Cabal

This Cabal Git repository contains the following packages:

• Cabal: the Cabal library package (license)
• cabal-install: the package containing the cabal tool (license)

The canonical upstream repository is located at https://github.com/haskell/cabal.

Installing Cabal

Assuming that you have a pre-existing, older version of cabal-install, run:

cabal install cabal-install

To get the latest version of cabal-install. (You may want to cabal update first.)

To install the latest version from the Git repository, clone the Git repository and then run:

(cd Cabal; cabal install)
(cd cabal-install; cabal install)

Building Cabal for hacking

The current recommended way of developing Cabal is to use the new-build feature which shipped in cabal-install-1.24. Assuming that you have a sufficiently recent cabal-install (see above), it is sufficient to run:

cabal new-build cabal-install

To build a local, development copy of cabal-install. The binary will be located at dist-newstyle/build/cabal-install-$VERSION/build/cabal/cabal; you can determine the $VERSION of cabal-install by looking at cabal-install/cabal-install.cabal.

Here are some other useful variations on the commands:

cabal new-build Cabal # build library only
cabal new-build Cabal:unit-tests # build Cabal's unit test suite
cabal new-build cabal-tests # etc...

Running tests

Using Travis and AppVeyor. The easiest way to run tests on Cabal is to make a branch on GitHub and then open a pull request; our continuous integration service on Travis and AppVeyor will build and test your code. Title your PR with WIP so we know that it does not need code review. Alternately, you can enable Travis on your fork in your own username and Travis should build your local branches.

Some tips for using Travis effectively:

• Watch over your jobs on the Travis website. If you know a build of yours is going to fail (because one job has already failed), be nice to others and cancel the rest of the jobs, so that other commits on the build queue can be processed.

• If you want realtime notification when builds of your PRs finish, we have a Slack team. To get issued an invite, fill in your email at this sign up page.

• If you enable Travis for the fork of Cabal in your local GitHub, you can have builds done automatically for your local branch separate from Cabal. This is an alternative to opening a PR, and has the bonus that you don't have to wait for the main queue on Haskell repository to finish. It is recommended that you enable Travis only on PRs, and open a PR on your local repository, so that you can also use GitHub to push and pull branches without triggering builds.

How to debug a failing CI test. One of the annoying things about running tests on CI is when they fail, there is often no easy way to further troubleshoot the broken build. Here are some guidelines for debugging continuous integration failures:

1. Can you tell what the problem is by looking at the logs? The cabal-testsuite tests run with -v logging by default, which is dumped to the log upon failure; you may be able to figure out what the problem is directly this way.

2. Can you reproduce the problem by running the test locally? See the next section for how to run the various test suites on your local machine.

3. Is the test failing only for a specific version of GHC, or a specific operating system? If so, try reproducing the problem on the specific configuration.

4. Is the test failing on a Travis per-GHC build (for example)? In this case, if you click on "Branch", you can get access to the precise binaries that were built by Travis that are being tested. If you have an Ubuntu system, you can download the binaries and run them directly. Note that the build is not relocatable, so you must exactly reproduce the file system layout of the Travis build (in particular, the build products need to live in the directory /home/travis/build/haskell/cabal, and the .cabal directory must live in /home/travis/.cabal).

5. Is the test failing on AppVeyor? Consider logging in via Remote Desktop to the build VM: https://www.appveyor.com/docs/how-to/rdp-to-build-worker/

If none of these let you reproduce, there might be some race condition or continuous integration breakage; please file a bug.

Running tests locally. To run tests locally with new-build, you will need to know the name of the test suite you want. Cabal and cabal-install have several. In general, the test executable for {Cabal,cabal-install}:$TESTNAME will be stored at dist-newstyle/build/{Cabal,cabal-install}-$VERSION/build/$TESTNAME/$TESTNAME.

The most important test suite is cabal-testsuite: most user-visible changes to Cabal should come with a test in this framework. See cabal-testsuite/README.md for more information about how to run tests and write new ones. Quick start: use cabal-tests to run Cabal tests, and cabal-tests --with-cabal=/path/to/cabal to run cabal-install tests.

Among the other tests, use -p which applies a regex filter to the test names.

• Cabal:unit-tests are small, quick-running unit tests on small pieces of functionality in Cabal. If you are working on some utility functions in the Cabal library you should run this test suite.

• cabal-install:unit-tests are small, quick-running unit tests on small pieces of functionality in cabal-install. If you are working on some utility functions in cabal-install you should run this test suite.

• cabal-install:solver-quickcheck are QuickCheck tests on cabal-install's dependency solver. If you are working on the solver you should run this test suite.

• cabal-install:integration-tests2 are integration tests on some top-level API functions inside the cabal-install source code. You should also run this test suite.

Conventions

• Spaces, not tabs.

• Try to follow style conventions of a file you are modifying, and avoid gratuitous reformatting (it makes merges harder!)

• A lot of Cabal does not have top-level comments. We are trying to fix this. If you add new top-level definitions, please Haddock them; and if you spend some time understanding what a function does, help us out and add a comment. We'll try to remind you during code review.

• If you do something tricky or non-obvious, add a comment.

• For local imports (Cabal module importing Cabal module), import lists are NOT required (although you may use them at your discretion.) For third-party and standard library imports, please use explicit import lists.

• You can use basically any GHC extension supported by a GHC in our support window, except Template Haskell, which would cause bootstrapping problems in the GHC compilation process.

• Our GHC support window is five years for the Cabal library and three years for cabal-install: that is, the Cabal library must be buildable out-of-the-box with the dependencies that shipped with GHC for at least five years. The Travis CI checks this, so most developers submit a PR to see if their code works on all these versions of GHC. cabal-install must also be buildable on all supported GHCs, although it does not have to be buildable out-of-the-box. Instead, the cabal-install/bootstrap.sh script must be able to download and install all of the dependencies (this is also checked by CI). Also, self-upgrade to the latest version (i.e. cabal install cabal-install) must work with all versions of cabal-install released during the last three years.

• Cabal has its own Prelude, in Distribution.Compat.Prelude, that provides a compatibility layer and exports some commonly used additional functions. Use it in all new modules.

• As far as possible, please do not use CPP. If you must use it, try to put it in a Compat module, and minimize the amount of code that is enclosed by CPP. For example, prefer:

  f :: Int -> Int
  #ifdef mingw32_HOST_OS
  f = (+1)
  #else
  f = (+2)
  #endif
  

  over:

  #ifdef mingw32_HOST_OS
  f :: Int -> Int
  f = (+1)
  #else
  f :: Int -> Int
  f = (+2)
  #endif
  

We like this style guide.

Communicating

There are a few main venues of communication:

• Most developers subscribe to receive messages from all issues; issues can be used to open discussion. If you know someone who should hear about a message, CC them explicitly using the @username GitHub syntax.

• For more organizational concerns, the mailing list is used.

• Many developers idle on #hackage on irc.freenode.net (archives). #ghc (archives) is also a decently good bet.

Releases

Notes for how to make a release are at the wiki page "Making a release". Currently, @23Skidoo, @rthomas, @tibbe and @dcoutts have access to haskell.org/cabal, and @davean is the point of contact for getting permissions.

API Documentation

Auto-generated API documentation for the master branch of Cabal is automatically uploaded here: http://haskell.github.io/cabal-website/doc/html/Cabal/.