[PATCH 1/4] object-name: do not read a peel suffix as a reflog selector

[Caspar Duregger <caspar.duregger@gmail.com>]

To find a "@{...}" reflog selector, get_oid_basic() checks that the
name ends in '}' and then takes the last "@{" in it.

For "HEAD@{1}^{blob}" the final '}' closes "^{blob}", nevertheless we
take "1}^{blob" as the selector. That is not a number, so it goes to
approxidate_careful(), which accepts it without complaint as "now".
The name then resolves to the current value of HEAD.

We only parse the whole string like this after peel_onion() has
failed, so a peel that should fail succeeds with the wrong object:

    $ git rev-parse --verify 'HEAD@{1}^{/no-such-subject}'
    <object name of HEAD>

Only accept a selector whose "@{" is closed by the final '}'. Reflog
selectors never contain a '}', so no valid selector is rejected.

Signed-off-by: Caspar Duregger <caspar.duregger@gmail.com>
---
 object-name.c              | 6 ++++++
 t/t1508-at-combinations.sh | 4 ++++
 2 files changed, 10 insertions(+)

diff --git a/object-name.c b/object-name.c
index 6546685760..13e4dc0f21 100644
--- a/object-name.c
+++ b/object-name.c
@@ -712,6 +712,12 @@ static int get_oid_basic(struct repository *r, const char *str, int len,
 					nth_prior = 1;
 					continue;
 				}
+				/*
+				 * The final '}' must close this "@{", not a
+				 * later suffix as in "ref@{1}^{tree}".
+				 */
+				if (memchr(str + at + 2, '}', len - at - 3))
+					break;
 				if (!upstream_mark(str + at, len - at) &&
 				    !push_mark(str + at, len - at)) {
 					reflog_len = (len-1) - (at+2);
diff --git a/t/t1508-at-combinations.sh b/t/t1508-at-combinations.sh
index 87a4286414..10a8c3ad9d 100755
--- a/t/t1508-at-combinations.sh
+++ b/t/t1508-at-combinations.sh
@@ -84,6 +84,10 @@ nonsense "@{-1}@{-1}"
 check "HEAD@{3}" commit old-two
 nonsense "@{3}"
 
+# a failed peel must not be retried as a reflog date
+nonsense "HEAD@{1}^{blob}"
+nonsense "@{1}^{/no-such-subject}"
+
 test_expect_success 'switch to old-branch' '
 	git checkout old-branch
 '
-- 
2.56.1.windows.1