rev-list: fix --pretty=oneline with empty message

55246aa (Dont use "<unknown>" for placeholders and suppress printing
of empty user formats) introduced a check to prevent empty
user-formats from being printed. This test didn't take empty commit
messages into account, and prevented the line-termination from being
output. This lead to multiple commits on a single line.

Correct it by guarding the check with a check for user-format. A
similar correction for the --graph code-path has been included.

Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-rev-list.c

@@ -133,9 +133,12 @@ static void show_commit(struct commit *commit, void *data)
 				 */
 				if (graph_show_remainder(revs->graph))
 					putchar('\n');
+				if (revs->commit_format == CMIT_FMT_ONELINE)
+					putchar('\n');
 			}
 		} else {
-			if (buf.len)
+			if (revs->commit_format != CMIT_FMT_USERFORMAT ||
+			    buf.len)
 				printf("%s%c", buf.buf, info->hdr_termination);
 		}
 		strbuf_release(&buf);

t/t6006-rev-list-format.sh

@@ -209,4 +209,13 @@ test_expect_success '%gd shortens ref name' '
 	test_cmp expect.gd-short actual.gd-short
 '
 
+test_expect_success 'oneline with empty message' '
+	git commit -m "dummy" --allow-empty &&
+	git commit -m "dummy" --allow-empty &&
+	git filter-branch --msg-filter "sed -e s/dummy//" HEAD^^.. &&
+	git rev-list --oneline HEAD > /tmp/test.txt &&
+	test $(git rev-list --oneline HEAD | wc -l) -eq 5 &&
+	test $(git rev-list --oneline --graph HEAD | wc -l) -eq 5
+'
+
 test_done