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GH-48316: [C++] Use FetchContent for bundled nlohmann-json #48320

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Merged
kou merged 4 commits into from
Dec 5, 2025
Merged

GH-48316: [C++] Use FetchContent for bundled nlohmann-json #48320

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62a64aa
GH-48316: [C++] Use FetchContent for bundled nlohmann-json
raulcd Dec 3, 2025
5250790
Add nlohmann_json_fc dependency conditionally to NLOHMANN_JSON_VENDORED
raulcd Dec 3, 2025
57bffa2
Case of nlohmann_json not being vendored
raulcd Dec 5, 2025
5d63ebc
Fix copy&paste error
raulcd Dec 5, 2025
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104 changes: 74 additions & 30 deletions cpp/cmake_modules/ThirdpartyToolchain.cmake
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Original file line number Diff line number Diff line change
Expand Up @@ -3465,38 +3465,73 @@ function(build_crc32c_once)
list(POP_BACK CMAKE_MESSAGE_INDENT)
endfunction()

macro(build_nlohmann_json)
message(STATUS "Building nlohmann-json from source")
# "Build" nlohmann-json
set(NLOHMANN_JSON_PREFIX "${CMAKE_CURRENT_BINARY_DIR}/nlohmann_json_ep-install")
set(NLOHMANN_JSON_INCLUDE_DIR "${NLOHMANN_JSON_PREFIX}/include")
set(NLOHMANN_JSON_CMAKE_ARGS
${EP_COMMON_CMAKE_ARGS} "-DCMAKE_INSTALL_PREFIX=<INSTALL_DIR>"
# google-cloud-cpp requires JSON_MultipleHeaders=ON
-DJSON_BuildTests=OFF -DJSON_MultipleHeaders=ON)
function(build_nlohmann_json)
list(APPEND CMAKE_MESSAGE_INDENT "nlohmann-json: ")
message(STATUS "Building nlohmann-json from source using FetchContent")
set(NLOHMANN_JSON_VENDORED
TRUE
PARENT_SCOPE)
set(NLOHMANN_JSON_PREFIX "${CMAKE_CURRENT_BINARY_DIR}/nlohmann_json_fc-install")
set(NLOHMANN_JSON_PREFIX
"${NLOHMANN_JSON_PREFIX}"
PARENT_SCOPE)

# We can remove this once we remove -DCMAKE_POLICY_VERSION_MINIMUM=3.5
# from EP_COMMON_CMAKE_ARGS.
list(REMOVE_ITEM NLOHMANN_JSON_CMAKE_ARGS -DCMAKE_POLICY_VERSION_MINIMUM=3.5)
fetchcontent_declare(nlohmann_json
${FC_DECLARE_COMMON_OPTIONS}
URL ${NLOHMANN_JSON_SOURCE_URL}
URL_HASH "SHA256=${ARROW_NLOHMANN_JSON_BUILD_SHA256_CHECKSUM}")

set(NLOHMANN_JSON_BUILD_BYPRODUCTS ${NLOHMANN_JSON_PREFIX}/include/nlohmann/json.hpp)
prepare_fetchcontent()

externalproject_add(nlohmann_json_ep
${EP_COMMON_OPTIONS}
INSTALL_DIR ${NLOHMANN_JSON_PREFIX}
URL ${NLOHMANN_JSON_SOURCE_URL}
URL_HASH "SHA256=${ARROW_NLOHMANN_JSON_BUILD_SHA256_CHECKSUM}"
CMAKE_ARGS ${NLOHMANN_JSON_CMAKE_ARGS}
BUILD_BYPRODUCTS ${NLOHMANN_JSON_BUILD_BYPRODUCTS})
# google-cloud-cpp requires JSON_MultipleHeaders=ON
set(JSON_BuildTests OFF)
set(JSON_MultipleHeaders ON)
set(JSON_Install ON)
fetchcontent_makeavailable(nlohmann_json)

# Work around https://gitlab.kitware.com/cmake/cmake/issues/15052
file(MAKE_DIRECTORY ${NLOHMANN_JSON_INCLUDE_DIR})
# google-cloud-cpp requires nlohmann_json to be installed to a known location.
# We have to do this in two steps to avoid double installation of nlohmann_json
# when Arrow is installed.
# This custom target ensures nlohmann_json is built before we install.
add_custom_target(nlohmann_json_built DEPENDS nlohmann_json::nlohmann_json)

