ghc-8.0.1: switch to sphinx for documentation

Fixes #20281

"Since GHC 8.0, the User’s Guide is authored in ReStructuredText (or ReST
or RST, for short) a rich but light-weight mark-up language aimed at
producing documentation. The Sphinx tool is used to produce the final
PDF and HTML documentation."
- http://ghc.readthedocs.io/en/8.0.1/editing-guide.html

pkgs/development/compilers/ghc/8.0.1.nix

@@ -1,5 +1,5 @@
 { stdenv, fetchurl, fetchpatch, bootPkgs, perl, gmp, ncurses, libiconv, binutils, coreutils
-, hscolour, patchutils, libxml2, libxslt, docbook_xsl, docbook_xml_dtd_45, docbook_xml_dtd_42
+, hscolour, patchutils, sphinx
 }:
 
 let
@@ -29,7 +29,7 @@ stdenv.mkDerivation rec {
     (fetchFilteredPatch { url = https://git.haskell.org/ghc.git/patch/2f8cd14fe909a377b3e084a4f2ded83a0e6d44dd; sha256 = "06zvlgcf50ab58bw6yw3krn45dsmhg4cmlz4nqff8k4z1f1bj01v"; })
   ] ++ stdenv.lib.optional stdenv.isLinux ./ghc-no-madv-free.patch;
 
-  buildInputs = [ ghc perl libxml2 libxslt docbook_xsl docbook_xml_dtd_45 docbook_xml_dtd_42 hscolour ];
+  buildInputs = [ ghc perl hscolour sphinx];
 
   enableParallelBuilding = true;
 

pkgs/top-level/haskell-packages.nix

@@ -45,6 +45,7 @@ rec {
     ghc801 = callPackage ../development/compilers/ghc/8.0.1.nix rec {
       bootPkgs = packages.ghc7103;
       inherit (bootPkgs) hscolour;
+      sphinx = pkgs.python27Packages.sphinx;
     };
     ghc802 = callPackage ../development/compilers/ghc/8.0.2.nix rec {
       bootPkgs = packages.ghc7103;