The Glasgow Haskell Compiler

a contributor's cheatsheet


The Wiki is a comprehensive resource about GHC development. Use it when this cheatsheet is insufficient.

Documentation for master is built with GitLab CI:

User's Guide – command line options, language extensions, and so on.

Libraries – Haddock for base, containers, transformers, and other boot libraries.

Getting the Code

GHC has its own GitLab instance.

git clone --recurse-submodules

git pull also requires --recurse-submodules because GHC uses git submodules.

Preparing the System

Nix users are fortunate to have ghc.nix:

git clone
nix develop ghc.nix

This will install alex, happy, texlive, and other build dependencies.

Building the Compiler

For the first time:

./boot && ./configure
cabal v2-update
hadrian/build -j

Quick stage2 rebuild:

hadrian/build -j --freeze1


The build artifacts are stored in the _build directory.

Run the freshly built GHCi:

_build/stage1/bin/ghc --interactive


Run a particular set of tests:

hadrian/build -j --freeze1 test --only="T1 T2 T3"

Use -a to accept the output of failing tests.

Omit --only to run the entire testsuite.


Pass the -ddump-tc-trace flag to dump the type checker debug output; -ddump-rn-trace for the renamer.

Build GHC with assertions enabled:

hadrian/build -j --flavour=Devel2

Note that some tests may not pass in this configuration.

Building the User's Guide

To build the User's Guide and Haddock documentation for boot libraries:

hadrian/build -j --freeze1 docs --docs=no-sphinx-pdfs

The generated HTML documentation is saved at:



To report a bug, use the GitLab issue tracker.

To contribute a change, open a GitLab merge request.

To propose a new language feature, the ghc-proposals platform.

For a technical discussion or a question, the ghc-devs mailing list or the #ghc channel on (IRC).