libcmd: add raw arg access to legacy commands

we'll need this to modify argv for socket-activated daemons. this is our
replacement for the old savedArgv mechanism that was unscoped and fucky.

Change-Id: Ie048eb8ea99f1c9cd627a051292c836c83197068

lix/libcmd/legacy.hh

@@ -5,18 +5,32 @@
 #include <functional>
 #include <list>
 #include <map>
+#include <span>
 #include <string>
 
 namespace nix {
 
-typedef std::function<int(AsyncIoRoot &, std::string, std::list<std::string>)> MainFunction;
-
 struct LegacyCommandRegistry
 {
-    using LegacyCommandMap = std::map<std::string, MainFunction>;
+    typedef std::function<int(AsyncIoRoot &, std::string, std::list<std::string>)> MainFunction;
+    typedef std::function<
+        int(AsyncIoRoot &, std::string, std::list<std::string>, std::span<char *>)>
+        RawMainFunction;
+
+    using LegacyCommandMap = std::map<std::string, RawMainFunction>;
     static LegacyCommandMap * commands;
 
     static void add(const std::string & name, MainFunction fun)
+    {
+        addWithRaw(
+            name,
+            [fun](AsyncIoRoot & aio, std::string name, std::list<std::string> args, std::span<char *>) {
+                return fun(aio, name, args);
+            }
+        );
+    }
+
+    static void addWithRaw(const std::string & name, RawMainFunction fun)
     {
         if (!commands) commands = new LegacyCommandMap;
         (*commands)[name] = fun;

lix/nix/main.cc

@@ -491,7 +491,12 @@ int mainWrapped(AsyncIoRoot & aio, int argc, char ** argv)
         registerLegacyCommands();
         auto legacy = (*LegacyCommandRegistry::commands)[programName];
         if (legacy) {
-            return legacy(aio, std::string(baseNameOf(argv[0])), Strings(argv + 1, argv + argc));
+            return legacy(
+                aio,
+                std::string(baseNameOf(argv[0])),
+                Strings(argv + 1, argv + argc),
+                {argv + 1, argv + argc}
+            );
         }
     }