14 KB
Newer Older
1 2 3

Andrey Mokhov's avatar
Andrey Mokhov committed
4 5 6 7
Hadrian is a new build system for the [Glasgow Haskell Compiler][ghc]. It is
based on the [Shake][shake] library and we hope that it will replace the current
[Make-based build system][make] starting from GHC 8.8. If you are curious about
the rationale behind the
8 9 10 11 12 13 14 15 16 17
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][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).

Your first build

Andrey Mokhov's avatar
Andrey Mokhov committed
Hadrian has not entirely caught up with the Make build system. Not afraid?
19 20
Then put on the helmet and run the following commands from the root of the GHC
21 22

./boot && ./configure
hadrian/build -j
25 26 27 28 29

or on Windows:

./boot && ./configure --enable-tarballs-autodownload
31 32 33
hadrian/build.bat -j

34 35 36 37
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 for you if you pass the flag `--configure`,
or simply `-c`. See the overview of command line flags below.
38 39 40


* If the default build script doesn't work, you might want to try another one,
42 43
e.g. based on Cabal sandboxes (`build-cabal.*`), Stack (`build-stack.*`) or Nix
44 45 46 47 48

* On Windows, if you do not want to install MSYS, you can use the Stack-based
build script (Stack provides a managed MSYS environment), as described in
[these instructions][windows-build]. If you don't mind installing MSYS yourself
or already have it, you can use the Cabal-based build script.

50 51 52 53 54
* 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][ghc-preparation].

56 57 58 59 60 61 62
Cheatsheet for Make users

You can find a cheatsheet-style document that shows the Hadrian equivalents of
commands that GHC users are used to run with the Make build system

63 64
Using the build system
65 66
Once your first build is successful, simply run `build` to rebuild after some
changes. Build results are placed into `_build` by default.
67 68 69 70 71 72

#### Command line flags

In addition to standard Shake flags (try `--help`), the build system
currently supports several others:

73 74 75
* `--build-root=PATH` or `-oPATH`: specify the directory in which you want to
store all build products. By default Hadrian builds everything in the `_build/`
subdirectory of the GHC source tree. Unlike the Make build system, Hadrian
Andrey Mokhov's avatar
Andrey Mokhov committed
doesn't have any "inplace" logic left any more. This option is therefore useful
77 78 79
for GHC developers who want to build GHC in different ways or at different
commits, from the same source directory, and have the build products sit in
different, isolated folders.
80 81

* `--configure` or `-c`: use this flag to run the `boot` and `configure` scripts
82 83
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):
84 85 86 87
    ./configure # On Windows run ./configure --enable-tarballs-autodownload
Andrey Mokhov's avatar
Andrey Mokhov committed
88 89 90 91 92 93 94 95
    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

Andrey Mokhov's avatar
Andrey Mokhov committed
98 99 100 101 102
* `--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.

Andrey Mokhov's avatar
Andrey Mokhov committed
104 105
* `--integer-simple`: build GHC using the `integer-simple` integer library
(instead of `integer-gmp`).

107 108
* `--color` and `--no-color`: choose whether to use colors when printing build
progress info. By default, Hadrian tries to determine if the terminal supports
colored output, and proceeds accordingly.

Andrey Mokhov's avatar
Andrey Mokhov committed
111 112 113 114
* `--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).

Andrey Mokhov's avatar
Andrey Mokhov committed
116 117
* `--verbose`: run Hadrian in verbose mode. In particular this prints diagnostic
messages by Shake oracles.

