Make subcommand construction in MultiCommand lazy

(cherry picked from commit a0de58f471c9087d8e6cc60a6078f9940a125b15)

2 files changed, 17 insertions, 11 deletions

diff --git a/src/libutil/args.cc b/src/libutil/args.cc
index 2837dacc9..217495c26 100644
--- a/src/libutil/args.cc
+++ b/src/libutil/args.cc
@@ -215,17 +215,15 @@ void Command::printHelp(const string & programName, std::ostream & out)
     }
 }
 
-MultiCommand::MultiCommand(const std::vector<ref<Command>> & _commands)
+MultiCommand::MultiCommand(const Commands & commands)
+    : commands(commands)
 {
-    for (auto & command : _commands)
-        commands.emplace(command->name(), command);
-
     expectedArgs.push_back(ExpectedArg{"command", 1, true, [=](std::vector<std::string> ss) {
         assert(!command);
         auto i = commands.find(ss[0]);
         if (i == commands.end())
             throw UsageError("'%s' is not a recognised command", ss[0]);
-        command = i->second;
+        command = i->second();
     }});
 }
 
@@ -246,10 +244,11 @@ void MultiCommand::printHelp(const string & programName, std::ostream & out)
     out << "Available commands:\n";
 
     Table2 table;
-    for (auto & command : commands) {
-        auto descr = command.second->description();
+    for (auto & i : commands) {
+        auto command = i.second();
+        auto descr = command->description();
         if (!descr.empty())
-            table.push_back(std::make_pair(command.second->name(), descr));
+            table.push_back(std::make_pair(command->name(), descr));
     }
     printTable(out, table);
 }
diff --git a/src/libutil/args.hh b/src/libutil/args.hh
index 21f4327c5..54336b17b 100644
--- a/src/libutil/args.hh
+++ b/src/libutil/args.hh
@@ -192,8 +192,15 @@ public:
    run() method. */
 struct Command : virtual Args
 {
+private:
+    std::string _name;
+
+public:
+
     virtual ~Command() { }
-    virtual std::string name() = 0;
+
+    std::string name() { return _name; }
+
     virtual void prepare() { };
     virtual void run() = 0;
 
@@ -210,7 +217,7 @@ struct Command : virtual Args
     void printHelp(const string & programName, std::ostream & out) override;
 };
 
-typedef std::map<std::string, ref<Command>> Commands;
+typedef std::map<std::string, std::function<ref<Command>()>> Commands;
 
 /* An argument parser that supports multiple subcommands,
    i.e. ‘<command> <subcommand>’. */
@@ -221,7 +228,7 @@ public:
 
     std::shared_ptr<Command> command;
 
-    MultiCommand(const std::vector<ref<Command>> & commands);
+    MultiCommand(const Commands & commands);
 
     void printHelp(const string & programName, std::ostream & out) override;