Of course, if you understand what's going on you can choose to "--quit" and *not* lose your work... but this is completely antithetical to the general intent of "--abort". There's another, smaller flaw here I think, common to Merge, Single-Cherry-Pick, and Sequence-Cherry-Pick, which is that *if* you start with unstaged changes, and you end up in a conflict resolution or "--no-commit" pause, and you then "git add" your unstaged changes during that pause/resolution, and you *then* later "--abort"... then your originally-unstaged changes are destroyed by the "--abort" - so it has *not* taken you back to where you were before the operation started. This is, to me as a user, non-obvious, and could potentially lead to data loss. The only way I see to fix that, is to have *all* of these operations refuse to operate on dirty worktrees altogether - like rebase already does. I suspect this level of "strictness" would be welcome to newcomers, and less welcome to existing experienced users. > > My (tentative) answer to that question is "yes", but the recovery > options of "cherry-pick" may want to work differently from what we > have seen them traditionally do. Namely, the user accepts that the > first step is already done, and stopping "cherry-pick", be it called > "--abort" or something else, should just remove the sequencer state > and behave as if the single-pick cherry-pick on the first step only > has just finished and leave such a state in the index and the > working tree. This behavior exists, and is called "--quit", right? The semantics as I understand it are: --quit: I know what I'm doing, just remove any "ongoing operation" metadata and let me work with the current index and worktree. --abort: This was a bad idea, please take me back to where I was before I started this operation (without losing any work I had ongoing, pls!) > If that is what we are going to do, then it would > make sense to adopt the same safety semantics we use for "git merge" > and "git checkout" to ensure only that the index is clean, relying > on the unpack-trees machinery that stops before clobbering a locally > modified working tree files. Yep > But if we are to aim for "all-or-none" > semantics people expect from aborting "git rebase", I suspect that > it would be way too complicated to allow random changes in the > working tree files that we may only discover to be problems after > starting the sequence of replaying commits one-by-one, and "too > restrictive" check may be justified. I don't think I understand this argument. If we want to support both sets of semantics, then that's exactly what "--quit" and "--abort" achieve, right? (as long as we check for the dirty index *before* committing to destroying the index in case of "--abort") > To put it differently, if it > is too restrictive for multi-pick, then we would want to loosen it > for "git rebase" as well, as the issues are likely to be the same. My argument for only changing "sequence-cherry-pick" here, and having it (continue to) use the index-safety-only semantics of single-cherry-pick and merge, is that *this is not a change in cabability* - it is only a bugfix. Switching to the worktree-safety semantics of rebase would be a substantial change in behavior beyond the bugfix. I, personally, would prefer to see the worktree-safety semantics of rebase be used in *all* these operations, so I could no longer shoot myself in the foot by starting a merge, accidentally staging some previously-unstaged changes during conflict resolution, and then losing those changes by "--abort"ing. But I expect that this kind of change would need to be behind a config option of some sort, trading off safety against low friction. I could imagine a setting like "core.OperationWorktreeSafety", with settings "default" (current behavior - rebase disallows dirty worktrees, the others disallow dirty index), "strict" (all behave like current rebase) and "lax" (all behave like merge). As discussed elsewhere, I would also like to (have an option to) treat untracked files as "worktree dirtiness"/unstaged changes in exactly the same way as changes to tracked files - but that's another topic :) I'll prepare a v2 with index-safety-only for sequence-cherry-pick for now, please let me know if a (better-named) "core.OperationWorktreeSafety" option is something that you'd be interested in / that would make sense to you. Thanks!
