[CMake] Use find or fetch mechanism for nlohmann json

CMakeLists.txt

@@ -53,7 +53,7 @@ option(SOFA_BUILD_RELEASE_PACKAGE "Run package specific configure" OFF)
 # Option to allow some dependencies such as cxxopts to be fetched by cmake if
 # the package is not found
 option(SOFA_ALLOW_FETCH_DEPENDENCIES "Allow compatible dependencies to be fetched if the package is not found by cmake.
-  List of dependencies that can be fetched: cxxopts, gtest, metis, CImg" ON)
+  List of dependencies that can be fetched: cxxopts, gtest, metis, CImg, nlohmann json" ON)
 
 # Option to accelerate the compilation
 # see https://cmake.org/cmake/help/v3.16/command/target_precompile_headers.html

Sofa/framework/Core/CMakeLists.txt

@@ -1,6 +1,21 @@
 cmake_minimum_required(VERSION 3.22)
 project(Sofa.Core LANGUAGES CXX)
 
+find_package(nlohmann_json QUIET)
+
+if(NOT TARGET nlohmann_json AND SOFA_ALLOW_FETCH_DEPENDENCIES)
+    message("Sofa.Core: DEPENDENCY nlohmann_json NOT FOUND. SOFA_ALLOW_FETCH_DEPENDENCIES is ON, fetching nlohmann_json...")
+
+    set(JSON_BuildTests OFF CACHE INTERNAL "")
+
+    sofa_fetch_dependency(nlohmann_json
+            GIT_REPOSITORY https://github.com/nlohmann/json.git
+            GIT_TAG        v3.12.0
+    )
+elseif(NOT TARGET nlohmann_json)
+    message(FATAL_ERROR "Sofa.Core: DEPENDENCY nlohmann_json NOT FOUND. SOFA_ALLOW_FETCH_DEPENDENCIES is OFF and thus cannot be fetched. Install nlohmann_json (version>=3.9.1), or enable SOFA_ALLOW_FETCH_DEPENDENCIES to fix this issue.")
+endif()
+
 set(SRC_ROOT "src/sofa/core")
 
 set(HEADER_FILES
@@ -352,6 +367,8 @@ add_library(${PROJECT_NAME} SHARED ${HEADER_FILES} ${SOURCE_FILES})
 
 target_link_libraries(${PROJECT_NAME} PUBLIC Sofa.Helper Sofa.Topology Sofa.DefaultType)
 
+target_link_libraries(${PROJECT_NAME} PRIVATE nlohmann_json::nlohmann_json)
+
 if(SOFA_BUILD_WITH_PCH_ENABLED)
     message("Adding precompiled header for Sofa.Core")
     target_precompile_headers(${PROJECT_NAME} PUBLIC ${SRC_ROOT}/objectmodel/BaseObject.h ${SRC_ROOT}/objectmodel/Data.h)

Sofa/framework/Core/src/sofa/core/ObjectFactoryJson.cpp

@@ -21,7 +21,7 @@
 ******************************************************************************/
 #include <sofa/core/ObjectFactoryJson.h>
 #include <sofa/core/ObjectFactory.h>
-#include <json.h>
+#include <nlohmann/json.hpp>
 #include <sofa/core/CategoryLibrary.h>
 
 

Sofa/framework/Helper/CMakeLists.txt

@@ -3,8 +3,23 @@ project(Sofa.Helper LANGUAGES CXX)
 
 # Eigen (header only)
 sofa_find_package(Eigen3 REQUIRED)
+
 # Json (header only) needed by AdvancedTimer
-sofa_find_package(Json 3.1.2 REQUIRED)
+find_package(nlohmann_json QUIET)
+
+if(NOT TARGET nlohmann_json AND SOFA_ALLOW_FETCH_DEPENDENCIES)
+    message("Sofa.GUI.Common: DEPENDENCY nlohmann_json NOT FOUND. SOFA_ALLOW_FETCH_DEPENDENCIES is ON, fetching nlohmann_json...")
+
+    set(JSON_BuildTests OFF CACHE INTERNAL "")
+
+    sofa_fetch_dependency(nlohmann_json
+            GIT_REPOSITORY https://github.com/nlohmann/json.git
+            GIT_TAG        v3.12.0
+    )
+elseif(NOT TARGET nlohmann_json)
+    message(FATAL_ERROR "Sofa.GUI.Common: DEPENDENCY nlohmann_json NOT FOUND. SOFA_ALLOW_FETCH_DEPENDENCIES is OFF and thus cannot be fetched. Install nlohmann_json (version>=3.9.1), or enable SOFA_ALLOW_FETCH_DEPENDENCIES to fix this issue.")
+endif()
+
 # STB (header only)
 sofa_find_package(STB REQUIRED)
 # DiffLib (header only)
@@ -249,7 +264,7 @@ elseif(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
 endif()
 
 # Json (header only) needed by AdvancedTimer
-target_include_directories(${PROJECT_NAME} SYSTEM PUBLIC "$<BUILD_INTERFACE:${JSON_INCLUDE_DIR}>")
+target_link_libraries(${PROJECT_NAME} PRIVATE nlohmann_json::nlohmann_json)
 
 # STB (header only) for Image
 target_include_directories(${PROJECT_NAME} SYSTEM PUBLIC "$<BUILD_INTERFACE:${STB_INCLUDE_DIR}>")

Sofa/framework/Helper/src/sofa/helper/AdvancedTimer.cpp

@@ -24,7 +24,7 @@
 #include <sofa/helper/logging/Messaging.h>
 #include <sofa/helper/AdvancedTimer.h>
 #include <sofa/type/vector.h>
-#include <json.h>
+#include <nlohmann/json.hpp>
 
 #include <iomanip>
 #include <cmath>
@@ -37,7 +37,7 @@
 
 #define DEFAULT_INTERVAL 100
 
-using json = sofa::helper::json;
+using json = nlohmann::json;
 
 
 namespace sofa::helper

extlibs/CMakeLists.txt

@@ -3,8 +3,6 @@ cmake_minimum_required(VERSION 3.22)
 
 ############# extlibs ##############
 
-# Nlohmann JSON (header-only)
-set(json_ROOT "${CMAKE_CURRENT_LIST_DIR}/json" CACHE PATH "Nlohmann JSON directory")
 # STB (header-only)
 set(STB_ROOT "${CMAKE_CURRENT_LIST_DIR}/stb" CACHE PATH "STB directory")
 # DiffLib