Document how to install windows manually, fixes #697

docs/install.md

@@ -240,6 +240,8 @@ Lower availability of bindists. Stack and HLS binaries are experimental.
 
 ## Manual installation
 
+### Unix
+
 Download the binary for your platform at [https://downloads.haskell.org/~ghcup/](https://downloads.haskell.org/~ghcup/)
 and place it into your `PATH` anywhere.
 
@@ -251,6 +253,60 @@ Then adjust your `PATH` in `~/.bashrc` (or similar, depending on your shell) lik
 export PATH="$HOME/.cabal/bin:$HOME/.ghcup/bin:$PATH"
 ```
 
+### Windows
+
+1. Install ghcup binary
+    - choose a base directory for installation, e.g. `C:\` that has sufficient space
+    - then create the directory, e.g. `C:\ghcup\bin`
+    - download the binary: https://downloads.haskell.org/~ghcup/x86_64-mingw64-ghcup.exe
+    - place it as `ghcup.exe` into e.g. `C:\ghcup\bin`
+2. Install MSYS2
+    - download https://repo.msys2.org/distrib/msys2-x86_64-latest.exe and execute it
+    - remember the installation destination you choose (default is `C:\msys64`)
+    - finish the installation
+* Add environment variables and update `Path`
+    - open search bar and type in "Edit the system environment variables", then open it
+    - click on "Environment Variables..." at the near bottom
+    - in the upper half, select `Path` variable and double click on it
+    - in the new window, click "New", type in `C:\ghcup\bin` (depending on step 1.) and press enter
+    - click "OK" at the bottom
+    - in the upper half, click on "New..."
+    - enter `GHCUP_MSYS2` under "Variable name" and the installation destination from step 2. under "Variable value"
+    - click "OK" at the bottom
+    - in the upper half, click on "New..."
+    - enter `GHCUP_INSTALL_BASE_PREFIX` under "Variable name" and based on the installation destination from step 1. enter the device directory (default `C:\`)
+    - click "OK" at the bottom
+    - in the upper half, click on "New..."
+    - enter `CABAL_DIR` under "Variable name" and based on the installation destination from step 1. enter the device directory + `cabal` subdir (default `C:\cabal`)
+    - click "OK" at the bottom
+    - click "OK" at the bottom
+    - click "OK" at the bottom
+3. Install tools
+    - open powershell
+    - run `ghcup install ghc --set recommended`
+    - run `ghcup install cabal latest`
+    - run `ghcup install stack latest`
+    - run `ghcup install hls latest`
+    - run `cabal update`
+4. Update msys2
+    - run `ghcup run -m -- pacman --noconfirm -Syuu`
+    - run `ghcup run -m -- pacman --noconfirm -Syuu`
+    - run `ghcup run -m -- pacman --noconfirm -S --needed curl autoconf mingw-w64-x86_64-pkgconf`
+    - run `ghcup run -m -- pacman --noconfirm -S ca-certificates`
+5. Update cabal config
+    - go to e.g. `C:\cabal` (based on device you picked in 1.)
+    - open file `config`
+    - uncomment `extra-include-dirs` (the `-- `) and add the value (depending on installation destination you chose in 2.), e.g. `C:\msys64\mingw64\include`... so the final line should be `extra-include-dirs: C:\msys64\mingw64\include`
+    - uncomment `extra-lib-dirs` and do the same, adding `C:\msys64\mingw64\lib`
+    - uncomment `extra-prog-path` and set it to `C:\ghcup\bin, C:\cabal\bin, C:\msys64\mingw64\bin, C:\msys64\usr\bin`, depending on your install destinations from 1. and 2.
+6. Set up msys2 shell
+    - run `ghcup run -m -- sed -i -e 's/db_home:.*$/db_home: windows/' /etc/nsswitch.conf` to make the HOME in your msys2 shell match the one from windows
+    - make a desktop shortcut from `C:\msys64\msys2_shell.cmd`, which will allow you to start a proper msys2 shell
+    - run `ghcup run -m -- sed -i -e 's/#MSYS2_PATH_TYPE=.*/MSYS2_PATH_TYPE=inherit/' /c/msys64/msys2.ini`
+    - run `ghcup run -m -- sed -i -e 's/rem set MSYS2_PATH_TYPE=inherit/set MSYS2_PATH_TYPE=inherit/' /c/msys64/msys2_shell.cmd`
+
+All set. You can run `cabal init` now in an empty directory to start a project.
+
 ## Vim integration
 
 See [ghcup.vim](https://github.com/hasufell/ghcup.vim).