[PATCH v2] bisect: don't use invalid oid as rev when starting

[Christian Couder <christian.couder@gmail.com>]

In 06f5608c14 (bisect--helper: `bisect_start` shell function
partially in C, 2019-01-02), we changed the following shell
code:

-                       rev=$(git rev-parse -q --verify "$arg^{commit}") || {
-                               test $has_double_dash -eq 1 &&
-                               die "$(eval_gettext "'\$arg' does not appear to be a valid revision")"
-                               break
-                       }
-                       revs="$revs $rev"

into:

+                       char *commit_id = xstrfmt("%s^{commit}", arg);
+                       if (get_oid(commit_id, &oid) && has_double_dash)
+                               die(_("'%s' does not appear to be a valid "
+                                     "revision"), arg);
+
+                       string_list_append(&revs, oid_to_hex(&oid));
+                       free(commit_id);

In case of an invalid "arg" when "has_double_dash" is false, the old
code would "break" out of the argument loop.

In the new C code though, `oid_to_hex(&oid)` is unconditonally
appended to "revs". This is wrong first because "oid" is junk as
`get_oid(commit_id, &oid)` failed and second because it doesn't break
out of the argument loop.

Not breaking out of the argument loop means that "arg" is then not
treated as a path restriction.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
This patch is made on top of e1cfff6765 (Sixteenth batch, 2020-09-22)
and incorporates Dscho's suggestions.

Thanks to Junio and Dscho for reviewing the first version.

 builtin/bisect--helper.c    | 14 ++++++--------
 t/t6030-bisect-porcelain.sh |  7 +++++++
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/builtin/bisect--helper.c b/builtin/bisect--helper.c
index 7dcc1b5188..f4762e1774 100644
--- a/builtin/bisect--helper.c
+++ b/builtin/bisect--helper.c
@@ -484,15 +484,13 @@ static int bisect_start(struct bisect_terms *terms, const char **argv, int argc)
 			terms->term_bad = xstrdup(arg);
 		} else if (starts_with(arg, "--")) {
 			return error(_("unrecognized option: '%s'"), arg);
-		} else {
-			char *commit_id = xstrfmt("%s^{commit}", arg);
-			if (get_oid(commit_id, &oid) && has_double_dash)
-				die(_("'%s' does not appear to be a valid "
-				      "revision"), arg);
-
+		} else if (!get_oid_committish(arg, &oid))
 			string_list_append(&revs, oid_to_hex(&oid));
-			free(commit_id);
-		}
+		else if (has_double_dash)
+			die(_("'%s' does not appear to be a valid "
+			      "revision"), arg);
+		else
+			break;
 	}
 	pathspec_pos = i;
 
diff --git a/t/t6030-bisect-porcelain.sh b/t/t6030-bisect-porcelain.sh
index b886529e59..70c39a9459 100755
--- a/t/t6030-bisect-porcelain.sh
+++ b/t/t6030-bisect-porcelain.sh
@@ -82,6 +82,13 @@ test_expect_success 'bisect fails if given any junk instead of revs' '
 	git bisect bad $HASH4
 '
 
+test_expect_success 'bisect start without -- uses unknown arg as path restriction' '
+	git bisect reset &&
+	git bisect start foo bar &&
+	grep foo ".git/BISECT_NAMES" &&
+	grep bar ".git/BISECT_NAMES"
+'
+
 test_expect_success 'bisect reset: back in the master branch' '
 	git bisect reset &&
 	echo "* master" > branch.expect &&
-- 
2.28.0.585.ge1cfff6765