Merge pull request #1026 from thecaralice/nochan

Allow disabling channels

modules/environment/default.nix

@@ -16,6 +16,10 @@ let
 in
 
 {
+  imports = [
+    (mkRenamedOptionModule ["environment" "postBuild"] ["environment" "extraSetup"])
+  ];
+
   options = {
     environment.systemPackages = mkOption {
       type = types.listOf types.package;
@@ -43,12 +47,6 @@ in
       description = "A list of profiles used to setup the global environment.";
     };
 
-    environment.postBuild = mkOption {
-      type = types.lines;
-      default = "";
-      description = "Commands to execute when building the global environment.";
-    };
-
     environment.extraOutputsToInstall = mkOption {
       type = types.listOf types.str;
       default = [];
@@ -147,6 +145,17 @@ in
       '';
       type = types.lines;
     };
+
+    environment.extraSetup = mkOption {
+      type = types.lines;
+      default = "";
+      description = ''
+        Shell fragments to be run after the system environment has been created.
+        This should only be used for things that need to modify the internals
+        of the environment, e.g. generating MIME caches.
+        The environment being built can be accessed at $out.
+      '';
+    };
   };
 
   config = {
@@ -188,7 +197,8 @@ in
     system.path = pkgs.buildEnv {
       name = "system-path";
       paths = cfg.systemPackages;
-      inherit (cfg) postBuild pathsToLink extraOutputsToInstall;
+      postBuild = cfg.extraSetup;
+      inherit (cfg) pathsToLink extraOutputsToInstall;
     };
 
     system.build.setEnvironment = pkgs.writeText "set-environment" ''
@@ -205,6 +215,5 @@ in
     system.build.setAliases = pkgs.writeText "set-aliases" ''
       ${concatStringsSep "\n" aliasCommands}
     '';
-
   };
 }

modules/nix/default.nix

@@ -380,14 +380,38 @@ in
         '';
       };
 
+      channel = {
+        enable = mkOption {
+          description = ''
+            Whether the `nix-channel` command and state files are made available on the machine.
+
+            The following files are initialized when enabled:
+              - `/nix/var/nix/profiles/per-user/root/channels`
+              - `$HOME/.nix-defexpr/channels` (on login)
+
+            Disabling this option will not remove the state files from the system.
+          '';
+          type = types.bool;
+          default = true;
+        };
+      };
+
       # Definition differs substantially from NixOS module
       nixPath = mkOption {
         type = nixPathType;
-        default = [
+        default = lib.optionals cfg.channel.enable [
           # Include default path <darwin-config>.
           { darwin-config = "${config.environment.darwinConfig}"; }
           "/nix/var/nix/profiles/per-user/root/channels"
         ];
+        
+        defaultText = lib.literalExpression ''
+          lib.optionals cfg.channel.enable [
+            # Include default path <darwin-config>.
+            { darwin-config = "''${config.environment.darwinConfig}"; }
+            "/nix/var/nix/profiles/per-user/root/channels"
+          ]
+        '';
         description = ''
           The default Nix expression search path, used by the Nix
           evaluator to look up paths enclosed in angle brackets
@@ -744,27 +768,21 @@ in
     ];
 
     # Not in NixOS module
-    nix.nixPath = mkMerge [
+    nix.nixPath = mkIf (config.system.stateVersion < 2) (mkDefault [
-      (mkIf (config.system.stateVersion < 2) (mkDefault
+      "darwin=$HOME/.nix-defexpr/darwin"
-      [ "darwin=$HOME/.nix-defexpr/darwin"
       "darwin-config=$HOME/.nixpkgs/darwin-configuration.nix"
       "/nix/var/nix/profiles/per-user/root/channels"
-      ]))
+    ]);
-      (mkIf (config.system.stateVersion > 3) (mkOrder 1200
-      [ { darwin-config = "${config.environment.darwinConfig}"; }
-        "/nix/var/nix/profiles/per-user/root/channels"
-      ]))
-    ];
 
     # Set up the environment variables for running Nix.
     environment.variables = cfg.envVars // { NIX_PATH = cfg.nixPath; };
 
-    environment.extraInit =
+    environment.extraInit = mkMerge [
-      ''
+      (mkIf cfg.channel.enable ''
         if [ -e "$HOME/.nix-defexpr/channels" ]; then
           export NIX_PATH="$HOME/.nix-defexpr/channels''${NIX_PATH:+:$NIX_PATH}"
         fi
-      '' +
+      '')
       # Not in NixOS module
       ''
         # Set up secure multi-user builds: non-root users build through the
@@ -772,6 +790,11 @@ in
         if [ ! -w /nix/var/nix/db ]; then
             export NIX_REMOTE=daemon
         fi
+      ''
+    ];
+
+    environment.extraSetup = mkIf (!cfg.channel.enable) ''
+      rm --force $out/bin/nix-channel
     '';
 
     nix.nrBuildUsers = mkDefault (max 32 (if cfg.settings.max-jobs == "auto" then 0 else cfg.settings.max-jobs));

modules/programs/info/default.nix

@@ -22,7 +22,7 @@ in
     environment.pathsToLink = [ "/info" "/share/info" ];
     environment.extraOutputsToInstall = [ "info" ];
 
-    environment.postBuild = ''
+    environment.extraSetup = ''
       if test -w $out/share/info; then
         shopt -s nullglob
         for i in $out/share/info/*.info $out/share/info/*.info.gz; do

modules/system/checks.nix

@@ -236,7 +236,7 @@ in
 
     system.checks.verifyNixChannels = mkOption {
       type = types.bool;
-      default = true;
+      default = config.nix.channel.enable;
       description = "Whether to run the nix-channels validation checks.";
     };