kargs: fix corner case when append and append-if-missing with

the same value which will append twice

Consider a safe way to fix `corner case where --append foo
--append-if-missing foo would append foo twice`.

src/daemon/rpmostreed-transaction-types.cxx

@@ -2708,7 +2708,8 @@ kernel_arg_apply_patching (KernelArgTransaction *self, RpmOstreeSysrootUpgrader
   for (char **iter = append_if_missing; iter && *iter; iter++)
     {
       const char *arg = *iter;
-      if (!g_strv_contains (existing_kargs, arg))
+      g_auto (GStrv) kargs_strv = ostree_kernel_args_to_strv (kargs);
+      if (!g_strv_contains (kargs_strv, arg))
         {
           ostree_kernel_args_append (kargs, arg);
           changed = TRUE;

tests/vmcheck/test-kernel-args.sh

@@ -187,7 +187,18 @@ vm_rpmostree kargs > kargs.txt
 assert_file_has_content_literal kargs.txt 'PACKAGE3=NEWTEST'
 rpm-ostree kargs --delete-if-present=PACKAGE3=TEST || rc=$?
 assert_streq $rc 0
-vm_rpmostree kargs --delete-if-present=PACKAGE3=TEST3
+echo "ok for append-if-missing and delete-if-present if existing key"
+
+# Test corner case for append and append-if-missing with the same value
+vm_rpmostree kargs --append=foo --append-if-missing=foo
+vm_rpmostree kargs > kargs.txt
+assert_not_file_has_content_literal kargs.txt 'foo foo'
+assert_file_has_content_literal kargs.txt 'foo'
+vm_rpmostree kargs --append-if-missing=PACKAGE4=TEST4 --append-if-missing=PACKAGE4=TEST4
+vm_rpmostree kargs > kargs.txt
+assert_not_file_has_content_literal kargs.txt 'PACKAGE4=TEST4 PACKAGE4=TEST4'
+assert_file_has_content_literal kargs.txt 'PACKAGE4=TEST4'
+echo "ok for append and append-if-missing with the same value"
 
 # Test for 'rpm-ostree kargs --editor'.
 vm_rpmostree kargs > kargs.txt