dune_2: init at 2.1.0

Changelog:
- https://github.com/ocaml/dune/releases/tag/2.0.0
- https://github.com/ocaml/dune/releases/tag/2.0.1
- https://github.com/ocaml/dune/releases/tag/2.1.0

pkgs/development/tools/ocaml/dune/2.nix

@@ -0,0 +1,31 @@
+{ stdenv, fetchurl, ocaml, findlib }:
+
+if stdenv.lib.versionOlder ocaml.version "4.07"
+then throw "dune is not available for OCaml ${ocaml.version}"
+else
+
+stdenv.mkDerivation rec {
+  pname = "dune";
+  version = "2.1.0";
+
+  src = fetchurl {
+    url = "https://github.com/ocaml/dune/releases/download/${version}/dune-${version}.tbz";
+    sha256 = "1hf8c0djx2v1jpjba0z096gw6qdr0igsljrf0qh0ggphg9valsmj";
+  };
+
+  buildInputs = [ ocaml findlib ];
+
+  buildFlags = "release";
+
+  dontAddPrefix = true;
+
+  installFlags = [ "PREFIX=${placeholder "out"}" "LIBDIR=$(OCAMLFIND_DESTDIR)" ];
+
+  meta = {
+    homepage = "https://dune.build/";
+    description = "A composable build system";
+    maintainers = [ stdenv.lib.maintainers.vbgl stdenv.lib.maintainers.marsam ];
+    license = stdenv.lib.licenses.mit;
+    inherit (ocaml.meta) platforms;
+  };
+}

pkgs/top-level/all-packages.nix

@@ -1614,7 +1614,7 @@ in
 
   dua = callPackage ../tools/misc/dua { };
 
-  inherit (ocamlPackages) dune;
+  inherit (ocamlPackages) dune dune_2;
 
   duperemove = callPackage ../tools/filesystems/duperemove { };
 

pkgs/top-level/ocaml-packages.nix

@@ -16,6 +16,8 @@ let
 
     buildDunePackage = callPackage ../build-support/ocaml/dune.nix {};
 
+    buildDune2Package = buildDunePackage.override { dune = dune_2; };
+
     alcotest = callPackage ../development/ocaml-modules/alcotest {};
 
     angstrom = callPackage ../development/ocaml-modules/angstrom { };
@@ -237,6 +239,8 @@ let
 
     dune = callPackage ../development/tools/ocaml/dune { };
 
+    dune_2 = callPackage ../development/tools/ocaml/dune/2.nix { };
+
     earley = callPackage ../development/ocaml-modules/earley { };
 
     earlybird = callPackage ../development/ocaml-modules/earlybird { };