Lean for Windows

A native Lean binary for Windows can be generated using MSYS2. It is easy to install all dependencies, it produces native 64/32-binaries, and supports a C++14 compiler.

An alternative to MSYS2 is to use Lean in Windows WSL.

While not necessary for pure building, you should first activate Developer Mode (Settings > Update & Security > For developers > Developer Mode), which will allow Lean to create symlinks that e.g. enable go-to-definition in the stdlib.

Installing dependencies

The official webpage of MSYS2 provides one-click installers. Once installed, you should run the "MSYS2 MinGW 64-bit shell" from the start menu (the one that runs mingw64.exe). Do not run "MSYS2 MSYS" instead! MSYS2 has a package management system, pacman, which is used in Arch Linux.

Here are the commands to install all dependencies needed to compile Lean on your machine.

pacman -S make python mingw-w64-x86_64-cmake mingw-w64-x86_64-clang mingw-w64-x86_64-ccache git unzip diffutils binutils

You should now be able to run these commands:

clang --version
cmake --version

Then follow the generic build instructions in the MSYS2 MinGW shell, using:

cmake ../.. -G "Unix Makefiles"  -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++

instead of cmake ../... This ensures that cmake will call sh instead of cmd.exe for script tasks and it will use the clang compiler instead of gcc, which is required.

Install lean

Follow the steps in Dev setup using elan regarding installation of the bits you just built. Note that in an msys2 environment elan-init.sh reports you need to add %USERPROFILE%\.elan\bin to your path, but of course in msys2 that needs to be a valid linux style path, like this:

export PATH="$PATH:/c/users/$USERNAME/.elan/bin"


You can run lean --version to see if your binaries work.

If you want a version that can run independently of your MSYS install then you need to copy the following dependent DLL's from where ever they are installed in your MSYS setup:

  • libgcc_s_seh-1.dll
  • libstdc++-6.dll
  • libgmp-10.dll
  • libwinpthread-1.dll

The following linux command will do that:

cp $(ldd lean.exe | cut -f3 -d' ' | grep mingw) .

However, if you plan to use this build to compile lean programs to executable binaries using lake build in normal Windows command prompt outside of msys2 environment you will also need to add a windows version clang to your path.

Trouble shooting

-bash: gcc: command not found

Make sure /mingw64/bin is in your PATH environment. If it is not then check you launched the MSYS2 MinGW 64-bit shell from the start menu. (The one that runs mingw64.exe).