git/sequencer.h, branch v2.26.1

Merge branch 'en/rebase-backend'

2020-03-02T23:07:19Z

"git rebase" has learned to use the merge backend (i.e. the machinery that drives "rebase -i") by default, while allowing "--apply" option to use the "apply" backend (e.g. the moral equivalent of "format-patch piped to am"). The rebase.backend configuration variable can be set to customize. * en/rebase-backend: rebase: rename the two primary rebase backends rebase: change the default backend from "am" to "merge" rebase: make the backend configurable via config setting rebase tests: repeat some tests using the merge backend instead of am rebase tests: mark tests specific to the am-backend with --am rebase: drop '-i' from the reflog for interactive-based rebases git-prompt: change the prompt for interactive-based rebases rebase: add an --am option rebase: move incompatibility checks between backend options a bit earlier git-rebase.txt: add more details about behavioral differences of backends rebase: allow more types of rebases to fast-forward t3432: make these tests work with either am or merge backends rebase: fix handling of restrict_revision rebase: make sure to pass along the quiet flag to the sequencer rebase, sequencer: remove the broken GIT_QUIET handling t3406: simplify an already simple test rebase (interactive-backend): fix handling of commits that become empty rebase (interactive-backend): make --keep-empty the default t3404: directly test the behavior of interest git-rebase.txt: update description of --allow-empty-message

rebase (interactive-backend): fix handling of commits that become empty

2020-02-16T23:40:42Z

As established in the previous commit and commit b00bf1c9a8dd (git-rebase: make --allow-empty-message the default, 2018-06-27), the behavior for rebase with different backends in various edge or corner cases is often more happenstance than design. This commit addresses another such corner case: commits which "become empty". A careful reader may note that there are two types of commits which would become empty due to a rebase: * [clean cherry-pick] Commits which are clean cherry-picks of upstream commits, as determined by `git log --cherry-mark ...`. Re-applying these commits would result in an empty set of changes and a duplicative commit message; i.e. these are commits that have "already been applied" upstream. * [become empty] Commits which are not empty to start, are not clean cherry-picks of upstream commits, but which still become empty after being rebased. This happens e.g. when a commit has changes which are a strict subset of the changes in an upstream commit, or when the changes of a commit can be found spread across or among several upstream commits. Clearly, in both cases the changes in the commit in question are found upstream already, but the commit message may not be in the latter case. When cherry-mark can determine a commit is already upstream, then because of how cherry-mark works this means the upstream commit message was about the *exact* same set of changes. Thus, the commit messages can be assumed to be fully interchangeable (and are in fact likely to be completely identical). As such, the clean cherry-pick case represents a case when there is no information to be gained by keeping the extra commit around. All rebase types have always dropped these commits, and no one to my knowledge has ever requested that we do otherwise. For many of the become empty cases (and likely even most), we will also be able to drop the commit without loss of information -- but this isn't quite always the case. Since these commits represent cases that were not clean cherry-picks, there is no upstream commit message explaining the same set of changes. Projects with good commit message hygiene will likely have the explanation from our commit message contained within or spread among the relevant upstream commits, but not all projects run that way. As such, the commit message of the commit being rebased may have reasoning that suggests additional changes that should be made to adapt to the new base, or it may have information that someone wants to add as a note to another commit, or perhaps someone even wants to create an empty commit with the commit message as-is. Junio commented on the "become-empty" types of commits as follows[1]: WRT a change that ends up being empty (as opposed to a change that is empty from the beginning), I'd think that the current behaviour is desireable one. "am" based rebase is solely to transplant an existing history and want to stop much less than "interactive" one whose purpose is to polish a series before making it publishable, and asking for confirmation ("this has become empty--do you want to drop it?") is more appropriate from the workflow point of view. [1] https://lore.kernel.org/git/xmqqfu1fswdh.fsf@gitster-ct.c.googlers.com/ I would simply add that his arguments for "am"-based rebases actually apply to all non-explicitly-interactive rebases. Also, since we are stating that different cases should have different defaults, it may be worth providing a flag to allow users to select which behavior they want for these commits. Introduce a new command line flag for selecting the desired behavior: --empty={drop,keep,ask} with the definitions: drop: drop commits which become empty keep: keep commits which become empty ask: provide the user a chance to interact and pick what to do with commits which become empty on a case-by-case basis In line with Junio's suggestion, if the --empty flag is not specified, pick defaults as follows: explicitly interactive: ask otherwise: drop Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano

