Hadrian

Hadrian is a new build system for the Glasgow Haskell Compiler. It is based on the Shake library and we hope that it will replace the current Make-based build system starting from GHC 8.8. 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).

Your first build

Hadrian has not entirely caught up with the Make build system. Not afraid? Then put on the helmet and run the following commands from the root of the GHC tree:

./boot && ./configure
hadrian/build -j

or on Windows:

./boot && ./configure --enable-tarballs-autodownload
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 for you 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 try another one, e.g. based on Cabal sandboxes (build-cabal.*), Stack (build-stack.*) or Nix (build-stack-nix.*).

• 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. If you don't mind installing MSYS yourself or already have it, you can use the Cabal-based build script.

• 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.

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 here.

Using the build system

Once your first build is successful, simply run build to rebuild after some changes. Build results are placed into _build by default.

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 build products. By default Hadrian builds everything in the _build/ subdirectory of the GHC source tree. Unlike the Make build system, Hadrian doesn't have any "inplace" logic left any more. This option is therefore useful 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.

• --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.

• --freeze2: just like --freeze1 but tell Hadrian to additionally freeze Stage2 GHC.

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

• --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.

• --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).

• --verbose: run Hadrian in verbose mode. In particular this prints diagnostic messages by Shake oracles.

• --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.

Expressions

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

User settings

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

Building libraries and executables

You can build a specific library or executable for a given stage by running build stage<N>:<lib|exe>:<package name>. Examples:

# Build the Stage1 GHC compiler, and place the binary to the directory
# _build/stage0/bin/ghc (because it is built by the Stage0 compiler).
build stage1:exe:ghc-bin

# Build the Stage2 GHC compiler, and place the binary to the directory
# _build/stage1/bin/ghc (because it is built by the Stage1 compiler).
build stage2:exe:ghc-bin

# Build the `ghc` library with the bootstrapping (Stage0) compiler, and register
# it in the package database stored in the directory _build/stage0/lib.
build stage0:lib:ghc

# Build the Cabal library with the Stage1 compiler and register it
# in the package database stored in the directory _build/stage1/lib.

# Build the `text` library with the Stage2 compiler and register it
# in the package database stored in the directory _build/stage2/lib.
build stage2:lib:text

# Build Haddock using the Stage1 compiler and place the binary into the
# directory _build/stage1/haddock.
build stage1:exe:haddock

Fast feedback using ghci

Running the ./hadrian/ghci script will load the main compiler into 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.

./hadrian/ghci

You can also use this target with ghcid.

ghcid --command="./hadrian/ghci"

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.

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

Testing

To run GHC testsuite, use build test. See doc/testsuite.md to learn about all associated command line flags, as well as about the equivalents of the features that the Make build system offers.

build selftest runs tests of the build system. The current test coverage is close to zero (see #197).

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 still up-to-date.

Staged compilation

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

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.
2. 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).
3. The stage1 compiler is used to build new core libraries (found in _build/stage1/lib).
4. The stage1 compiler is used to build a stage2 compiler (found in _build/stage1/bin/ghc), linking against these new core libraries.
5. Optionally (see the 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:

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.

Building Stage3

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.

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
-hide-all-packages -no-user-package-db -package-db _build/stage0/lib/packag...

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

Troubleshooting

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

• 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 which case you might be better off running ./configure manually before Hadrian.

• The call to build test sometimes fails with libCffi_p.a: copyFile: does not exist (as noticed here). The workaround is to rm _build/stage1/libffi/build/inst/lib/libffi.a and start over.

If you need help in debugging Hadrian, read the wiki and Shake's debugging tutorial. If nothing helps, don't hesitate to create a GHC issue.

Current limitations

The new build system still lacks many important features:

• Dynamic linking on Windows is not supported #343.

How to contribute

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.

Acknowledgements

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. 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.