Commit 5fdb8588 authored by Ben Gamari's avatar Ben Gamari 🐢


This was unfortunately overwritten by the Hadrian README in a previous
Hadrian merge.
parent 341013e2
The Glasgow Haskell Compiler
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Hadrian is a new build system for the [Glasgow Haskell Compiler][ghc]. It is based
on [Shake][shake] and we hope that it will soon replace the current
[Make-based build system][make]. 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][paper] and this [Haskell eXchange 2016 talk][talk].
This is the source tree for [GHC][1], a compiler and interactive
environment for the Haskell functional programming language.
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. the resulting GHC is `inplace/bin/ghc-stage2`.
For more information, visit [GHC's web site][1].
Your first build
Information for developers of GHC can be found on the [GHC Trac][2].
Beware, the build system is in the alpha development phase. Things are shaky and sometimes
break; there are numerous [known issues][issues]. Not afraid? Then put on the helmet and
run the following command from root of the GHC tree:
hadrian/ -j
Getting the Source
or on Windows:
There are two ways to get a source tree:
hadrian/build.bat -j
1. *Download source tarballs*
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.
Download the GHC source distribution:
* 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
(`*`). Also see [instructions for building GHC on Windows using Stack][windows-build].
which contains GHC itself and the "boot" libraries.
* Hadrian is written in Haskell and depends on `shake` (plus a few packages that `shake` depends on),
`ansi-terminal`, `mtl`, `quickcheck`, and GHC core libraries.
2. *Check out the source code from git*
* If you have never built GHC before, start with the [preparation guide][ghc-preparation].
$ git clone --recursive git://
Using the build system
Once your first build is successful, simply run `build` to rebuild. Build results
are placed into `_build` and `inplace` directories.
Note: cloning GHC from Github requires a special setup. See [Getting a GHC
repository from Github][7].
#### Command line flags
*See the GHC team's working conventions regarding [how to contribute a patch to GHC](* First time contributors are encouraged to get started by just sending a Pull Request.
In addition to standard Shake flags (try `--help`), the build system
currently supports several others:
* `--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):
./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.
Building & Installing
* `--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
For full information on building GHC, see the [GHC Building Guide][3].
Here follows a summary - if you get into trouble, the Building Guide
has all the answers.
* `--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.
Before building GHC you may need to install some other tools and
libraries. See, [Setting up your system for building GHC][8].
* `--integer-simple`: build GHC using the `integer-simple` integer library (instead
of `integer-gmp`).
*NB.* In particular, you need [GHC][1] installed in order to build GHC,
because the compiler is itself written in Haskell. You also need
[Happy][4], [Alex][5], and [Cabal][9]. For instructions on how
to port GHC to a new platform, see the [GHC Building Guide][3].
* `--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
For building library documentation, you'll need [Haddock][6]. To build
the compiler documentation, you need [Sphinx](
and Xelatex (only for PDF output).
* `--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][ghc-split-objs-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](doc/
#### 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 sdist-ghc`.
#### Installation
To build and install GHC artifacts, run `build install`.
By default, GHC will be installed to the specified _prefix_ path on your system,
relative to the root of the file system. For example on UNIX, GHC will be installed
to `/usr/local/bin`. By setting the command line flag `--install-destdir=[DESTDIR]`,
you can install GHC to path `DESTDIR/<prefix>` instead. Make sure you use correct
absolute path as `DESTDIR` on Windows, e.g. `C:/path`, which installs GHC
into `C:/path/usr/local`.
#### 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/` python
script with appropriate flags. The current implementation is limited and cannot
replace the `validate` script (see [#187][validation-issue]).
* `build selftest` runs tests of the build system. Current test coverage is close to
zero (see [#197][test-issue]).
Current limitations
The new build system still lacks many important features:
* Validation is not implemented: [#187][validation-issue].
* Dynamic linking on Windows is not supported [#343][dynamic-windows-issue].
* There is no support for binary distribution: [#219][bin-dist-issue].
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.
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][contributors], who helped me endure and
enjoy the project.
**Quick start**: the following gives you a default build:
$ ./boot
$ ./configure
$ make # can also say 'make -jX' for X number of jobs
$ make install
On Windows, you need an extra repository containing some build tools.
These can be downloaded for you by configure. This only needs to be done once by running:
$ ./configure --enable-tarballs-autodownload
(NB: **Do you have multiple cores? Be sure to tell that to `make`!** This can
save you hours of build time depending on your system configuration, and is
almost always a win regardless of how many cores you have. As a simple rule,
you should have about N+1 jobs, where `N` is the amount of cores you have.)
The `./boot` step is only necessary if this is a tree checked out
from git. For source distributions downloaded from [GHC's web site][1],
this step has already been performed.
These steps give you the default build, which includes everything
optimised and built in various ways (eg. profiling libs are built).
It can take a long time. To customise the build, see the file ``.
Filing bugs and feature requests
If you've encountered what you believe is a bug in GHC, or you'd like
to propose a feature request, please let us know! Submit a ticket in
our [bug tracker][10] and we'll be sure to look into it. Remember:
**Filing a bug is the best way to make sure your issue isn't lost over
time**, so please feel free.
If you're an active user of GHC, you may also be interested in joining
the [glasgow-haskell-users][11] mailing list, where developers and
GHC users discuss various topics and hang out.
Hacking & Developing GHC
Once you've filed a bug, maybe you'd like to fix it yourself? That
would be great, and we'd surely love your company! If you're looking
to hack on GHC, check out the guidelines in the `` file in
this directory - they'll get you up to speed quickly.
Contributors & Acknowledgements
GHC in its current form wouldn't exist without the hard work of
[its many contributors][12]. Over time, it has grown to include the
efforts and research of many institutions, highly talented people, and
groups from around the world. We'd like to thank them all, and invite
you to join!
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