commit 8a0566e4c808caec658856641706f560bb6a5a1b · pyrox.dev/nixpkgs

+56

doc/languages-frameworks/haskell.md

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       nix-build -A haskell.packages.integer-simple.ghc802.scientific

     

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       ```

     

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       ### Quality assurance

     

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       The `haskell.lib` library includes a number of functions for checking for

     

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       various imperfections in Haskell packages. It's useful to apply these functions

     

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       to your own Haskell packages and integrate that in a Continuous Integration

     

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       server like [hydra](https://nixos.org/hydra/) to assure your packages maintain a

     

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       minimum level of quality. This section discusses some of these functions.

     

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       #### buildStrictly

     

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       Applying `haskell.lib.buildStrictly` to a Haskell package enables the `-Wall`

     

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       and `-Werror` GHC options to turn all warnings into build failures. Additionally

     

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       the source of your package is gotten from first invoking `cabal sdist` to ensure

     

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       all needed files are listed in the Cabal file.

     

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       #### checkUnusedPackages

     

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       Applying `haskell.lib.checkUnusedPackages` to a Haskell package invokes

     

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       the [packunused](http://hackage.haskell.org/package/packunused) tool on the

     

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       package. `packunused` complains when it finds packages listed as build-depends

     

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       in the Cabal file which are redundant. For example:

     

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       ```

     

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       $ nix-build -E 'let pkgs = import <nixpkgs> {}; in pkgs.haskell.lib.checkUnusedPackages {} pkgs.haskellPackages.scientific'

     

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       these derivations will be built:

     

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         /nix/store/3lc51cxj2j57y3zfpq5i69qbzjpvyci1-scientific-0.3.5.1.drv

     

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       ...

     

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       detected package components

     

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       ~~~~~~~~~~~~~~~~~~~~~~~~~~~

     

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        - library

     

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        - testsuite(s): test-scientific

     

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        - benchmark(s): bench-scientific*

     

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       (component names suffixed with '*' are not configured to be built)

     

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       library

     

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       ~~~~~~~

     

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       The following package dependencies seem redundant:

     

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        - ghc-prim-0.5.0.0

     

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       testsuite(test-scientific)

     

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       ~~~~~~~~~~~~~~~~~~~~~~~~~~

     

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       no redundant packages dependencies found

     

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       builder for ‘/nix/store/3lc51cxj2j57y3zfpq5i69qbzjpvyci1-scientific-0.3.5.1.drv’ failed with exit code 1

     

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       error: build of ‘/nix/store/3lc51cxj2j57y3zfpq5i69qbzjpvyci1-scientific-0.3.5.1.drv’ failed

     

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       ```

     

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       As you can see, `packunused` finds out that although the testsuite component has

     

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       no redundant dependencies the library component of `scientific-0.3.5.1` depends

     

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       on `ghc-prim` which is unused in the library.

     

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       ## Other resources

     

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         - The Youtube video [Nix Loves Haskell](https://www.youtube.com/watch?v=BsBhi_r-OeE)

+17 -1

pkgs/development/haskell-modules/lib.nix

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       # TODO(@Ericson2314): Remove `pkgs` param, which is only used for

     

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       # `buildStackProject` and `justStaticExecutables`

     

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       # `buildStackProject`, `justStaticExecutables` and `checkUnusedPackages`

     

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       { pkgs, lib }:

     

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       rec {

     
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         });

     

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         buildStrictly = pkg: buildFromSdist (appendConfigureFlag pkg "--ghc-option=-Wall --ghc-option=-Werror");

     

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         checkUnusedPackages =

     

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           { ignoreEmptyImports ? false

     

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           , ignoreMainModule   ? false

     

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           , ignorePackages     ? []

     

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           } : drv :

     

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             overrideCabal (appendConfigureFlag drv "--ghc-option=-ddump-minimal-imports") (_drv: {

     

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               postBuild = with lib;

     

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                 let args = concatStringsSep " " (

     

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                              optional ignoreEmptyImports "--ignore-empty-imports" ++

     

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                              optional ignoreMainModule   "--ignore-main-module" ++

     

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                              map (pkg: "--ignore-package ${pkg}") ignorePackages

     

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                            );

     

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                 in "${pkgs.haskellPackages.packunused}/bin/packunused" +

     

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                    optionalString (args != "") " ${args}";

     

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             });

     

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         buildStackProject = pkgs.callPackage ./generic-stack-builder.nix { };

     

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