status: show the branch name if possible in in-progress info

The typical use-case is starting a rebase, do something else, come
back the day after, run "git status" or make a new commit and wonder
what in the world's going on. Which branch is being rebased is
probably the most useful tidbit to help, but the target may help
too.

Ideally, I would have loved to see "rebasing master on
origin/master", but the target ref name is not stored during rebase,
so this patch writes "rebasing master on a78c8c98b" as a
half-measure to remind future users of that potential improvement.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7512-status-help.sh

@@ -73,10 +73,11 @@ test_expect_success 'prepare for rebase conflicts' '
 
 test_expect_success 'status when rebase in progress before resolving conflicts' '
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD^^) &&
 	test_must_fail git rebase HEAD^ --onto HEAD^^ &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently rebasing.
+	# You are currently rebasing branch '\''rebase_conflicts'\'' on '\''$ONTO'\''.
 	#   (fix conflicts and then run "git rebase --continue")
 	#   (use "git rebase --skip" to skip this patch)
 	#   (use "git rebase --abort" to check out the original branch)
@@ -97,12 +98,13 @@ test_expect_success 'status when rebase in progress before resolving conflicts'
 test_expect_success 'status when rebase in progress before rebase --continue' '
 	git reset --hard rebase_conflicts &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD^^) &&
 	test_must_fail git rebase HEAD^ --onto HEAD^^ &&
 	echo three >main.txt &&
 	git add main.txt &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently rebasing.
+	# You are currently rebasing branch '\''rebase_conflicts'\'' on '\''$ONTO'\''.
 	#   (all conflicts fixed: run "git rebase --continue")
 	#
 	# Changes to be committed:
@@ -130,10 +132,11 @@ test_expect_success 'prepare for rebase_i_conflicts' '
 
