How to use Cabal in Windows

doc/how-to-run-in-windows.rst

@@ -0,0 +1,153 @@
+How to use Cabal in Windows
+===========================
+
+This document describes how to use Cabal in a Windows system. See the
+:ref:`Further reading` section for some other references that might provide some
+more explanations. For a TL;DR, jump to the :ref:`Complete configuration`.
+
+Install the Haskell environment
+-------------------------------
+
+Haskell development on Windows makes use of the `MSYS2 <https://www.msys2.org/>`_ 
+tools.
+
+The recommended way of setting up a Haskell environment in Windows is by using
+`GHCup <https://www.haskell.org/ghcup/>`_. Follow the steps outlined in its
+webpage to install at least GHC and Cabal. GHCup will install its own MSYS2
+system in your computer unless told not to do so: refer to `its documentation
+<https://www.haskell.org/ghcup/install/#windows_1>`_ for more information.
+
+.. NOTE::
+   Stack is another tool you can use to set up a Haskell environment on Windows. Stack
+   can be installed on its own or via GHCup. See 
+   `Stack's webpage <https://docs.haskellstack.org/en/stable/>`_ and/or 
+   `GHCup's section on Stack integration <https://www.haskell.org/ghcup/guide/#stack-integration>`_,
+   in particular the `Windows related subsection <https://www.haskell.org/ghcup/guide/#windows>`_.
+
+Ensure that Cabal can call the tools it needs
+---------------------------------------------
+
+Cabal sometimes needs to call tools that do not come with Windows (such as
+``make`` or even ``git``). The MSYS2 project makes many of them available on
+Windows. The directories where those are located need to be made visible in the
+``PATH`` when executing ``cabal``. For that, Cabal provides the
+``extra-prog-path`` configuration option. Your :ref:`global configuration
+<config-file-discovery>` should include this option:
+
+::
+
+   extra-prog-path: <msys-dir>\<environment>\bin
+                    <msys-dir>\usr\bin
+
+Where ``<msys-dir>`` points to the location of your MSYS2 installation. Refer to
+GHCup's documentation on the default location of this directory.
+``<environment>`` has to be one of the environments of MSYS2, which for GHCup is
+``mingw64``. You can learn more about the different environments in the `MSYS2
+documentation <https://www.msys2.org/docs/environments/>`_.
+
+.. note::
+
+   Unless told otherwise, the GHCup bootstrap script already adds these directories to `extra-prog-path`
+   by default.
+
+Ensure that Cabal can use system libraries
+------------------------------------------
+
+Third-party libraries can be installed using the ``pacman`` package manager on
+the MSYS2 installation. When installing a third party package its libraries and
+header files will (usually) be placed in
+``<msys-dir>\<environment>\{lib,include}`` respectively. These directories need
+to be specified in the ``extra-lib-dirs`` and ``extra-include-dirs``
+respectively. Your :ref:`global configuration <config-file-discovery>` should
+include these options:
+
+::
+
+   extra-include-dirs: <msys-dir>\<environment>\include
+   extra-lib-dirs: <msys-dir>\<environment>\lib
+
+
+.. note::
+
+   Unless told otherwise, the GHCup bootstrap script already adds these directories to `extra-include-dirs` and `extra-lib-dirs`
+   by default.
+
+.. warning::
+
+   Packages in the ``msys/`` repo are not native Windows libraries and will
+   probably not work when one tries to link to them. Install the packages for
+   your selected environment, which for GHCup is ``mingw64/``. Refer to `MSYS2's
+   package management documentation
+   <https://www.msys2.org/docs/package-management/>`_ for more information.
+
+Ensure that Cabal can call Haskell tools
+----------------------------------------
+
+Haskell tools are located in two places:
+
+- ``<ghcup-dir>\bin`` for standard Haskell tools such as GHC, Cabal, Haddock, ``hsc2hs``...
+
+- The ``installdir`` that Cabal is configured with for user-installed Haskell tools.
+
+For Cabal to be able to invoke these tools, those directories need to be made
+visible in the ``PATH``. Your :ref:`global configuration <config-file-discovery>` should
+include these options:
+
+::
+
+   installdir: <installdir>
+   extra-prog-path: ...
+                    <ghcup-dir>\bin
+                    <installdir>
+
+.. note::
+
+   Unless told otherwise, the GHCup bootstrap script already adds these directories to `extra-prog-path`
+   by default.
+
+.. _Complete configuration:
+
+Complete configuration
+----------------------
+
+The complete :ref:`global configuration <config-file-discovery>` should finally
+look like this:
+
+::
+
+   installdir: <installdir>
+   extra-include-dirs: <msys-dir>\<environment>\include
+   extra-lib-dirs: <msys-dir>\<environment>\lib
+   extra-prog-path: <ghcup-dir>\bin
+                    <installdir>
+                    <msys-dir>\<environment>\bin
+                    <msys-dir>\usr\bin
+
+.. note::
+
+   Unless told otherwise, the GHCup bootstrap script already sets this configuration file to the right
+   values by default.
+
+.. _Further reading:
+
+Further reading
+---------------
+
+- MSYS2 homepage: https://www.msys2.org
+- MinGW-W64 homepage: https://www.mingw-w64.org/
+- Setting up Windows to build GHC:
+  https://gitlab.haskell.org/ghc/ghc/-/wikis/building/preparation/windows
+- Some definitions and useful tools:
+  https://gitlab.haskell.org/ghc/ghc/-/wikis/surviving-windows
+
+Outdated links
+~~~~~~~~~~~~~~
+
+These links are outdated but still useful to understand the overall picture:
+
+- GHC's wiki about the Windows platform (outdated, GHC now uses MSYS2):
+  https://gitlab.haskell.org/ghc/ghc/-/wikis/building/platforms/windows
+- The Windows toolchain (outdated, GHC now uses the ``CLANG64`` environment):
+  https://gitlab.haskell.org/ghc/ghc/-/wikis/working-conventions/windows-toolchain
+- Haskell Wiki on Windows (outdated, it talks about MSYS and old tools such as
+  the Haskell platform): https://wiki.haskell.org/Windows

doc/index.rst

@@ -15,6 +15,7 @@ Welcome to the Cabal User Guide
 
    how-to-package-haskell-code
    how-to-build-like-nix
+   how-to-run-in-windows
    how-to-use-backpack
    how-to-report-bugs