nix: Make all options available as flags

Thus, instead of ‘--option <name> <value>’, you can write ‘--<name>
<value>’. So

  --option http-connections 100

becomes

  --http-connections 100

Apart from brevity, the difference is that it's not an error to set a
non-existent option via --option, but unrecognized arguments are
fatal.

Boolean options have special treatment: they're mapped to the
argument-less flags ‘--<name>’ and ‘--no-<name>’. E.g.

  --option auto-optimise-store false

becomes

  --no-auto-optimise-store

1 files changed, 7 insertions, 0 deletions

diff --git a/src/libstore/globals.cc b/src/libstore/globals.cc
index 3dd2508a2..3f2bea8e7 100644
--- a/src/libstore/globals.cc
+++ b/src/libstore/globals.cc
@@ -98,6 +98,13 @@ template<> void BaseSetting<SandboxMode>::toJSON(JSONPlaceholder & out)
     AbstractSetting::toJSON(out);
 }
 
+template<> void BaseSetting<SandboxMode>::convertToArg(Args & args)
+{
+    args.mkFlag(0, name, {}, "Enable sandboxing.", 0, [=](Strings ss) { value = smEnabled; });
+    args.mkFlag(0, "no-" + name, {}, "Disable sandboxing.", 0, [=](Strings ss) { value = smDisabled; });
+    args.mkFlag(0, "relaxed-" + name, {}, "Enable sandboxing, but allow builds to disable it.", 0, [=](Strings ss) { value = smRelaxed; });
+}
+
 void MaxBuildJobsSetting::set(const std::string & str)
 {
     if (str == "auto") value = std::max(1U, std::thread::hardware_concurrency());