python3Packages.mlx: use nlohmann_json from nixpkgs

pkgs/development/python-modules/mlx/default.nix

@@ -52,8 +52,9 @@ buildPythonPackage (finalAttrs: {
   };
 
   patches = [
-    # Use system nanobind instead of fetching its sources
+    # Use nix packages instead of fetching their sources
     ./dont-fetch-nanobind.patch
+    ./dont-fetch-json.patch
   ]
   ++ lib.optionals stdenv.hostPlatform.isDarwin [
     (replaceVars ./darwin-build-fixes.patch {
@@ -88,7 +89,7 @@ buildPythonPackage (finalAttrs: {
       (lib.cmakeBool "MLX_BUILD_METAL" false)
       (lib.cmakeBool "USE_SYSTEM_FMT" true)
       (lib.cmakeOptionType "filepath" "FETCHCONTENT_SOURCE_DIR_GGUFLIB" "${gguf-tools}")
-      (lib.cmakeOptionType "filepath" "FETCHCONTENT_SOURCE_DIR_JSON" "${nlohmann_json.src}")
+      (lib.cmakeFeature "CMAKE_CXX_FLAGS" "-I${lib.getDev nlohmann_json}/include/nlohmann")
 
       # Cmake cannot find nanobind-config.cmake by itself
       (lib.cmakeFeature "nanobind_DIR" "${nanobind}/${python.sitePackages}/nanobind/cmake")

pkgs/development/python-modules/mlx/dont-fetch-json.patch

@@ -0,0 +1,20 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index 2451aa65..f88d4889 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -241,14 +241,6 @@ else()
+   set(MLX_BUILD_ACCELERATE OFF)
+ endif()
+ 
+-message(STATUS "Downloading json")
+-FetchContent_Declare(
+-  json
+-  URL https://github.com/nlohmann/json/releases/download/v3.11.3/json.tar.xz)
+-FetchContent_MakeAvailable(json)
+-target_include_directories(
+-  mlx PRIVATE $<BUILD_INTERFACE:${json_SOURCE_DIR}/single_include/nlohmann>)
+-
+ add_subdirectory(${CMAKE_CURRENT_LIST_DIR}/mlx)
+ 
+ target_include_directories(
+