pkgs-lib: Implement settings formats for JSON, INI, YAML and TOML

pkgs/pkgs-lib/default.nix

@@ -2,6 +2,10 @@
 # they depend on some packages. This notably is *not* for supporting package
 # building, instead pkgs/build-support is the place for that.
 { lib, pkgs }: {
-
+  # setting format types and generators. These do not fit in lib/types.nix,
+  # because they depend on pkgs for rendering some formats
+  formats = import ./formats.nix {
+    inherit lib pkgs;
+  };
 }
 

pkgs/pkgs-lib/formats.nix

@@ -0,0 +1,109 @@
+{ lib, pkgs }:
+rec {
+
+  /*
+
+  Every following entry represents a format for program configuration files
+  used for `settings`-style options (see https://github.com/NixOS/rfcs/pull/42).
+  Each entry should look as follows:
+
+    <format> = <parameters>: {
+      #        ^^ Parameters for controlling the format
+
+      # The module system type most suitable for representing such a format
+      # The description needs to be overwritten for recursive types
+      type = ...;
+
+      # generate :: Name -> Value -> Path
+      # A function for generating a file with a value of such a type
+      generate = ...;
+
+    });
+  */
+
+
+  json = {}: {
+
+    type = with lib.types; let
+      valueType = nullOr (oneOf [
+        bool
+        int
+        float
+        str
+        (attrsOf valueType)
+        (listOf valueType)
+      ]) // {
+        description = "JSON value";
+      };
+    in valueType;
+
+    generate = name: value: pkgs.runCommandNoCC name {
+      nativeBuildInputs = [ pkgs.jq ];
+      value = builtins.toJSON value;
+      passAsFile = [ "value" ];
+    } ''
+      jq . "$valuePath"> $out
+    '';
+
+  };
+
+  # YAML has been a strict superset of JSON since 1.2
+  yaml = {}:
+    let jsonSet = json {};
+    in jsonSet // {
+      type = jsonSet.type // {
+        description = "YAML value";
+      };
+    };
+
+  ini = { listsAsDuplicateKeys ? false, ... }@args: {
+
+    type = with lib.types; let
+
+      singleIniAtom = nullOr (oneOf [
+        bool
+        int
+        float
+        str
+      ]) // {
+        description = "INI atom (null, bool, int, float or string)";
+      };
+
+      iniAtom =
+        if listsAsDuplicateKeys then
+          coercedTo singleIniAtom lib.singleton (listOf singleIniAtom) // {
+            description = singleIniAtom.description + " or a list of them for duplicate keys";
+          }
+        else
+          singleIniAtom;
+
+    in attrsOf (attrsOf iniAtom);
+
+    generate = name: value: pkgs.writeText name (lib.generators.toINI args value);
+
+  };
+
+  toml = {}: json {} // {
+    type = with lib.types; let
+      valueType = oneOf [
+        bool
+        int
+        float
+        str
+        (attrsOf valueType)
+        (listOf valueType)
+      ] // {
+        description = "TOML value";
+      };
+    in valueType;
+
+    generate = name: value: pkgs.runCommandNoCC name {
+      nativeBuildInputs = [ pkgs.remarshal ];
+      value = builtins.toJSON value;
+      passAsFile = [ "value" ];
+    } ''
+      json2toml "$valuePath" "$out"
+    '';
+
+  };
+}

pkgs/top-level/all-packages.nix

@@ -524,7 +524,7 @@ in
   writers = callPackage ../build-support/writers {};
 
   # lib functions depending on pkgs
-  inherit (import ../pkgs-lib { inherit lib pkgs; });
+  inherit (import ../pkgs-lib { inherit lib pkgs; }) formats;
 
   ### TOOLS