rebase -i: mark commits that begin empty in todo editor

Changes since v2:

* Addressed feedback from Junio in patch 2, including moving some of the wording to the new patch (see next point)
* Edited jt/rebase-allow-duplicate to include the changes Jonathan mentioned on the list, then rebased it on top of this series, and made the related options mention each other.

Elijah Newren (3):
rebase -i: mark commits that begin empty in todo editor
rebase: reinstate --no-keep-empty
rebase: fix an incompatible-options error message

Jonathan Tan (1):
rebase --merge: optionally skip upstreamed commits

 Documentation/git-rebase.txt      | 70 +++++++++++++++++++++-------
 builtin/rebase.c                  | 24 +++++++---
 sequencer.c                       | 14 +++++-
 sequencer.h                       |  4 +-
 t/t3402-rebase-merge.sh           | 77 +++++++++++++++++++++++++++++++
 t/t3421-rebase-topology-linear.sh | 10 ++--
 t/t3424-rebase-empty.sh           | 36 +++++++++++++++
 7 files changed, 202 insertions(+), 33 deletions(-)

base-commit: 274b9cc25322d9ee79aa8e6d4e86f0ffe5ced925
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-757%2Fnewren%2Frebase-mark-empty-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-757/newren/rebase-mark-empty-v3
Pull-Request: https://github.com/git/git/pull/757

Range-diff vs v2:

 1:  0d94eea376a = 1:  0d94eea376a rebase -i: mark commits that begin empty in todo editor
 2:  e15c599c874 ! 2:  3a5bedc68d6 rebase: reinstate --no-keep-empty

@@ Commit message

Commit d48e5e21da ("rebase (interactive-backend): make --keep-empty the default", 2020-02-15) turned --keep-empty (for keeping commits which
- start empty) into the default. That commit viewed this, though as
- turning that flag into a no-op. As such, --no-keep-empty was translated
- into undoing a no-op, i.e. also a no-op. The logic underpinning that
- commit was:
+ start empty) into the default. The logic underpinning that commit was:

1) 'git commit' errors out on the creation of empty commits without an override flag
@@ Commit message
look really weird despite making perfect sense (the first will drop commits which become empty, but keep commits that started empty; the second will keep commits which become empty, but drop commits which
- started empty).
+ started empty). However, --no-keep-empty was named years ago and we are
+ predominantly keeping it for backward compatibility; also we suspect it
+ will only be used rarely since folks already have a simple way to drop
+ commits they don't want with an interactive rebase.

@@ Documentation/git-rebase.txt: See also INCOMPATIBLE OPTIONS below.
-always dropped.
+Note that commits which start empty are kept (unless --no-keep-empty +is specified), and commits which are clean cherry-picks (as determined
-+by git log --cherry-mark ...) are detected and dropped as a preliminary -+step (unless --keep-cherry-picks is passed).
++by git log --cherry-mark ...) are always dropped.
+
See also INCOMPATIBLE OPTIONS below.

@@ Documentation/git-rebase.txt: See also INCOMPATIBLE OPTIONS below.
- to halt.
+ Do not keep commits that start empty before the rebase
+ (i.e. that do not change anything from its parent) in the
-+ result. For commits which become empty after rebasing, see
-+ the --empty and --keep-cherry-pick flags.
++ result. The default is to keep commits which start empty,
++ since creating such commits requires passing the --allow-empty
++ override flag to git commit, signifying that a user is very
++ intentionally creating such a commit and thus wants to keep
++ it.
+
-See also BEHAVIORAL DIFFERENCES and INCOMPATIBLE OPTIONS below.
++Usage of this flag will probably be rare, since you can get rid of ++commits that start empty by just firing up an interactive rebase and ++removing the lines corresponding to the commits you don't want. This ++flag exists as a convenient shortcut, such as for cases where external ++tools generate many empty commits and you want them all removed.
+++
++For commits which do not start empty but become empty after rebasing, ++see the --empty flag.
+++
+See also INCOMPATIBLE OPTIONS below.

--allow-empty-message::

 3:  ee5e42361fc = 3:  5c8863b9d34 rebase: fix an incompatible-options error message
 -:  ----------- > 4:  20d3a50f5a4 rebase --merge: optionally skip upstreamed commits

gitgitgadget