2 files changed, 34 insertions, 21 deletions
diff --git a/pkgs/pkgs-lib/formats.nix b/pkgs/pkgs-lib/formats.nix
index 44c8f9135439..5e17519d4ce1 100644
--- a/pkgs/pkgs-lib/formats.nix
+++ b/pkgs/pkgs-lib/formats.nix
@@ -48,14 +48,31 @@ rec {
 
   };
 
-  # YAML has been a strict superset of JSON since 1.2
-  yaml = {}:
-    let jsonSet = json {};
-    in jsonSet // {
-      type = jsonSet.type // {
+  yaml = {}: {
+
+    generate = name: value: pkgs.runCommand name {
+        nativeBuildInputs = [ pkgs.remarshal ];
+        value = builtins.toJSON value;
+        passAsFile = [ "value" ];
+      } ''
+        json2yaml "$valuePath" "$out"
+      '';
+
+    type = with lib.types; let
+      valueType = nullOr (oneOf [
+        bool
+        int
+        float
+        str
+        path
+        (attrsOf valueType)
+        (listOf valueType)
+      ]) // {
         description = "YAML value";
       };
-    };
+    in valueType;
+
+  };
 
   ini = {
     # Represents lists as duplicate keys
diff --git a/pkgs/pkgs-lib/tests/formats.nix b/pkgs/pkgs-lib/tests/formats.nix
index af19f6100eef..14cc85eff31d 100644
--- a/pkgs/pkgs-lib/tests/formats.nix
+++ b/pkgs/pkgs-lib/tests/formats.nix
@@ -72,21 +72,17 @@ in runBuildTests {
       path = ./formats.nix;
     };
     expected = ''
-      {
-        "attrs": {
-          "foo": null
-        },
-        "false": false,
-        "float": 3.141,
-        "list": [
-          null,
-          null
-        ],
-        "null": null,
-        "path": "${./formats.nix}",
-        "str": "foo",
-        "true": true
-      }
+      attrs:
+        foo: null
+      'false': false
+      float: 3.141
+      list:
+        - null
+        - null
+      'null': null
+      path: ${./formats.nix}
+      str: foo
+      'true': true
     '';
   };