Introduce CHERRY_PICK_HEAD

When a cherry-pick conflicts git advises:

 $ git commit -c <original commit id>

to preserve the original commit message and authorship. Instead, let's
record the original commit id in CHERRY_PICK_HEAD and advise:

  $ git commit -c CHERRY_PICK_HEAD

A later patch teaches git to handle the '-c CHERRY_PICK_HEAD' part.
Note that we record CHERRY_PICK_HEAD even in the case where there
are no conflicts so that we may use it to communicate authorship to
commit; this will then allow us to remove set_author_ident_env from
revert.c. However, we do not record CHERRY_PICK_HEAD when --no-commit
is used, as presumably the user intends to further edit the commit
and possibly even cherry-pick additional commits on top.

Tests and documentation contributed by Jonathan Nieder.

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 75 insertions, 1 deletions

diff --git a/t/t3507-cherry-pick-conflict.sh b/t/t3507-cherry-pick-conflict.sh
index 2313d79bd4..e0bf3563ac 100755
--- a/t/t3507-cherry-pick-conflict.sh
+++ b/t/t3507-cherry-pick-conflict.sh
@@ -52,13 +52,87 @@ test_expect_success 'advice from failed cherry-pick' "
 	error: could not apply \$picked... picked
 	hint: after resolving the conflicts, mark the corrected paths
 	hint: with 'git add <paths>' or 'git rm <paths>'
-	hint: and commit the result with 'git commit -c \$picked'
+	hint: and commit the result with 'git commit -c CHERRY_PICK_HEAD'
 	EOF
 	test_must_fail git cherry-pick picked 2>actual &&
 
 	test_cmp expected actual
 "
 
+test_expect_success 'failed cherry-pick sets CHERRY_PICK_HEAD' '
+	pristine_detach initial &&
+	test_must_fail git cherry-pick picked &&
+	test_cmp_rev picked CHERRY_PICK_HEAD
+'
+
+test_expect_success 'successful cherry-pick does not set CHERRY_PICK_HEAD' '
+	pristine_detach initial &&
+	git cherry-pick base &&
+	test_must_fail git rev-parse --verify CHERRY_PICK_HEAD
+'
+
+test_expect_success 'cherry-pick --no-commit does not set CHERRY_PICK_HEAD' '
+	pristine_detach initial &&
+	git cherry-pick --no-commit base &&
+	test_must_fail git rev-parse --verify CHERRY_PICK_HEAD
+'
+
+test_expect_success 'GIT_CHERRY_PICK_HELP suppresses CHERRY_PICK_HEAD' '
+	pristine_detach initial &&
+	(
+		GIT_CHERRY_PICK_HELP="and then do something else" &&
+		export GIT_CHERRY_PICK_HELP &&
+		test_must_fail git cherry-pick picked
+	) &&
+	test_must_fail git rev-parse --verify CHERRY_PICK_HEAD
+'
+
+test_expect_success 'git reset clears CHERRY_PICK_HEAD' '
+	pristine_detach initial &&
+
+	test_must_fail git cherry-pick picked &&
+	git reset &&
+
+	test_must_fail git rev-parse --verify CHERRY_PICK_HEAD
+'
+
+test_expect_success 'failed commit does not clear CHERRY_PICK_HEAD' '
+	pristine_detach initial &&
+
+	test_must_fail git cherry-pick picked &&
+	test_must_fail git commit &&
+
+	test_cmp_rev picked CHERRY_PICK_HEAD
+'
+
+test_expect_success 'cancelled commit does not clear CHERRY_PICK_HEAD' '
+	pristine_detach initial &&
+
+	test_must_fail git cherry-pick picked &&
+	echo resolved >foo &&
+	git add foo &&
+	git update-index --refresh -q &&
+	test_must_fail git diff-index --exit-code HEAD &&
+	(
+		GIT_EDITOR=false &&
+		export GIT_EDITOR &&
+		test_must_fail git commit
+	) &&
+
+	test_cmp_rev picked CHERRY_PICK_HEAD
+'
+
+test_expect_success 'successful commit clears CHERRY_PICK_HEAD' '
+	pristine_detach initial &&
+
+	test_must_fail git cherry-pick picked &&
+	echo resolved >foo &&
+	git add foo &&
+	git commit &&
+
+	test_must_fail git rev-parse --verify CHERRY_PICK_HEAD
+'
+
 test_expect_success 'failed cherry-pick produces dirty index' '
 	pristine_detach initial &&