We recently updated our SoPlex installation instructions (https://github.com/aibasel/downward/blob/main/BUILD.md#installing-soplex-on-linuxmacos) if there is something missing there, we should also update them.

Boost is a dependency of SoPlex. How did you install SoPlex and do you have multiple versions installed?

The way this should work is this:
1) You install SoPlex from source.
2) While building SoPlex, its CMake scripts locate Boost on your system.
3) During the install step of SoPlex, its CMake scripts create a CMake package - a set of CMake scripts that contain all file locations necessary to include SoPlex. This package should have the path to Boost.
4) In the Fast Downward build step, we locate the CMake package of SoPlex and add a dependency to it. This should inherit all the dependencies (including boost) with the correct paths.

Only step 4 is under our control. If there is an error in steps 1-3, this is likely a broken SoPlex installation or a environment variable that is pointing to the wrong installation.

Here's the full output:

Running /usr/bin/cmake -S /home/jendrik/projects/Downward/downward/src -B /home/jendrik/projects/Downward/downward/build-src-Qt6-Debug '-DCMAKE_GENERATOR:STRING=Unix Makefiles' -DCMAKE_BUILD_TYPE:STRING=Debug -DCMAKE_PROJECT_INCLUDE_BEFORE:FILEPATH=/app/share/qtcreator/package-manager/auto-setup.cmake -DQT_QMAKE_EXECUTABLE:FILEPATH=/app/bin/qmake -DCMAKE_PREFIX_PATH:PATH=/app -DCMAKE_C_COMPILER:FILEPATH=/usr/bin/gcc -DCMAKE_CXX_COMPILER:FILEPATH=/usr/bin/g++ -DCMAKE_CXX_FLAGS_INIT:STRING=-DQT_QML_DEBUG in /home/jendrik/projects/Downward/downward/build-src-Qt6-Debug.
-- The C compiler identification is GNU 11.3.0
-- The CXX compiler identification is GNU 11.3.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/gcc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/g++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Building for 64-bit.
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Failed
-- Looking for pthread_create in pthreads
-- Looking for pthread_create in pthreads - not found
-- Looking for pthread_create in pthread
-- Looking for pthread_create in pthread - found
-- Found Threads: TRUE  
-- Found Cplex: /home/jendrik/lib/cplex64/cplex/include/ilcplex (found suitable version "12.6.3", minimum required is "12") 
-- Could NOT find Boost (missing: Boost_INCLUDE_DIR) (Required is at least version "1.71.0")
-- Found SoPlex: /home/jendrik/lib/soplex-6.0.3x/lib/cmake/soplex/../../../include
-- Configuring done
CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
Boost_INCLUDE_DIR (ADVANCED)
   used as include directory in directory /home/jendrik/projects/Downward/downward/src/search
   used as include directory in directory /home/jendrik/projects/Downward/downward/src/search
   used as include directory in directory /home/jendrik/projects/Downward/downward/src/search

CMake Error in search/CMakeLists.txt:
  Found relative path while evaluating include directories of "downward":

    "Boost_INCLUDE_DIR-NOTFOUND"



-- Generating done
CMake Generate step failed.  Build files cannot be regenerated correctly.
CMake process exited with exit code 1.

Elapsed time: 00:00.

When I try to open the latest Fast Downward revision in QtCreator 8.0.1, I get the following error:

.../src/CMakeLists.txt:-1: error: Found relative path while evaluating include directories of "downward": "Boost_INCLUDE_DIR-NOTFOUND"

I have no idea where this comes from, since I don't see any place where we might be searching for Boost libraries in the code. Which makes sense, since we don't use Boost (except for the parts that we copied from Boost).