If external nlohmann::json is not found, then use one from our submod…

…ule (#865)

CMakeLists.txt

@@ -228,6 +228,24 @@ endif()
 # GNUInstallDirs.
 include(GNUInstallDirs)
 
+find_package(nlohmann_json QUIET)
+if(NOT nlohmann_json_FOUND)
+  message("Using local nlohmann::json from submodule")
+  set(JSON_BuildTests
+      OFF
+      CACHE INTERNAL "")
+  set(JSON_Install
+      OFF
+      CACHE INTERNAL "")
+  # This option allows to link nlohmann_json::nlohmann_json target
+  add_subdirectory(${PROJECT_SOURCE_DIR}/third_party/nlohmann-json)
+  # This option allows to add header to include directories
+  include_directories(
+    ${PROJECT_SOURCE_DIR}/third_party/nlohmann-json/single_include)
+else()
+  message("Using external nlohmann::json")
+endif()
+
 if(WITH_OTLP)
   set(protobuf_MODULE_COMPATIBLE ON)
   find_package(Protobuf)
@@ -268,13 +286,13 @@ if(WITH_OTLP)
   include(cmake/opentelemetry-proto.cmake)
   include(CMakeDependentOption)
   find_package(CURL)
-  find_package(nlohmann_json)
+
   cmake_dependent_option(
     WITH_OTLP_GRPC "Whether to include the OTLP gRPC exporter in the SDK" ON
     "gRPC_FOUND" OFF)
   cmake_dependent_option(
     WITH_OTLP_HTTP "Whether to include the OTLP http exporter in the SDK" ON
-    "CURL_FOUND;nlohmann_json_FOUND" OFF)
+    "CURL_FOUND" OFF)
 endif()
 
 list(APPEND CMAKE_PREFIX_PATH "${CMAKE_BINARY_DIR}")
@@ -329,9 +347,6 @@ if(NOT WITH_API_ONLY)
   endif()
 endif()
 
-# Add nlohmann/json submodule to include directories
-include_directories(third_party/nlohmann-json/single_include)
-
 # Export cmake config and support find_packages(opentelemetry-cpp CONFIG) Write
 # config file for find_packages(opentelemetry-cpp CONFIG)
 set(INCLUDE_INSTALL_DIR "${CMAKE_INSTALL_INCLUDEDIR}")

exporters/etw/CMakeLists.txt

@@ -1,5 +1,3 @@
-find_package(nlohmann_json REQUIRED)
-
 add_library(opentelemetry_exporter_etw INTERFACE)
 
 target_include_directories(

exporters/otlp/CMakeLists.txt

@@ -28,16 +28,13 @@ endif()
 
 if(WITH_OTLP_HTTP)
   find_package(CURL REQUIRED)
-  find_package(nlohmann_json REQUIRED)
   add_library(opentelemetry_exporter_otlp_http src/otlp_http_exporter.cc)
 
   set_target_properties(opentelemetry_exporter_otlp_http
                         PROPERTIES EXPORT_NAME otlp_http_exporter)
 
-  target_link_libraries(
-    opentelemetry_exporter_otlp_http
-    PUBLIC opentelemetry_otlp_recordable http_client_curl
-           nlohmann_json::nlohmann_json)
+  target_link_libraries(opentelemetry_exporter_otlp_http
+                        PUBLIC opentelemetry_otlp_recordable http_client_curl)
 
   list(APPEND OPENTELEMETRY_OTLP_TARGETS opentelemetry_exporter_otlp_http)
 endif()

ext/test/w3c_tracecontext_test/CMakeLists.txt

@@ -4,19 +4,10 @@ find_package(CURL)
 if(NOT CURL_FOUND)
   message(WARNING "Skipping example_w3c_tracecontext_test: CURL not found")
 else()
-  find_package(nlohmann_json QUIET)
-  if(NOT nlohmann_json_FOUND)
-    # Add library from git submodule to include path
-    include_directories(
-      ${PROJECT_SOURCE_DIR}/third_party/nlohmann-json/single_include)
-  else()
-    # Add header-only library found by CMake
-    set(NLOHMANN_JSON_LIB nlohmann_json::nlohmann_json)
-  endif()
   add_executable(w3c_tracecontext_test main.cc)
   target_link_libraries(
     w3c_tracecontext_test
     PRIVATE ${CMAKE_THREAD_LIBS_INIT} opentelemetry_trace http_client_curl
             opentelemetry_exporter_ostream_span ${CURL_LIBRARIES}
-            ${NLOHMANN_JSON_LIB})
+            nlohmann_json::nlohmann_json)
 endif()