Readme for cabal2nix-1.49
How to maintain Haskell Packages in Nix
Overview over the tool-chain
There are two utilities, cabal2nix
and hackage4nix
, that automate
maintenance to a large extend. We intend to merge them into one program,
eventually, but the necessary re-factoring hasn't been done yet since
this is not a high priority.
Cabal2nix
cabal2nix
converts a single Cabal file into a single Nix build
expression. For example:
$ cabal2nix cabal://yesod-0.9.1
{ cabal, attoparsecText, blazeBuilder, blazeHtml, hamlet, httpTypes
, monadControl, parsec, shakespeareCss, shakespeareJs, text, time
, transformers, unixCompat, wai, waiExtra, warp, yesodAuth
, yesodCore, yesodForm, yesodJson, yesodPersistent
}:
cabal.mkDerivation (self: {
pname = "yesod";
version = "0.9.1";
sha256 = "1ag3lca75lrriycbscspb5yyishacgxjx0rybc3x4z1dqnkn1r71";
isLibrary = true;
isExecutable = true;
buildDepends = [
attoparsecText blazeBuilder blazeHtml hamlet httpTypes monadControl
parsec shakespeareCss shakespeareJs text time transformers
unixCompat wai waiExtra warp yesodAuth yesodCore yesodForm
yesodJson yesodPersistent
];
meta = {
homepage = "http://www.yesodweb.com/";
description = "Creation of type-safe, RESTful web applications";
license = self.stdenv.lib.licenses.bsd3;
platforms = self.ghc.meta.platforms;
};
})
Cabal files can be referred to using the magic URL
cabal://NAME-VERSION
, which will automatically download the file from
Hackage. Alternatively, a direct http://host/path/pkg.cabal
URL can be
provided, as well as a file:///local/path/pkg.cabal
URI that doesn't
depend on network access. Run the utility with --help
to see the
complete list of supported command line flags.
To add a new package to Nix, the following steps need to be performed:
$ cd $NIXPKGS_ALL/pkgs/development/libraries/haskell
$ mkdir foo
$ cabal2nix cabal://foo-1.0 >foo/default.nix
Then add an appropriate attribute to
pkgs/top-level/haskell-packages.nix
, for example:
foo = callPackage ../development/libraries/haskell/foo {};
Hackage4nix
The hackage4nix
utility re-generates all expressions found in the
nixpkgs
database in place. This is useful to ensure that all packages
have been generated with a recent version of the tool-chain.
Furthermore, hackage4nix
adds default settings for the
meta.maintainers
and meta.platforms
attribute if these aren't
configured yet. Generally speaking, running
$ hackage4nix $NIXPKGS_ALL
should be a no-op --- i.e. no files should change! If there are changes, these indicate that a file has been modified manually, and then these changes must be investigated to find out what is going on.
Last but not least, hackage4nix
generates a list of all updates
available from Hackage. (Run cabal update
to make sure that your local
copy of the Hackage database is up-to-date!) For example:
$ hackage4nix $NIXPKGS_ALL
The following updates are available:
WebBits-Html-1.0.1:
cabal2nix cabal://WebBits-Html-1.0.2 >$NIXPKGS_ALL/pkgs/development/libraries/haskell/WebBits-Html/default.nix
happstack-server-6.1.6:
cabal2nix cabal://happstack-server-6.2.1 >$NIXPKGS_ALL/pkgs/development/libraries/haskell/happstack/happstack-server.nix
cabal2nix cabal://happstack-server-6.2.2 >$NIXPKGS_ALL/pkgs/development/libraries/haskell/happstack/happstack-server.nix
primitive-0.3.1:
cabal2nix cabal://primitive-0.4 >$NIXPKGS_ALL/pkgs/development/libraries/haskell/primitive/default.nix
repa-2.1.1.5:
cabal2nix cabal://repa-2.1.1.6 >$NIXPKGS_ALL/pkgs/development/libraries/haskell/repa/default.nix
unix-compat-0.2.2.1:
cabal2nix cabal://unix-compat-0.3 >$NIXPKGS_ALL/pkgs/development/libraries/haskell/unix-compat/default.nix
vector-0.7.1:
cabal2nix cabal://vector-0.8 >$NIXPKGS_ALL/pkgs/development/libraries/haskell/vector/default.nix
These updates can be performed automatically by running the cabal2nix
command given by hackage4nix
. If there is more than one possible
update, then all of them will be shown. Note, however, that some updates
break compilation of other packages, because they depend on very
specific versions of their build inputs, so please be careful when
performing updates!
Current State of Affairs
The tool-chain is stable. As of today, 2011-08-30, almost all Haskell packages available in Nix have been generated automatically from their Cabal files. The exceptions are:
-
"Bad packages" that cannot be generated automatically because there is no proper Cabal file for them, or because their builds are so complicated that the
cabal.nix
build doesn't suffice to do the trick. The list of bad packages is hard-coded intohackage4nix.hs
, in the functionsbadPackagePaths
andpatchedPackages
. Any package list in there is going to be ignored byhackage4nix
. -
"Patched packages" cannot be generated automatically, because their build instructions need patches that
cabal2nix
doesn't (yet) know about. There is a hard-coded list of patched packages inhackage4nix
. Furthermore, all build expressions that define any of the attributes(pre|post)Configure (pre|post)Install patchPhase patches
are considered "patched". That list of attributes is hard-coded in
hackage4nix.hs
in the functionregenerateDerivation
.
The complete list of Haskell packages available in Nix is generated by
the tool package-list
,
and published at http://cryp.to/haskell-in-nixpkgs.txt. Hackage picks
it up from there and generates links on each package's homepage to the
corresponding page in Hydra automatically. See ticket
875 for further
details.