CMake MinGW fails to link boost - boost

Question

I've been struggling to understand why CMake does not compile my program anymore. I made a container for cross-compile a C++ program for Windows. The environment:
Fedora 31
cmake 3.17.4
x86_64-w64-mingw32-g++ 9.2.1
boost 1.69
The following code is my current cmake toolchain file for mingw:
set(CMAKE_SYSTEM_NAME Windows)
set(TOOLCHAIN_PFX x86_64-w64-mingw32)
set(Boost_ARCHITECTURE -x64)
set(Boost_DEBUG ON)
set(Boost_INCLUDE_DIR /usr/${TOOLCHAIN_PFX}/sys-root/mingw/include)
set(Boost_LIBRARY_DIR /usr/${TOOLCHAIN_PFX}/sys-root/mingw/lib)
set(Boost_USE_STATIC_LIBS ON)
find_package(Boost 1.69 REQUIRED)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -I/usr/local/include -L/usr/local/lib")
set(CMAKE_C_COMPILER ${TOOLCHAIN_PFX}-gcc)
set(CMAKE_CXX_COMPILER ${TOOLCHAIN_PFX}-g++)
set(CMAKE_FIND_ROOT_PATH /usr/${TOOLCHAIN_PFX})
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
The building process interrupts when linking the executable. It produces:
/usr/lib/gcc/x86_64-w64-mingw32/9.2.1/../../../../x86_64-w64-mingw32/bin/ld: cannot find -lboost_thread-mt
/usr/lib/gcc/x86_64-w64-mingw32/9.2.1/../../../../x86_64-w64-mingw32/bin/ld: cannot find -lboost_log-mt
/usr/lib/gcc/x86_64-w64-mingw32/9.2.1/../../../../x86_64-w64-mingw32/bin/ld: cannot find -lboost_system
What shocks me the most is that it used to build (no changes have been made to the environment) and boost is installed from RPM. Funny things is that if I omit -lboost_thread-mt, off course, it complains.

Answer 1

You are overwriting many variables that should be correctly set by find_package() such as Boost_LIBRARY_DIR.
Also, you don't specify any components with find_package, as would be the standard way, unless you just want to use the header-only part of boost.
Thus, you are using find_package boost in unsupported/unspecified ways which might have worked in the past, by chance, but broke later.
What definitely works on Fedora 36 is the following:
cmake_minimum_required(VERSION 3.0...3.22.1)
project(some_project CXX)
# work-around: FindBoost: Boost_ARCHITECTURE not detected on MinGW
# https://gitlab.kitware.com/cmake/cmake/-/issues/20587
if(MINGW)
if (CMAKE_SIZEOF_VOID_P EQUAL 8)
set(Boost_ARCHITECTURE "-x64")
else()
set(Boost_ARCHITECTURE "-x32")
endif()
endif()
# works with/without
set(Boost_USE_STATIC_LIBS ON)
# set(Boost_DEBUG ON)
set(Boost_USE_STATIC_LIBS ON)
find_package(Boost 1.54
REQUIRED COMPONENTS
system
filesystem) # just an example, add what you need
add_executable(somebinary main.cc sometranslationunit.cc)
target_link_libraries(somebinary ${Boost_LIBRARIES})
Build with:
mkdir build-cross
cd build-cross
mingw64-cmake -DCMAKE_BUILD_TYPE=Debug .. # or whatever build type
mingw64-make somebinary