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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].

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`.

Your first build

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

or on Windows:

hadrian/build.bat -j

Here flag `-j` enables parallelism and is optional. We will further refer to the build script
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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.
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* 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].

* Hadrian is written in Haskell and depends on the following packages:
`ansi-terminal extra mtl quickcheck shake`.

* If you have never built GHC before, start with the [preparation guide][ghc-preparation].

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:
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* `--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.

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* `--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

* `--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

* `--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.