generalized module for write-text

- use custom etc activation script

config.nix

@@ -8,10 +8,11 @@ let
       modules =
         [ config
           ./modules/system.nix
+          ./modules/system/activation-scripts.nix
+          ./modules/system/etc.nix
           ./modules/environment.nix
           ./modules/launchd
           ./modules/tmux.nix
-          <nixpkgs/nixos/modules/system/etc/etc.nix>
         ];
     };
 

modules/system.nix

@@ -6,35 +6,9 @@ let
 
   cfg = config.system;
 
-  script =
-    { config, name, ... }:
-    { options = {
-        text = mkOption {
-          type = types.nullOr types.lines;
-          default = null;
-          description = "Text of the file.";
-        };
-        source = mkOption {
-          type = types.path;
-          description = "Path of the source file.";
-        };
+in
 
-        deps = mkOption {
-          type = types.listOf types.str;
-          default = [];
-        };
-      };
-      config = {
-        source = pkgs.writeScript "activate-${name}" ''
-          #! ${pkgs.stdenv.shell}
-
-          #### Activation script snippet ${name}:
-          ${config.text}
-        '';
-      };
-    };
-
-in {
+{
   options = {
 
     system.build = mkOption {
@@ -58,49 +32,10 @@ in {
       default = "16.09";
     };
 
-    system.activationScripts = mkOption {
-      internal = true;
-      type = types.attrsOf (types.submodule script);
-      default = {};
-      description = ''
-        A set of shell script fragments that are executed when a NixOS
-        system configuration is activated.  Examples are updating
-        /etc, creating accounts, and so on.  Since these are executed
-        every time you boot the system or run
-        <command>nixos-rebuild</command>, it's important that they are
-        idempotent and fast.
-      '';
-    };
-
   };
 
   config = {
 
-    system.activationScripts.script.text = ''
-      #! ${pkgs.stdenv.shell}
-
-      systemConfig=@out@
-
-      _status=0
-      trap "_status=1" ERR
-
-      # Ensure a consistent umask.
-      umask 0022
-
-      # Make this configuration the current configuration.
-      # The readlink is there to ensure that when $systemConfig = /system
-      # (which is a symlink to the store), /run/current-system is still
-      # used as a garbage collection root.
-      ln -sfn "$(readlink -f "$systemConfig")" /run/current-system
-
-      # Prevent the current configuration from being garbage-collected.
-      ln -sfn /run/current-system /nix/var/nix/gcroots/current-system
-
-      ${cfg.activationScripts.etc.text}
-
-      exit $_status
-    '';
-
     system.build.toplevel = pkgs.stdenvNoCC.mkDerivation {
       name = "nixdarwin-system-${cfg.nixdarwinLabel}";
       preferLocalBuild = true;

modules/system/activation-scripts.nix

@@ -0,0 +1,63 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.system;
+
+  script = import ./write-text.nix {
+    inherit lib;
+    mkTextDerivation = name: text: pkgs.writeScript "activate-${name}" text;
+  };
+
+in
+
+{
+  options = {
+
+    system.activationScripts = mkOption {
+      internal = true;
+      type = types.attrsOf (types.submodule script);
+      default = {};
+      description = ''
+        A set of shell script fragments that are executed when a NixOS
+        system configuration is activated.  Examples are updating
+        /etc, creating accounts, and so on.  Since these are executed
+        every time you boot the system or run
+        <command>nixos-rebuild</command>, it's important that they are
+        idempotent and fast.
+      '';
+    };
+
+  };
+
+  config = {
+
+    system.activationScripts.script.text = ''
+      #! ${pkgs.stdenv.shell}
+
+      systemConfig=@out@
+
+      _status=0
+      trap "_status=1" ERR
+
+      # Ensure a consistent umask.
+      umask 0022
+
+      # Make this configuration the current configuration.
+      # The readlink is there to ensure that when $systemConfig = /system
+      # (which is a symlink to the store), /run/current-system is still
+      # used as a garbage collection root.
+      ln -sfn "$(readlink -f "$systemConfig")" /run/current-system
+
+      # Prevent the current configuration from being garbage-collected.
+      ln -sfn /run/current-system /nix/var/nix/gcroots/current-system
+
+      ${cfg.activationScripts.etc.text}
+
+      exit $_status
+    '';
+
+  };
+}

modules/system/etc.nix

@@ -0,0 +1,63 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  text = import ./write-text.nix {
+    inherit lib;
+    mkTextDerivation = name: text: pkgs.writeText "etc-${name}" text;
+  };
+
+  etc = filter (f: f.enable) (attrValues config.environment.etc);
+
+in
+
+{
+  options = {
+
+    environment.etc = mkOption {
+      type = types.loaOf (types.submodule text);
+      default = {};
+      description = ''
+        Set of files that have to be linked in <filename>/etc</filename>.
+      '';
+    };
+
+  };
+
+  config = {
+
+    system.build.etc = pkgs.runCommand "etc" {} ''
+      mkdir -p $out/etc
+      cd $out/etc
+      ${concatMapStringsSep "\n" (attr: "ln -s '${attr.source}' '${attr.target}'") etc}
+    '';
+
+    system.activationScripts.etc.text = ''
+      # Set up the statically computed bits of /etc.
+      echo "setting up /etc..."
+
+      ln -sfn "$(readlink -f $systemConfig/etc)" /etc/static
+
+      for link in $(ls /etc/static/); do
+        if [ -e "/etc/$link" ]; then
+          if [ ! -L "/etc/$link" ]; then
+            echo "warning: /etc/$link is a file, skipping..." >&2
+          fi
+        else
+          ln -sfn "/etc/static/$link" "/etc/$link"
+        fi
+      done
+
+      for link in $(find /etc/ -maxdepth 1 -type l); do
+        if [[ "$(readlink $link)" == /etc/static/* ]]; then
+          if [ ! -e "$(readlink -f $link)" ]; then
+            rm $link
+          fi
+        fi
+      done
+    '';
+
+  };
+}

modules/system/write-text.nix

@@ -0,0 +1,56 @@
+{ lib, mkTextDerivation }:
+
+with lib;
+
+{ config, name, ... }:
+let
+
+  sourceDrv = mkTextDerivation name config.text;
+
+in
+
+{
+  options = {
+
+    enable = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether this /etc file should be generated.  This
+        option allows specific /etc files to be disabled.
+      '';
+    };
+
+    text = mkOption {
+      default = null;
+      type = types.nullOr types.lines;
+      description = ''
+        Text of the file.
+      '';
+    };
+
+    target = mkOption {
+      type = types.str;
+      default = name;
+      description = ''
+        Name of symlink (relative to
+        <filename>/etc</filename>).  Defaults to the attribute
+        name.
+      '';
+    };
+
+    source = mkOption {
+      type = types.path;
+      description = ''
+        Path of the source file.
+      '';
+    };
+
+  };
+
+  config = {
+
+    source = mkIf (config.text != null) (mkDefault sourceDrv);
+
+  };
+}