Hadrian

Hadrian is a new build system for the Glasgow Haskell Compiler. It is based on Shake and we hope that it will soon replace the current Make-based build system. If you are curious about the rationale behind the project and the architecture of the 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, since it places all build artefacts in a dedicated directory (called _build by default). See this guide if you'd like to start using Hadrian for building GHC.

Your first build

Beware, the build system is in the alpha development phase. Things are shaky and sometimes break; there are numerous known issues. Not afraid? Then put on the helmet and run the following command from root of the GHC tree:

hadrian/build.sh -j

or on Windows:

hadrian/build.bat -j

Here flag -j enables parallelism and is optional. We will further refer to the build script simply as build. Note that Hadrian can also run the boot and configure scripts automatically if you pass the flag --configure, or simply -c. See the overview of command line flags below.

Notes:

• If the default build script doesn't work, you might want to give a try to another one, e.g. based on Cabal sandboxes (build.cabal.*), Stack (build.stack.*) or the global package database (build.global-db.*). Also see instructions for building GHC on Windows using Stack.

• Hadrian is written in Haskell and depends on shake (plus a few packages that shake depends on), mtl, quickcheck, and GHC core libraries.

• If you have never built GHC before, start with the preparation guide.

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:

• --build-root=PATH or -oPATH: specify the directory in which you want to store all the build artifacts. If none is specified by the user, hadrian will store everything under _build/ at the top of ghc's source tree. Unlike GHC's make build system, hadrian doesn't have any "inplace" logic left anymore. This option is therefore useful for GHC developers who want to build GHC in different ways or at different commits, from the same directory, and have the build products sit in different, isolated folders.

• --configure or -c: use this flag to run the boot and configure scripts automatically, so that you don't have to remember to run them manually as you normally do when using Make (typically only in the first build):

  ./boot
  ./configure # On Windows run ./configure --enable-tarballs-autodownload

  Beware that with this flag Hadrian may do network I/O on Windows to download necessary tarballs, which may sometimes be undesirable.

• --flavour=FLAVOUR: choose a build flavour. The following settings are currently supported: default, quick, quickest, perf, prof, devel1 and devel2. As an example, the quickest flavour adds -O0 flag to all GHC invocations and builds libraries only in the vanilla way, which speeds up builds by 3-4x. Build flavours are documented here.

• --freeze1: freeze Stage1 GHC, i.e. do not rebuild it even if some of its source files are out-of-date. This allows to significantly reduce the rebuild time when you are working on a feature that affects both Stage1 and Stage2 compilers, but may lead to incorrect build results. To unfreeze Stage1 GHC simply drop the --freeze1 flag and Hadrian will rebuild all out-of-date files.

• --integer-simple: build GHC using the integer-simple integer library (instead of integer-gmp).

• --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; this is the default setting), normal (typically a box per build command), and unicorn (when normal just won't do).

• --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/build.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.

Documentation

To build GHC documentation, run build docs. Note that finer-grain documentation targets (e.g. building only HTML documentation or only the GHC User's Guide) are currently not supported.

Source distribution

To build a GHC source distribution tarball, run build source-dist.

Binary distribution

To build a GHC binary distribution, run build binary-dist. The resulting tarball contains just enough to support the

$ ./configure [--prefix=PATH] && make install

workflow, for now.

Testing

• 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/runtests.py 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).

Troubleshooting

Here are a few simple suggestions that might help you fix the build:

• The Hadrian submodule in GHC is occasionally behind the master branch of this repository, which contains most recent bug fixes. To switch to the most recent version of Hadrian, run git pull https://github.com/snowleopard/hadrian.git. Beware: the most recent version contains the most recent bugs too! If this works, please raise an issue and we will try to push the changes to the GHC submodule as soon as possible.

• Hadrian is occasionally broken by changes in GHC. If this happens, you might want to switch to an earlier GHC commit.

• If Hadrian fails with the message Configuration file hadrian/cfg/system.config is missing, you have probably forgotten to pass the --configure flag during the first build.

• If you need help in debugging Hadrian, read the wiki and Shake's debugging tutorial.

If everything fails, don't hesitate to raise an issue.

Current limitations

The new build system still lacks many important features:

• Validation is not implemented: #187.
• Dynamic linking on Windows is not supported #343.
• There is no support for binary distribution: #219.

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

How to contribute

The best way to contribute is to try the new build system, report the issues you found, and attempt to fix them. Please note: the codebase is very unstable at present and we expect a lot of further refactoring. If you would like to work on a particular issue, please let everyone know by adding a comment about this. The issues that are currently on the critical path and therefore require particular attention are listed in #239. Also have a look at projects where open issues and pull requests are grouped into categories.

Acknowledgements

I started this project as part of my 6-month research visit to Microsoft Research Cambridge, which was funded by Newcastle University, EPSRC, and Microsoft Research. I would like to thank Simon Peyton Jones, Neil Mitchell and Simon Marlow for kick-starting the project and for their guidance. Zhen Zhang has done fantastic work on Hadrian as part of his Summer of Haskell 2017 project, solving a few heavy and long-overdue issues. Last but not least, big thanks to all other project contributors, who helped me endure and enjoy the project.