sequencer: rewrite update-refs as user edits todo list

An interactive rebase provides opportunities for the user to edit the
todo list. The --update-refs option initializes the list with some
'update-ref <ref>' steps, but the user could add these manually.
Further, the user could add or remove these steps during pauses in the
interactive rebase.

Add a new method, todo_list_filter_update_refs(), that scans a todo_list
and compares it to the stored update-refs file. There are two actions
that can happen at this point:

1. If a '<ref>/<before>/<after>' triple in the update-refs file does not
   have a matching 'update-ref <ref>' command in the todo-list _and_ the
   <after> value is the null OID, then remove that triple. Here, the
   user removed the 'update-ref <ref>' command before it was executed,
   since if it was executed then the <after> value would store the
   commit at that position.

2. If a 'update-ref <ref>' command in the todo-list does not have a
   matching '<ref>/<before>/<after>' triple in the update-refs file,
   then insert a new one. Store the <before> value to be the current
   OID pointed at by <ref>. This is handled inside of the
   init_update_ref_record() helper method.

We can test that this works by rewriting the todo-list several times in
the course of a rebase. Check that each ref is locked or unlocked for
updates after each todo-list update. We can also verify that the ref
update fails if a concurrent process updates one of the refs after the
rebase process records the "locked" ref location.

To help these tests, add a new 'set_replace_editor' helper that will
replace the todo-list with an exact file.

Reported-by: Phillip Wood <phillip.wood123@gmail.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 154 insertions, 0 deletions

diff --git a/t/lib-rebase.sh b/t/lib-rebase.sh
index ec6b9b1..b575413 100644
--- a/t/lib-rebase.sh
+++ b/t/lib-rebase.sh
@@ -207,3 +207,18 @@ check_reworded_commits () {
 		>reword-log &&
 	test_cmp reword-expected reword-log
 }
+
+# usage: set_replace_editor <file>
+#
+# Replace the todo file with the exact contents of the given file.
+set_replace_editor () {
+	cat >script <<-\EOF &&
+	cat FILENAME >"$1"
+
+	echo 'rebase -i script after editing:'
+	cat "$1"
+	EOF
+
+	sed -e "s/FILENAME/$1/g" <script | write_script fake-editor.sh &&
+	test_set_editor "$(pwd)/fake-editor.sh"
+}
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 2fffcf5..bebf9b4 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -1834,6 +1834,145 @@ test_expect_success '--update-refs updates refs correctly' '
 	test_cmp_rev HEAD refs/heads/no-conflict-branch
 '
 
+test_expect_success 'respect user edits to update-ref steps' '
+	git checkout -B update-refs-break no-conflict-branch &&
+	git branch -f base HEAD~4 &&
+	git branch -f first HEAD~3 &&
+	git branch -f second HEAD~3 &&
+	git branch -f third HEAD~1 &&
+	git branch -f unseen base &&
+
+	# First, we will add breaks to the expected todo file
+	cat >fake-todo-1 <<-EOF &&
+	pick $(git rev-parse HEAD~3)
+	break
+	update-ref refs/heads/second
+	update-ref refs/heads/first
+
+	pick $(git rev-parse HEAD~2)
+	pick $(git rev-parse HEAD~1)
+	update-ref refs/heads/third
+
+	pick $(git rev-parse HEAD)
+	update-ref refs/heads/no-conflict-branch
+	EOF
+
+	# Second, we will drop some update-refs commands (and move one)
+	cat >fake-todo-2 <<-EOF &&
+	update-ref refs/heads/second
+
+	pick $(git rev-parse HEAD~2)
+	update-ref refs/heads/third
+	pick $(git rev-parse HEAD~1)
+	break
+
+	pick $(git rev-parse HEAD)
+	EOF
+
+	# Third, we will:
+	# * insert a new one (new-branch),
+	# * re-add an old one (first), and
+	# * add a second instance of a previously-stored one (second)
+	cat >fake-todo-3 <<-EOF &&
+	update-ref refs/heads/unseen
+	update-ref refs/heads/new-branch
+	pick $(git rev-parse HEAD)
+	update-ref refs/heads/first
+	update-ref refs/heads/second
+	EOF
+
+	(
+		set_replace_editor fake-todo-1 &&
+		git rebase -i --update-refs primary &&
+
+		# These branches are currently locked.
+		for b in first second third no-conflict-branch
+		do
+			test_must_fail git branch -f $b base || return 1
+		done &&
+
+		set_replace_editor fake-todo-2 &&
+		git rebase --edit-todo &&
+
+		# These branches are currently locked.
+		for b in second third
+		do
+			test_must_fail git branch -f $b base || return 1
+		done &&
+
+		# These branches are currently unlocked for checkout.
+		for b in first no-conflict-branch
+		do
+			git worktree add wt-$b $b &&
+			git worktree remove wt-$b || return 1
+		done &&
+
+		git rebase --continue &&
+
+		set_replace_editor fake-todo-3 &&
+		git rebase --edit-todo &&
+
+		# These branches are currently locked.
+		for b in second third first unseen
+		do
+			test_must_fail git branch -f $b base || return 1
+		done &&
+
+		# These branches are currently unlocked for checkout.
+		for b in no-conflict-branch
+		do
+			git worktree add wt-$b $b &&
+			git worktree remove wt-$b || return 1
+		done &&
+
+		git rebase --continue
+	) &&
+
+	test_cmp_rev HEAD~2 refs/heads/third &&
+	test_cmp_rev HEAD~1 refs/heads/unseen &&
+	test_cmp_rev HEAD~1 refs/heads/new-branch &&
+	test_cmp_rev HEAD refs/heads/first &&
+	test_cmp_rev HEAD refs/heads/second &&
+	test_cmp_rev HEAD refs/heads/no-conflict-branch
+'
+
+test_expect_success '--update-refs: check failed ref update' '
+	git checkout -B update-refs-error no-conflict-branch &&
+	git branch -f base HEAD~4 &&
+	git branch -f first HEAD~3 &&
+	git branch -f second HEAD~2 &&
+	git branch -f third HEAD~1 &&
+
+	cat >fake-todo <<-EOF &&
+	pick $(git rev-parse HEAD~3)
+	break
+	update-ref refs/heads/first
+
+	pick $(git rev-parse HEAD~2)
+	update-ref refs/heads/second
+
+	pick $(git rev-parse HEAD~1)
+	update-ref refs/heads/third
+
+	pick $(git rev-parse HEAD)
+	update-ref refs/heads/no-conflict-branch
+	EOF
+
+	(
+		set_replace_editor fake-todo &&
+		git rebase -i --update-refs base
+	) &&
+
+	# At this point, the values of first, second, and third are
+	# recorded in the update-refs file. We will force-update the
+	# "second" ref, but "git branch -f" will not work because of
+	# the lock in the update-refs file.
+	git rev-parse third >.git/refs/heads/second &&
+
+	git rebase --continue 2>err &&
+	grep "update_ref failed for ref '\''refs/heads/second'\''" err
+'
+
 # This must be the last test in this file
 test_expect_success '$EDITOR and friends are unchanged' '
 	test_editor_unchanged