rebase: update refs from 'update-ref' commands

The previous change introduced the 'git rebase --update-refs' option
which added 'update-ref <ref>' commands to the todo list of an
interactive rebase.

Teach Git to record the HEAD position when reaching these 'update-ref'
commands. The ref/before/after triple is stored in the
$GIT_DIR/rebase-merge/update-refs file. A previous change parsed this
file to avoid having other processes updating the refs in that file
while the rebase is in progress.

Not only do we update the file when the sequencer reaches these
'update-ref' commands, we then update the refs themselves at the end of
the rebase sequence. If the rebase is aborted before this final step,
then the refs are not updated. The 'before' value is used to ensure that
we do not accidentally obliterate a ref that was updated concurrently
(say, by an older version of Git or a third-party tool).

Now that the 'git rebase --update-refs' command is implemented to write
to the update-refs file, we can remove the fake construction of the
update-refs file from a test in t2407-worktree-heads.sh.

Signed-off-by: Derrick Stolee <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: derrickstolee

sequencer.c

@@ -36,6 +36,7 @@
 #include "rebase-interactive.h"
 #include "reset.h"
 #include "branch.h"
+#include "log-tree.h"
 
 #define GIT_REFLOG_ACTION "GIT_REFLOG_ACTION"
 
@@ -193,6 +194,21 @@ struct update_ref_record {
 	struct object_id after;
 };
 
+static struct update_ref_record *init_update_ref_record(const char *ref)
+{
+	struct update_ref_record *rec;
+
+	CALLOC_ARRAY(rec, 1);
+
+	oidcpy(&rec->before, null_oid());
+	oidcpy(&rec->after, null_oid());
+
+	/* This may fail, but that's fine, we will keep the null OID. */
+	read_ref(ref, &rec->before);
+
+	return rec;
+}
+
 static int git_sequencer_config(const char *k, const char *v, void *cb)
 {
 	struct replay_opts *opts = cb;
@@ -4106,11 +4122,97 @@ static int do_merge(struct repository *r,
 	return ret;
 }
 
-static int do_update_ref(struct repository *r, const char *ref_name)
+static int write_update_refs_state(struct string_list *refs_to_oids)
+{
+	int result = 0;
+	struct lock_file lock = LOCK_INIT;
+	FILE *fp = NULL;
+	struct string_list_item *item;
+	char *path;
+
+	if (!refs_to_oids->nr)
+		return 0;
+
+	path = rebase_path_update_refs(the_repository->gitdir);
+
+	if (safe_create_leading_directories(path)) {
+		result = error(_("unable to create leading directories of %s"),
+			       path);
+		goto cleanup;
+	}
+
+	if (hold_lock_file_for_update(&lock, path, 0) < 0) {
+		result = error(_("another 'rebase' process appears to be running; "
+				 "'%s.lock' already exists"),
+			       path);
+		goto cleanup;
+	}
+
+	fp = fdopen_lock_file(&lock, "w");
+	if (!fp) {
+		result = error_errno(_("could not open '%s' for writing"), path);
+		rollback_lock_file(&lock);
+		goto cleanup;
+	}
+
+	for_each_string_list_item(item, refs_to_oids) {
+		struct update_ref_record *rec = item->util;
+		fprintf(fp, "%s\n%s\n%s\n", item->string,
+			oid_to_hex(&rec->before), oid_to_hex(&rec->after));
+	}
+
+	result = commit_lock_file(&lock);
+
+cleanup:
+	free(path);
+	return result;
+}
+
+static int do_update_ref(struct repository *r, const char *refname)
 {
+	struct string_list_item *item;
+	struct string_list list = STRING_LIST_INIT_DUP;
+
+	if (sequencer_get_update_refs_state(r->gitdir, &list))
+		return -1;
+
+	for_each_string_list_item(item, &list) {
+		if (!strcmp(item->string, refname)) {
+			struct update_ref_record *rec = item->util;
+			if (read_ref("HEAD", &rec->after))
+				return -1;
+			break;
+		}
+	}
+
+	write_update_refs_state(&list);
+	string_list_clear(&list, 1);
 	return 0;
 }
 