119 120 121
* `--lint`: run [Shake Lint]( during the
build to check that the build system is well formed. Note that the Lint check
currently fails under certain circumstances, as discussed in
[this ticket](

124 125 126 127 128
#### Expressions

Hadrian expressions are used extensively for specifying build settings. For an
explanation of how they work, see the [documentation](doc/

129 130
#### User settings

Andrey Mokhov's avatar
Andrey Mokhov committed
131 132 133
The Make-based build system uses `mk/` to specify user build settings.
Hadrian uses `hadrian/UserSettings.hs` for the same purpose, see

135 136
#### Building libraries and executables

Andrey Mokhov's avatar
Andrey Mokhov committed
You can build a specific library or executable for a given stage by running
138 139
`build stage<N>:<lib|exe>:<package name>`. Examples:

Andrey Mokhov's avatar
Andrey Mokhov committed
140 141 142
# Build the Stage1 GHC compiler, and place the binary to the directory
# _build/stage0/bin/ghc (because it is built by the Stage0 compiler).
143 144
build stage1:exe:ghc-bin

Andrey Mokhov's avatar
Andrey Mokhov committed
145 146
# Build the Stage2 GHC compiler, and place the binary to the directory
# _build/stage1/bin/ghc (because it is built by the Stage1 compiler).
147 148
build stage2:exe:ghc-bin

Andrey Mokhov's avatar
Andrey Mokhov committed
149 150
# Build the `ghc` library with the bootstrapping (Stage0) compiler, and register
# it in the package database stored in the directory _build/stage0/lib.
151 152
build stage0:lib:ghc

Andrey Mokhov's avatar
Andrey Mokhov committed
153 154
# Build the Cabal library with the Stage1 compiler and register it
# in the package database stored in the directory _build/stage1/lib.

Andrey Mokhov's avatar
Andrey Mokhov committed
156 157
# Build the `text` library with the Stage2 compiler and register it
# in the package database stored in the directory _build/stage2/lib.
158 159
build stage2:lib:text

Andrey Mokhov's avatar
Andrey Mokhov committed
160 161 162
# Build Haddock using the Stage1 compiler and place the binary into the
# directory _build/stage1/haddock.
build stage1:exe:haddock
163 164

165 166
#### Fast feedback using ghci

Running the `./hadrian/ghci` script will load the main compiler into
168 169 170 171
a ghci session. This is intended for fast development feedback, modules are only
typechecked so it isn't possible to run any functions in the repl.

173 174 175 176 177

You can also use this target with `ghcid`.

ghcid --command="./hadrian/ghci"
179 180 181 182 183 184 185

The first time this command is run hadrian will need to compile a few dependencies
which will take 1-2 minutes. Loading GHC into GHCi itself takes about 30 seconds and
reloads after that take in the region of 1-5 seconds depending on which modules
need to be recompiled.

186 187 188 189 190
You can further speed up the script by passing `-j` as an argument. This will
have the effect of passing `-j` to both hadrian and ghci so they will both
build in parallel.

./hadrian/ghci -j8
192 193

194 195
#### Testing

Andrey Mokhov's avatar
Andrey Mokhov committed
196 197 198 199
To run GHC testsuite, use `build test`. See
[doc/](doc/ to learn about all associated command line
flags, as well as about the equivalents of the features that the Make build
system offers.

Andrey Mokhov's avatar
Andrey Mokhov committed
`build selftest` runs tests of the build system. The current test coverage
202 203
is close to zero (see [#197][test-issue]).

204 205 206 207
#### Clean and full rebuild

* `build clean` removes all build artefacts.

Andrey Mokhov's avatar
Andrey Mokhov committed
* `build -B` forces Shake to rerun all rules, even if the previous build results
209 210
are still up-to-date.

211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236
#### Staged compilation

GHC is a self-hosted compiler and consequently the build proceeds in several

1. The build begins with a user-provided installation of GHC called the
   stage0 (or bootstrap) compiler which is used (via the `build.*.sh` scripts)
   to build Hadrian.
1. Hadrian uses the stage0 compiler to build a stage1 compiler (somewhat
   confusingly found in `_build/stage0/bin/ghc`), linking against the stage0
   compiler's core libraries (e.g. `base`).
1. The stage1 compiler is used to build new core libraries (found in
1. The stage1 compiler is used to build a stage2 compiler (found in
   `_build/stage1/bin/ghc`), linking against these new core libraries.
1. Optionally (see the [Building Stage3](#building-stage3) section below) the
   stage2 compiler can be used to build a stage3 compiler (found in
   `build/stage2/bin/ghc`) as a further smoke-test.

