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Overlay Hackage Package Index for GHC HEAD

The official repository is moved to

How to contribute

Submit PRs with patch(es) relative to the source tarball(s) of existing Hackage package(s).

  • The patches MUST apply cleanly by patch -p1 when inside the original unpacked source-tarball. (Travis CI will verify this when you submit a PR).

  • The patches SHOULD work with at least GHC HEAD and the most recent stable released GHC version (currently this means with GHC 8.6.1 and GHC 8.7).

  • The patches SHOULD ideally result in the same code being compiled, as one of the main purposes of these patches is to make regression testing possible. I.e. try to avoid conditional compilation.

  • If only the .cabal file needs to be modified, a .cabal file SHOULD be used instead of a .patch file. If the changes to the .cabal file are too invasive (e.g. removing modules, changing the structure of the package etc), a .patch file must be used.

How this works

This repo contains <pkg-id>.patch and <pkg-id>.cabal files in the patches/ folder (where <pkg-id> refers to a specific release of a package, e.g. lens-4.15.3).

Once merged to master, all package releases whose <pkg-id> is mentioned will enter the HEAD.hackage package index; if there is a .patch file, the respective releases tarballs are patched (i.e. mutated!). If there is a .cabal file, it is included as a revision in the package index. Consequently, if there is only a .cabal file and no .patch file, the original source .tar.gz is included verbatimely (i.e. not mutated).

If this operation succeeds, the HEAD.hackage package index at is updated to contain the new index state.

HEAD.hackage contains only a small subset of package releases, and needs to be combined with the main Hackage repository.

Cabal's new nix-style local build facility makes sure that the modified packages don't contaminate your package databases, while allowing to maximise sharing via the nix-style package-db cache store.

How to use

As an add-on remote repository

It is not recommended to add the HEAD.hackage repository index to your global cabal configuration.

Instead, you should mix in the HEAD.hackage repository on a per-project level. Then the packages in the HEAD.hackage will overlay those from the main package index, by adding the repository stanza (as shown on to the cabal.project(.local) file or use init (see below).

To workaround some current issues in cabal and make it more convenient, the script scripts/ is provided, which facilitates common tasks.

It's been tested on Linux so far. Other operating systems may require tweaks (patches welcome!).

The main operations provided are

  • update: Resets & syncs the local package download cache for the HEAD.hackage repo.

  • init: generates a new cabal.project file with a repository stanza enabling the HEAD.hackage repo locally. This command also takes an optional list of arguments which are included as optional-packages: declarations in the resulting cabal.project file.

  • init-local: generate a cabal.project.local file instead.

  • dump-repo: print repository stanza to stdout

As an add-on local repository

The HEAD.hackage package repo can also be generated as a file-based local repository. The handling is similiar to using HEAD.hackage via a remote repo.

TODO: provide scripting

As locally patched packages

The process of applying patches can be used in a cabal project with local packages.

You can add something like optional-packages: */*.cabal to your cabal.project file, and then for each package-id with a .patch or .cabal file you want to provide as a locally patched package do

$ cabal unpack --pristine $PKGID
$ cd $PKGID/
$ patch -p1 -i ${WhereThisGitHubRepoIsCloned}/patches/$PKGID.patch
$ cp ${WhereThisGitHubRepoIsCloned}/patches/$PKGID.cabal ./*.cabal
$ cd ..

Alternatively, you can use the handy patch-tool utility:

$ scripts/patch-tool unpack-patch patches/$PKGID.patch

This will extract the given package into the packages/$PKGID directory, initialize it as a git repository, and the patch.

Adding a patch

The scripts/patch-tool script is a tool for conveniently authoring and updating patches. For instance, if you find that the doctest package needs to be patched first run:

$ scripts/patch-tool unpack doctest

This will extract a doctest source tree to packages/doctest-$version and initialize it as a git repository. You can now proceed to edit the tree as necessary and run

$ scripts/patch-tool update-patches

This will create an appropriately-named patch in patches/ from the edits in the doctest tree.

Usage with nix

default.nix is a Nix expression which can be used to build head.hackage packages using GHC 8.6.1-alpha2:

$ nix build -f ./. haskellPackages.servant

It can also be used to build a compiler from a local source tree and use this to build head.hackage packages:

$ nix build -f ./. --arg ghc "(import ghc-from-source.nix {ghc-path=$GHC_TREE;})"

Travis CI

The Travis CI script generator has recently added support for enabling the HEAD.hackage repository automatically for jobs using unreleased GHC versions.


The patches maintained for the head.hackage project can also be used with Nix (not to be confused with Cabal's Nix-style local builds). See the README in the script/ folder and/or the Using a development version of GHC with nix blogpost for more information.

Other Package Index Overlays


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