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Wednesday, 21 December 2016

Hadrian: a new build system for the Glasgow Haskell Compiler


Linux & OS X status Windows status
Hadrian is a new build system for the Glasgow Haskell Compiler. It is based on Shake and we hope that it will eventually replace the current make-based build system. If you are curious about the rationale behind the project and the architecture of the new build system you can find more details in this Haskell Symposium 2016 paper and this Haskell eXchange 2016 talk.
The new build system can work side-by-side with the existing build system. Note, there is some interaction between them: they put (some) build results in the same directories, e.g. inplace/bin/ghc-stage1.

Your first build

Beware, the build system is in the alpha development phase. Things are shaky and often break; there are numerous known issues. Not afraid? Then put on the helmet and follow these steps:
  • If you have never built GHC before, start with the preparation guide.
  • This build system is written in Haskell (obviously) and depends on the following Haskell packages, which need to be installed: ansi-terminal mtl shake quickcheck.
  • Get the sources. It is important for the build system to be in the hadrian directory of the GHC source tree:
    git clone --recursive git://
    cd ghc
    git clone git://
  • Build GHC using hadrian/ or hadrian/build.bat (on Windows) instead of make. You might want to enable parallelism with -j. We will further refer to the build script simply as build. If you are interested in building in a Cabal sandbox or using Stack, have a look at and scripts. Also see instructions for building GHC on Windows using Stack. Note, Hadrian runs the boot and configure scripts automatically on the first build, so that you don't need to. Use --skip-configure to suppress this behaviour (see overview of command line flags below).

Using the build system

Once your first build is successful, simply run build to rebuild. Build results are placed into _build and inplace directories.

Command line flags

In addition to standard Shake flags (try --help), the build system currently supports several others:
  • --flavour=FLAVOUR: choose a build flavour. Two settings are currently supported: default and quick (adds -O0 flag to all GHC invocations and disables library profiling, which speeds up builds by 3-4x).
  • --haddock: build Haddock documentation.
  • --progress-colour=MODE: choose whether to use colours when printing build progress info. There are three settings: never (do not use colours), auto (attempt to detect whether the console supports colours; this is the default setting), and always (use colours).
  • --progress-info=STYLE: choose how build progress info is printed. There are four settings: none, brief (one line per build command), normal (typically a box per build command; this is the default setting), and unicorn (when normal just won't do).
  • --skip-configure: use this flag to suppress the default behaviour of Hadrian that runs the boot and configure scripts automatically if need be, so that you don't have to remember to run them manually. With --skip-configure you will need to manually run:
    ./configure # On Windows run ./configure --enable-tarballs-autodownload
    as you normally do when using make. Beware, by default Hadrian may do network I/O on Windows to download necessary tarballs, which may sometimes be undesirable; --skip-configure is your friend in such cases.
  • --split-objects: generate split objects, which are switched off by default. Due to a GHC bug, you need a full clean rebuild when using this flag.
  • --verbose: run Hadrian in verbose mode. In particular this prints diagnostic messages by Shake oracles.

User settings

The make-based build system uses mk/ to specify user build settings. We use hadrian/UserSettings.hs for the same purpose, see documentation.

Clean and full rebuild

  • build clean removes all build artefacts.
  • build -B forces Shake to rerun all rules, even if the previous build results are are still up-to-date.

Source distribution

To build a GHC source distribution tarball, run Hadrian with the sdist-ghc target.


  • build validate runs GHC tests by simply executing make fast in testsuite/tests directory. This can be used instead of sh validate --fast --no-clean in the existing build system. Note: this will rebuild Stage2 GHC, ghc-pkg and hpc if they are out of date.
  • build test runs GHC tests by calling the testsuite/driver/ python script with appropriate flags. The current implementation is limited and cannot replace the validate script (see #187).
  • build selftest runs tests of the build system. Current test coverage is close to zero (see #197).

Current limitations

The new build system still lacks many important features:
  • We only build vanilla and profiling way: #4.
  • Validation is not implemented: #187.
  • Only HTML Haddock documentation is supported (use --haddock flag).
  • Build flavours and conventional command line flags are not implemented: #188.
  • Cross-compilation is not implemented: #177.
  • There is no support for installation or binary distribution: #219.

Check out milestones to see when we hope to resolve the above limitations.