core: refresh unit cache when building a transaction if UNIT_NOT_FOUND

When a command asks to load a unit directly and it is in state
UNIT_NOT_FOUND, and the cache is outdated, we refresh it and
attempto to load again.
Use the same logic when building up a transaction and a dependency in
UNIT_NOT_FOUND state is encountered.
Update the unit test to exercise this code path.

1 files changed, 18 insertions, 0 deletions

diff --git a/src/core/transaction.c b/src/core/transaction.c
index ef6470656c..4a57b8e3f9 100644
--- a/src/core/transaction.c
+++ b/src/core/transaction.c
@@ -954,6 +954,24 @@ int transaction_add_job_and_dependencies(
 
         if (type != JOB_STOP) {
                 r = bus_unit_validate_load_state(unit, e);
+                /* The time-based cache allows to start new units without daemon-reload,
+                 * but if they are already referenced (because of dependencies or ordering)
+                 * then we have to force a load of the fragment. As an optimization, check
+                 * first if anything in the usual paths was modified since the last time
+                 * the cache was loaded. Also check if the last time an attempt to load the
+                 * unit was made was before the most recent cache refresh, so that we know
+                 * we need to try again - even if the cache is current, it might have been
+                 * updated in a different context before we had a chance to retry loading
+                 * this particular unit.
+                 * Given building up the transaction is a synchronous operation, attempt
+                 * to load the unit immediately. */
+                if (r < 0 && manager_unit_file_maybe_loadable_from_cache(unit)) {
+                        unit->load_state = UNIT_STUB;
+                        r = unit_load(unit);
+                        if (r < 0 || unit->load_state == UNIT_STUB)
+                                unit->load_state = UNIT_NOT_FOUND;
+                        r = bus_unit_validate_load_state(unit, e);
+                }
                 if (r < 0)
                         return r;
         }