+static int do_update_refs(struct repository *r)
+{
+	int res = 0;
+	struct string_list_item *item;
+	struct string_list refs_to_oids = STRING_LIST_INIT_DUP;
+	struct ref_store *refs = get_main_ref_store(r);
+
+	if ((res = sequencer_get_update_refs_state(r->gitdir, &refs_to_oids)))
+		return res;
+
+	for_each_string_list_item(item, &refs_to_oids) {
+		struct update_ref_record *rec = item->util;
+
+		res |= refs_update_ref(refs, "rewritten during rebase",
+				       item->string,
+				       &rec->after, &rec->before,
+				       0, UPDATE_REFS_MSG_ON_ERR);
+	}
+
+	string_list_clear(&refs_to_oids, 1);
+	return res;
+}
+
 static int is_final_fixup(struct todo_list *todo_list)
 {
 	int i = todo_list->current;
@@ -4627,6 +4729,9 @@ static int pick_commits(struct repository *r,
 
 		strbuf_release(&buf);
 		strbuf_release(&head_ref);
+
+		if (do_update_refs(r))
+			return -1;
 	}
 
 	/*
@@ -5711,7 +5816,7 @@ static int add_decorations_to_list(const struct commit *commit,
 
 			sti = string_list_insert(&ctx->refs_to_oids,
 						 decoration->name);
-			sti->util = oiddup(the_hash_algo->null_oid);
+			sti->util = init_update_ref_record(decoration->name);
 		}
 
 		item->offset_in_buf = base_offset;
@@ -5731,7 +5836,7 @@ static int add_decorations_to_list(const struct commit *commit,
  */
 static int todo_list_add_update_ref_commands(struct todo_list *todo_list)
 {
-	int i;
+	int i, res;
 	static struct string_list decorate_refs_exclude = STRING_LIST_INIT_NODUP;
 	static struct string_list decorate_refs_exclude_config = STRING_LIST_INIT_NODUP;
 	static struct string_list decorate_refs_include = STRING_LIST_INIT_NODUP;
@@ -5767,7 +5872,16 @@ static int todo_list_add_update_ref_commands(struct todo_list *todo_list)
 		}
 	}
 
+	res = write_update_refs_state(&ctx.refs_to_oids);
+
 	string_list_clear(&ctx.refs_to_oids, 1);
+
+	if (res) {
+		/* we failed, so clean up the new list. */
+		free(ctx.items);
+		return res;
+	}
+
 	free(todo_list->items);
 	todo_list->items = ctx.items;
 	todo_list->nr = ctx.items_nr;

t/t2407-worktree-heads.sh

@@ -81,25 +81,16 @@ test_expect_success !SANITIZE_LEAK 'refuse to overwrite: worktree in rebase (mer
 	grep "cannot force update the branch '\''wt-2'\'' checked out at.*wt-2" err
 '
 
-test_expect_success 'refuse to overwrite: worktree in rebase with --update-refs' '
-	test_when_finished rm -rf .git/worktrees/wt-3/rebase-merge &&
-
-	mkdir -p .git/worktrees/wt-3/rebase-merge &&
-	touch .git/worktrees/wt-3/rebase-merge/interactive &&
+test_expect_success !SANITIZE_LEAK 'refuse to overwrite: worktree in rebase with --update-refs' '
+	test_when_finished git -C wt-3 rebase --abort &&
 
-	cat >.git/worktrees/wt-3/rebase-merge/update-refs <<-EOF &&
-	refs/heads/fake-3
-	$(git rev-parse HEAD~1)
-	$(git rev-parse HEAD)
-	refs/heads/fake-4
-	$(git rev-parse HEAD)
-	$(git rev-parse HEAD)
-	EOF
+	git branch -f can-be-updated wt-3 &&
+	test_must_fail git -C wt-3 rebase --update-refs conflict-3 &&
 
 	for i in 3 4
 	do
-		test_must_fail git branch -f fake-$i HEAD 2>err &&
-		grep "cannot force update the branch '\''fake-$i'\'' checked out at.*wt-3" err ||
+		test_must_fail git branch -f can-be-updated HEAD 2>err &&
+		grep "cannot force update the branch '\''can-be-updated'\'' checked out at.*wt-3" err ||
 			return 1
 	done
 '

t/t3404-rebase-interactive.sh

@@ -1817,6 +1817,23 @@ test_expect_success '--update-refs adds commands with --rebase-merges' '
 	)
 '
 
+test_expect_success '--update-refs updates refs correctly' '
+	git checkout -B update-refs 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 &&
+	test_commit extra2 fileX &&
+	git commit --amend --fixup=L &&
+
+	git rebase -i --autosquash --update-refs primary &&
+
+	test_cmp_rev HEAD~3 refs/heads/first &&
+	test_cmp_rev HEAD~3 refs/heads/second &&
+	test_cmp_rev HEAD~1 refs/heads/third &&
+	test_cmp_rev HEAD refs/heads/no-conflict-branch
+'
+
 # This must be the last test in this file
 test_expect_success '$EDITOR and friends are unchanged' '
 	test_editor_unchanged