Merge branch 'dl/reflog-with-single-entry'

After expiring a reflog and making a single commit, the reflog for
the branch would record a single entry that knows both @{0} and
@{1}, but we failed to answer "what commit were we on?", i.e. @{1}

* dl/reflog-with-single-entry:
  refs: allow @{n} to work with n-sized reflog
  refs: factor out set_read_ref_cutoffs()

3 files changed, 63 insertions, 32 deletions

diff --git a/refs.c b/refs.c
index 13dc2c3291..03968ad787 100644
--- a/refs.c
+++ b/refs.c
@@ -882,51 +882,71 @@ struct read_ref_at_cb {
 	int *cutoff_cnt;
 };
 
+static void set_read_ref_cutoffs(struct read_ref_at_cb *cb,
+		timestamp_t timestamp, int tz, const char *message)
+{
+	if (cb->msg)
+		*cb->msg = xstrdup(message);
+	if (cb->cutoff_time)
+		*cb->cutoff_time = timestamp;
+	if (cb->cutoff_tz)
+		*cb->cutoff_tz = tz;
+	if (cb->cutoff_cnt)
+		*cb->cutoff_cnt = cb->reccnt;
+}
+
 static int read_ref_at_ent(struct object_id *ooid, struct object_id *noid,
 		const char *email, timestamp_t timestamp, int tz,
 		const char *message, void *cb_data)
 {
 	struct read_ref_at_cb *cb = cb_data;
+	int reached_count;
 
-	cb->reccnt++;
 	cb->tz = tz;
 	cb->date = timestamp;
 
-	if (timestamp <= cb->at_time || cb->cnt == 0) {
-		if (cb->msg)
-			*cb->msg = xstrdup(message);
-		if (cb->cutoff_time)
-			*cb->cutoff_time = timestamp;
-		if (cb->cutoff_tz)
-			*cb->cutoff_tz = tz;
-		if (cb->cutoff_cnt)
-			*cb->cutoff_cnt = cb->reccnt - 1;
+	/*
+	 * It is not possible for cb->cnt == 0 on the first iteration because
+	 * that special case is handled in read_ref_at().
+	 */
+	if (cb->cnt > 0)
+		cb->cnt--;
+	reached_count = cb->cnt == 0 && !is_null_oid(ooid);
+	if (timestamp <= cb->at_time || reached_count) {
+		set_read_ref_cutoffs(cb, timestamp, tz, message);
 		/*
 		 * we have not yet updated cb->[n|o]oid so they still
 		 * hold the values for the previous record.
 		 */
-		if (!is_null_oid(&cb->ooid)) {
-			oidcpy(cb->oid, noid);
-			if (!oideq(&cb->ooid, noid))
-				warning(_("log for ref %s has gap after %s"),
+		if (!is_null_oid(&cb->ooid) && !oideq(&cb->ooid, noid))
+			warning(_("log for ref %s has gap after %s"),
 					cb->refname, show_date(cb->date, cb->tz, DATE_MODE(RFC2822)));
-		}
-		else if (cb->date == cb->at_time)
+		if (reached_count)
+			oidcpy(cb->oid, ooid);
+		else if (!is_null_oid(&cb->ooid) || cb->date == cb->at_time)
 			oidcpy(cb->oid, noid);
 		else if (!oideq(noid, cb->oid))
 			warning(_("log for ref %s unexpectedly ended on %s"),
 				cb->refname, show_date(cb->date, cb->tz,
 						       DATE_MODE(RFC2822)));
-		oidcpy(&cb->ooid, ooid);
-		oidcpy(&cb->noid, noid);
 		cb->found_it = 1;
-		return 1;
 	}
+	cb->reccnt++;
 	oidcpy(&cb->ooid, ooid);
 	oidcpy(&cb->noid, noid);
-	if (cb->cnt > 0)
-		cb->cnt--;
-	return 0;
+	return cb->found_it;
+}
+
+static int read_ref_at_ent_newest(struct object_id *ooid, struct object_id *noid,
+				  const char *email, timestamp_t timestamp,
+				  int tz, const char *message, void *cb_data)
+{
+	struct read_ref_at_cb *cb = cb_data;
+
+	set_read_ref_cutoffs(cb, timestamp, tz, message);
+	oidcpy(cb->oid, noid);
+	/* We just want the first entry */
+	return 1;
 }
 
 static int read_ref_at_ent_oldest(struct object_id *ooid, struct object_id *noid,
@@ -935,14 +955,7 @@ static int read_ref_at_ent_oldest(struct object_id *ooid, struct object_id *noid
 {
 	struct read_ref_at_cb *cb = cb_data;
 
-	if (cb->msg)
-		*cb->msg = xstrdup(message);
-	if (cb->cutoff_time)
-		*cb->cutoff_time = timestamp;
-	if (cb->cutoff_tz)
-		*cb->cutoff_tz = tz;
-	if (cb->cutoff_cnt)
-		*cb->cutoff_cnt = cb->reccnt;
+	set_read_ref_cutoffs(cb, timestamp, tz, message);
 	oidcpy(cb->oid, ooid);
 	if (is_null_oid(cb->oid))
 		oidcpy(cb->oid, noid);
@@ -967,6 +980,11 @@ int read_ref_at(struct ref_store *refs, const char *refname,
 	cb.cutoff_cnt = cutoff_cnt;
 	cb.oid = oid;
 
+	if (cb.cnt == 0) {
+		refs_for_each_reflog_ent_reverse(refs, refname, read_ref_at_ent_newest, &cb);
+		return 0;
+	}
+
 	refs_for_each_reflog_ent_reverse(refs, refname, read_ref_at_ent, &cb);
 
 	if (!cb.reccnt) {
diff --git a/t/t1503-rev-parse-verify.sh b/t/t1503-rev-parse-verify.sh
index dc9fe3cbf1..a7e9b4863d 100755
--- a/t/t1503-rev-parse-verify.sh
+++ b/t/t1503-rev-parse-verify.sh
@@ -86,8 +86,8 @@ test_expect_success 'fails silently when using -q' '
 test_expect_success 'fails silently when using -q with deleted reflogs' '
 	ref=$(git rev-parse HEAD) &&
 	git update-ref --create-reflog -m "message for refs/test" refs/test "$ref" &&
-	git reflog delete --updateref --rewrite refs/test@{0} &&
-	test_must_fail git rev-parse -q --verify refs/test@{0} >error 2>&1 &&
+	git reflog delete --updateref --rewrite refs/test@{1} &&
+	test_must_fail git rev-parse -q --verify refs/test@{1} >error 2>&1 &&
 	test_must_be_empty error
 '
 
diff --git a/t/t1508-at-combinations.sh b/t/t1508-at-combinations.sh
index 4a9964e9dc..e4521b7b97 100755
--- a/t/t1508-at-combinations.sh
+++ b/t/t1508-at-combinations.sh
@@ -99,4 +99,17 @@ test_expect_success 'create path with @' '
 check "@:normal" blob content
 check "@:fun@ny" blob content
 
+test_expect_success '@{1} works with only one reflog entry' '
+	git checkout -B newbranch master &&
+	git reflog expire --expire=now refs/heads/newbranch &&
+	git commit --allow-empty -m "first after expiration" &&
+	test_cmp_rev newbranch~ newbranch@{1}
+'
+
+test_expect_success '@{0} works with empty reflog' '
+	git checkout -B newbranch master &&
+	git reflog expire --expire=now refs/heads/newbranch &&
+	test_cmp_rev newbranch newbranch@{0}
+'
+
 test_done