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Johannes Schindelin 8f6aed71d2 rebase: introduce the --rebase-merges option
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 move commits between branches or, deity forbid, to split topic branches
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 <label>`. And once this mode will
have become stable and universally accepted, we can deprecate the design
mistake that was `--preserve-merges`.

Link *1*:
https://github.com/msysgit/msysgit/blob/master/share/msysGit/shears.sh
Link *2*:
https://github.com/git-for-windows/build-extra/blob/master/shears.sh

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2018-04-26 12:28:43 +09:00
..
buildsystems
coccinelle Merge branch 'rs/cocci-strbuf-addf-to-addstr' 2018-02-15 14:55:44 -08:00
completion rebase: introduce the --rebase-merges option 2018-04-26 12:28:43 +09:00
contacts git-contacts: also recognise "Reported-by:" 2017-07-27 09:42:55 -07:00
credential Merge branch 'tz/fsf-address-update' into maint 2017-11-21 14:05:32 +09:00
diff-highlight diff-highlight: detect --graph by indent 2018-03-21 10:24:19 -07:00
emacs Replace Free Software Foundation address in license notices 2017-11-09 13:21:21 +09:00
examples Remove contrib/examples/* 2018-03-26 13:48:50 -07:00
fast-import Replace Free Software Foundation address in license notices 2017-11-09 13:21:21 +09:00
git-jump git-jump: give contact instructions in the README 2017-11-21 11:01:02 +09:00
git-shell-commands
hg-to-git Replace Free Software Foundation address in license notices 2017-11-09 13:21:21 +09:00
hooks hooks/pre-auto-gc-battery: allow gc to run on non-laptops 2018-02-28 14:24:46 -08:00
long-running-filter
mw-to-git Merge branch 'ab/mediawiki-namespace' 2017-11-15 12:14:32 +09:00
persistent-https docs/config: mention protocol implications of url.insteadOf 2017-06-01 10:07:10 +09:00
remote-helpers
stats
subtree Merge branch 'sg/subtree-signed-commits' 2018-03-08 12:36:25 -08:00
svn-fe
thunderbird-patch-inline
update-unicode unicode_width.h: rename to use dash in file name 2018-04-11 18:11:00 +09:00
workdir
convert-grafts-to-replace-refs.sh
git-resurrect.sh
README
remotes2config.sh
rerere-train.sh contrib/rerere-train: optionally overwrite existing resolutions 2017-07-26 13:38:48 -07:00

Contributed Software

Although these pieces are available as part of the official git
source tree, they are in somewhat different status.  The
intention is to keep interesting tools around git here, maybe
even experimental ones, to give users an easier access to them,
and to give tools wider exposure, so that they can be improved
faster.

I am not expecting to touch these myself that much.  As far as
my day-to-day operation is concerned, these subdirectories are
owned by their respective primary authors.  I am willing to help
if users of these components and the contrib/ subtree "owners"
have technical/design issues to resolve, but the initiative to
fix and/or enhance things _must_ be on the side of the subtree
owners.  IOW, I won't be actively looking for bugs and rooms for
enhancements in them as the git maintainer -- I may only do so
just as one of the users when I want to scratch my own itch.  If
you have patches to things in contrib/ area, the patch should be
first sent to the primary author, and then the primary author
should ack and forward it to me (git pull request is nicer).
This is the same way as how I have been treating gitk, and to a
lesser degree various foreign SCM interfaces, so you know the
drill.

I expect that things that start their life in the contrib/ area
to graduate out of contrib/ once they mature, either by becoming
projects on their own, or moving to the toplevel directory.  On
the other hand, I expect I'll be proposing removal of disused
and inactive ones from time to time.

If you have new things to add to this area, please first propose
it on the git mailing list, and after a list discussion proves
there are some general interests (it does not have to be a
list-wide consensus for a tool targeted to a relatively narrow
audience -- for example I do not work with projects whose
upstream is svn, so I have no use for git-svn myself, but it is
of general interest for people who need to interoperate with SVN
repositories in a way git-svn works better than git-svnimport),
submit a patch to create a subdirectory of contrib/ and put your
stuff there.

-jc