| Safe Haskell | Safe-Inferred |
|---|---|
| Language | Haskell2010 |
Distribution.Nixpkgs.Meta
Description
A representation of the meta section used in Nix expressions. A
detailed description can be found in section 4, "Meta-attributes",
of the Nixpkgs manual at http://nixos.org/nixpkgs/docs.html.
Synopsis
- data Meta
- nullMeta :: Meta
- homepage :: Lens' Meta String
- description :: Lens' Meta String
- license :: Lens' Meta License
- platforms :: Lens' Meta (Maybe (Set NixpkgsPlatform))
- badPlatforms :: Lens' Meta (Maybe (Set NixpkgsPlatform))
- hydraPlatforms :: Lens' Meta (Maybe (Set NixpkgsPlatform))
- mainProgram :: Lens' Meta (Maybe String)
- maintainers :: Lens' Meta (Set Identifier)
- broken :: Lens' Meta Bool
- data NixpkgsPlatform
- nixpkgsPlatformFromString :: String -> Maybe NixpkgsPlatform
Representation of the Nixpkgs Meta Set
A representation of the meta section used in Nix expressions.
>>>:set -XOverloadedStrings>>>:{let meta = nullMeta & homepage .~ "http://example.org" & description .~ "An example package" & license .~ Unknown Nothing & platforms .~ Just (Set.singleton (NixpkgsPlatformSingle (Platform X86_64 Linux))) & badPlatforms .~ Nothing & hydraPlatforms .~ Just Set.empty & mainProgram .~ Just "example-binary" & maintainers .~ Set.fromList ["joe", "jane"] & broken .~ True in print $ pPrint meta :} homepage = "http://example.org"; description = "An example package"; license = "unknown"; platforms = [ "x86_64-linux" ]; hydraPlatforms = lib.platforms.none; mainProgram = "example-binary"; maintainers = [ lib.maintainers.jane lib.maintainers.joe ]; broken = true;
Instances
Meta record with no field set, i.e. evaluating any will throw:
>>>nullMeta ^. homepage"*** Exception: undefined Meta.homepage ...
Lenses for Meta
badPlatforms :: Lens' Meta (Maybe (Set NixpkgsPlatform)) Source #
hydraPlatforms :: Lens' Meta (Maybe (Set NixpkgsPlatform)) Source #
maintainers :: Lens' Meta (Set Identifier) Source #
Representation of Nixpkgs Platform Descriptions
data NixpkgsPlatform Source #
Representation of platform(s) as supported by nixpkgs:
NixpkgsPlatformGrouprepresents the name of a platform list as found inlib.platforms. For example, at the time of writingNixpkgsPlatformGroup "darwin"would represent the platform tuplesx86_64-darwin,aarch64-darwin,i686-darwinandarmv7a-darwin. Naturally, this is subject to change as nixpkgs updateslib.platforms.NixpkgsPlatformSingleindicates a single platform tuple represented using Cabal'sPlatform.
The former is useful to express related groups of platforms which have similar properties. The latter can be used to, for example, exclude a single, specific platform.
hackage2nix has used the latter approach historically
and is being extended to support nixpkgs' platform
groups as well for increased maintainer convenience.
The Pretty instance allows for converting a NixpkgsPlatform
into a Nix expression compatible with meta.platforms:
>>>pPrint $ NixpkgsPlatformSingle $ Platform X86_64 NetBSD"x86_64-netbsd"
For NixpkgsPlatformGroup we assume that the lib attribute set is in
scope:
>>>pPrint $ NixpkgsPlatformGroup $ ident # "riscv"lib.platforms.riscv
Constructors
| NixpkgsPlatformSingle Platform | Single platform represented as a Cabal platform. Can be understood as equivalent to Nix's system strings and will be converted to one usually. |
| NixpkgsPlatformGroup Identifier |
|
Instances
nixpkgsPlatformFromString :: String -> Maybe NixpkgsPlatform Source #
Obtain a NixpkgsPlatform from a string representation intended for config
files.
- Every string starting with
lib.platforms.orplatforms.is parsed intoNixpkgsPlatformGroup. - All other strings are attempted to be interpreted as a nix(pkgs) style
system tuple and parsed into
NixpkgsPlatformSingle.
If none of these formats match the input String, Nothing is returned.
A Just result thus only indicates that the format of the platform is
sound — nixpkgsPlatformFromString does not check if the parsed platform
actually exists.
NixpkgsPlatformSingle is parsed from system tuples as understood by Nix
and nixpkgs. System tuples are derived from autoconf's
target triplets,
dropping the vendor part. They have the form cpu-os where os can either
be a single component or of the form kernel-system (system is an autoconf
term here, not a Nix system). Note that three component systems are very
rare. The two main candidates x86_64-linux-musl and x86_64-linux-gnu
are prohibited for historical reasons
and represented as plain x86_64-linux instead.
Note that nixpkgsPlatformFromString expects to receive a valid system
tuple, i.e. it will accept all system tuples that have a sound format
(with the caveat that it will accept n-tuples for n >= 4 even though
they are technically invalid). This is done because the ambiguity of
system tuples requires knowledge over its legal contents in order to check
their validity properly. Since lib.systems.elaborate from nixpkgs is the
source of truth in this case, we want to avoid the need to continuously
update distribution-nixpkgs to reflect its inner workings.
nixpkgsPlatformFromString does, however, some conversions to alleviate some
discrepancies between Cabal and nixpkgs. Parsing and rendering system tuples
using nixpkgsPlatformFromString and rendering them via the Pretty
instance of NixpkgsPlatform should not change the system tuple
for tuples accepted by nixpkgs. This has been tested for all known tuples
(from lib.platforms and lib.systems.examples) as of 2022-05-08.
Please open an issue if any newly added ones are not recognized properly.
Warning: nixpkgsPlatformFromString consequently tries to preserve all
information of the passed system tuple. This means that it distinguishes
between things that Cabal wouldn't, e.g. powerpc64 and powerpc64le. If
you use this function to obtain a Platform that is later used to evaluate
a .cabal file, it will behave unexpectedly in some situation. It is
recommended to use Cabal's own facilities or
Distribution.Nixpkgs.Haskell.Platform, provided by cabal2nix, instead.
nixpkgsPlatformFromString is also not the inverse operation for
NixpkgsPlatform's Pretty instance. It is not intended for parsing Nix
expressions.
>>>nixpkgsPlatformFromString "x86_64-netbsd"Just (NixpkgsPlatformSingle (Platform X86_64 NetBSD))>>>nixpkgsPlatformFromString "platforms.riscv"Just (NixpkgsPlatformGroup (Identifier "riscv"))>>>nixpkgsPlatformFromString "garbage"Nothing