how to get cmake to use the gnu stack of tools under msys2 (mingw) - c++

Question

On Windows 10, with an installed msys2, which is a variant of mingw, I have an installed cmake with the gcc toolchain and all the standard tools like make.
The version of g++ is 6.2 and make is 4.2.1 Both are in the path.
When I build using cmake:
cmake .
it tries to build using nmake and cl. So somehow because I am on windows cmake is trying to use the visual studio toolchain.
export CMAKE_CXX_COMPILER=g++
does not help. The error is:
-- Building for: NMake Makefiles
-- The C compiler identification is unknown
-- The CXX compiler identification is Clang 3.8.0
-- Check for working C compiler: D:/msys64/mingw64/bin/clang++.exe
CMake Error: Generator: execution of make failed. Make command was: "nmake" "/NOLOGO" "cmTC_87e5f\fast"
-- Check for working C compiler: D:/msys64/mingw64/bin/clang++.exe -- broken
CMake Error at D:/msys64/mingw64/share/cmake-3.6/Modules/CMakeTestCCompiler.cmake:61 (message):
The C compiler "D:/msys64/mingw64/bin/clang++.exe" is not able to compile a
simple test program.
It fails with the following output:
Change Dir: D:/git/CSP/CMakeFiles/CMakeTmp
Run Build Command:"nmake" "/NOLOGO" "cmTC_87e5f\fast"
Generator: execution of make failed. Make command was: "nmake" "/NOLOGO"
"cmTC_87e5f\fast"
CMake will not be able to correctly generate this project.
Call Stack (most recent call first):
CMakeLists.txt:2 (project)
-- Configuring incomplete, errors occurred!
See also "D:/git/CSP/CMakeFiles/CMakeOutput.log".
See also "D:/git/CSP/CMakeFiles/CMakeError.log".

Answer 1

To use MSYS2 toolchain, you need to specify the build system generator explicitly, i.e.
cmake -G 'MSYS Makefiles' .
Additional note, it's a good practice to separate the application . source file and cmake's generated file, e.g.
mkdir build
cd build
cmake -G 'MSYS Makefiles' ..