CMake find_package not handling multi-configurations

Question

We're using Jenkins 2.60.2 and CMake 3.9.1 to automate our build system. This all works well for multiple versions of build tools, architectures and debug/release targets (if ALL configurations have been built and installed, so both Debug AND Release).

A Debug-only configuration that uses find_package() typically ignores the CMAKE_BUILD_TYPE at discovery. Internally the scripts search for file and libraries and store the locations in variables. At the end of the script, the variables are scanned for _NOTFOUND strings, which is the result of a file or library not found in all the reference paths/hints. So essentially a find_package() will fail if the Release lib can not be found, and mark the whole package as not installed properly, even though the build is only strictly interested in the Debug target.

Typically the XXXConfig.cmake files use a call to find_package_handle_standard_args(.. PATH_TO_LIB) that scans for _NOTFOUND strings in the path variables to the libraries. These variables typically get set to _NOTFOUND by earlier calls to find_library(PATH_TO_LIB libname ..). For more information I refer to the CMake docs.

The user can indeed tag debug libraries with 'debug' and release libs with 'optimized', but this does not seem to help during the lib discovery and is only used during linking.

Anyone knows how to handle this properly?

Kind regards

Answer 1

This is one of the unfortunate shortcomings of the classic use of find_package.

Note that find_package also allows a different mode of operation, based on config file packages, which is well-suited to address this particular problem, but will require some changes to your build system. You will need config scripts for all your libraries (CMake can generate them for you if the libraries are themselves also built by CMake; if not, this can be a bit of a hassle), and depending targets will refer to those libraries via imported targets instead of variables (which usually makes things way easier for those depending targets). I would strongly recommend you adopt this as the long-term solution.

If for some reason you cannot do this, you will have to modify your find scripts. A common technique is to search for debug and release binaries separately, but then combine the find libraries from those calls into a single variable (together with the debug and optimized specifiers) and then have that variable as an argument to find_package_handle_standard_args. That way, as long as one of the two is found, your find script will be happy, although you might not be able to build all possible configurations in the end. Alternatively, you can also skip the call to find_package_handle_standard_args altogether and manually implement your own logic for detecting whether the library was found. As you can see from the manpage for that function, it does mostly boilerplate stuff and can be easily replaced by a more flexible, handwritten implementation if necessary.