Skip building tests by default when included in other projects

[ankane]

Hi, I think it'd be nice to skip building tests by default when libpqxx is included in other projects. For instance, with FetchContent:

include(FetchContent)

FetchContent_Declare(libpqxx GIT_REPOSITORY https://github.com/jtv/libpqxx.git GIT_TAG 7.10.0)
FetchContent_MakeAvailable(libpqxx)

target_link_libraries(app PRIVATE libpqxx::pqxx)

Currently, projects need to set:

set(SKIP_BUILD_TEST ON)

nlohmann/json is one project that does this.

[tt4g]

When the changes are merged, the test code that was previously built in the subproject will no longer be built.
It would be better to add to CHANGELOG that “Users who want to continue to build libpqxx tests in subprojects must add set(BUILD_TEST ON) to their CMake project”.

[jtv]

It's not clear to me why the tests break on this PR, but at any rate I'm not confident yet that I get this idea.

Also, it relies on a string comparison and I'd like to be sure that that check is robust in the face of soft links, unicode normalisation, etc. if possible.

[tt4g]

@jtv

CMAKE_SOURCE_DIR is the path to CMakeLists.txt at the top level of the project and CMAKE_CURRENT_SOURCE_DIR is the path to the current CMakeLists.txt.
The two paths are the same for CMakeLists.txt at the top level of the project.
When importing another CMakeLists.txt from CMakeLists.txt at the top level of the project, the two paths will be different in the imported CMakeLists.txt.

See also:

• https://cmake.org/cmake/help/v3.31/variable/CMAKE_SOURCE_DIR.html#variable:CMAKE_SOURCE_DIR
• https://cmake.org/cmake/help/v3.31/variable/CMAKE_CURRENT_SOURCE_DIR.html

In libpqxx, CMakeLists.txt is the top of the project.
In this, CMAKE_SOURCE_DIR and CMAKE_CURRENT_SOURCE_DIR are the same path.

 CMAKE_SOURCE_DIR:         path/to/libpqxx/CMakeLists.txt
 CMAKE_CURRENT_SOURCE_DIR: path/to/libpqxx/CMakeLists.txt

From CMakeLists.txt, test/CMakeLists.txt is imported by add_subdirectory(test).

libpqxx/CMakeLists.txt

Line 35 in d280c6c

add_subdirectory(test)

At this time test/CMakeLists.txt is evaluated, but at this time CMAKE_SOURCE_DIR and CMAKE_CURRENT_SOURCE_DIR are different paths.

-CMAKE_SOURCE_DIR:         path/to/libpqxx/CMakeLists.txt
+CMAKE_CURRENT_SOURCE_DIR: path/to/libpqxx/test/CMakeLists.txt

Also, it relies on a string comparison and I'd like to be sure that that check is robust in the face of soft links, unicode normalisation, etc. if possible.

These two variables are generated by CMake, so there is no need to worry about them.

[jtv]

Trying to figure out why the CircleCI test is failing... It doesn't look related but it's entirely unclear. :-(

Thanks @tt4g for the explanation. I'm warming to the idea. On the one hand the tests even when they don't actually run may expose some compile problems on other systems out there before they actually hit any users. On the other hand, the tests take up most of the compile time and most portability problems and such will show up soon enough as people build applications.

[jtv]

@ankane it looks like the build is failing because you're not logged into CircleCI.

[jtv]

@ankane I've merged it anyway — bit silly that the test pipeline gets run under your identity but does not check that this is in fact possible. A local build still works. Thanks for the contribution, it'll save a lot of people some time.

[ankane]

Thanks @jtv! Another method I've seen is CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME (like CLI11), but seems like there could be collisions.