buildDunePackage: new support function; use it to refactor some OCaml derivations

pkgs/development/ocaml-modules/cohttp/default.nix

@@ -1,11 +1,11 @@
-{ stdenv, fetchFromGitHub, ocaml, findlib, dune
+{ stdenv, fetchFromGitHub, buildDunePackage
 , ppx_fields_conv, ppx_sexp_conv, ppx_deriving
 , base64, fieldslib, jsonm, re, stringext, uri
 }:
 
-stdenv.mkDerivation rec {
+buildDunePackage rec {
+  pname = "cohttp";
 	version = "1.1.1";
-	name = "ocaml${ocaml.version}-cohttp-${version}";
 
 	src = fetchFromGitHub {
 		owner = "mirage";
@@ -14,19 +14,14 @@ stdenv.mkDerivation rec {
 		sha256 = "1dzd6vy43b7p9xplzg2whylz5br59zxaqywa14b4l377f31gnwq1";
 	};
 
-	buildInputs = [ ocaml findlib dune jsonm ppx_fields_conv ppx_sexp_conv ];
+	buildInputs = [ jsonm ppx_fields_conv ppx_sexp_conv ];
 
 	propagatedBuildInputs = [ ppx_deriving base64 fieldslib re stringext uri ];
 
-	buildPhase = "dune build -p cohttp";
-
-	inherit (dune) installPhase;
-
 	meta = {
 		description = "HTTP(S) library for Lwt, Async and Mirage";
 		license = stdenv.lib.licenses.isc;
 		maintainers = [ stdenv.lib.maintainers.vbgl ];
 		inherit (src.meta) homepage;
-		inherit (ocaml.meta) platforms;
 	};
 }