How to compile Boost-1.76.0 with Emscripten-1.38.31 (??) - c++

Question

I've searched high and low for this answer and I think it should be answered in a modern setting. Most things I see are from 2013 or at the latest 2015 with comments from 2019.
to start off I am using macOS 11.2 with the most recent version of xcode 12.4.
I cloned and installed from git the most recent (as of today) repositories for boost and emscripten.
for some reason on my project when trying to integrate enscripten flags into my CMakeLists.txt file I get an error running
$ cmake .. then $ make.
the CMakeLists.txt file:
cmake_minimum_required(VERSION 3.17)
project(FernQuest) #emscripten version
if (${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
message(STATUS "using emscripten")
endif ()
if (NOT ${CMAKE_SYSTEM_NAME} MATCHES "Emscripten")
message(STATUS "using cmake")
endif ()
#options
option(JS_ONLY "Compiles to native JS (No WASM)" OFF)
set(CMAKE_CXX_STANDARD 14)
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/out)
include_directories(.)
include_directories(/usr/local/include) #where boost in located
message(STATUS "finding boost!")
find_package(Boost 1.74.0 REQUIRED serialization system filesystem COMPONENTS serialization system filesystem)
if(Boost_FOUND)
message(STATUS "found boost!")
endif()
include_directories(${Boost_INCLUDE_DIR})
link_directories(${Boost_LIBRARY_DIR})
if(NOT Boost_FOUND)
message(FATAL_ERROR "Could not find boost!")
endif()
message(STATUS "setting sources")
SET(FQ_SRCS
../src/FernQuest.cpp
../src/Item.cpp
../src/Item.h
../src/Player.cpp
../src/Player.h
../src/Game.cpp
../src/Game.h
../src/QuestLog.cpp
../src/QuestLog.h)
SET(CMAKE_C_COMPILER emcc)
SET(CMAKE_CPP_COMPILER em++)
add_executable(FernQuest ${FQ_SRCS})
if(Boost_FOUND)
if(JS_ONLY)
message(STATUS "Setting compilation target to native JavaScript")
set(CMAKE_EXECUTABLE_SUFFIX ".js")
set_target_properties(FernQuest PROPERTIES COMPILE_FLAGS "-s USE_BOOST_HEADERS=1" LINK_FLAGS "-s USE_BOOST_HEADERS=1 -s WASM=0 -s EXPORTED_FUNCTIONS='[_main]'")
else(JS_ONLY)
message(STATUS "Setting compilation target to WASM")
set(CMAKE_EXECUTABLE_SUFFIX ".wasm.js")
set_target_properties(FernQuest PROPERTIES COMPILE_FLAGS "-s USE_BOOST_HEADERS=1" LINK_FLAGS " -s USE_BOOST_HEADERS=1 -s WASM=1 -s EXPORTED_FUNCTIONS='[_main]'")
endif(JS_ONLY)
endif()
the error:
-- The C compiler identification is AppleClang 12.0.0.12000032
-- The CXX compiler identification is AppleClang 12.0.0.12000032
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc - 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: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- using cmake
-- finding boost!
-- Found Boost: /usr/local/lib/cmake/Boost-1.76.0/BoostConfig.cmake (found suitable version "1.76.0", minimum required is "1.74.0") found components: serialization system filesystem serialization system filesystem
-- found boost!
-- setting sources
-- Setting compilation target to WASM
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/codiecottrell/Documents/FernQuest/emscripten/build
Scanning dependencies of target FernQuest
[ 16%] Building CXX object CMakeFiles/FernQuest.dir/Users/codiecottrell/Documents/FernQuest/src/FernQuest.cpp.o
clang: error: no such file or directory: 'USE_BOOST_HEADERS=1'
make[2]: *** [CMakeFiles/FernQuest.dir/Users/codiecottrell/Documents/FernQuest/src/FernQuest.cpp.o] Error 1
make[1]: *** [CMakeFiles/FernQuest.dir/all] Error 2
make: *** [all] Error 2
so I read up and they say that to fix this you use this below as to actually run it using the -DCMAKE_TOOLCHAIN_FILE:
$ emcmake cmake .. then $ emmake make
this error occurs:
configure: cmake .. -DCMAKE_TOOLCHAIN_FILE=/Users/codiecottrell/emsdk/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -DCMAKE_CROSSCOMPILING_EMULATOR="/Users/codiecottrell/emsdk/node/14.15.5_64bit/bin/node"
-- using emscripten
-- finding boost!
CMake Error at /usr/local/Cellar/cmake/3.19.4/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:218 (message):
Could NOT find Boost (missing: Boost_INCLUDE_DIR serialization system
filesystem serialization system filesystem) (Required is at least version
"1.74.0")
Call Stack (most recent call first):
/usr/local/Cellar/cmake/3.19.4/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:582 (_FPHSA_FAILURE_MESSAGE)
/usr/local/Cellar/cmake/3.19.4/share/cmake/Modules/FindBoost.cmake:2193 (find_package_handle_standard_args)
CMakeLists.txt:21 (find_package)
-- Configuring incomplete, errors occurred!
See also "/Users/codiecottrell/Documents/FernQuest/emscripten/build/CMakeFiles/CMakeOutput.log".
make: make
-- using emscripten
-- finding boost!
CMake Error at /usr/local/Cellar/cmake/3.19.4/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:218 (message):
Could NOT find Boost (missing: Boost_INCLUDE_DIR serialization system
filesystem serialization system filesystem) (Required is at least version
"1.74.0")
Call Stack (most recent call first):
/usr/local/Cellar/cmake/3.19.4/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:582 (_FPHSA_FAILURE_MESSAGE)
/usr/local/Cellar/cmake/3.19.4/share/cmake/Modules/FindBoost.cmake:2193 (find_package_handle_standard_args)
CMakeLists.txt:21 (find_package)
-- Configuring incomplete, errors occurred!
See also "/Users/codiecottrell/Documents/FernQuest/emscripten/build/CMakeFiles/CMakeOutput.log".
make: *** [cmake_check_build_system] Error 1
My Question:
it seems that enscripten cannot find boost when running it through its own means, however cmake can clearly find it. There is also support for running boost through emscripten as I've read in both documentations however there is no clear way. What is this way and where am I going wrong? I'm going to continue to troubleshoot
EDIT
just tried $ emconfigure ./b2 toolset=gcc --prefix=/usr/local/B2
and it didn't change anything

Answer 1

If you're building with emscripten then the libraries on your mac (where cmake is searching) won't work; you will need to compile them statically.
I recommend trying to build your project without CMake.
If you're project only uses the boost headers (not libraries), then something like this might work:
$ em++ ../src/*.cpp -o index.html -s USE_BOOST_HEADERS=1
Otherwise you'll need to compile Boost also. Once you've done that and you have a libboost.a file, you'd compile your program like this:
$ em++ ../src/*.cpp -c -s USE_BOOST_HEADERS=1
Then link it:
$ em++ *.o /path/to/libboost.a -o index.html
Of course, depending on what other libraries you use you'll need to tweak those commands. But the general idea is to compile all the dependencies into static archive (.a) files, then compile those together to get the resulting .html (or .js or .wasm) file.
Read more about compiling with emcc.