xtensor: Unable use project as sub directory

In my project, I added xtl, xsimd and xtensor as submodules and then in my CMakeLists.txt

set(BUILD_TESTS "" CACHE BOOL OFF)
set(BUILD_EXAMPLES "" CACHE BOOL OFF)
set(DOWNLOAD_GTEST "" CACHE BOOL OFF)
set(ENABLE_FALLBACK "" CACHE BOOL ON)
set(XTENSOR_USE_XSIMD "" CACHE BOOL ON)

add_subdirectory(xtl)
add_subdirectory(xsimd)
add_subdirectory(xtensor)

The cmake failed configure due to xtensor try to find_package.

I think in this case the CMakeLists.txt for xtensor et. al. should identify itself is added as subproject and do not find_package at all, just target_link_libraries

e.g., with the test of if( CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR )

BTW, is there better solution in this case?

About this issue

Original URL
State: closed
Created 5 years ago
Comments: 17 (12 by maintainers)

Most upvoted comments

The problem is not actually finding xtensor, but the very fact that the main officially supported way of using it is via installing it into the environment. Header-only libraries should never need to be installed. For me, change control is an integral part of dependency management. In our company, all build processes are required not to depend on the system environment except very basic libraries (i.e. what is available from a fresh system install). All other dependencies must be managed by each project itself. Within CI, there are plenty of tools managing the environment to deal with system-installing dependencies. But the developer experience suffers.

Using gitsub* for that purpose is certainly not the best possible way, but it is convenient for small projects that are otherwise self-contained. Now, we can of course just do a separate

add_library(xtensor INTERFACE)
target_include_directories(xtensor INTERFACE whatever/path/to/the/however/managed/dependencies/quantstack/xtensor)

in our projects, and then go on with possible compilation options -DXTENSOR_USE_XSIMD etc. But add_subproject(.../xtensor) would be more convenient and help avoiding duplicate effort.

I don’t want to convince anyone that he should be using gitsub* - that’s not the point. I’m just looking for an improved experience using xtensor via CMake without installing, directly from the source tree. I’d be happy to contribute a pull-request to that end in the x* projects that I use ( xtl, xsimd, xtensor and xtensor-python), if there is interest.

@tdegeus: I believe there are ways to specify the paths CMake uses for find_package and friends. So, technically, we could install xtensor into some dedicated location and let CMake find them there. It’s just a separate build step (implying a separate configuration step which hopefully matches the project configuration), which feels kind of unnecessary for a header-only library.

burnpanck on Sep 15, 2019

I very much agree with the sentiments @burnpanck has voiced. In my case, my company vendors all dependencies in git submodules. I don’t like it and I wished we used a real dependency management system like conan. But regardless of how I feel on the matter, or whether its a terrible idea or not, we aren’t going to redesign our entire build system and CI right now. Many people vendor dependencies via CMake’s add_subdirectory command, and although maybe a bad idea, its fairly standard practice. For this reason, having an interface target to link to that respects add_subdirectory is something that will be a sticking point for a lot of people, myself included, in order to use this project.

TheButlah on Jan 2, 2020