coq-mathcomp: also build and install the documentation

pkgs/development/coq-modules/mathcomp/default.nix

@@ -1,4 +1,6 @@
-{stdenv, fetchurl, coq, ssreflect}:
+{ stdenv, fetchurl, coq, ssreflect
+, graphviz, ocaml, withDoc ? true
+}:
 
 stdenv.mkDerivation {
 
@@ -9,12 +11,19 @@ stdenv.mkDerivation {
     sha256 = "1297svwi18blrlyd8vsqilar2h5nfixlvlifdkbx47aljq4m5bam";
   };
 
+  nativeBuildInputs = stdenv.lib.optionals withDoc [ graphviz ocaml ];
   propagatedBuildInputs = [ coq ssreflect ];
 
   enableParallelBuilding = true;
 
+  buildFlags = stdenv.lib.optionalString withDoc "doc";
+
   installFlags = "COQLIB=$(out)/lib/coq/${coq.coq-version}/";
 
+  postInstall = stdenv.lib.optionalString withDoc ''
+    make -f Makefile.coq install-doc DOCDIR=$out/share/coq/${coq.coq-version}/
+  '';
+
   meta = with stdenv.lib; {
     homepage = http://ssr.msr-inria.inria.fr/;
     license = licenses.cecill-b;