rebase (interactive-backend): make --keep-empty the default

2020-02-16T23:40:42Z

Different rebase backends have different treatment for commits which start empty (i.e. have no changes relative to their parent), and the --keep-empty option was added at some point to allow adjusting behavior. The handling of commits which start empty is actually quite similar to commit b00bf1c9a8dd (git-rebase: make --allow-empty-message the default, 2018-06-27), which pointed out that the behavior for various backends is often more happenstance than design. The specific change made in that commit is actually quite relevant as well and much of the logic there directly applies here. It makes a lot of sense in 'git commit' to error out on the creation of empty commits, unless an override flag is provided. However, once someone determines that there is a rare case that merits using the manual override to create such a commit, it is somewhere between annoying and harmful to have to take extra steps to keep such intentional commits around. Granted, empty commits are quite rare, which is why handling of them doesn't get considered much and folks tend to defer to existing (accidental) behavior and assume there was a reason for it, leading them to just add flags (--keep-empty in this case) that allow them to override the bad defaults. Fix the interactive backend so that --keep-empty is the default, much like we did with --allow-empty-message. The am backend should also be fixed to have --keep-empty semantics for commits that start empty, but that is not included in this patch other than a testcase documenting the failure. Note that there was one test in t3421 which appears to have been written expecting --keep-empty to not be the default as correct behavior. This test was introduced in commit 00b8be5a4d38 ("add tests for rebasing of empty commits", 2013-06-06), which was part of a series focusing on rebase topology and which had an interesting original cover letter at https://lore.kernel.org/git/1347949878-12578-1-git-send-email-martinvonz@gmail.com/ which noted Your input especially appreciated on whether you agree with the intent of the test cases. and then went into a long example about how one of the many tests added had several questions about whether it was correct. As such, I believe most the tests in that series were about testing rebase topology with as many different flags as possible and were not trying to state in general how those flags should behave otherwise. Signed-off-by: Elijah Newren Signed-off-by: Junio C Hamano

Merge branch 'ag/edit-todo-drop-check'

2020-02-14T20:54:21Z

Allow the rebase.missingCommitsCheck configuration to kick in when "rebase --edit-todo" and "rebase --continue" restarts the procedure. * ag/edit-todo-drop-check: rebase-interactive: warn if commit is dropped with `rebase --edit-todo' sequencer: move check_todo_list_from_file() to rebase-interactive.c

Merge branch 'ag/rebase-avoid-unneeded-checkout'

2020-02-14T20:54:21Z

"git rebase -i" (and friends) used to unnecessarily check out the tip of the branch to be rebased, which has been corrected. * ag/rebase-avoid-unneeded-checkout: rebase -i: stop checking out the tip of the branch to rebase

rebase-interactive: warn if commit is dropped with `rebase --edit-todo'

2020-01-28T22:14:57Z

When set to "warn" or "error", `rebase.missingCommitsCheck' would make `rebase -i' warn if the user removed commits from the todo list to prevent mistakes. Unfortunately, `rebase --edit-todo' and `rebase --continue' don't take it into account. This adds the ability for `rebase --edit-todo' and `rebase --continue' to check if commits were dropped by the user. As both edit_todo_list() and complete_action() parse the todo list and check for dropped commits, the code doing so in the latter is removed to reduce duplication. `edit_todo_list_advice' is removed from sequencer.c as it is no longer used there. This changes when a backup of the todo list is made. Until now, it was saved only once, before the initial edit. Now, it is also made if the original todo list has no errors or no dropped commits. Thus, the backup should be error-free. Without this, sequencer_continue() (`rebase --continue') could only compare the current todo list against the original, unedited list. Before this change, this file was only used by edit_todo_list() and `rebase -p' to create the backup before the initial edit, and check_todo_list_from_file(), only used by `rebase -p' to check for dropped commits after its own initial edit. If the edited list has an error, a file, `dropped', is created to report the issue. Otherwise, it is deleted. Usually, the edited list is compared against the list before editing, but if this file exists, it will be compared to the backup. Also, if the file exists, sequencer_continue() checks the list for dropped commits. If the check was performed every time, it would fail when resuming a rebase after resolving a conflict, as the backup will contain commits that were picked, but they will not be in the new list. It's safe to ignore this check if `dropped' does not exist, because that means that no errors were found at the last edition, so any missing commits here have already been picked. Five tests are added to t3404. The tests for `rebase.missingCommitsCheck = warn' and `rebase.missingCommitsCheck = error' have a similar structure. First, we start a rebase with an incorrect command on the first line. Then, we edit the todo list, removing the first and the last lines. This demonstrates that `--edit-todo' notices dropped commits, but not when the command is incorrect. Then, we restore the original todo list, and edit it to remove the last line. This demonstrates that if we add a commit after the initial edit, then remove it, `--edit-todo' will notice that it has been dropped. Then, the actual rebase takes place. In the third test, it is also checked that `--continue' will refuse to resume the rebase if commits were dropped. The fourth test checks that no errors are raised when resuming a rebase after resolving a conflict, the fifth checks that no errors are raised when editing the todo list after pausing the rebase. Signed-off-by: Alban Gruin Signed-off-by: Junio C Hamano