add_library(nlohmann_json::nlohmann_json INTERFACE IMPORTED)
target_include_directories(nlohmann_json::nlohmann_json BEFORE
INTERFACE "${NLOHMANN_JSON_INCLUDE_DIR}")
add_dependencies(nlohmann_json::nlohmann_json nlohmann_json_ep)
endmacro()
# Disable nlohmann_json's install script after it's built to prevent double installation.
add_custom_command(OUTPUT "${nlohmann_json_BINARY_DIR}/cmake_install.cmake.saved"
COMMAND ${CMAKE_COMMAND} -E copy_if_different
"${nlohmann_json_BINARY_DIR}/cmake_install.cmake"
"${nlohmann_json_BINARY_DIR}/cmake_install.cmake.saved"
COMMAND ${CMAKE_COMMAND} -E echo
"# nlohmann-json install disabled to prevent double installation with Arrow"
> "${nlohmann_json_BINARY_DIR}/cmake_install.cmake"
DEPENDS nlohmann_json_built
COMMENT "Disabling nlohmann-json install to prevent double installation"
VERBATIM)

add_custom_target(nlohmann_json_install_disabled ALL
DEPENDS "${nlohmann_json_BINARY_DIR}/cmake_install.cmake.saved")

# Install nlohmann_json to NLOHMANN_JSON_PREFIX for google-cloud-cpp to find.
add_custom_command(OUTPUT "${NLOHMANN_JSON_PREFIX}/.nlohmann_json_installed"
COMMAND ${CMAKE_COMMAND} -E copy_if_different
"${nlohmann_json_BINARY_DIR}/cmake_install.cmake.saved"
"${nlohmann_json_BINARY_DIR}/cmake_install.cmake.tmp"
COMMAND ${CMAKE_COMMAND}
-DCMAKE_INSTALL_PREFIX=${NLOHMANN_JSON_PREFIX}
-DCMAKE_INSTALL_CONFIG_NAME=$<CONFIG> -P
"${nlohmann_json_BINARY_DIR}/cmake_install.cmake.tmp" ||
${CMAKE_COMMAND} -E true
COMMAND ${CMAKE_COMMAND} -E touch
"${NLOHMANN_JSON_PREFIX}/.nlohmann_json_installed"
DEPENDS nlohmann_json_install_disabled
COMMENT "Installing nlohmann-json to ${NLOHMANN_JSON_PREFIX} for google-cloud-cpp"
VERBATIM)

# Make nlohmann_json_fc depend on the install completion marker.
add_custom_target(nlohmann_json_fc
DEPENDS "${NLOHMANN_JSON_PREFIX}/.nlohmann_json_installed")

list(POP_BACK CMAKE_MESSAGE_INDENT)
endfunction()
if(ARROW_WITH_NLOHMANN_JSON)
resolve_dependency(nlohmann_json)
get_target_property(nlohmann_json_INCLUDE_DIR nlohmann_json::nlohmann_json
Expand Down Expand Up @@ -3559,7 +3594,11 @@ macro(build_google_cloud_cpp_storage)
add_dependencies(google_cloud_cpp_dependencies zlib_ep)
endif()
add_dependencies(google_cloud_cpp_dependencies crc32c_fc)
add_dependencies(google_cloud_cpp_dependencies nlohmann_json::nlohmann_json)
if(NLOHMANN_JSON_VENDORED)
add_dependencies(google_cloud_cpp_dependencies nlohmann_json_fc)
else()
add_dependencies(google_cloud_cpp_dependencies nlohmann_json::nlohmann_json)
endif()

set(GOOGLE_CLOUD_CPP_STATIC_LIBRARY_STORAGE
"${GOOGLE_CLOUD_CPP_INSTALL_PREFIX}/lib/${CMAKE_STATIC_LIBRARY_PREFIX}google_cloud_cpp_storage${CMAKE_STATIC_LIBRARY_SUFFIX}"
Expand Down Expand Up @@ -4052,9 +4091,14 @@ macro(build_opentelemetry)
CONFIGURE_COMMAND ""
INSTALL_COMMAND ""
EXCLUDE_FROM_ALL OFF)
if(NLOHMANN_JSON_VENDORED)
add_dependencies(opentelemetry_dependencies nlohmann_json_fc)
else()
add_dependencies(opentelemetry_dependencies nlohmann_json::nlohmann_json)
endif()

add_dependencies(opentelemetry_dependencies nlohmann_json::nlohmann_json
opentelemetry_proto_ep ${ARROW_PROTOBUF_LIBPROTOBUF})
add_dependencies(opentelemetry_dependencies opentelemetry_proto_ep
${ARROW_PROTOBUF_LIBPROTOBUF})

# Ensure vendored protobuf is installed before OpenTelemetry builds
if(PROTOBUF_VENDORED)
Expand Down
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