documentation: add module for darwin manual

Fixes #72

modules/documentation/default.nix

@@ -0,0 +1,99 @@
+{ config, lib, pkgs, baseModules, modules, ... }:
+
+with lib;
+
+let
+  cfg = config.documentation;
+
+  /* For the purpose of generating docs, evaluate options with each derivation
+    in `pkgs` (recursively) replaced by a fake with path "\${pkgs.attribute.path}".
+    It isn't perfect, but it seems to cover a vast majority of use cases.
+    Caveat: even if the package is reached by a different means,
+    the path above will be shown and not e.g. `${config.services.foo.package}`. */
+  manual = import ../../doc/manual rec {
+    inherit pkgs config;
+    version = "0.0.1";
+    revision = "release-${version}";
+    options =
+      let
+        scrubbedEval = evalModules {
+          modules = [ { nixpkgs.localSystem = config.nixpkgs.localSystem; } ] ++ baseModules;
+          args = (config._module.args) // { modules = [ ]; };
+          specialArgs = { pkgs = scrubDerivations "pkgs" pkgs; };
+        };
+        scrubDerivations = namePrefix: pkgSet: mapAttrs
+          (name: value:
+            let wholeName = "${namePrefix}.${name}"; in
+            if isAttrs value then
+              scrubDerivations wholeName value
+              // (optionalAttrs (isDerivation value) { outPath = "\${${wholeName}}"; })
+            else value
+          )
+          pkgSet;
+      in scrubbedEval.options;
+  };
+
+  helpScript = pkgs.writeScriptBin "darwin-help"
+    ''
+      #! ${pkgs.stdenv.shell} -e
+      open ${manual.manualHTMLIndex}
+    '';
+in
+
+{
+  options = {
+    documentation.enable = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether to install documentation of packages from
+        <option>environment.systemPackages</option> into the generated system path.
+
+        See "Multiple-output packages" chapter in the nixpkgs manual for more info.
+      '';
+      # which is at ../../../doc/multiple-output.xml
+    };
+
+    documentation.man.enable = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether to install manual pages and the <command>man</command> command.
+        This also includes "man" outputs.
+      '';
+    };
+
+    documentation.info.enable = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether to install info pages and the <command>info</command> command.
+        This also includes "info" outputs.
+      '';
+    };
+
+    documentation.doc.enable = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether to install documentation distributed in packages' <literal>/share/doc</literal>.
+        Usually plain text and/or HTML.
+        This also includes "doc" outputs.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+
+    programs.man.enable = cfg.man.enable;
+    programs.info.enable = cfg.info.enable;
+
+    environment.systemPackages = mkMerge [
+      (mkIf cfg.man.enable [ manual.manpages ])
+      (mkIf cfg.doc.enable [ manual.manualHTML helpScript ])
+    ];
+
+    system.build.manual = manual;
+
+  };
+}

modules/system/default.nix

@@ -20,7 +20,7 @@ in
 
     system.build = mkOption {
       internal = true;
-      type = types.attrsOf types.package;
+      type = types.attrsOf types.unspecified;
       default = {};
       description = ''
         Attribute set of derivation used to setup the system.