nixos/services.picom: use libconfig to generate the config (#480156)

nixos/modules/services/x11/picom.nix

@@ -20,43 +20,8 @@ let
 
   mkDefaultAttrs = mapAttrs (n: v: mkDefault v);
 
-  # Basically a tinkered lib.generators.mkKeyValueDefault
-  # It either serializes a top-level definition "key: { values };"
-  # or an expression "key = { values };"
-  mkAttrsString =
-    top:
-    mapAttrsToList (
-      k: v:
-      let
-        sep = if (top && isAttrs v) then ":" else "=";
-      in
-      "${escape [ sep ] k}${sep}${mkValueString v};"
-    );
-
-  # This serializes a Nix expression to the libconfig format.
-  mkValueString =
-    v:
-    if types.bool.check v then
-      boolToString v
-    else if types.int.check v then
-      toString v
-    else if types.float.check v then
-      toString v
-    else if types.str.check v then
-      "\"${escape [ "\"" ] v}\""
-    else if builtins.isList v then
-      "[ ${concatMapStringsSep " , " mkValueString v} ]"
-    else if types.attrs.check v then
-      "{ ${concatStringsSep " " (mkAttrsString false v)} }"
-    else
-      throw ''
-        invalid expression used in option services.picom.settings:
-        ${v}
-      '';
-
-  toConf = attrs: concatStringsSep "\n" (mkAttrsString true cfg.settings);
-
-  configFile = pkgs.writeText "picom.conf" (toConf cfg.settings);
+  libconfig = pkgs.formats.libconfig { };
+  configFile = libconfig.generate "picom.conf" cfg.settings;
 
 in
 {
@@ -279,56 +244,22 @@ in
       '';
     };
 
-    settings =
-      with types;
-      let
-        scalar =
-          oneOf [
-            bool
-            int
-            float
-            str
-          ]
-          // {
-            description = "scalar types";
+    settings = mkOption {
+      type = libconfig.type;
+      default = { };
+      example = literalExpression ''
+        blur =
+          { method = "gaussian";
+            size = 10;
+            deviation = 5.0;
           };
-
-        libConfig =
-          oneOf [
-            scalar
-            (listOf libConfig)
-            (attrsOf libConfig)
-          ]
-          // {
-            description = "libconfig type";
-          };
-
-        topLevel = attrsOf libConfig // {
-          description = ''
-            libconfig configuration. The format consists of an attributes
-            set (called a group) of settings. Each setting can be a scalar type
-            (boolean, integer, floating point number or string), a list of
-            scalars or a group itself
-          '';
-        };
-
-      in
-      mkOption {
-        type = topLevel;
-        default = { };
-        example = literalExpression ''
-          blur =
-            { method = "gaussian";
-              size = 10;
-              deviation = 5.0;
-            };
-        '';
-        description = ''
-          Picom settings. Use this option to configure Picom settings not exposed
-          in a NixOS option or to bypass one.  For the available options see the
-          CONFIGURATION FILES section at {manpage}`picom(1)`.
-        '';
-      };
+      '';
+      description = ''
+        Picom settings. Use this option to configure Picom settings not exposed
+        in a NixOS option or to bypass one.  For the available options see the
+        CONFIGURATION FILES section at {manpage}`picom(1)`.
+      '';
+    };
   };
 
   config = mkIf cfg.enable {