bisect--helper: reimplement bisect_state & bisect_head shell functions in C

Reimplement the `bisect_state()` shell functions in C and also add a
subcommand `--bisect-state` to `git-bisect--helper` to call them from
git-bisect.sh .

Using `--bisect-state` subcommand is a temporary measure to port shell
function to C so as to use the existing test suite. As more functions
are ported, this subcommand will be retired and will be called by some
other methods.

`bisect_head()` is only called from `bisect_state()`, thus it is not
required to introduce another subcommand.

Note that the `eval` in the changed line of `git-bisect.sh` cannot be
dropped: it is necessary because the `rev` and the `tail`
variables may contain multiple, quoted arguments that need to be
passed to `bisect--helper` (without the quotes, naturally).

Mentored-by: Lars Schneider <larsxschneider@gmail.com>
Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Mentored-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Pranit Bauva <pranit.bauva@gmail.com>
Signed-off-by: Tanushree Tumane <tanushreetumane@gmail.com>
Signed-off-by: Miriam Rubio <mirucam@gmail.com>
Reviewed-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/bisect--helper.c

@@ -31,6 +31,8 @@ static const char * const git_bisect_helper_usage[] = {
 	N_("git bisect--helper --bisect-next"),
 	N_("git bisect--helper --bisect-auto-next"),
 	N_("git bisect--helper --bisect-autostart"),
+	N_("git bisect--helper --bisect-state (bad|new) [<rev>]"),
+	N_("git bisect--helper --bisect-state (good|old) [<rev>...]"),
 	NULL
 };
 
@@ -855,6 +857,80 @@ static int bisect_autostart(struct bisect_terms *terms)
 	return res;
 }
 
+static enum bisect_error bisect_state(struct bisect_terms *terms, const char **argv,
+				      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)
+		return error(_("Please call `--bisect-state` with at least one argument"));
+
+	if (bisect_autostart(terms))
+		return BISECT_FAILED;
+
+	state = argv[0];
+	if (check_and_set_terms(terms, state) ||
+	    !one_of(state, terms->term_good, terms->term_bad, "skip", NULL))
+		return BISECT_FAILED;
+
+	argv++;
+	argc--;
+	if (argc > 1 && !strcmp(state, terms->term_bad))
+		return error(_("'git bisect %s' can take only one argument."), terms->term_bad);
+
+	if (argc == 0) {
+		const char *head = "BISECT_HEAD";
+		enum get_oid_result res_head = get_oid(head, &oid);
+
+		if (res_head == MISSING_OBJECT) {
+			head = "HEAD";
+			res_head = get_oid(head, &oid);
+		}
+
+		if (res_head)
+			error(_("Bad rev input: %s"), head);
+		oid_array_append(&revs, &oid);
+	}
+
+	/*
+	 * All input revs must be checked before executing bisect_write()
+	 * to discard junk revs.
+	 */
+
+	for (; argc; argc--, argv++) {
+		if (get_oid(*argv, &oid)){
+			error(_("Bad rev input: %s"), *argv);
+			oid_array_clear(&revs);
+			return BISECT_FAILED;
+		}
+		oid_array_append(&revs, &oid);
+	}
+
+	if (strbuf_read_file(&buf, git_path_bisect_expected_rev(), 0) < the_hash_algo->hexsz ||
+	    get_oid_hex(buf.buf, &expected) < 0)
+		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)) {
+			oid_array_clear(&revs);
+			return BISECT_FAILED;
+		}
+		if (verify_expected && !oideq(&revs.oid[i], &expected)) {
+			unlink_or_warn(git_path_bisect_ancestors_ok());
+			unlink_or_warn(git_path_bisect_expected_rev());
+			verify_expected = 0;
+		}
+	}
+
+	oid_array_clear(&revs);
+	return bisect_auto_next(terms, NULL);
+}
+
 int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
 {
 	enum {
@@ -868,7 +944,8 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
 		BISECT_START,
 		BISECT_AUTOSTART,
 		BISECT_NEXT,
-		BISECT_AUTO_NEXT
+		BISECT_AUTO_NEXT,
+		BISECT_STATE
 	} cmdmode = 0;
 	int res = 0, nolog = 0;
 	struct option options[] = {
@@ -894,6 +971,8 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
 			 N_("verify the next bisection state then checkout the next bisection commit"), BISECT_AUTO_NEXT),
 		OPT_CMDMODE(0, "bisect-autostart", &cmdmode,
 			 N_("start the bisection if it has not yet been started"), BISECT_AUTOSTART),
+		OPT_CMDMODE(0, "bisect-state", &cmdmode,
+			 N_("mark the state of ref (or refs)"), BISECT_STATE),
 		OPT_BOOL(0, "no-log", &nolog,
 			 N_("no log for BISECT_WRITE")),
 		OPT_END()
@@ -964,6 +1043,11 @@ int cmd_bisect__helper(int argc, const char **argv, const char *prefix)
 		set_terms(&terms, "bad", "good");
 		res = bisect_autostart(&terms);
 		break;
+	case BISECT_STATE:
+		set_terms(&terms, "bad", "good");
+		get_terms(&terms);
+		res = bisect_state(&terms, argv, argc);
+		break;
 	default:
 		BUG("unknown subcommand %d", cmdmode);
 	}