Note that the stage directories in the `_build` directory can be thought of as
named after the stage that was used to *build* the artifacts in each directory.

These stages can be summarized graphically:

![an overview of the stages of a Hadrian compilation](doc/staged-compilation.svg)

237 238
#### Documentation

Andrey Mokhov's avatar
Andrey Mokhov committed
239 240 241
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.
242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257

#### 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

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

workflow, for now.

Andrey Mokhov's avatar
Andrey Mokhov committed
#### Building Stage3

Andrey Mokhov's avatar
Andrey Mokhov committed
260 261 262 263
It is possible to define a build flavour that builds a Stage3 compiler, which is
a compiler built using Stage2. This is useful for cross-compilation. Detailed
instructions can be found in the corresponding
[part of the user settings manual](doc/

265 266 267 268 269 270 271 272 273 274
#### Integrating Hadrian into other tooling

The `tool-args` target is designed to allow hadrian to be integrated into other
tooling which uses the GHC API.
`tool-args` prints out a list of flags which hadrian will use to compile
a module in the `compiler` directory. Using these flags you can then set up
a GHC API session with the correct environment to load a module into your own
GHC session. This is how `haskell-ide-engine` is able to support hadrian.

> ./hadrian/build tool-args
276 277 278 279
-hide-all-packages -no-user-package-db -package-db _build/stage0/lib/packag...

The `./hadrian/ghci` script is implemented using this target.

282 283 284 285

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

Andrey Mokhov's avatar
Andrey Mokhov committed
287 288
* 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.

* With the `--configure` (`-c`) flag, Hadrian sometimes fetches a wrong
  Happy saying something like: `HappyTemplate-arrays-coerce: openFile: does not exist`
  (as mentioned [here](, in
294 295
  which case you might be better off running `./configure` manually before Hadrian.

296 297 298 299
* The call to `build test` sometimes fails with
  `libCffi_p.a: copyFile: does not exist` (as noticed
  The workaround is to `rm _build/stage1/libffi/build/inst/lib/libffi.a` and
300 301
  start over.

If you need help in debugging Hadrian, read the
303 304 305
and Shake's [debugging tutorial](
If nothing helps, don't hesitate to create a GHC issue.
306 307 308 309 310 311 312 313 314

Current limitations
The new build system still lacks many important features:
* Dynamic linking on Windows is not supported [#343][dynamic-windows-issue].

How to contribute

Andrey Mokhov's avatar
Andrey Mokhov committed
315 316 317 318 319 320
The best way to contribute is to try Hadrian, report the issues you found, and
attempt to fix them. Documentation patches are particularly welcome. Please
note: the codebase is still unstable and we expect some further refactoring. In
particular, we would like to separate the general-purpose "Hadrian library" for
building Haskell projects using Shake (`src/Hadrian/*`) from GHC specifics; see
[this issue](
321 322 323 324


Andrey Mokhov's avatar
Andrey Mokhov committed
325 326 327 328 329 330 331 332 333 334 335 336
The list of people who helped create Hadrian is long, and we hope that it will
soon become even longer! The project was first developed in a separate GitHub
repository, where you can find the list of original
[contributors][contributors]. They had to stare at Makefiles for months, so give
them all a round of applause. Simon Peyton Jones and Simon Marlow helped with
deciphering these Makefiles, and Neil Mitchell patiently explained how to
translate Makefiles to (much nicer) Shakefiles.

The initial development of Hadrian was funded by Newcastle University, EPSRC and
Microsoft Research. Other organisations that contributed at various stages of
the project are Haskell.Org and Google (both through supporting summer student
projects), as well as Well-Typed.
337 338 339

341 342
343 344
346 347 348 349