build-remote: Add dependencies as temproots on the remote

Otherwise dependencies can be removed from under builds if the remote
store runs a GC.

Author: dramforever

src/nix/build-remote/build-remote.cc

@@ -305,7 +305,15 @@ static int main_build_remote(int argc, char ** argv)
 
         {
             Activity act(*logger, lvlTalkative, actUnknown, fmt("copying dependencies to '%s'", storeUri));
-            copyPaths(*store, *sshStore, store->parseStorePathSet(inputs), NoRepair, NoCheckSigs, substitute);
+
+            auto storePaths = store->parseStorePathSet(inputs);
+
+            /* We don't have goals on the remote tracking our dependencies as
+               temp roots, so add them as temproots ourselves. */
+            for (auto & path : storePaths)
+                sshStore->addTempRoot(path);
+
+            copyPaths(*store, *sshStore, storePaths, NoRepair, NoCheckSigs, substitute);
         }
 
         uploadLock = -1;