CMake can't find installed package

Question

I often have lots of trouble getting CMake to accept that I do in fact have some package installed and it's because I don't understand what info to give to CMake and/or how to do that.

For example, I've installed libnest2d through apt install libnlopt-dev.

However, when I run the CMake from pynest2d, it still complains that it cannot find it:

CMake Error at /usr/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:146 (message):
  NLopt library cannot be found.  Consider set NLopt_PATH environment
  variable (missing: NLopt_INCLUDE_DIRS)
Call Stack (most recent call first):
  /usr/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:393 (_FPHSA_FAILURE_MESSAGE)
  cmake/FindNLopt.cmake:63 (find_package_handle_standard_args)
  CMakeLists.txt:15 (find_package)

I get this quite often when compiling & installing, but I'm not really sure what it wants me to do about it. I've tried locating the library myself, but then I always end up with loads of possible directories and I'm not sure what to even do with those directories if I manage to find the correct one.

What files is CMake looking for specifically?

How do I tell CMake (preferably via cmake-gui) to look at the directory where I know those file to be?

Here's all of the directories which could be candidates to provide to CMake.

$ locate libnlopt-dev
/usr/share/doc/libnlopt-dev
/var/lib/dpkg/info/libnlopt-dev:amd64.list
/var/lib/dpkg/info/libnlopt-dev:amd64.md5sums

$ dpkg -L libnlopt-dev
/.
/usr
/usr/include
/usr/include/nlopt.f
/usr/include/nlopt.h
/usr/lib
/usr/lib/x86_64-linux-gnu
/usr/lib/x86_64-linux-gnu/cmake
/usr/lib/x86_64-linux-gnu/cmake/nlopt
/usr/lib/x86_64-linux-gnu/cmake/nlopt/NLoptConfig.cmake
/usr/lib/x86_64-linux-gnu/cmake/nlopt/NLoptConfigVersion.cmake
/usr/lib/x86_64-linux-gnu/cmake/nlopt/NLoptLibraryDepends-none.cmake
/usr/lib/x86_64-linux-gnu/cmake/nlopt/NLoptLibraryDepends.cmake
/usr/lib/x86_64-linux-gnu/pkgconfig
/usr/lib/x86_64-linux-gnu/pkgconfig/nlopt.pc
/usr/share
/usr/share/doc
/usr/share/man
/usr/share/man/man3
/usr/share/man/man3/nlopt.3.gz
/usr/share/man/man3/nlopt_minimize.3.gz
/usr/share/man/man3/nlopt_minimize_constrained.3.gz
/usr/lib/x86_64-linux-gnu/libnlopt.so
/usr/share/doc/libnlopt-dev

I'm currently on XFCE4 in WSL2.

Answer 1

in file pynest2d/cmake/FindNLopt.cmake in the call find_path(NLopt_INCLUDE_DIRS ..) you may need to modify the file name fromm nlopt.hpp to nlopt.h