Make subcommand construction in MultiCommand lazy

(cherry picked from commit a0de58f471c9087d8e6cc60a6078f9940a125b15)

1 files changed, 11 insertions, 4 deletions

diff --git a/src/nix/command.hh b/src/nix/command.hh
index aa34301d9..7474c5eae 100644
--- a/src/nix/command.hh
+++ b/src/nix/command.hh
@@ -151,15 +151,22 @@ struct StorePathCommand : public InstallablesCommand
 /* A helper class for registering commands globally. */
 struct RegisterCommand
 {
-    static std::vector<ref<Command>> * commands;
+    static Commands * commands;
 
-    RegisterCommand(ref<Command> command)
+    RegisterCommand(const std::string & name,
+        std::function<ref<Command>()> command)
     {
-        if (!commands) commands = new std::vector<ref<Command>>;
-        commands->push_back(command);
+        if (!commands) commands = new Commands;
+        commands->emplace(name, command);
     }
 };
 
+template<class T>
+static RegisterCommand registerCommand(const std::string & name)
+{
+    return RegisterCommand(name, [](){ return make_ref<T>(); });
+}
+
 std::shared_ptr<Installable> parseInstallable(
     SourceExprCommand & cmd, ref<Store> store, const std::string & installable,
     bool useDefaultInstallables);