sequencer: move check_todo_list_from_file() to rebase-interactive.c

2020-01-28T22:13:41Z

The message contained in `edit_todo_list_advice' (sequencer.c) is printed after the initial edit of the todo list if it can't be parsed or if commits were dropped. This is done either in complete_action() for `rebase -i', or in check_todo_list_from_file() for `rebase -p'. Since we want to add this check when editing the list, we also want to use this message from edit_todo_list() (rebase-interactive.c). To this end, check_todo_list_from_file() is moved to rebase-interactive.c, and `edit_todo_list_advice' is copied there. In the next commit, complete_action() will stop using it, and `edit_todo_list_advice' will be removed from sequencer.c. Signed-off-by: Alban Gruin Signed-off-by: Junio C Hamano

rebase -i: stop checking out the tip of the branch to rebase

2020-01-24T18:29:42Z

One of the first things done when using a sequencer-based rebase (ie. `rebase -i', `rebase -r', or `rebase -m') is to make a todo list. This requires knowledge of the commit range to rebase. To get the oid of the last commit of the range, the tip of the branch to rebase is checked out with prepare_branch_to_be_rebased(), then the oid of the head is read. After this, the tip of the branch is not even modified. The `am' backend, on the other hand, does not check out the branch. On big repositories, it's a performance penalty: with `rebase -i', the user may have to wait before editing the todo list while git is extracting the branch silently, and "quiet" rebases will be slower than `am'. Since we already have the oid of the tip of the branch in `opts->orig_head', it's useless to switch to this commit. This removes the call to prepare_branch_to_be_rebased() in do_interactive_rebase(), and adds a `orig_head' parameter to get_revision_ranges(). prepare_branch_to_be_rebased() is removed as it is no longer used. This introduces a visible change: as we do not switch on the tip of the branch to rebase, no reflog entry is created at the beginning of the rebase for it. Unscientific performance measurements, performed on linux.git, are as follow: Before this patch: $ time git rebase -m --onto v4.18 463fa44eec2fef50~ 463fa44eec2fef50 real 0m8,940s user 0m6,830s sys 0m2,121s After this patch: $ time git rebase -m --onto v4.18 463fa44eec2fef50~ 463fa44eec2fef50 real 0m1,834s user 0m0,916s sys 0m0,206s Reported-by: SZEDER Gábor Signed-off-by: Alban Gruin Signed-off-by: Junio C Hamano

Revert "Merge branch 'ra/rebase-i-more-options'"

2020-01-12T21:25:18Z

This reverts commit 5d9324e0f4210bb7d52bcb79efe3935703083f72, reversing changes made to c58ae96fc4bb11916b62a96940bb70bb85ea5992. The topic turns out to be too buggy for real use. cf.

Merge branch 'ra/rebase-i-more-options'

2019-12-10T21:11:41Z

"git rebase -i" learned a few options that are known by "git rebase" proper. * ra/rebase-i-more-options: rebase -i: finishing touches to --reset-author-date rebase: add --reset-author-date rebase -i: support --ignore-date sequencer: rename amend_author to author_to_rename rebase -i: support --committer-date-is-author-date sequencer: allow callers of read_author_script() to ignore fields rebase -i: add --ignore-whitespace flag