Use hpack to generate cabal files when required (#82)

* Use hpack to generate cabal files when required

Author: qrilka

builder/comp-builder.nix

@@ -1,4 +1,4 @@
-{ stdenv, buildPackages, ghc, lib, pkgconfig, writeText, runCommand, haskellLib, nonReinstallablePkgs, withPackage }:
+{ stdenv, buildPackages, ghc, lib, pkgconfig, writeText, runCommand, haskellLib, nonReinstallablePkgs, withPackage, hsPkgs }:
 
 { componentId
 , component
@@ -9,6 +9,7 @@
 , flags
 , revision
 , cabalFile
+, cabal-generator
 , patches ? []
 
 , preUnpack ? null, postUnpack ? null
@@ -242,9 +243,11 @@ stdenv.mkDerivation ({
   # Phases
   preInstallPhases = lib.optional doHaddock' "haddockPhase";
 
-  prePatch = lib.optionalString (cabalFile != null) ''
-    cat ${cabalFile} > ${package.identifier.name}.cabal
-  '';
+  prePatch = if (cabalFile != null)
+     then ''cat ${cabalFile} > ${package.identifier.name}.cabal''
+     else lib.optionalString (cabal-generator == "hpack") ''
+       ${hsPkgs.hpack.components.exes.hpack}/bin/hpack
+     '';
 
   configurePhase = ''
     runHook preConfigure

builder/default.nix

@@ -1,8 +1,9 @@
-{ pkgs, buildPackages, stdenv, lib, haskellLib, ghc, buildGHC, fetchurl, writeText, runCommand, pkgconfig, nonReinstallablePkgs, withPackage }:
+{ pkgs, buildPackages, stdenv, lib, haskellLib, ghc, buildGHC, fetchurl, writeText, runCommand, pkgconfig, nonReinstallablePkgs, withPackage, hsPkgs }:
 
 { flags
 , package
 , components
+, cabal-generator
 
 , name
 , sha256
@@ -71,10 +72,10 @@ let
       '';
     };
 
-  comp-builder = haskellLib.weakCallPackage pkgs ./comp-builder.nix { inherit ghc haskellLib nonReinstallablePkgs withPackage; };
+  comp-builder = haskellLib.weakCallPackage pkgs ./comp-builder.nix { inherit ghc haskellLib nonReinstallablePkgs withPackage hsPkgs; };
 
   buildComp = componentId: component: comp-builder {
-    inherit componentId component package name src flags setup cabalFile patches revision
+    inherit componentId component package name src flags setup cabalFile cabal-generator patches revision
             preUnpack postUnpack preConfigure postConfigure
             preBuild postBuild preCheck postCheck
             preInstall postInstall preHaddock postHaddock

modules/component-driver.nix

@@ -5,7 +5,7 @@ let
     inherit haskellLib;
     ghc = config.ghc.package;
     buildGHC = buildModules.config.ghc.package;
-    inherit (config) nonReinstallablePkgs;
+    inherit (config) nonReinstallablePkgs hsPkgs;
     inherit withPackage;
   };