There are two utilities, cabal2nix
and hackage4nix
, that automate
maintenance to a large extent. 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
converts a single Cabal file into a single Nix build
expression. For example:
$ cabal2nix cabal:https://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 = "https://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:https://NAME-VERSION
, which will automatically download the file from
Hackage. Alternatively, a direct https://host/path/pkg.cabal
URL can be
provided, as well as a file:https:///local/path/pkg.cabal
URI that doesn't
depend on network access. However, if the source hash is not already in cabal2nix
's cache or
provided using the --sha256
option, cabal2nix
still needs to download the source code to
compute the hash, which obviously still causes network traffic.
Run the utility with --help
to see the complete list of supported command line flags.
To add a new package to Nix, checkout the Nixpkgs project from https://github.com/nixos/nixpkgs.git and run
$ cd pkgs/development/libraries/haskell
$ mkdir foo
$ cabal2nix cabal:https://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 {};
cabal2nix
can also build derivations for projects from other
sources than hackage. You only need to provide an URI that points
to a cabal project. The most common usecase for this is probably to
generate a derivation for a project on the local file system:
aeson:$ cabal2nix ./.
# This file was auto-generated by cabal2nix. Please do NOT edit manually!
{ cabal, attoparsec, blazeBuilder, deepseq, dlist, hashable, HUnit
, mtl, QuickCheck, scientific, syb, testFramework
, testFrameworkHunit, testFrameworkQuickcheck2, text, time
, unorderedContainers, vector
}
cabal.mkDerivation (self: {
pname = "aeson";
version = "0.7.0.2";
src = ./.;
buildDepends = [
attoparsec blazeBuilder deepseq dlist hashable mtl scientific syb
text time unorderedContainers vector
];
testDepends = [
attoparsec HUnit QuickCheck testFramework testFrameworkHunit
testFrameworkQuickcheck2 text time unorderedContainers vector
];
meta = {
homepage = "https://github.com/bos/aeson";
description = "Fast JSON parsing and encoding";
license = self.stdenv.lib.licenses.bsd3;
platforms = self.ghc.meta.platforms;
};
})
This derivation will not fetch from hackage, but instead use the directory which contains the derivation as the source repository.
cabal2nix
currently supports the following respository types:
- directory
- source archive (zip, tar.gz, ...) from http or https URL or local file.
- git, mercurial, svn or bazaar repository
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 pkgs
in your checked-out copy of the Nixpkgs tree 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 pkgs
The following updates are available:
WebBits-Html-1.0.1:
cabal2nix cabal:https://WebBits-Html-1.0.2 >pkgs/pkgs/development/libraries/haskell/WebBits-Html/default.nix
happstack-server-6.1.6:
cabal2nix cabal:https://happstack-server-6.2.1 >pkgs/pkgs/development/libraries/haskell/happstack/happstack-server.nix
cabal2nix cabal:https://happstack-server-6.2.2 >pkgs/pkgs/development/libraries/haskell/happstack/happstack-server.nix
primitive-0.3.1:
cabal2nix cabal:https://primitive-0.4 >pkgs/pkgs/development/libraries/haskell/primitive/default.nix
repa-2.1.1.5:
cabal2nix cabal:https://repa-2.1.1.6 >pkgs/pkgs/development/libraries/haskell/repa/default.nix
unix-compat-0.2.2.1:
cabal2nix cabal:https://unix-compat-0.3 >pkgs/pkgs/development/libraries/haskell/unix-compat/default.nix
vector-0.7.1:
cabal2nix cabal:https://vector-0.8 >pkgs/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!
The tool-chain is stable. As of today, 2013-04-12, virtually all Haskell
packages available in Nix have been generated automatically from their
Cabal files. There are only a handful of exceptions, which we cannot
generate because these packages aren't available on Hackage. The list of
those packages is hard-coded into the
hackage4nix.hs
binary in the function badPackagePaths
.
Furthermore, Hackage4Nix will not re-generate packages that have been patched, i.e. that define any of the following attributes:
(pre|post)Configure
(pre|post)Install
patchPhase
patches
These packages are considered for updates, however.
The complete list of Haskell packages available in Nix is generated by
the tool package-list
,
and published at https://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.