[PATCH] prune: mark rebase autostash and orig-head as reachable

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

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

Rebase records the oid of HEAD before rebasing and the commit created by
"--autostash" in files in the rebase state directory. This means that
the autostash commit is never reachable from any ref or reflog and when
rebasing a detached HEAD the original HEAD can become unreachable if the
user expires HEAD's the reflog while the rebase is running. Fix this by
reading the relevant files when marking reachable commits.

Note that it is possible for the commit recorded in
.git/rebase-merge/amend to be unreachable but pruning that object does
not affect the operation of "git rebase --continue" as we're only
interested in the object id, not in the object itself.

Reported-by: Orgad Shaneh <orgads@gmail.com>
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
    prune: mark rebase autostash and orig-head as reachable
    
    Thanks for reporting this Orgad, it reminded me that I've been meaning
    to clean up this patch for a while.
    
    I've got a patch on top of this that marks selected pseudorefs such as
    ORIG_HEAD and AUTO_MERGE as reachable but I've held off sending that as
    I think it would be better to rebase it on kn/for-all-refs once that has
    stabilized as that will hopefully allows us to mark all pseudorefs as
    reachable rather than using a hard-coded list.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1656%2Fphillipwood%2Fprune-protect-rebase-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1656/phillipwood/prune-protect-rebase-v1
Pull-Request: https://github.com/gitgitgadget/git/pull/1656

 reachable.c                 | 51 +++++++++++++++++++++++++++++++++++++
 t/t3407-rebase-abort.sh     | 17 ++++++++++++-
 t/t3420-rebase-autostash.sh | 10 ++++++++
 3 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/reachable.c b/reachable.c
index f29b06a5d05..fef29422d4a 100644
--- a/reachable.c
+++ b/reachable.c
@@ -17,6 +17,7 @@
 #include "pack-mtimes.h"
 #include "config.h"
 #include "run-command.h"
+#include "sequencer.h"
 
 struct connectivity_progress {
 	struct progress *progress;
@@ -30,6 +31,53 @@ static void update_progress(struct connectivity_progress *cp)
 		display_progress(cp->progress, cp->count);
 }
 
+static int add_one_file(const char *path, struct rev_info *revs)
+{
+	struct strbuf buf = STRBUF_INIT;
+	struct object_id oid;
+	struct object *object;
+
+	if (!read_oneliner(&buf, path, READ_ONELINER_SKIP_IF_EMPTY)) {
+		strbuf_release(&buf);
+		return 0;
+	}
+	strbuf_trim(&buf);
+	if (!get_oid_hex(buf.buf, &oid)) {
+		object = parse_object_or_die(&oid, buf.buf);
+		add_pending_object(revs, object, "");
+	}
+	return 0;
+}
+
+/* Mark objects recored in rebase state files as reachable. */
+static int add_rebase_files(struct rev_info *revs)
+{
+	struct strbuf buf = STRBUF_INIT;
+	size_t len;
+	const char *path[] = {
+		"rebase-apply/autostash",
+		"rebase-apply/orig-head",
+		"rebase-merge/autostash",
+		"rebase-merge/orig-head",
+	};
+	struct worktree **worktrees = get_worktrees();
+
+	for (struct worktree **wt = worktrees; *wt; wt++) {
+		strbuf_reset(&buf);
+		strbuf_addstr(&buf, get_worktree_git_dir(*wt));
+		strbuf_complete(&buf, '/');
+		len = buf.len;
+		for (size_t i = 0; i < ARRAY_SIZE(path); i++) {
+			strbuf_setlen(&buf, len);
+			strbuf_addstr(&buf, path[i]);
+			add_one_file(buf.buf, revs);
+		}
+	}
+	strbuf_release(&buf);
+	free_worktrees(worktrees);
+	return 0;
+}
+
 static int add_one_ref(const char *path, const struct object_id *oid,
 		       int flag, void *cb_data)
 {
@@ -322,6 +370,9 @@ void mark_reachable_objects(struct rev_info *revs, int mark_reflog,
 	head_ref(add_one_ref, revs);
 	other_head_refs(add_one_ref, revs);
 
+	/* rebase autostash and orig-head */
+	add_rebase_files(revs);
+
 	/* Add all reflog info */
 	if (mark_reflog)
 		add_reflogs_to_pending(revs, 0);
diff --git a/t/t3407-rebase-abort.sh b/t/t3407-rebase-abort.sh
index ebbaed147a6..9f49c4228b6 100755
--- a/t/t3407-rebase-abort.sh
+++ b/t/t3407-rebase-abort.sh
@@ -40,9 +40,24 @@ testrebase() {
 		test_path_is_missing "$state_dir"
 	'
 
+	test_expect_success "pre rebase$type head is marked as reachable" '
+		# Clean up the state from the previous one
+		git checkout -f --detach pre-rebase &&
+		test_tick &&
+		git commit --amend --only -m "reworded" &&
+		orig_head=$(git rev-parse HEAD) &&
+		test_must_fail git rebase$type main &&
+		# Stop ORIG_HEAD marking $state_dir/orig-head as reachable
+		git update-ref -d ORIG_HEAD &&
+		git reflog expire --expire="$GIT_COMMITTER_DATE" --all &&
+		git prune --expire=now &&
+		git rebase --abort &&
+		test_cmp_rev $orig_head HEAD
+	'
+
 	test_expect_success "rebase$type --abort after --skip" '
 		# Clean up the state from the previous one
-		git reset --hard pre-rebase &&
+		git checkout -B to-rebase pre-rebase &&
 		test_must_fail git rebase$type main &&
 		test_path_is_dir "$state_dir" &&
 		test_must_fail git rebase --skip &&
diff --git a/t/t3420-rebase-autostash.sh b/t/t3420-rebase-autostash.sh
index 693934ee8be..1a820f14815 100755
--- a/t/t3420-rebase-autostash.sh
+++ b/t/t3420-rebase-autostash.sh
@@ -333,4 +333,14 @@ test_expect_success 'never change active branch' '
 	test_cmp_rev not-the-feature-branch unrelated-onto-branch
 '
 
+test_expect_success 'autostash commit is marked as reachable' '
+	echo changed >file0 &&
+	git rebase --autostash --exec "git prune --expire=now" \
+		feature-branch^ feature-branch &&
+	# git rebase succeeds if the stash cannot be applied so we need to check
+	# the contents of file0
+	echo changed >expect &&
+	test_cmp expect file0
+'
+
 test_done

base-commit: 2a540e432fe5dff3cfa9d3bf7ca56db2ad12ebb9
-- 
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