Find nlohmann_json dependency only when required (#342)

* only find nlohmann_json test dep when required

* provide config-variable JWT_EXTERNAL_TEST_NLOHMANN_JSON

* be a doll and make PICOJSON variables dependent

* dont mention test in the option name

I think in the longer term we'll probably switch to this since it;s maintained unlike the current default

---------

Co-authored-by: Chris Mc <prince.chrismc@gmail.com>

Author: justend29

CMakeLists.txt

@@ -21,9 +21,15 @@ option(JWT_BUILD_DOCS "Adds a target for building the doxygen documentation" OFF
 option(JWT_ENABLE_COVERAGE "Enable code coverage testing" OFF)
 option(JWT_ENABLE_FUZZING "Enable fuzz testing" OFF)
 
-option(JWT_EXTERNAL_PICOJSON "Use find_package() to locate picojson, provided to integrate with package managers" OFF)
-option(JWT_DISABLE_BASE64 "Do not include the base64 implementation from this library" OFF)
 option(JWT_DISABLE_PICOJSON "Do not provide the picojson template specialiaze" OFF)
+option(JWT_DISABLE_BASE64 "Do not include the base64 implementation from this library" OFF)
+include(CMakeDependentOption)
+cmake_dependent_option(JWT_EXTERNAL_PICOJSON
+  "Use find_package() to locate picojson, provided to integrate with package managers" OFF
+  "NOT JWT_DISABLE_PICOJSON" OFF)
+cmake_dependent_option(JWT_EXTERNAL_NLOHMANN_JSON
+  "Use find_package() to locate nlohman-json required for tests and examples" OFF
+  "JWT_BUILD_EXAMPLES OR JWT_BUILD_TESTS" OFF)
 
 set(JWT_SSL_LIBRARY_OPTIONS OpenSSL LibreSSL wolfSSL)
 set(JWT_SSL_LIBRARY OpenSSL CACHE STRING "Determines which SSL library to build with")
@@ -63,18 +69,22 @@ elseif(${JWT_SSL_LIBRARY} MATCHES "wolfSSL")
   list(TRANSFORM wolfssl_INCLUDE_DIRS APPEND "/wolfssl") # This is required to access OpenSSL compatibility API
 endif()
 
-if(JWT_EXTERNAL_PICOJSON)
+if(NOT JWT_DISABLE_PICOJSON AND JWT_EXTERNAL_PICOJSON)
   find_package(picojson 1.3.0 REQUIRED)
 endif()
 
-find_package(nlohmann_json CONFIG)
-
-if(NOT nlohmann_json_FOUND)
-  message(STATUS "jwt-cpp: using FetchContent for nlohmann json")
-  include(FetchContent)
-  fetchcontent_declare(nlohmann_json URL https://github.com/nlohmann/json/releases/download/v3.11.2/json.tar.xz
-                       URL_MD5 127794b2c82c0c5693805feaa2a703e2)
-  fetchcontent_makeavailable(nlohmann_json)
+if(JWT_BUILD_EXAMPLES OR JWT_BUILD_TESTS)
+  if(JWT_EXTERNAL_NLOHMANN_JSON)
+    message(STATUS "jwt-cpp: using find_package for nlohmann-json required for tests")
+    find_package(nlohmann_json CONFIG REQUIRED)
+  else()
+    message(STATUS "jwt-cpp: using FetchContent for nlohmann-json required for tests")
+    include(FetchContent)
+    fetchcontent_declare(nlohmann_json
+      URL https://github.com/nlohmann/json/releases/download/v3.11.2/json.tar.xz
+      URL_MD5 127794b2c82c0c5693805feaa2a703e2)
+    fetchcontent_makeavailable(nlohmann_json)
+  endif()
 endif()
 
 set(JWT_INCLUDE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/include)
@@ -118,7 +128,7 @@ if(${JWT_SSL_LIBRARY} MATCHES "wolfSSL")
   target_compile_definitions(jwt-cpp INTERFACE OPENSSL_EXTRA OPENSSL_ALL)
 endif()
 
-if(JWT_EXTERNAL_PICOJSON)
+if(NOT JWT_DISABLE_PICOJSON AND JWT_EXTERNAL_PICOJSON)
   target_link_libraries(jwt-cpp INTERFACE picojson::picojson>)
 endif()
 
@@ -129,7 +139,7 @@ endif()
 
 configure_package_config_file(
   ${CMAKE_CURRENT_LIST_DIR}/cmake/jwt-cpp-config.cmake.in ${CMAKE_CURRENT_BINARY_DIR}/jwt-cpp-config.cmake
-  INSTALL_DESTINATION ${JWT_CMAKE_FILES_INSTALL_DIR} PATH_VARS JWT_EXTERNAL_PICOJSON JWT_SSL_LIBRARY)
+  INSTALL_DESTINATION ${JWT_CMAKE_FILES_INSTALL_DIR})
 write_basic_package_version_file(${CMAKE_CURRENT_BINARY_DIR}/jwt-cpp-config-version.cmake VERSION 0.7.0
                                  COMPATIBILITY ExactVersion)
 

cmake/jwt-cpp-config.cmake.in

@@ -1,5 +1,6 @@
 @PACKAGE_INIT@
 
+set(JWT_DISABLE_PICOJSON @JWT_DISABLE_PICOJSON@)
 set(JWT_EXTERNAL_PICOJSON @JWT_EXTERNAL_PICOJSON@)
 set(JWT_SSL_LIBRARY @JWT_SSL_LIBRARY@)
 
@@ -12,7 +13,7 @@ else()
   find_dependency(${JWT_SSL_LIBRARY} REQUIRED)
 endif()
 
-if(JWT_EXTERNAL_PICOJSON)
+if(NOT JWT_DISABLE_PICOJSON AND JWT_EXTERNAL_PICOJSON)
   find_dependency(picojson REQUIRED)
 endif()