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Author: metascroy

backends/mlx/CMakeLists.txt

@@ -212,12 +212,30 @@ set(MLX_METAL_JIT
     CACHE BOOL "Use JIT compiled Metal kernels"
 )
 
-# Pre-populate json FetchContent to use ET's copy. MLX unconditionally calls
-# FetchContent_MakeAvailable(json) which would conflict with ET's
-# third-party/json. By pre-populating, CMake skips MLX's download.
-include(FetchContent)
-FetchContent_Declare(json SOURCE_DIR ${EXECUTORCH_ROOT}/third-party/json)
-FetchContent_MakeAvailable(json)
+# Auto-apply json patch so MLX reuses executorch's nlohmann_json instead of
+# downloading its own copy via FetchContent. TODO: upstream a patch to MLX
+set(MLX_JSON_PATCH "${CMAKE_CURRENT_SOURCE_DIR}/patches/mlx_json.patch")
+if(EXISTS "${MLX_JSON_PATCH}" AND EXISTS "${MLX_SOURCE_DIR}")
+  execute_process(
+    COMMAND git apply --check ${MLX_JSON_PATCH}
+    WORKING_DIRECTORY ${MLX_SOURCE_DIR}
+    RESULT_VARIABLE _mlx_json_patch_check
+    OUTPUT_QUIET ERROR_QUIET
+  )
+  if(_mlx_json_patch_check EQUAL 0)
+    execute_process(
+      COMMAND git apply ${MLX_JSON_PATCH} WORKING_DIRECTORY ${MLX_SOURCE_DIR}
+    )
+    message(STATUS "Applied mlx_json.patch to MLX submodule")
+  else()
+    message(STATUS "mlx_json.patch already applied or not applicable")
+  endif()
+endif()
+
+# Provide executorch's nlohmann_json so the patched MLX skips its own download
+add_subdirectory(
+  ${EXECUTORCH_ROOT}/third-party/json ${CMAKE_CURRENT_BINARY_DIR}/nlohmann_json
+)
 
 # Add MLX subdirectory
 message(STATUS "Adding MLX from submodule: ${MLX_SOURCE_DIR}")

third-party/CMakeLists.txt

@@ -5,9 +5,7 @@
 # LICENSE file in the root directory of this source tree.
 
 set(CMAKE_POLICY_VERSION_MINIMUM 3.5)
-if(NOT TARGET nlohmann_json)
-  add_subdirectory(json)
-endif()
+add_subdirectory(json)
 add_subdirectory(gflags)
 
 if(EXECUTORCH_BUILD_PYBIND)