treewide: restructure modules

make every module contain config attribute
and if module doesn't use module arguments,
don't make it a function

nix-os/core.nix

@@ -10,78 +10,80 @@
     ./module-overrides.nix
     ./nix.nix
   ];
+  config = {
 
-  # kernel
-  boot.kernelPackages = pkgs.linuxPackages_latest;
+    # kernel
+    boot.kernelPackages = pkgs.linuxPackages_latest;
 
-  # Enable networking
-  networking.networkmanager.enable = true;
-
-  # Allow unfree packages
-  nixpkgs.config.allowUnfree = true;
-  nix = {
-    channel.enable = false;
-    settings.experimental-features = [
-      "no-url-literals"
-    ];
-    nixPath = [
-      "nixpkgs=${pkgs.selfExpr { useConfig = false; }}"
-      "systemNixpkgs=${pkgs.selfExpr { useConfig = true; name = "systemNixpkgs-self"; }}"
-      # don't garbage collect the nixpkgs input
-      "inputsNixpkgs=${inputs.nixpkgs}"
-      "nixos-system=/etc/nixos/default.nix"
-    ];
-  };
-
-  # List packages installed in system profile. To search, run:
-  # $ nix search wget
-  environment.systemPackages = with pkgs; [
-    waypipe
-    wget
-    ffmpeg
-    yt-dlp
-    htop
-    btop
-    fastfetch
-    smartmontools
-    ddrescue
-  ];
-  programs.git.enable = true;
-  programs.git.config = {
-    commit.verbose = true;
-    init.defaultBranch = "main";
-    merge.conflictstyle = "diff3";
-    rerere.enabled = true;
-  };
-
-  # Use nix-index for command-not-found handler
-  programs.command-not-found.enable = false;
-  programs.nix-index = {
-    package = pkgs.nix-index.override {
-      nix-index-unwrapped = pkgs.nix-index-unwrapped.overrideAttrs (oldAttrs: {
-        patches = oldAttrs.patches or [] ++ [
-          ../pkgs/by-name/ni/nix-index/cnfOutput.patch
-        ];
-      });
+    # Enable networking
+    networking.networkmanager.enable = true;
 
+    # Allow unfree packages
+    nixpkgs.config.allowUnfree = true;
+    nix = {
+      channel.enable = false;
+      settings.experimental-features = [
+        "no-url-literals"
+      ];
+      nixPath = [
+        "nixpkgs=${pkgs.selfExpr { useConfig = false; }}"
+        "systemNixpkgs=${pkgs.selfExpr { useConfig = true; name = "systemNixpkgs-self"; }}"
+        # don't garbage collect the nixpkgs input
+        "inputsNixpkgs=${inputs.nixpkgs}"
+        "nixos-system=/etc/nixos/default.nix"
+      ];
     };
-    enable = true;
-    enableBashIntegration = true;
-  };
 
-  # Enable fail2ban because of the OpenSSH server
-  services.fail2ban = {
-    enable = true;
-    maxretry = 10;
-    bantime = "7d";
-  };
-
-  # Enable the OpenSSH daemon.
-  services.openssh = {
-    enable = true;
-    ports = [
-      22
-      8022
+    # List packages installed in system profile. To search, run:
+    # $ nix search wget
+    environment.systemPackages = with pkgs; [
+      waypipe
+      wget
+      ffmpeg
+      yt-dlp
+      htop
+      btop
+      fastfetch
+      smartmontools
+      ddrescue
     ];
+    programs.git.enable = true;
+    programs.git.config = {
+      commit.verbose = true;
+      init.defaultBranch = "main";
+      merge.conflictstyle = "diff3";
+      rerere.enabled = true;
+    };
+
+    # Use nix-index for command-not-found handler
+    programs.command-not-found.enable = false;
+    programs.nix-index = {
+      package = pkgs.nix-index.override {
+        nix-index-unwrapped = pkgs.nix-index-unwrapped.overrideAttrs (oldAttrs: {
+          patches = oldAttrs.patches or [] ++ [
+            ../pkgs/by-name/ni/nix-index/cnfOutput.patch
+          ];
+        });
+
+      };
+      enable = true;
+      enableBashIntegration = true;
+    };
+
+    # Enable fail2ban because of the OpenSSH server
+    services.fail2ban = {
+      enable = true;
+      maxretry = 10;
+      bantime = "7d";
+    };
+
+    # Enable the OpenSSH daemon.
+    services.openssh = {
+      enable = true;
+      ports = [
+        22
+        8022
+      ];
+    };
   };
 }