 test_expect_success 'status during rebase -i when conflicts unresolved' '
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short rebase_i_conflicts) &&
 	test_must_fail git rebase -i rebase_i_conflicts &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently rebasing.
+	# You are currently rebasing branch '\''rebase_i_conflicts_second'\'' on '\''$ONTO'\''.
 	#   (fix conflicts and then run "git rebase --continue")
 	#   (use "git rebase --skip" to skip this patch)
 	#   (use "git rebase --abort" to check out the original branch)
@@ -154,11 +157,12 @@ test_expect_success 'status during rebase -i when conflicts unresolved' '
 test_expect_success 'status during rebase -i after resolving conflicts' '
 	git reset --hard rebase_i_conflicts_second &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short rebase_i_conflicts) &&
 	test_must_fail git rebase -i rebase_i_conflicts &&
 	git add main.txt &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently rebasing.
+	# You are currently rebasing branch '\''rebase_i_conflicts_second'\'' on '\''$ONTO'\''.
 	#   (all conflicts fixed: run "git rebase --continue")
 	#
 	# Changes to be committed:
@@ -182,10 +186,11 @@ test_expect_success 'status when rebasing -i in edit mode' '
 	FAKE_LINES="1 edit 2" &&
 	export FAKE_LINES &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD~2) &&
 	git rebase -i HEAD~2 &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently editing a commit during a rebase.
+	# You are currently editing a commit while rebasing branch '\''rebase_i_edit'\'' on '\''$ONTO'\''.
 	#   (use "git commit --amend" to amend the current commit)
 	#   (use "git rebase --continue" once you are satisfied with your changes)
 	#
@@ -206,11 +211,12 @@ test_expect_success 'status when splitting a commit' '
 	FAKE_LINES="1 edit 2 3" &&
 	export FAKE_LINES &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD~3) &&
 	git rebase -i HEAD~3 &&
 	git reset HEAD^ &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently splitting a commit during a rebase.
+	# You are currently splitting a commit while rebasing branch '\''split_commit'\'' on '\''$ONTO'\''.
 	#   (Once your working directory is clean, run "git rebase --continue")
 	#
 	# Changes not staged for commit:
@@ -236,11 +242,12 @@ test_expect_success 'status after editing the last commit with --amend during a
 	FAKE_LINES="1 2 edit 3" &&
 	export FAKE_LINES &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD~3) &&
 	git rebase -i HEAD~3 &&
 	git commit --amend -m "foo" &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently editing a commit during a rebase.
+	# You are currently editing a commit while rebasing branch '\''amend_last'\'' on '\''$ONTO'\''.
 	#   (use "git commit --amend" to amend the current commit)
 	#   (use "git rebase --continue" once you are satisfied with your changes)
 	#
@@ -265,11 +272,12 @@ test_expect_success 'status: (continue first edit) second edit' '
 	FAKE_LINES="edit 1 edit 2 3" &&
 	export FAKE_LINES &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD~3) &&
 	git rebase -i HEAD~3 &&
 	git rebase --continue &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently editing a commit during a rebase.
+	# You are currently editing a commit while rebasing branch '\''several_edits'\'' on '\''$ONTO'\''.
 	#   (use "git commit --amend" to amend the current commit)
 	#   (use "git rebase --continue" once you are satisfied with your changes)
 	#
@@ -285,12 +293,13 @@ test_expect_success 'status: (continue first edit) second edit and split' '
 	FAKE_LINES="edit 1 edit 2 3" &&
 	export FAKE_LINES &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD~3) &&
 	git rebase -i HEAD~3 &&
 	git rebase --continue &&
 	git reset HEAD^ &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently splitting a commit during a rebase.
+	# You are currently splitting a commit while rebasing branch '\''several_edits'\'' on '\''$ONTO'\''.
 	#   (Once your working directory is clean, run "git rebase --continue")
 	#
 	# Changes not staged for commit:
@@ -311,12 +320,13 @@ test_expect_success 'status: (continue first edit) second edit and amend' '
 	FAKE_LINES="edit 1 edit 2 3" &&
 	export FAKE_LINES &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD~3) &&
 	git rebase -i HEAD~3 &&
 	git rebase --continue &&
 	git commit --amend -m "foo" &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently editing a commit during a rebase.
+	# You are currently editing a commit while rebasing branch '\''several_edits'\'' on '\''$ONTO'\''.
 	#   (use "git commit --amend" to amend the current commit)
 	#   (use "git rebase --continue" once you are satisfied with your changes)
 	#
@@ -332,12 +342,13 @@ test_expect_success 'status: (amend first edit) second edit' '
 	FAKE_LINES="edit 1 edit 2 3" &&
 	export FAKE_LINES &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD~3) &&
 	git rebase -i HEAD~3 &&
 	git commit --amend -m "a" &&
 	git rebase --continue &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently editing a commit during a rebase.
+	# You are currently editing a commit while rebasing branch '\''several_edits'\'' on '\''$ONTO'\''.
 	#   (use "git commit --amend" to amend the current commit)
 	#   (use "git rebase --continue" once you are satisfied with your changes)
 	#
@@ -353,13 +364,14 @@ test_expect_success 'status: (amend first edit) second edit and split' '
 	FAKE_LINES="edit 1 edit 2 3" &&
 	export FAKE_LINES &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD~3) &&
 	git rebase -i HEAD~3 &&
 	git commit --amend -m "b" &&
 	git rebase --continue &&
 	git reset HEAD^ &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently splitting a commit during a rebase.
+	# You are currently splitting a commit while rebasing branch '\''several_edits'\'' on '\''$ONTO'\''.
 	#   (Once your working directory is clean, run "git rebase --continue")
 	#
 	# Changes not staged for commit:
@@ -380,13 +392,14 @@ test_expect_success 'status: (amend first edit) second edit and amend' '
 	FAKE_LINES="edit 1 edit 2 3" &&
 	export FAKE_LINES &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD~3) &&
 	git rebase -i HEAD~3 &&
 	git commit --amend -m "c" &&
 	git rebase --continue &&
 	git commit --amend -m "d" &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently editing a commit during a rebase.
+	# You are currently editing a commit while rebasing branch '\''several_edits'\'' on '\''$ONTO'\''.
 	#   (use "git commit --amend" to amend the current commit)
 	#   (use "git rebase --continue" once you are satisfied with your changes)
 	#
@@ -402,14 +415,15 @@ test_expect_success 'status: (split first edit) second edit' '
 	FAKE_LINES="edit 1 edit 2 3" &&
 	export FAKE_LINES &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD~3) &&
 	git rebase -i HEAD~3 &&
 	git reset HEAD^ &&
 	git add main.txt &&
 	git commit -m "e" &&
 	git rebase --continue &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently editing a commit during a rebase.
+	# You are currently editing a commit while rebasing branch '\''several_edits'\'' on '\''$ONTO'\''.
 	#   (use "git commit --amend" to amend the current commit)
 	#   (use "git rebase --continue" once you are satisfied with your changes)
 	#
@@ -425,15 +439,16 @@ test_expect_success 'status: (split first edit) second edit and split' '
 	FAKE_LINES="edit 1 edit 2 3" &&
 	export FAKE_LINES &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD~3) &&
 	git rebase -i HEAD~3 &&
 	git reset HEAD^ &&
 	git add main.txt &&
 	git commit --amend -m "f" &&
 	git rebase --continue &&
 	git reset HEAD^ &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently splitting a commit during a rebase.
+	# You are currently splitting a commit while rebasing branch '\''several_edits'\'' on '\''$ONTO'\''.
 	#   (Once your working directory is clean, run "git rebase --continue")
 	#
 	# Changes not staged for commit:
@@ -454,15 +469,16 @@ test_expect_success 'status: (split first edit) second edit and amend' '
 	FAKE_LINES="edit 1 edit 2 3" &&
 	export FAKE_LINES &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD~3) &&
 	git rebase -i HEAD~3 &&
 	git reset HEAD^ &&
 	git add main.txt &&
 	git commit --amend -m "g" &&
 	git rebase --continue &&
 	git commit --amend -m "h" &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently editing a commit during a rebase.
+	# You are currently editing a commit while rebasing branch '\''several_edits'\'' on '\''$ONTO'\''.
 	#   (use "git commit --amend" to amend the current commit)
 	#   (use "git rebase --continue" once you are satisfied with your changes)
 	#
@@ -558,7 +574,7 @@ test_expect_success 'status when bisecting' '
 	git bisect good one_bisect &&
 	cat >expected <<-\EOF &&
 	# Not currently on any branch.
-	# You are currently bisecting.
+	# You are currently bisecting branch '\''bisect'\''.
 	#   (use "git bisect reset" to get back to the original branch)
 	#
 	nothing to commit (use -u to show untracked files)
@@ -577,10 +593,11 @@ test_expect_success 'status when rebase conflicts with statushints disabled' '
 	test_commit two_statushints main.txt two &&
 	test_commit three_statushints main.txt three &&
 	test_when_finished "git rebase --abort" &&
+	ONTO=$(git rev-parse --short HEAD^^) &&
 	test_must_fail git rebase HEAD^ --onto HEAD^^ &&
-	cat >expected <<-\EOF &&
+	cat >expected <<-EOF &&
 	# Not currently on any branch.
-	# You are currently rebasing.
+	# You are currently rebasing branch '\''statushints_disabled'\'' on '\''$ONTO'\''.
 	#
 	# Unmerged paths:
 	#	both modified:      main.txt