The --rebase-merges mode is probably not half as intuitive to use as its inventor hopes, so let's document it some.
Signed-off-by: Johannes Schindelin <johannes.schinde...@gmx.de> --- Documentation/git-rebase.txt | 132 +++++++++++++++++++++++++++++++++++ 1 file changed, 132 insertions(+) diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt index 8feadf6e663..0ff83b62821 100644 --- a/Documentation/git-rebase.txt +++ b/Documentation/git-rebase.txt @@ -389,6 +389,8 @@ By default, or when `no-rebase-cousins` was specified, commits which do not have `<upstream>` as direct ancestor will keep their original branch point. If the `rebase-cousins` mode is turned on, such commits are rebased onto `<upstream>` (or `<onto>`, if specified). ++ +See also REBASING MERGES below. -p:: --preserve-merges:: @@ -787,6 +789,136 @@ The ripple effect of a "hard case" recovery is especially bad: 'everyone' downstream from 'topic' will now have to perform a "hard case" recovery too! +REBASING MERGES +----------------- + +The interactive rebase command was originally designed to handle +individual patch series. As such, it makes sense to exclude merge +commits from the todo list, as the developer may have merged the +current `master` while working on the branch, only to eventually +rebase all the commits onto `master` (skipping the merge commits). + +However, there are legitimate reasons why a developer may want to +recreate merge commits: to keep the branch structure (or "commit +topology") when working on multiple, inter-related branches. + +In the following example, the developer works on a topic branch that +refactors the way buttons are defined, and on another topic branch +that uses that refactoring to implement a "Report a bug" button. The +output of `git log --graph --format=%s -5` may look like this: + +------------ +* Merge branch 'report-a-bug' +|\ +| * Add the feedback button +* | Merge branch 'refactor-button' +|\ \ +| |/ +| * Use the Button class for all buttons +| * Extract a generic Button class from the DownloadButton one +------------ + +The developer might want to rebase those commits to a newer `master` +while keeping the branch topology, for example when the first topic +branch is expected to be integrated into `master` much earlier than the +second one, say, to resolve merge conflicts with changes to the +DownloadButton class that made it into `master`. + +This rebase can be performed using the `--rebase-merges` option. +It will generate a todo list looking like this: + +------------ +label onto + +# Branch: refactor-button +reset onto +pick 123456 Extract a generic Button class from the DownloadButton one +pick 654321 Use the Button class for all buttons +label refactor-button + +# Branch: report-a-bug +reset refactor-button # Use the Button class for all buttons +pick abcdef Add the feedback button +label report-a-bug + +reset onto +merge -C a1b2c3 refactor-button # Merge 'refactor-button' +merge -C 6f5e4d report-a-bug # Merge 'report-a-bug' +------------ + +In contrast to a regular interactive rebase, there are `label`, `reset` and +`merge` commands in addition to `pick` ones. + +The `label` command associates a label with the current HEAD when that +command is executed. These labels are created as worktree-local refs +(`refs/rewritten/<label>`) that will be deleted when the rebase +finishes. That way, rebase operations in multiple worktrees linked to +the same repository do not interfere with one another. If the `label` command +fails, it is rescheduled immediately, with a helpful message how to proceed. + +The `reset` command is essentially a `git read-tree -m -u` (think: `git +reset --hard`, but refusing to overwrite untracked files) to the +specified revision (typically a previously-labeled one). If the `reset` +command fails, it is rescheduled immediately, with a helpful message how to +proceed. + +The `merge` command will merge the specified revision into whatever is +HEAD at that time. With `-C <original-commit>`, the commit message of +the specified merge commit will be used. When the `-C` is changed to +a lower-case `-c`, the message will be opened in an editor after a +successful merge so that the user can edit the message. + +If a `merge` command fails for any reason other than merge conflicts (i.e. +when the merge operation did not even start), it is rescheduled immediately. + +At this time, the `merge` command will *always* use the `recursive` +merge strategy, with no way to choose a different one. To work around +this, an `exec` command can be used to call `git merge` explicitly, +using the fact that the labels are worktree-local refs (the ref +`refs/rewritten/onto` would correspond to the label `onto`). + +Note: the first command (`label onto`) labels the revision onto which +the commits are rebased; The name `onto` is just a convention, as a nod +to the `--onto` option. + +It is also possible to introduce completely new merge commits from scratch +by adding a command of the form `merge <merge-head>`. This form will +generate a tentative commit message and always open an editor to let the +user edit it. This can be useful e.g. when a topic branch turns out to +address more than a single concern and wants to be split into two or +even more topic branches. Consider this todo list: + +------------ +pick 192837 Switch from GNU Makefiles to CMake +pick 5a6c7e Document the switch to CMake +pick 918273 Fix detection of OpenSSL in CMake +pick afbecd http: add support for TLS v1.3 +pick fdbaec Fix detection of cURL in CMake on Windows +------------ + +The one commit in this list that is not related to CMake may very well +have been motivated by working on fixing all those bugs introduced by +switching to CMake, but it addresses a different concern. To split this +branch into two topic branches, the todo list could be edited like this: + +------------ +label onto + +pick afbecd http: add support for TLS v1.3 +label tlsv1.3 + +reset onto +pick 192837 Switch from GNU Makefiles to CMake +pick 918273 Fix detection of OpenSSL in CMake +pick fdbaec Fix detection of cURL in CMake on Windows +pick 5a6c7e Document the switch to CMake +label cmake + +reset onto +merge tlsv1.3 +merge cmake +------------ + BUGS ---- The todo list presented by `--preserve-merges --interactive` does not -- 2.17.0.windows.1.4.g7e4058d72e3
