Make copyClosureTo take a regular C++ ref to the store

This is syntactically lighter wait, and demonstates there are no weird
dynamic lifetimes involved, just regular passing reference to callee
which it only borrows for the duration of the call.

src/hydra-queue-runner/build-remote.cc

@@ -104,29 +104,29 @@ static void openConnection(Machine::ptr machine, Path tmpDir, int stderrFD, Chil
 }
 
 
-static void copyClosureTo(std::timed_mutex & sendMutex, ref<Store> destStore,
+static void copyClosureTo(std::timed_mutex & sendMutex, Store & destStore,
     FdSource & from, FdSink & to, const StorePathSet & paths,
     bool useSubstitutes = false)
 {
     StorePathSet closure;
-    destStore->computeFSClosure(paths, closure);
+    destStore.computeFSClosure(paths, closure);
 
     /* Send the "query valid paths" command with the "lock" option
        enabled. This prevents a race where the remote host
        garbage-collect paths that are already there. Optionally, ask
        the remote host to substitute missing paths. */
     // FIXME: substitute output pollutes our build log
     to << cmdQueryValidPaths << 1 << useSubstitutes;
-    worker_proto::write(*destStore, to, closure);
+    worker_proto::write(destStore, to, closure);
     to.flush();
 
     /* Get back the set of paths that are already valid on the remote
        host. */
-    auto present = worker_proto::read(*destStore, from, Phantom<StorePathSet> {});
+    auto present = worker_proto::read(destStore, from, Phantom<StorePathSet> {});
 
     if (present.size() == closure.size()) return;
 
-    auto sorted = destStore->topoSortPaths(closure);
+    auto sorted = destStore.topoSortPaths(closure);
 
     StorePathSet missing;
     for (auto i = sorted.rbegin(); i != sorted.rend(); ++i)
@@ -138,7 +138,7 @@ static void copyClosureTo(std::timed_mutex & sendMutex, ref<Store> destStore,
         std::chrono::seconds(600));
 
     to << cmdImportPaths;
-    destStore->exportPaths(missing, to);
+    destStore.exportPaths(missing, to);
     to.flush();
 
     if (readInt(from) != 1)
@@ -308,7 +308,7 @@ void State::buildRemote(ref<Store> destStore,
                 destStore->computeFSClosure(inputs, closure);
                 copyPaths(*destStore, *localStore, closure, NoRepair, NoCheckSigs, NoSubstitute);
             } else {
-                copyClosureTo(machine->state->sendLock, destStore, from, to, inputs, true);
+                copyClosureTo(machine->state->sendLock, *destStore, from, to, inputs, true);
             }
 
             auto now2 = std::chrono::steady_clock::now();