Added Hunter, install and MSVC fix

Author: themarpe

CMakeLists.txt

@@ -8,6 +8,16 @@ cmake_minimum_required(VERSION 3.2)
 option(BUILD_TESTS    "Build tests"    ON)
 option(BUILD_EXAMPLES "Build examples" ON)
 
+option(HUNTER_ENABLED "Enable Hunter package manager support" OFF)
+if(HUNTER_ENABLED)
+    include(cmake/HunterGate.cmake)
+    HunterGate(URL https://github.com/cpp-pm/hunter/archive/v0.23.253.tar.gz
+               SHA1 88ea6d37c897a81a080eb9ae0f69d7807bbb3c73)
+
+    # Add nlohmann_json::nlohmann_json (if HUNTER_ENABLED=ON, otherwise command is ignored)
+    hunter_add_package(nlohmann_json)
+endif()
+
 # the library
 add_library(nlohmann_json_schema_validator
     src/json-schema-draft7.json.cpp
@@ -158,8 +168,8 @@ endif()
 if(JSON_VALIDATOR_INSTALL)
     # Set Up the Project Targets and Config Files for CMake
 
-    # Set the install path to the cmake config files
-    set(INSTALL_CMAKE_DIR ${CMAKE_INSTALL_PREFIX}/lib/cmake/${PROJECT_NAME})
+    # Set the install path to the cmake config files (Relative, so install works correctly under Hunter as well)
+    set(INSTALL_CMAKE_DIR "lib/cmake/${PROJECT_NAME}")
 
     # Create the ConfigVersion file
     include(CMakePackageConfigHelpers) # write_basic_package_version_file
@@ -168,7 +178,7 @@ if(JSON_VALIDATOR_INSTALL)
                                       COMPATIBILITY SameMajorVersion)
 
     # Get the relative path from the INSTALL_CMAKE_DIR to the include directory
-    file(RELATIVE_PATH REL_INCLUDE_DIR "${INSTALL_CMAKE_DIR}" "${CMAKE_INSTALL_PREFIX}/include")
+    file(RELATIVE_PATH REL_INCLUDE_DIR "${CMAKE_INSTALL_PREFIX}/${INSTALL_CMAKE_DIR}" "${CMAKE_INSTALL_PREFIX}/include")
 
 
     # Configure the Config.cmake file with the proper include directory

README.md

@@ -106,6 +106,14 @@ access nlohmann-json:
 a sub-directory (via `add_subdirectory()`), 2 and 3 can be
 assisted by setting the `nlohmann_json_DIR`-variable.
 
+### Building with Hunter package manager
+
+To enable access to nlohmann json library, Hunter can be used. Just run with HUNTER_ENABLED=ON option. No further dependencies needed
+
+```bash
+cmake [..] -DHUNTER_ENABLED=ON [..]
+```
+
 ### Building as a CMake-subdirectory from within another project
 
 Adding this library as a subdirectory to a parent project is one way of