bisect: consistently write BISECT_EXPECTED_REV via the refdb

We're inconsistently writing BISECT_EXPECTED_REV both via the filesystem
and via the refdb, which violates the newly established rules for how
special refs must be treated. This works alright in practice with the
reffiles reference backend, but will cause bugs once we gain additional
backends.

Fix this issue and consistently write BISECT_EXPECTED_REV via the refdb
so that it is no longer a special ref.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

bisect.c

@@ -471,7 +471,6 @@ static int read_bisect_refs(void)
 }
 
 static GIT_PATH_FUNC(git_path_bisect_names, "BISECT_NAMES")
-static GIT_PATH_FUNC(git_path_bisect_expected_rev, "BISECT_EXPECTED_REV")
 static GIT_PATH_FUNC(git_path_bisect_ancestors_ok, "BISECT_ANCESTORS_OK")
 static GIT_PATH_FUNC(git_path_bisect_run, "BISECT_RUN")
 static GIT_PATH_FUNC(git_path_bisect_start, "BISECT_START")
@@ -707,26 +706,10 @@ static enum bisect_error error_if_skipped_commits(struct commit_list *tried,
 
 static int is_expected_rev(const struct object_id *oid)
 {
-	const char *filename = git_path_bisect_expected_rev();
-	struct stat st;
-	struct strbuf str = STRBUF_INIT;
-	FILE *fp;
-	int res = 0;
-
-	if (stat(filename, &st) || !S_ISREG(st.st_mode))
+	struct object_id expected_oid;
+	if (read_ref("BISECT_EXPECTED_REV", &expected_oid))
 		return 0;
-
-	fp = fopen_or_warn(filename, "r");
-	if (!fp)
-		return 0;
-
-	if (strbuf_getline_lf(&str, fp) != EOF)
-		res = !strcmp(str.buf, oid_to_hex(oid));
-
-	strbuf_release(&str);
-	fclose(fp);
-
-	return res;
+	return oideq(oid, &expected_oid);
 }
 
 enum bisect_error bisect_checkout(const struct object_id *bisect_rev,
@@ -1185,10 +1168,10 @@ int bisect_clean_state(void)
 	struct string_list refs_for_removal = STRING_LIST_INIT_NODUP;
 	for_each_ref_in("refs/bisect", mark_for_removal, (void *) &refs_for_removal);
 	string_list_append(&refs_for_removal, xstrdup("BISECT_HEAD"));
+	string_list_append(&refs_for_removal, xstrdup("BISECT_EXPECTED_REV"));
 	result = delete_refs("bisect: remove", &refs_for_removal, REF_NO_DEREF);
 	refs_for_removal.strdup_strings = 1;
 	string_list_clear(&refs_for_removal, 0);
-	unlink_or_warn(git_path_bisect_expected_rev());
 	unlink_or_warn(git_path_bisect_ancestors_ok());
 	unlink_or_warn(git_path_bisect_log());
 	unlink_or_warn(git_path_bisect_names());

builtin/bisect.c

@@ -17,7 +17,6 @@
 #include "revision.h"
 
 static GIT_PATH_FUNC(git_path_bisect_terms, "BISECT_TERMS")
-static GIT_PATH_FUNC(git_path_bisect_expected_rev, "BISECT_EXPECTED_REV")
 static GIT_PATH_FUNC(git_path_bisect_ancestors_ok, "BISECT_ANCESTORS_OK")
 static GIT_PATH_FUNC(git_path_bisect_start, "BISECT_START")
 static GIT_PATH_FUNC(git_path_bisect_log, "BISECT_LOG")
@@ -921,7 +920,6 @@ static enum bisect_error bisect_state(struct bisect_terms *terms, int argc,
 	const char *state;
 	int i, verify_expected = 1;
 	struct object_id oid, expected;
-	struct strbuf buf = STRBUF_INIT;
 	struct oid_array revs = OID_ARRAY_INIT;
 
 	if (!argc)
@@ -976,10 +974,8 @@ static enum bisect_error bisect_state(struct bisect_terms *terms, int argc,
 		oid_array_append(&revs, &commit->object.oid);
 	}
 
-	if (strbuf_read_file(&buf, git_path_bisect_expected_rev(), 0) < the_hash_algo->hexsz ||
-	    get_oid_hex(buf.buf, &expected) < 0)
+	if (read_ref("BISECT_EXPECTED_REV", &expected))
 		verify_expected = 0; /* Ignore invalid file contents */
-	strbuf_release(&buf);
 
 	for (i = 0; i < revs.nr; i++) {
 		if (bisect_write(state, oid_to_hex(&revs.oid[i]), terms, 0)) {
@@ -988,7 +984,7 @@ static enum bisect_error bisect_state(struct bisect_terms *terms, int argc,
 		}
 		if (verify_expected && !oideq(&revs.oid[i], &expected)) {
 			unlink_or_warn(git_path_bisect_ancestors_ok());
-			unlink_or_warn(git_path_bisect_expected_rev());
+			delete_ref(NULL, "BISECT_EXPECTED_REV", NULL, REF_NO_DEREF);
 			verify_expected = 0;
 		}
 	}

refs.c

@@ -1840,6 +1840,8 @@ static int is_special_ref(const char *refname)
 	 * There are some exceptions that you might expect to see on this list
 	 * but which are handled exclusively via the reference backend:
 	 *
+	 * - BISECT_EXPECTED_REV
+	 *
 	 * - CHERRY_PICK_HEAD
 	 *
 	 * - HEAD
@@ -1857,7 +1859,6 @@ static int is_special_ref(const char *refname)
 	 */
 	static const char * const special_refs[] = {
 		"AUTO_MERGE",
-		"BISECT_EXPECTED_REV",
 		"FETCH_HEAD",
 		"MERGE_AUTOSTASH",
 		"MERGE_HEAD",

t/t6030-bisect-porcelain.sh

@@ -1176,7 +1176,7 @@ test_expect_success 'git bisect reset cleans bisection state properly' '
 	git bisect bad $HASH4 &&
 	git bisect reset &&
 	test -z "$(git for-each-ref "refs/bisect/*")" &&
-	test_path_is_missing ".git/BISECT_EXPECTED_REV" &&
+	test_ref_missing BISECT_EXPECTED_REV &&
 	test_path_is_missing ".git/BISECT_ANCESTORS_OK" &&
 	test_path_is_missing ".git/BISECT_LOG" &&
 	test_path_is_missing ".git/BISECT_RUN" &&