The current recommended way of developing Cabal is to use the
v2-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 v2-build cabal
To build a local, development copy of cabal-install. The location
of your build products will vary depending on which version of
cabal-install you use to build; see the documentation section
Where are my build products?
to find the binary (or just run find -type f -executable -name cabal
).
Here are some other useful variations on the commands:
cabal v2-build Cabal # build library only
cabal v2-build Cabal-tests:unit-tests # build Cabal's unit test suite
cabal v2-build cabal-tests # etc...
Using Github Actions. If you are not in a hurry, the most convenient way to run tests on Cabal is to make a branch on GitHub and then open a pull request; our continuous integration service on Github Actions builds and tests your code. Title your PR with WIP so we know that it does not need code review.
Some tips for using Github Actions effectively:
-
Github Actions builds take a long time. Use them when you are pretty sure everything is OK; otherwise, try to run relevant tests locally first.
-
Watch over your jobs on the Github Actions 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.
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:
-
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. -
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.
-
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.
-
Is the test failing on a Github Actions per-GHC build. In this case, if you click on "Branch", you can get access to the precise binaries that were built by Github Actions that are being tested. If you have an Ubuntu system, you can download the binaries and run them directly.
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 v2-build
, you will need to know the
name of the test suite you want. Cabal and cabal-install have
several. Also, you'll want to read Where are my build products?
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
(don't forget --with-cabal
! Your cabal-install tests won't
run without it).
There are also other test suites:
-
Cabal-tests: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:long-tests
are QuickCheck tests on cabal-install's dependency solver, VCS, and file monitoring code. 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 thecabal-install
source code.
For these test executables, -p
which applies a regex filter to the test
names. When running cabal-install
test suites, one need only use cabal test
or
cabal run <test-target>
in order to test locally.
-
Spaces, not tabs.
-
Try to follow style conventions of a file you are modifying, and avoid gratuitous reformatting (it makes merges harder!)
-
Format your commit messages in the standard way.
-
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 either qualified imports or 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, thecabal-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 ofcabal-install
released during the last three years. -
Cabal
has its own Prelude, inDistribution.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.
When opening a pull request, you should write a changelog entry
(or more in case of multiple independent changes).
This is done by adding files in the changelog.d
directory.
The files follow a simple key-value format similar to the one for .cabal files.
Here's an exhaustive example:
synopsis: Add feature xyz
packages: cabal-install
prs: #0000
issues: #0000 #0000
significance: significant
description: {
- Detail number 1
- Detail number 2
}
Only the synopsis
field is actually required, but you should also set the others where applicable.
Field | Description |
---|---|
synopsis |
Brief description of the change. Often just the pr title. |
description |
Longer description, with a list of sub-changes. Not needed for small/atomic changes. |
packages |
Packages affected by the change (cabal-install , Cabal ...). Omit if it's an overarching or non-package change. |
prs |
Space-separated hash-prefixed pull request numbers containing the change (usually just one). |
issues |
Space-separated hash-prefixed issue numbers that the change fixes/closes/affects. |
significance |
Set to significant if the change is significant, that is if it warrants being put near the top of the changelog. |
You can find a large number of real-world examples of changelog files here.
At release time, the entries will be merged with this tool.
In addition, if you're changing the .cabal file format specification you should
add an entry in doc/file-format-changelog.rst
.
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
onirc.libera.chat
. The#ghc
channel is also a decently good bet.- You can join the channel using a web client, even anonymously: https://web.libera.chat/#hackage
- Alternatively you can join it using matrix: https://matrix.to/#/#hackage:libera.chat
Notes for how to make a release are at the
wiki page "Making a release".
Currently, @emilypi, @fgaz and @Mikolaj have access to
haskell.org/cabal
, and @Mikolaj is the point of contact for getting
permissions.
Auto-generated API documentation for the master
branch of Cabal is automatically uploaded here: http://haskell.github.io/cabal-website/doc/html/Cabal/.
You can contribute by triaging issues which may include reproducing bug reports or asking for vital information, such as version numbers or reproduction instructions. If you would like to start triaging issues, one easy way to get started is to subscribe to cabal on CodeTriage.