message: Update `installation.md`
  Summary: Make note of option to compile Redex on Windows under MSYS2.
diff: @@ -33,6 +33,20 @@ on older OS versions.
  sudo ./setup_oss_toolchain.sh
  ```
  +### Experimental: Windows (64-bit) with MSYS2
  +
  +You need [MSYS2](https://www.msys2.org/#installation) to build `redex-all` (only MingW-w64 is supported) and [Python 3.6+](https://www.python.org/downloads/windows/) to run `redex.py`.
  +
  +Install the build requirements in an MSYS or MingW64 shell:
  +```
  +pacman -Syuu && pacman -Sy make mingw-w64-x86_64-boost mingw-w64-x86_64-cmake mingw-w64-x86_64-gcc mingw-w64-x86_64-jsoncpp mingw-w64-x86_64-make
  +```
  +
  +If you do not use Git on Windows directly, you may install and use it under MSYS2:
  +```
  +pacman -S git
  +```
  +
  ### Experimental: Windows 10 (64-bit)
  You need Visual Studio 2017. Visual Studio 2015 is also possible, but a couple of C++ compile errors need to be fixed. We use [vcpkg](https://github.com/Microsoft/vcpkg) for dependencies. Install vcpkg from their [document](https://github.com/Microsoft/vcpkg):
  @@ -67,6 +81,35 @@ sudo make install
  ```
  If you experience out-of-memory errors, reduce Make parallelism, e.g., to `-j4`.
  +### Experimental: Windows (64-bit) with MSYS2
  +
  +The MSYS2 build relies on CMake. In a MingW64 shell:
  +```
  +# Assumes you want to use Git under MSYS. Else skip to below.
  +git clone https://github.com/facebook/redex.git
  +cd redex
  +# Assumes you are in the redex directory
  +mkdir build-cmake
  +cd build-cmake
  +cmake -G "MSYS Makefiles" ..
  +make -j
  +```
  +If you experience out-of-memory errors, reduce Make parallelism, e.g., to `-j4`.
  +
  +You may check whether the produced binary seems in a working condition:
  +```
  +# In the MingW64 shell:
  +./redex-all.exe --show-passes
  +# Or in a standard Windows command prompt in the same directory
  +redex-all.exe --show-passes
  +```
  +The output should show a large number of included passes, at the time of writing 81.
  +
  +Bundling the `redex-all` binary with the python scripts is not supported on Windows. Manually copy the binary into the same directory as `redex.py` and use `redex.py` that way, or ensure that `redex.py` is called with the `--redex-binary` parameter:
  +```
  +python redex.py --redex-binary PATH_TO_BINARY [...]
  +```
  +
  ### Experimental: CMake for Mac, Linux, and Windows
  Alternatively, build using CMake. Note that the current `CMakeLists.txt` only implements a rule for `redex-all` binary. We will support installation and testing soon.
  @@ -110,6 +153,8 @@ You should see a `redex-all` executable, and the executable should show about 45
  Optionally, you can run our unit test suite. We use gtest, which is automatically
  downloaded when testing (or by invoking a setup script directly).
  +Note: Testing is currently not supported for CMake-based builds.
  +
  ### Dependencies
  Some ReDex tests require a Java environment and Android compiler tooling. If a JDK and the
  Android SDK are available on the machine, ensure that `javac` and `dx` are available on
  