OCaml build support: add oasis build system

pkgs/build-support/ocaml/oasis.nix

@@ -0,0 +1,31 @@
+{ buildOcaml, ocaml_oasis }:
+
+{ name, version, buildInputs ? [], ...
+}@args:
+
+buildOcaml (args // {
+  buildInputs = [ ocaml_oasis ] ++ buildInputs;
+
+  buildPhase = ''
+    runHook preBuild
+    oasis setup
+    ocaml setup.ml -configure
+    ocaml setup.ml -build
+    runHook postBuild
+  '';
+
+  checkPhase = ''
+    runHook preCheck
+    ocaml setup.ml -test
+    runHook postCheck
+  '';
+
+  installPhase = ''
+    runHook preInstall
+    mkdir -p $out
+    sed -i s+/usr/local+$out+g setup.ml
+    sed -i s+/usr/local+$out+g setup.data
+    prefix=$OCAMLFIND_DESTDIR ocaml setup.ml -install
+    runHook postInstall
+  '';
+})

pkgs/top-level/ocaml-packages.nix

@@ -12,6 +12,8 @@ let
 
     buildOcaml = callPackage ../build-support/ocaml { };
 
+    buildOasisPackage = callPackage ../build-support/ocaml/oasis.nix { buildOcaml = buildOcaml; };
+
     buildDunePackage = callPackage ../build-support/ocaml/dune.nix {};
 
     alcotest = callPackage ../development/ocaml-modules/alcotest {};