Contributing to GHC 1: Preparation

In the last few weeks, we’ve looked at a few different open source Haskell projects like and . This week, we’ll start looking at perhaps the biggest and most important open source element of the Haskell ecosystem. This is , the Glasgow Haskell Compiler. Without GHC and the hard work that goes into it from many volunteers, Haskell would not be the language it is today. So in the next few weeks we’ll be explore the process of building and (hopefully) contributing to GHC. HNix Codeworld GHC I’m currently operating on a Windows laptop, which brings many frustrations. Getting GHC to build on Windows is a non-trivial task with many potential hurdles. On the bright side, I view this as an opportunity to show that one can contribute even in the most adverse circumstances. So most of this article will focus on the trials of using Windows. There is a section further down that goes over the most important parts of building for Mac and Linux. I’ll be following by Simon Peyton Jones, sharing my own complications. this guide Now, you need to walk before you can run. If you’ve never used Haskell before, you have to try it out first to understand GHC! Download our to get started! You can also read our to learn more about the language basics. Beginner’s Checklist Liftoff Series MSYS The main complication with Windows is that the build tools for GHC are made for Unix-like environments. These tools include programs like and . And they don’t work in the normal Windows terminal environment. This means we need some way of emulating a Unix terminal environment in Windows. There are a couple different options for this. One is , but the more supported option for GHC is . So my first step was to install this program. This terminal will apply the “Minimalist GNU for Windows” libraries, abbreviated as “MinGW”. autoconf make Cygwin MSYS 2 Installing this worked fine the first time. However, there did come a couple points where I decided to nuke everything and start from scratch. Re-installing did bring about one problem I’ll share. In a couple circumstances where I decided to start over, I would run the installer, only to find an error stating . This occurred because the old version of this program was still running on a process. You can delete the process or else just restart your machine to get around this. bash.exe: permission denied Once MSys is working, you’ll want to set up your terminal to use programs by default. To do this, you’ll want to set the path to put the directory first: MinGW mingw echo “export PATH=/mingw /bin:\$PATH” >> ~/.bash_profile Use either or for depending on your system. Also don’t forget the quotation marks around the command itself! 32 64 Package Preparation Our next step will be to get all the necessary packages for GHC. MSys 2 uses an older package manager called , which operates kind’ve like . First you’ll need to update your package repository with this command: pacman apt-get pacman -Syuu As per the instructions in SPJ’s description, you may need to run this a couple times if a connection times out. This happened to me once. Now that pacman is working, you’ll need to install a host of programs and libraries that will assist in building GHC: pacman -S --needed git tar bsdtar binutils autoconf make xz \ curl libtool automake python python2 p7zip patch ca-certificates \ mingw-w64-$(uname -m)-gcc mingw-w64-$(uname -m)-python3-sphinx \ mingw-w64-$(uname -m)-tools-git This command typically worked fine for me. The final items we’ll need are and . These are Haskell programs for lexing and parsing. We’ll want to install Cabal to do this. First let’s set a couple variables for our system: alex happy arch=x64_64 # could also be i386bitness=64 # could also be 32 Now we’ll get a pre-built GHC binary that we’ll use to Bootstrap our own build later: curl -L https://downloads.haskell.org/~ghc/8.2.2/ghc-8.2.2-${arch}-unknown-mingw32.tar.xz | tar -xJ -C /mingw${bitness} --strip-components=1 Now we’ll use Cabal to get those packages. We’ll place them (and Cabal) in , so we’ll make sure that’s created first: /usr/local/bin mkdir -p /usr/local/bincurl -L https://www.haskell.org/cabal/release/cabal-install-2.2.0.0/cabal-install-2.2.0.0-${arch}-unknown-mingw32.zip | bsdtar -xzf- -C /usr/local/bin Now we’ll update our Cabal repository and get both and : alex happy cabal updatecabal install -j --prefix=/usr/local/bin alex happy Once while running this command I found that failed to install due to an issue with the library. I got errors of this sort when running the command: happy mtl ghc-pkg check Cannot find any of [“Control\\Monad\\Cont.hi”, “Control\\Monad\Cont.p_hi”, “Control\\Monad\\Cont.dyn_hi”]Cannot find any of [“Control\\Monad\\Cont\\Class.hi”, “Control\\Monad\Cont\\Class.p_hi”, “Control\\Monad\\Cont\\Class.dyn_hi”] I managed to fix this by doing a manual re-install of the package: mtl cabal install -j --prefix=/usr/local/ mtl --reinstall After this step, there were no errors on , and I was able to install without any problems. ghc-pkg check happy cabal install -j --prefix=/usr/local/ happyResolving dependencies…Configuring happy-1.19.9…Building happy-1.19.9…Installed happy-1.19.9 Getting the Source and Building Now our dependencies are all set up, so we can actually go get the source code now! The main workflow for contributing to GHC uses some other tools, but we can start from Github. git clone --recursive git://git.haskell.org/ghc.git Now, you should run the command from the directory. This resulted in some particularly nasty problems for me thanks to my antivirus. It decided that was an existential threat to my system and threw it in the Virus Chest. You might see an error like this: ./boot ghc perl sh: /usr/bin/autoreconf: /usr/bin/perl: bad interpreter: No such file or directory Even after copying another version of perl over to the directory, I saw errors like the following: Could not locate Autom4te/ChannelDefs.pm in @INC (@INC contains /usr/share/autoconf C:/msys64/usr/lib .) at C:/msys64/usr/bin/autoreconf line 39 In reality, the path should have a lot more entries than that! It took me a while (and a couple complete do-overs) to figure out that my antivirus was the problem here. Everything worked once I dug out of the Virus chest. Once runs, you’re almost set! You now need to configure everything: @INC perl boot ./configure --enable-tarballs-autodownload The extra option is only necessary on Windows. Finally you’ll use to command to build everything. Expect this to take a while (12 hours and counting for me!). Once you’re familiar with the codebase, there are a few different ways you can make things build faster. For instance, you can customize the file in a couple different ways. You can set , or you can set . The latter will skip the first stage of the compiler. make build.mk BuildFlavor=devel2 stage=2 You can also run from the sub-directories rather than the main directory. This will only build the sub-component, rather than the full compiler. Finally, there’s also a command that will skip building a lot of the dependencies. make make fast Mac And Linux I won’t go into depth on the instructions for Mac and Linux here, since I haven’t gotten the chance to try them myself. But due to the developer-friendly nature of those systems, they’re likely to have fewer hitches than Windows. On Linux for instance, you can actually do most of the setup by using a Docker container. You’ll download the source first, and then you can run this docker command: >> sudo docker run --rm -i -t -v `pwd`:/home/ghc gregweber/ghc-haskell-dev /bin/bash On Mac, you’ll need to install some similar programs to windows, but there’s no need to use a terminal emulator like MSys. If you have the basic developer tools and a working version of GHC and Cabal already, it might be as simple as: >> brew install autoconf automake>> cabal install alex happy haddock>> sudo easy_install pip>> sudo pip install sphinx For more details, check . But once you’re set up, you’ll follow the same , and instructions as for Windows. here boot configure make Conclusion So that wraps up our first look at GHC. There’s plenty of work to do just to get it to build! But next week we’ll start looking at some of the simplest modifications we can make to GHC. That way, we can start getting a feel for how the code base works. If you haven’t written Haskell, it’s hard to appreciate the brilliance of GHC! Get started by downloading our and reading our ! Beginners Checklist Liftoff Series