[PATCH 4/5] rebase --keep-base: imply --reapply-cherry-picks

["Phillip Wood via GitGitGadget" <gitgitgadget@gmail.com>]

From: Phillip Wood <phillip.wood@dunelm.org.uk>

As --keep-base does not rebase the branch it is confusing if it
removes commits that have been cherry-picked to the upstream branch.
As --reapply-cherry-picks is not supported by the "apply" backend this
commit ensures that cherry-picks are reapplied by forcing the upstream
commit to match the onto commit unless --no-reapply-cherry-picks is
given.

Reported-by: Philippe Blain <levraiphilippeblain@gmail.com>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
 Documentation/git-rebase.txt     |  2 +-
 builtin/rebase.c                 | 15 ++++++++++++++-
 t/t3416-rebase-onto-threedots.sh | 21 +++++++++++++++++++++
 3 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt
index 080658c8710..dc0c6c54e27 100644
--- a/Documentation/git-rebase.txt
+++ b/Documentation/git-rebase.txt
@@ -218,7 +218,7 @@ leave out at most one of A and B, in which case it defaults to HEAD.
 	merge base of `<upstream>` and `<branch>`. Running
 	`git rebase --keep-base <upstream> <branch>` is equivalent to
 	running
-	`git rebase --onto <upstream>...<branch> <upstream> <branch>`.
+	`git rebase --reapply-cherry-picks --onto <upstream>...<branch> <upstream> <branch>`.
 +
 This option is useful in the case where one is developing a feature on
 top of an upstream branch. While the feature is being worked on, the
diff --git a/builtin/rebase.c b/builtin/rebase.c
index 86ea731ca3a..b6b3e00e3b1 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -1181,6 +1181,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	prepare_repo_settings(the_repository);
 	the_repository->settings.command_requires_full_index = 0;
 
+	options.reapply_cherry_picks = -1;
 	options.allow_empty_message = 1;
 	git_config(rebase_config, &options);
 	/* options.gpg_sign_opt will be either "-S" or NULL */
@@ -1240,6 +1241,12 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		if (options.root)
 			die(_("options '%s' and '%s' cannot be used together"), "--keep-base", "--root");
 	}
+	/*
+	 * --keep-base defaults to --reapply-cherry-picks as it is confusing if
+	 * commits disappear when using this option.
+	 */
+	if (options.reapply_cherry_picks < 0)
+		options.reapply_cherry_picks = keep_base;
 
 	if (options.root && options.fork_point > 0)
 		die(_("options '%s' and '%s' cannot be used together"), "--root", "--fork-point");
@@ -1416,7 +1423,11 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	if (options.empty != EMPTY_UNSPECIFIED)
 		imply_merge(&options, "--empty");
 
-	if (options.reapply_cherry_picks)
+	/*
+	 * --keep-base implements --reapply-cherry-picks by altering upstream so
+	 * it works with both backends.
+	 */
+	if (options.reapply_cherry_picks && !keep_base)
 		imply_merge(&options, "--reapply-cherry-picks");
 
 	if (gpg_sign)
@@ -1680,6 +1691,8 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 	if (keep_base) {
 		oidcpy(&merge_base, &options.onto->object.oid);
+		if (options.reapply_cherry_picks)
+			options.upstream = options.onto;
 	} else {
 		fill_merge_base(&options, &merge_base);
 	}
diff --git a/t/t3416-rebase-onto-threedots.sh b/t/t3416-rebase-onto-threedots.sh
index e1fc2dbd48e..e0410bfc2a8 100755
--- a/t/t3416-rebase-onto-threedots.sh
+++ b/t/t3416-rebase-onto-threedots.sh
@@ -197,6 +197,27 @@ test_expect_success 'rebase -i --keep-base main from side' '
 	test_must_fail git rebase -i --keep-base main
 '
 
+test_expect_success 'rebase --keep-base keeps cherry picks' '
+	git checkout -f -B main E &&
+	git cherry-pick F &&
+	(
+		set_fake_editor &&
+		EXPECT_COUNT=2 git rebase -i --keep-base HEAD G
+	) &&
+	test_cmp_rev HEAD G
+'
+
+test_expect_success 'rebase --keep-base --no-reapply-cherry-picks' '
+	git checkout -f -B main E &&
+	git cherry-pick F &&
+	(
+		set_fake_editor &&
+		EXPECT_COUNT=1 git rebase -i --keep-base \
+					--no-reapply-cherry-picks HEAD G
+	) &&
+	test_cmp_rev HEAD^ C
+'
+
 # This must be the last test in this file
 test_expect_success '$EDITOR and friends are unchanged' '
 	test_editor_unchanged
-- 
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