[WinError 123] The filename, directory name, or volume label syntax is incorrect: '-DIMGUI_USER_CONFIG="C:\\Users\\rayga\\Projects\\reaimgui-cpp-meson-addon\\subprojects\\reaimgui-cpp-components\\src\\imconfig.h"'

I don't understand much about C++, but all I am trying to do is write a program which calls a function from another file in a C++ project, and publish it as a .dll

In other languages, this would be generally something like:

import { ClassName } from "./subproject-or-published-package/filename.ext"
ClassName.doThing()

The project is CMake based. It includes some dependencies as git submodules (imgui and a few others), and suggested I use vcpkg to globally install boost-core boost-preprocessor boost-type-index gl3w.

So I have this structure:

├── build
│   ├── meson-info
│   ├── meson-logs
│   ├── meson-private
│   └── subprojects
│       └── reaimgui-cpp-components
├── cross.ini
├── meson.build
├── reaimgui_cpp_meson_addon.cpp
├── reaimgui_cpp_meson_addon.hpp
├── reaimgui_cpp_meson_addon_test.cpp
├── run.sh
└── subprojects
    └── reaimgui-cpp-components
        ├── CMakeLists.txt
        ├── compile_commands.json
        ├── src
        ├── tools
        ├── vendor
            ├── WDL
            ├── imgui
            ├── reaper-sdk
            ├── reaper_colortheme.h
            ├── reaper_plugin_secrets.h
            └── vcpkg-deps.txt

This is my current code:

project('reaimgui-cpp-meson-addon', 'cpp',
  version : '0.1',
  default_options : ['warning_level=3', 'cpp_std=c++17'],
)

lib_args = ['-DBUILDING_REAIMGUI_CPP_MESON_ADDON']

cmake = import('cmake')
reaimgui_cmake_options = cmake.subproject_options()
reaimgui_cmake_options.add_cmake_defines({
  'CMAKE_PREFIX_PATH': 'C:\\Users\\rayga\\projects\\vcpkg;',
  'EXPORT_COMPILE_COMMANDS': true,
})

# Configure the CMake project
sub_proj = cmake.subproject('reaimgui-cpp-components', options: reaimgui_cmake_options)
# Fetch the dependency object - This is the value from "project(PROJECT_NAME ....)" in CMake
reaimgui_lib = sub_proj.dependency('reaimgui', dependencies: [gl3w])

shared_lib = shared_library('reaimgui_cpp_meson_addon', 'reaimgui_cpp_meson_addon.cpp',
  install : true,
  cpp_args : lib_args,
  gnu_symbol_visibility : 'hidden',
)

test_exe = executable('reaimgui_cpp_meson_addon_test', 'reaimgui_cpp_meson_addon_test.cpp',
  link_with : shared_lib)
test('reaimgui_cpp_meson_addon', test_exe)

# Make this library usable as a Meson subproject.
reaimgui_cpp_meson_addon_dep = declare_dependency(
  include_directories: include_directories('.'),
  link_with : shared_lib)

# Make this library usable from the system's
# package manager.
install_headers('reaimgui_cpp_meson_addon.hpp', subdir : 'reaimgui_cpp_meson_addon')

pkg_mod = import('pkgconfig')
pkg_mod.generate(
  name : 'reaimgui-cpp-meson-addon',
  filebase : 'reaimgui_cpp_meson_addon',
  description : 'Meson sample project.',
  subdirs : 'reaimgui_cpp_meson_addon',
  libraries : shared_lib,
  version : '0.1',
)

However, it throws this error:

rayga@DESKTOP-88A51E5 MINGW64 ~/Projects/reaimgui-cpp-meson-addon
$  meson setup build --cross cross.ini 
The Meson build system
Version: 0.57.1
Source dir: C:\Users\rayga\Projects\reaimgui-cpp-meson-addon
Build dir: C:\Users\rayga\Projects\reaimgui-cpp-meson-addon\build
Build type: cross build
Project name: reaimgui-cpp-meson-addon
Project version: 0.1
C++ compiler for the host machine: c++ (gcc 8.1.0 "c++ (x86_64-posix-seh-rev0, Built by MinGW-W64 project) 8.1.0")
C++ linker for the host machine: c++ ld.bfd 2.30
C++ compiler for the build machine: c++ (gcc 8.1.0 "c++ (x86_64-posix-seh-rev0, Built by MinGW-W64 project) 8.1.0")
C++ linker for the build machine: c++ ld.bfd 2.30
Build machine cpu family: x86_64
Build machine cpu: x86_64
Host machine cpu family: x86_64
Host machine cpu: x86_64
Target machine cpu family: x86_64
Target machine cpu: x86_64
WARNING: Setting CMAKE_TOOLCHAIN_FILE is not supported. See the meson docs for cross compilation support:
WARNING:   - URL: https://mesonbuild.com/CMake-module.html#cross-compilation
WARNING:   --> Ignoring this option

