Rename `nix show-config` to `nix config show`

Part of #7672

My main motivation is to be able to use `nix.checkConfig`[1]. This
doesn't work with Lix currently since the module uses `nix show-config`
if the Nix version is <2.20pre and `nix config show` otherwise. I think
this is the only instance where nixpkgs checks for which Nix commands
exist that affects us now, so I figured we could just perform the rename
here as well[2] and still provide the current version number[3].

I don't have a strong opinion on whether to deprecate `nix show-config`,
the warning is added there automatically.

(cherry picked from commit f300e11b056dea414d7d77bbc6e5a7dc5d9ddd41)

[1] https://nixos.org/manual/nixos/stable/options.html#opt-nix.checkConfig
[2] I should add that I don't use the "official" ways of installing Lix
    because using the flake directly and callPackaging it seemed to fit
    better into my workflow: I already have a little mess to make
    sure Hydra from the flake uses the correct pkgs.nix and I didn't
    want to complicate it further while keeping a single package-set I
    can build in CI. Don't get me wrong, I think such a module for a
    quick-start is very important, just giving context on why I bother
    in the first place :)
[3] When we go public, I think it's worth considering to add support in
    nixpkgs itself for Lix.

Change-Id: I47b4239b05cbeda3c370d2fa56ea768b768768ac

3 files changed, 26 insertions, 4 deletions

diff --git a/src/nix/show-config.cc b/src/nix/config.cc
index 3530584f9..5b280d11d 100644
--- a/src/nix/show-config.cc
+++ b/src/nix/config.cc
@@ -7,11 +7,31 @@
 
 using namespace nix;
 
-struct CmdShowConfig : Command, MixJSON
+struct CmdConfig : virtual NixMultiCommand
+{
+    CmdConfig() : MultiCommand(RegisterCommand::getCommandsFor({"config"}))
+    { }
+
+    std::string description() override
+    {
+        return "manipulate the Nix configuration";
+    }
+
+    Category category() override { return catUtility; }
+
+    void run() override
+    {
+        if (!command)
+            throw UsageError("'nix config' requires a sub-command.");
+        command->second->run();
+    }
+};
+
+struct CmdConfigShow : Command, MixJSON
 {
     std::optional<std::string> name;
 
-    CmdShowConfig() {
+    CmdConfigShow() {
         expectArgs({
             .label = {"name"},
             .optional = true,
@@ -56,4 +76,5 @@ struct CmdShowConfig : Command, MixJSON
     }
 };
 
-static auto rShowConfig = registerCommand<CmdShowConfig>("show-config");
+static auto rCmdConfig = registerCommand<CmdConfig>("config");
+static auto rShowConfig = registerCommand2<CmdConfigShow>({"config", "show"});
diff --git a/src/nix/main.cc b/src/nix/main.cc
index 6bc46eba3..64755d445 100644
--- a/src/nix/main.cc
+++ b/src/nix/main.cc
@@ -151,6 +151,7 @@ struct NixArgs : virtual MultiCommand, virtual MixCommonArgs, virtual RootArgs
         {"ping-store", {"store", "ping"}},
         {"sign-paths", {"store", "sign"}},
         {"show-derivation", {"derivation", "show"}},
+        {"show-config", {"config", "show"}},
         {"to-base16", {"hash", "to-base16"}},
         {"to-base32", {"hash", "to-base32"}},
         {"to-base64", {"hash", "to-base64"}},
diff --git a/src/nix/meson.build b/src/nix/meson.build
index cb8f73174..e41399b5d 100644
--- a/src/nix/meson.build
+++ b/src/nix/meson.build
@@ -59,7 +59,7 @@ nix_sources = files(
   'repl.cc',
   'run.cc',
   'search.cc',
-  'show-config.cc',
+  'config.cc',
   'sigs.cc',
   'store-copy-log.cc',
   'store-delete.cc',