shared: end string with % if one was found at the end of a expandible string (#6828)

Current behavior is that %X where X is an unidentified specifier, then the result is
the same %X string. This was not the case when the string ended with a stray %, where
the character would have not been output. Lets add that missing character.

Fixes: #6374

2 files changed, 6 insertions, 1 deletions

diff --git a/src/shared/specifier.c b/src/shared/specifier.c
index 1c17eb5251..81379041cc 100644
--- a/src/shared/specifier.c
+++ b/src/shared/specifier.c
@@ -107,6 +107,10 @@ int specifier_printf(const char *text, const Specifier table[], void *userdata,
                         *(t++) = *f;
         }
 
+        /* if string ended with a stray %, also end with % */
+        if (percent)
+                *(t++) = '%';
+
         *t = 0;
         *_ret = ret;
         return 0;
diff --git a/src/test/test-unit-name.c b/src/test/test-unit-name.c
index b8979c0e95..dcccc9080c 100644
--- a/src/test/test-unit-name.c
+++ b/src/test/test-unit-name.c
@@ -237,7 +237,8 @@ static int test_unit_printf(void) {
         /* general tests */
         expect(u, "%%", "%");
         expect(u, "%%s", "%s");
-        expect(u, "%", "");    // REALLY?
+        expect(u, "%,", "%,");
+        expect(u, "%", "%");
 
         /* normal unit */
         expect(u, "%n", "blah.service");