Without SYSTEM static analysis like clang-tidy raise warnings on
json.hpp. This is not desirable for projects embedding nlohmann_json
Tests:
- Validated that without the option OFF the warnings are raised as
before
- Validated that with the option ON the warnings are silenced
When the testsuite is enabled, the "cmake_add_subdirectory" test
adds a second copy of the project into the build configuration, and the
project files are installed twice.
This becomes super problematic when it tries to install a file from
CMAKE_BINARY_DIR which is only available in CMAKE_CURRENT_BINARY_DIR
and bombs out with the following error message:
```
[...]
-- Installing: <DESTDIR>/usr/lib/cmake/nlohmann_json/nlohmann_jsonTargets.cmake
CMake Error at test/cmake_add_subdirectory/nlohmann_json/cmake_install.cmake:73 (file):
file INSTALL cannot find
"......./nlohmann-json/builddir/test/cmake_add_subdirectory/nlohmann_json.pc":
No such file or directory.
Call Stack (most recent call first):
test/cmake_add_subdirectory/cmake_install.cmake:47 (include)
test/cmake_install.cmake:49 (include)
cmake_install.cmake:94 (include)
```
The meson builds install a pkg-config file, but the cmake builds don't.
This adds a pkg-config file to the cmake builds that is functionally
equivalent to the one generated from meson.
Projects that import json via [FetchContent](https://cmake.org/cmake/help/latest/module/FetchContent.html) or `add_subdirectory` pointed at a git submodule may want to set `JSON_BuildTests` to "NO". However, this doesn't work without creating an identical `option()` in the importing project. Enabling CMP0077 in supported versions of CMake changes the behavior of `option()` to allow importing projects to set default values for the variables without touching the cache.
See the documentation for CMP0077 here: https://cmake.org/cmake/help/latest/policy/CMP0077.html
Commit 73cc5089 (Using target_compile_features to specify C++ 11
standard) bumped the required cmake version, from 3.0 to 3.8, so
as to get the definition of target_compile_features().
However, target_compile_features() was introduced in cmake-3.1:
https://cmake.org/cmake/help/v3.1/command/target_compile_features.html
And using cmake-3.1 is indeed sufficient to properly build.
As such, relax the minimum required version down to cmake-3.1,
so we can build on oldish, entreprise-grade distributions that
only have cmake-3.1 (or at least, don't have up to cmake-3.8).
Reported-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
When adding this library as embedded library with private
"target link", e.g. only used inside private source files, the
library does not need to be installed when the main project gets
installed.
This adds an additional option `JSON_Install` similar to the
test-build control switch in order to skip installing headers and
CMake config files if requested.
Avoids using
```cmake
add_subdirectory(path/to/nlohmann_json EXCLUDE_FROM_ALL)
```
which has further side-effects:
https://cmake.org/cmake/help/v3.0/command/add_subdirectory.html
