Ndtyjky

I use CMake 3.10.2 for a C++ project and are experiencing a strange behavior of CMake when requiring a 3rd party library package and running CMake in different environments: I require a library (which I here call SOME_LIB) via

find_package(SOME_LIB REQUIRED)

and the search paths differ (the paths where CMake looks for packages) although the CMake call is the same in both enviroments. Both times CMake is called with some parameters, one being

-DSOME_LIB_DIR=/path/to/lib

providing the package's installation path.

In the first environment this works fine, but in the second system the library is not found:

CMake Warning at CMakeLists.txt:123 (find_package):

  By not providing "FindSOME_LIB.cmake" in CMAKE_MODULE_PATH this project has

  asked CMake to find a package configuration file provided by "SOME_LIB", but

  CMake did not find one.



  Could not find a package configuration file provided by "SOME_LIB" with any of

  the following names:



    SOME_LIBConfig.cmake

    SOME_LIB-config.cmake



  Add the installation prefix of "SOME_LIB" to CMAKE_PREFIX_PATH or set

  "SOME_LIB_DIR" to a directory containing one of the above files.  If "SOME_LIB"

  provides a separate development package or SDK, be sure it has been

  installed.

Adding the option

 -DCMAKE_FIND_DEBUG_MODE=ON

to the CMake call reveals that the search paths are different for the two environments. In particular only the first of the following documented search patterns is applied on the second system:

<prefix>/                                                       (W)

<prefix>/(cmake|CMake)/                                         (W)

<prefix>/<name>*/                                               (W)

<prefix>/<name>*/(cmake|CMake)/                                 (W)

<prefix>/(lib/<arch>|lib|share)/cmake/<name>*/                  (U)

<prefix>/(lib/<arch>|lib|share)/<name>*/                        (U)

<prefix>/(lib/<arch>|lib|share)/<name>*/(cmake|CMake)/          (U)

<prefix>/<name>*/(lib/<arch>|lib|share)/cmake/<name>*/          (W/U)

<prefix>/<name>*/(lib/<arch>|lib|share)/<name>*/                (W/U)

<prefix>/<name>*/(lib/<arch>|lib|share)/<name>*/(cmake|CMake)/  (W/U)

Since the search pattern <prefix>/(lib/<arch>|lib|share)/<name>*/(cmake|CMake)/ would be the one that finds the package in my situation, I thought initially that the second system is not recognized as a unix-like system, but the documentation also states, that "This is merely a convention, so all (W) and (U) directories are still searched on all platforms". So I should see all paths in CMake's debug output, shouldn't I?

The environments are:

1. the first environment (works fine) is a Ubuntu 18.04 based docker container used for continuous integration with GitLab CI; the image is provisioned with some basic development tools and the 3rd party library I am using




2. the second environment (package cannot be found; missing search paths) is a Ubuntu 18.04 windows subsystem for linux environment used for local development (freshly setup following the steps of the docker image)

Both environments have installed the same software packages including the cmake from the Ubuntu repositories (CMake 3.10.2). The library I want to use with find_package was built with CMake and installed in the same way in both environments. The directory contents of the library in the two environments are the same.

I also tried upgrading CMake in the second environment to 3.10.3 and 3.12.4 (both times built from sources), but the problem stays the same.

The comment by Tsyvarev led me to the answer of my problem:

The problem was caused by my missunderstanding of the

-D<PACKAGE>_DIR=/path/to/config

parameter. As Tsyvarev pointed out the documentation says that <PACKAGE>_DIR must point to the exact path to the directory contatining the config files <PACKAGE>-config.cmake. In other words it is not a prefix path.

It remains the question why it worked in one of the two enviroments: the reason is that I had a small but important variation between the library's installation paths in both environments that I did not notice before:

1. First environment (docker container): /opt/<library_name>-<version-number>/ (note the - which is important!)


2. Second environment (Windows Subsystem for Linux Ubuntu): /opt/<library_name>/<version-number>/

Note: both paths contained the same contents with the CMake configuration being in

1. 
   /opt/<library_name>-<version-number>/lib/cmake/<library_name>/<library_name>-config.cmake for the first environment and, respectively, in


2. 
   /opt/<library_name>/<version-number>/lib/cmake/<library_name>/<library_name>-config.cmake for the second environment.

In the first environment the library was found since the pattern <prefix>/<name>*/(lib/<arch>|lib|share)/cmake/<name>*/ matched, where /opt is one of CMake's <prefix> paths and the <name>* was expanded to <library_name>-<version-number> - an expansion which was not possible for the path in the second environment.

Many thanks for the helpful comments. My apologies for missing the path variation (have looked at the problem for two days but did not see that).