cmake: allow this project to be used as a cmake-subdirectory

Needs to have a json-hpp-target-available.

CMakeLists.txt

@@ -2,6 +2,8 @@ project(json-schema-validator CXX)
 
 cmake_minimum_required(VERSION 3.2)
 
+# if used as a subdirectory just define a json-hpp-target (INTERFACE)
+if(NOT TARGET json-hpp)
 # find nlohmann's json.hpp
     find_path(NLOHMANN_JSON_DIR
         NAMES
@@ -11,11 +13,12 @@ if(NOT NLOHMANN_JSON_DIR)
         message(FATAL_ERROR "please set NLOHMANN_JSON_DIR to a path in which NLohmann's json.hpp can be found.")
     endif()
 
-# create an interface-library for simple linking
+# create an interface-library for simple cmake-linking
-add_library(json INTERFACE)
+    add_library(json-hpp INTERFACE)
-target_include_directories(json
+    target_include_directories(json-hpp
         INTERFACE
             ${NLOHMANN_JSON_DIR})
+endif()
 
 # and one for the validator
 add_library(json-schema-validator INTERFACE)
@@ -27,7 +30,7 @@ target_compile_options(json-schema-validator
         -Wall -Wextra) # bad, better use something else based on compiler type
 target_link_libraries(json-schema-validator
     INTERFACE
-        json)
+        json-hpp)
 
 install(
     FILES
@@ -44,6 +47,7 @@ target_link_libraries(json-schema-validate json-schema-validator)
 add_executable(json-schema-test app/json-schema-test.cpp)
 target_link_libraries(json-schema-test json-schema-validator)
 
+# test-zone
 enable_testing()
 
 # find schema-test-suite
@@ -63,7 +67,7 @@ if(JSON_SCHEMA_TEST_SUITE_PATH)
         )
     endforeach()
 else()
-    message(STATUS "Please test JSON_SCHEMA_TEST_SUITE_PATH to a path in which you've cloned JSON-Schema-Test-Suite (github.com/json-schema-org/JSON-Schema-Test-Suite).")
+    message(STATUS "Consider setting JSON_SCHEMA_TEST_SUITE_PATH to a path in which JSON-Schema-Test-Suite is located (github.com/json-schema-org/JSON-Schema-Test-Suite).")
 endif()
 
 

README.md

@@ -14,7 +14,7 @@ C++](https://github.com/nlohmann/json). This validator is based on this
 library, hence the name.
 
 The name is for the moment purely marketing, because there is, IMHO, not much
-modern C++ inside.
+modern C++ inside. But I think the whole thing could be rewritten mode "modern".
 
 External documentation is missing as well. However the API of the validator
 will be rather simple.
@@ -23,6 +23,8 @@ will be rather simple.
 
 ## Build
 
+Directly
+
 ```Bash
 git clone https://github.com/pboettch/json-schema-validator.git
 cd json-schema-validator
@@ -32,6 +34,20 @@ cmake .. \
     -DNLOHMANN_JSON_DIR=<path/to/json.hpp> \
     -DJSON_SCHEMA_TEST_SUITE_PATH=<path/to/JSON-Schema-test-suite> # optional
 make # install
+ctest # if test-suite has been given
+```
+or from another CMakeLists.txt as a subdirectory:
+
+```CMake
+# create an interface-target called json-hpp
+add_library(json-hpp INTERFACE)
+target_include_directories(json-hpp
+    INTERFACE
+        path/to/json.hpp)
+set(JSON_SCHEMA_TEST_SUITE_PATH "path/to/json-schema-test-suite")
+
+enable_testing() # if you want to inherit tests
+add_subdirectory(path-to-this-project json-schema-validator)
 ```
 
 ## Code