[PATCH 5/5] pretty: avoid reading past end-of-string with "%G"

[Jeff King <peff@peff.net>]

If the user asks for --format=%G with nothing else, we
correctly realize that "%G" is not a valid placeholder (it
should be "%G?", "%GK", etc). But we still tell the
strbuf_expand code that we consumed 2 characters, causing it
to jump over the trailing NUL and output garbage.

This also fixes the case where "%GX" would be consumed (and
produce no output). In other cases, we pass unrecognized
placeholders through to the final string.

Signed-off-by: Jeff King <peff@peff.net>
---
Same as before, but with the test included along with the fix, rather
than in another commit.

 pretty.c                 | 2 ++
 t/t7510-signed-commit.sh | 6 ++++++
 2 files changed, 8 insertions(+)

diff --git a/pretty.c b/pretty.c
index e1e2cad..70d8776 100644
--- a/pretty.c
+++ b/pretty.c
@@ -1267,6 +1267,8 @@ static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
 			if (c->signature_check.key)
 				strbuf_addstr(sb, c->signature_check.key);
 			break;
+		default:
+			return 0;
 		}
 		return 2;
 	}
diff --git a/t/t7510-signed-commit.sh b/t/t7510-signed-commit.sh
index e97477a..9810242 100755
--- a/t/t7510-signed-commit.sh
+++ b/t/t7510-signed-commit.sh
@@ -147,4 +147,10 @@ test_expect_success GPG 'show lack of signature with custom format' '
 	test_cmp expect actual
 '
 
+test_expect_success 'unused %G placeholders are passed through' '
+	echo "%GX %G" >expect &&
+	git log -1 --format="%GX %G" >actual &&
+	test_cmp expect actual
+'
+
 test_done
-- 
2.0.0.566.gfe3e6b2