CMake add_custom_target; Cannot find 32-bit commands in Visual Studio - visual-studio

Question

I am using CMake to generate my Visual Studio project files. I wanted to see if I could "trick" Visual Studio into also compiling for Linux using Bash on Ubuntu on Windows from Windows 10, so I created a small dummy project with the following CMakeLists.txt:
cmake_minimum_required (VERSION 3.5)
project(linux)
set(BASH_EXE C:/Windows/System32/bash.exe)
add_custom_target(Linux ALL
COMMAND ${BASH_EXE} -c "make -C ${CMAKE_SOURCE_DIR}/build"
)
To my surprise, this actually got the job done and created a project called Linux which ran the above command. Unfortunately that command crashed with this error:
'C:\Windows\System32\bash.exe' is not recognized as an internal or external command, operable program or batch file.
But I can run this exact command from my cmd prompt and it works fine:
C:\Windows\System32\bash.exe -c "make -C build"
Why can't Visual Studio/CMake find the bash executable?

Answer 1

This was probably the dumbest issue I've encountered... This blog post is what led me to the answer: http://www.samlogic.net/articles/sysnative-folder-64-bit-windows.htm
The problem was with how Windows handles 32-bit vs 64-bit programs: it keeps 64-bit programs in System32 and 32-bit programs in SysWOW64. Only 32-bit programs can see SysWOW64 and only 64-bit programs can see System32. If a 32-bit program needs a program in System32, it has to use the pseudo-folder called sysnative.
Turns out Visual Studio was launching my CMake commands in a 32-bit shell, meaning it couldn't find a program in C:/Windows/System32/
So I had to change my CMakeLists.txt to this:
cmake_minimum_required (VERSION 3.5)
project(linux)
set(BASH_EXE C:/Windows/sysnative/bash.exe)
add_custom_target(Linux ALL
COMMAND ${BASH_EXE} -c "make -C ../../build"
)
Unfortunately because of the nature of the CMAKE_SOURCE_DIR variable, I had to change this to use a relative path instead of an absolute one (CMAKE_SOURCE_DIR expands to the Windows path, not the Linux path).