|Executing subproject reaimgui-cpp-components method cmake
|
|Found CMake: C:\Program Files\CMake\bin\cmake.EXE (3.20.0)
|
||Configuring the build directory with CMake version 3.20.0
||Running CMake with: -G Ninja -DCMAKE_INSTALL_PREFIX=c:\ -DCMAKE_PREFIX_PATH=C:\Users\rayga\projects\vcpkg; -DEXPORT_COMPILE_COMMANDS=True
||  - build directory:          C:/Users/rayga/Projects/reaimgui-cpp-meson-addon/build/subprojects/reaimgui-cpp-components/__CMake_build
||  - source directory:         C:/Users/rayga/Projects/reaimgui-cpp-meson-addon/subprojects/reaimgui-cpp-components
||  - toolchain file:           C:/Users/rayga/Projects/reaimgui-cpp-meson-addon/build/subprojects/reaimgui-cpp-components/CMakeMesonToolchainFile.cmake
||  - preload file:             C:/Users/rayga/Projects/reaimgui-cpp-meson-addon/build/meson-private/data/preload.cmake
||  - trace args:               --trace-expand --trace-format=json-v1 --no-warn-unused-cli --trace-redirect=cmake_trace.txt
||  - disabled policy warnings: [CMP0025, CMP0047, CMP0056, CMP0060, CMP0065, CMP0066, CMP0067, CMP0082, CMP0089, CMP0102]
||
||Running with expanded trace output on.
||Not searching for unused variables given on the command line.
||Trace will be written to cmake_trace.txt
||Trace will be written to cmake_trace.txt
||-- Could NOT find PkgConfig (missing: PKG_CONFIG_EXECUTABLE) 
||-- Found Boost: C:/Users/rayga/Projects/vcpkg/installed/x64-windows-static/include (found version "1.75.0")  
||-- Found ImGui: C:/Users/rayga/Projects/reaimgui-cpp-meson-addon/subprojects/reaimgui-cpp-components/vendor/imgui (found version "1.81") 
||-- Looking for C++ include optional
||-- Looking for C++ include optional - found
||-- Configuring done
||-- Generating done
||-- Build files have been written to: C:/Users/rayga/Projects/reaimgui-cpp-meson-addon/build/subprojects/reaimgui-cpp-components/__CMake_build
|
|CMake configuration: SUCCEEDED
Traceback (most recent call last):
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\mesonmain.py", line 132, in run
    return options.run_func(options)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\msetup.py", line 275, in run
    app.generate()
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\msetup.py", line 183, in generate
    self._generate(env)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\msetup.py", line 222, in _generate
    intr.run()
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreter.py", line 4798, in run
    super().run()
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreterbase.py", line 641, in run
    self.evaluate_codeblock(self.ast, start=1)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreterbase.py", line 666, in evaluate_codeblock
    raise e
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreterbase.py", line 659, in evaluate_codeblock
    self.evaluate_statement(cur)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreterbase.py", line 674, in evaluate_statement
    self.assignment(cur)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreterbase.py", line 1341, in assignment
    value = self.evaluate_statement(node.value)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreterbase.py", line 676, in evaluate_statement
    return self.method_call(cur)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreterbase.py", line 1073, in method_call
    return obj.method_call(method_name, args, kwargs)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreter.py", line 1840, in method_call
    value = fn(self.interpreter, state, args, kwargs)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreterbase.py", line 423, in wrapped
    return f(*wrapped_args, **wrapped_kwargs)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreterbase.py", line 515, in wrapped
    return f(*wrapped_args, **wrapped_kwargs)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreterbase.py", line 515, in wrapped
    return f(*wrapped_args, **wrapped_kwargs)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreterbase.py", line 229, in wrapped
    return f(*wrapped_args, **wrapped_kwargs)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreterbase.py", line 198, in wrapped
    return f(*wrapped_args, **wrapped_kwargs)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\modules\cmake.py", line 389, in subproject
    subp = interpreter.do_subproject(dirname, 'cmake', kwargs)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreter.py", line 2969, in do_subproject
    raise e
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreter.py", line 2955, in do_subproject
    return self._do_subproject_cmake(subp_name, subdir, subdir_abs, default_options, kwargs)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\interpreter.py", line 3026, in _do_subproject_cmake
    cm_int.analyse()
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\cmake\interpreter.py", line 1041, in analyse
    tgt.postprocess(self.output_target_map, self.src_dir, self.subdir, self.install_prefix, self.trace)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\cmake\interpreter.py", line 312, in postprocess
    ctgt = output_target_map.generated(Path(j))
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\cmake\interpreter.py", line 184, in generated
    res = self._return_first_valid_key([self._rel_generated_file_key(name), self._base_generated_file_key(name)])
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\cmake\interpreter.py", line 200, in _rel_generated_file_key
    path = self._rel_path(fname)
  File "C:\Users\rayga\AppData\Roaming\Python\Python38\site-packages\mesonbuild\cmake\interpreter.py", line 191, in _rel_path
    return fname.resolve().relative_to(self.build_dir)
  File "c:\programdata\miniconda3\lib\pathlib.py", line 1177, in resolve
    s = self._flavour.resolve(self, strict=strict)
  File "c:\programdata\miniconda3\lib\pathlib.py", line 205, in resolve
    s = self._ext_to_normal(_getfinalpathname(s))
OSError: [WinError 123] The filename, directory name, or volume label syntax is incorrect: '-DIMGUI_USER_CONFIG="C:\\Users\\rayga\\Projects\\reaimgui-cpp-meson-addon\\subprojects\\reaimgui-cpp-components\\src\\imconfig.h"'

This is really hard. I've been trying to import one function in C++ for 8 hours and have tried a bunch of build systems =(

Would be grateful for help.