lib.formats.yaml: use well known YAML format

The way `(lib.formats.yaml {}).generate` generates YAML is compliant
because on YAML 1.2 spec JSON is a subset of YAML but it bugs people's
minds and can lead to problems with software that is not compatible with
YAML 1.2.

This commit also changes the test of the generation function. Data
validation/typing remains the same.

See #133802.

Signed-off-by: lucasew <lucas59356@gmail.com>

1 files changed, 23 insertions, 6 deletions

diff --git a/pkgs/pkgs-lib/formats.nix b/pkgs/pkgs-lib/formats.nix
index 44c8f91354391..5e17519d4ce18 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