shared/install: fix DefaultInstance expansion in %n, %N

We should substitute DefaultInstance if the instance is not specified.

Test case:
[Install]
DefaultInstance=bond1
WantedBy= foobar-n-%n.device
WantedBy= foobar-N-%N.device

$ systemctl --root=/ enable testing4@.service
Created symlink /etc/systemd/system/foobar-n-testing4@bond1.service.device.wants/testing4@bond1.service → /etc/systemd/system/testing4@.service.
Created symlink /etc/systemd/system/foobar-N-testing4@bond1.device.wants/testing4@bond1.service → /etc/systemd/system/testing4@.service.

(before, the symlink would be created with empty %n, %N parts).

1 files changed, 38 insertions, 4 deletions

diff --git a/src/shared/install-printf.c b/src/shared/install-printf.c
index 9fc915d62e..267762d84f 100644
--- a/src/shared/install-printf.c
+++ b/src/shared/install-printf.c
@@ -32,15 +32,49 @@
 #include "user-util.h"
 
 static int specifier_prefix_and_instance(char specifier, void *data, void *userdata, char **ret) {
-        UnitFileInstallInfo *i = userdata;
+        const UnitFileInstallInfo *i = userdata;
+        _cleanup_free_ char *prefix = NULL;
+        int r;
+
+        assert(i);
+
+        r = unit_name_to_prefix_and_instance(i->name, &prefix);
+        if (r < 0)
+                return r;
+
+        if (endswith(prefix, "@") && i->default_instance) {
+                char *ans;
+
+                ans = strjoin(prefix, i->default_instance, NULL);
+                if (!ans)
+                        return -ENOMEM;
+                *ret = ans;
+        } else {
+                *ret = prefix;
+                prefix = NULL;
+        }
+
+        return 0;
+}
+
+static int specifier_name(char specifier, void *data, void *userdata, char **ret) {
+        const UnitFileInstallInfo *i = userdata;
+        char *ans;
 
         assert(i);
 
-        return unit_name_to_prefix_and_instance(i->name, ret);
+        if (unit_name_is_valid(i->name, UNIT_NAME_TEMPLATE) && i->default_instance)
+                return unit_name_replace_instance(i->name, i->default_instance, ret);
+
+        ans = strdup(i->name);
+        if (!ans)
+                return -ENOMEM;
+        *ret = ans;
+        return 0;
 }
 
 static int specifier_prefix(char specifier, void *data, void *userdata, char **ret) {
-        UnitFileInstallInfo *i = userdata;
+        const UnitFileInstallInfo *i = userdata;
 
         assert(i);
 
@@ -111,7 +145,7 @@ int install_full_printf(UnitFileInstallInfo *i, const char *format, char **ret)
          */
 
         const Specifier table[] = {
-                { 'n', specifier_string,              i->name },
+                { 'n', specifier_name,                NULL },
                 { 'N', specifier_prefix_and_instance, NULL },
                 { 'p', specifier_prefix,              NULL },
                 { 'i', specifier_instance,            NULL },