nixos/lighttpd: add services.lighttpd.enableModules option

This option makes the coupling between lighttpd and its sub-services
more "loose".

While the option is a list, its purpose is to provide a "set" of needed
modules to load for lighttpd to function correctly with its config. The
NixOS lighttpd module ensures that lighttpd modules are loaded no more
than once (because lighttpd dislikes that), and in the correct order.

Also add an assertion that all modules listed in .enableModules are
valid.

nixos/modules/services/web-servers/lighttpd/cgit.nix

@@ -44,6 +44,9 @@ in
     # make the cgitrc manpage available
     environment.systemPackages = [ pkgs.cgit ];
 
+    # declare module dependencies
+    services.lighttpd.enableModules = [ "mod_cgi" "mod_alias" "mod_setenv" ];
+
     services.lighttpd.extraConfig = ''
       $HTTP["url"] =~ "^/cgit" {
           cgi.assign = (

nixos/modules/services/web-servers/lighttpd/default.nix

@@ -8,12 +8,54 @@ let
 
   cfg = config.services.lighttpd;
 
-  needModRedirect = cfg.gitweb.enable;
-  needModAlias = cfg.cgit.enable || cfg.gitweb.enable;
-  needModSetenv = cfg.cgit.enable || cfg.gitweb.enable;
-  needModCgi = cfg.cgit.enable || cfg.gitweb.enable;
-  needModStatus = cfg.mod_status;
-  needModUserdir = cfg.mod_userdir;
+  # List of known lighttpd modules, ordered by how the lighttpd documentation
+  # recommends them being imported:
+  # http://redmine.lighttpd.net/projects/1/wiki/Server_modulesDetails
+  #
+  # Some modules are always imported and should not appear in the config:
+  # disallowedModules = [ "mod_indexfile" "mod_dirlisting" "mod_staticfile" ];
+  #
+  # Get full module list: "ls -1 $lighttpd/lib/*.so"
+  allKnownModules = [
+    "mod_rewrite"
+    "mod_redirect"
+    "mod_alias"
+    "mod_access"
+    "mod_auth"
+    "mod_status"
+    "mod_simple_vhost"
+    "mod_evhost"
+    "mod_userdir"
+    "mod_secdownload"
+    "mod_fastcgi"
+    "mod_proxy"
+    "mod_cgi"
+    "mod_ssi"
+    "mod_compress"
+    "mod_usertrack"
+    "mod_expire"
+    "mod_rrdtool"
+    "mod_accesslog"
+    # Remaining list of modules, order assumed to be unimportant.
+    "mod_cml"
+    "mod_dirlisting"
+    "mod_evasive"
+    "mod_extforward"
+    "mod_flv_streaming"
+    "mod_magnet"
+    "mod_mysql_vhost"
+    "mod_rewrite"
+    "mod_scgi"
+    "mod_setenv"
+    "mod_trigger_b4_dl"
+    "mod_webdav"
+  ];
+
+  maybeModuleString = moduleName:
+    if elem moduleName cfg.enableModules then ''"${moduleName}"'' else "";
+
+  modulesIncludeString = concatStringsSep ",\n"
+    (filter (x: x != "") (map maybeModuleString allKnownModules));
 
   configFile = if cfg.configText != "" then
     pkgs.writeText "lighttpd.conf" ''
@@ -38,13 +80,7 @@ let
       # been loaded already. So if two services were to put the same module in
       # server.modules += (), that would break the lighttpd configuration.
       server.modules = (
-          ${optionalString needModRedirect ''"mod_redirect",''}
-          ${optionalString needModAlias ''"mod_alias",''}
-          ${optionalString needModSetenv ''"mod_setenv",''}
-          ${optionalString needModCgi ''"mod_cgi",''}
-          ${optionalString needModStatus ''"mod_status",''}
-          ${optionalString needModUserdir ''"mod_userdir",''}
-          "mod_accesslog"
+          ${modulesIncludeString}
       )
 
       # Logging (logs end up in systemd journal)
@@ -117,6 +153,19 @@ in
         '';
       };
 
+      enableModules = mkOption {
+        type = types.listOf types.str;
+        default = [ ];
+        example = [ "mod_cgi" "mod_status" ];
+        description = ''
+          List of lighttpd modules to enable. Sub-services take care of
+          enabling modules as needed, so this option is mainly for when you
+          want to add custom stuff to
+          <option>services.lighttpd.extraConfig</option> that depends on a
+          certain module.
+        '';
+      };
+
       mod_status = mkOption {
         default = false;
         type = types.uniq types.bool;
@@ -152,6 +201,26 @@ in
 
   config = mkIf cfg.enable {
 
+    assertions = [
+      { assertion = all (x: elem x allKnownModules) cfg.enableModules;
+        message = ''
+          One (or more) modules in services.lighttpd.enableModules are
+          unrecognized.
+
+          Known modules: ${toString allKnownModules}
+
+          services.lighttpd.enableModules: ${toString cfg.enableModules}
+        '';
+      }
+    ];
+
+    services.lighttpd.enableModules = mkMerge
+      [ (mkIf cfg.mod_status [ "mod_status" ])
+        (mkIf cfg.mod_userdir [ "mod_userdir" ])
+        # always load mod_accesslog so that we can log to the journal
+        [ "mod_accesslog" ]
+      ];
+
     systemd.services.lighttpd = {
       description = "Lighttpd Web Server";
       after = [ "network.target" ];

nixos/modules/services/web-servers/lighttpd/gitweb.nix

@@ -44,6 +44,9 @@ in
 
   config = mkIf cfg.enable {
 
+    # declare module dependencies
+    services.lighttpd.enableModules = [ "mod_cgi" "mod_redirect" "mod_alias" "mod_setenv" ];
+
     services.lighttpd.extraConfig = ''
       $HTTP["url"] =~ "^/gitweb" {
           cgi.assign = (