From 7601f8a10854992b594fc85ecb4685a1a0ec3346 Mon Sep 17 00:00:00 2001
From: Yuriy Taraday <yuriy.taraday@tweag.io>
Date: Tue, 23 Jun 2026 15:42:14 +0200
Subject: [PATCH] pkgs-lib/formats: Add tests for serializing null values

In the effort to pass values directly as structured values, we ran into
issue with serializing null's.
This adds tests for null for all formats that support it and negative
tests for some others.

See https://github.com/NixOS/nixpkgs/pull/524404#issuecomment-4665694636
---
 pkgs/pkgs-lib/formats.nix       |  8 +++-
 pkgs/pkgs-lib/tests/formats.nix | 83 +++++++++++++++++++++++++++++++++
 2 files changed, 90 insertions(+), 1 deletion(-)

diff --git a/pkgs/pkgs-lib/formats.nix b/pkgs/pkgs-lib/formats.nix
index ef7d104f20e4..a184b0cbce53 100644
--- a/pkgs/pkgs-lib/formats.nix
+++ b/pkgs/pkgs-lib/formats.nix
@@ -1017,7 +1017,13 @@ optionalAttrs allowAliases aliases
     }:
     if format == "badgerfish" then
       {
-        type = serializableValueWith { typeName = "XML"; };
+        type =
+          attrsOf (serializableValueWith {
+            typeName = "XML";
+          })
+          // {
+            description = "XML value";
+          };
 
         generate =
           name: value:
diff --git a/pkgs/pkgs-lib/tests/formats.nix b/pkgs/pkgs-lib/tests/formats.nix
index ee6d817287c2..242fd64bc70a 100644
--- a/pkgs/pkgs-lib/tests/formats.nix
+++ b/pkgs/pkgs-lib/tests/formats.nix
@@ -142,6 +142,14 @@ runBuildTests {
     '';
   };
 
+  jsonNull = shouldPass {
+    format = formats.json { };
+    input = null;
+    expected = ''
+      null
+    '';
+  };
+
   yaml_1_1Atoms = shouldPass {
     format = formats.yaml_1_1 { };
     input = {
@@ -176,6 +184,15 @@ runBuildTests {
     '';
   };
 
+  yaml_1_1Null = shouldPass {
+    format = formats.yaml_1_1 { };
+    input = null;
+    expected = ''
+      null
+      ...
+    '';
+  };
+
   yaml_1_2Atoms = shouldPass {
     format = formats.yaml_1_2 { };
     input = {
@@ -210,6 +227,16 @@ runBuildTests {
     '';
   };
 
+  yaml_1_2Null = shouldPass {
+    format = formats.yaml_1_2 { };
+    input = null;
+    # nixfmt insists on removing indentation, so force it with ${"  "}
+    expected = ''
+
+      ${"  "}null
+    '';
+  };
+
   iniAtoms = shouldPass {
     format = formats.ini { };
     input = {
@@ -879,6 +906,14 @@ runBuildTests {
     '';
   };
 
+  cdnNull = shouldPass {
+    format = formats.cdn { };
+    input = null;
+    expected = ''
+      null: null
+    '';
+  };
+
   # This test is responsible for
   #   1. testing type coercions
   #   2. providing a more readable example test
@@ -989,6 +1024,14 @@ runBuildTests {
     '';
   };
 
+  luaNull = shouldPass {
+    format = formats.lua { };
+    input = null;
+    expected = ''
+      return nil
+    '';
+  };
+
   nixConfAtoms = shouldPass {
     format = formats.nixConf {
       package = pkgs.nix;
@@ -1014,6 +1057,15 @@ runBuildTests {
     '';
   };
 
+  nixConfNull = shouldFail {
+    format = formats.nixConf {
+      package = pkgs.nix;
+      version = pkgs.nix.version;
+      extraOptions = "ignore-try = false";
+    };
+    input = null;
+  };
+
   phpAtoms = shouldPass rec {
     format = formats.php { finalVariable = "config"; };
     input = {
@@ -1043,6 +1095,16 @@ runBuildTests {
     '';
   };
 
+  phpNull = shouldPass {
+    format = formats.php { finalVariable = "config"; };
+    input = null;
+    expected = ''
+      <?php
+      declare(strict_types=1);
+      $config = null;
+    '';
+  };
+
   pythonVars = shouldPass (
     let
       format = formats.pythonVars { };
@@ -1100,6 +1162,11 @@ runBuildTests {
     }
   );
 
+  pythonVarsNull = shouldFail {
+    format = formats.pythonVars { };
+    input = null;
+  };
+
   phpReturn = shouldPass {
     format = formats.php { };
     input = {
@@ -1145,6 +1212,11 @@ runBuildTests {
     '';
   };
 
+  xmlNull = shouldFail {
+    format = formats.xml { };
+    input = null;
+  };
+
   PlistGenerate = shouldPass {
     format = formats.plist { };
     input = {
@@ -1220,6 +1292,17 @@ runBuildTests {
       </plist>'';
   };
 
+  PlistNull = shouldPass {
+    format = formats.plist { };
+    input = null;
+    expected = ''
+      <?xml version="1.0" encoding="UTF-8"?>
+      <!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+      <plist version="1.0">
+
+      </plist>'';
+  };
+
   hcl1Atoms = shouldPass {
     format = formats.hcl1 { };
     input = {