ocamlPackages.buildDunePackage: deprecate useDune2

doc/languages-frameworks/ocaml.section.md

@@ -38,12 +38,12 @@ Here is a simple package example.
 
 - It uses the `fetchFromGitHub` fetcher to get its source.
 
-- `duneVersion = "2"` ensures that Dune version 2 is used for the
-  build (this is the default; valid values are `"1"`, `"2"`, and `"3"`);
-  note that there is also a legacy `useDune2` boolean attribute:
-  set to `false` it corresponds to `duneVersion = "1"`; set to `true` it
-  corresponds to `duneVersion = "2"`. If both arguments (`duneVersion` and
-  `useDune2`) are given, the second one (`useDune2`) is silently ignored.
+- It also accept `duneVersion` parameter (valid value are `"1"`, `"2"`, and
+  `"3"`). The recommended practice it to set only if you don't want the default
+  value and/or it depends on something else like package version. You might see
+  a not-supported argument `useDune2`. The behavior was `useDune2 = true;` =>
+  `duneVersion = "2";` and `useDune2 = false;` => `duneVersion = "1";`. It was
+  used at the time when dune3 didn't existed.
 
 - It sets the optional `doCheck` attribute such that tests will be run with
   `dune runtest -p angstrom` after the build (`dune build -p angstrom`) is
@@ -71,7 +71,6 @@ Here is a simple package example.
 buildDunePackage rec {
   pname = "angstrom";
   version = "0.15.0";
-  duneVersion = "2";
 
   minimalOCamlVersion = "4.04";
 
@@ -104,8 +103,6 @@ buildDunePackage rec {
   pname = "wtf8";
   version = "1.0.2";
 
-  useDune2 = true;
-
   minimalOCamlVersion = "4.02";
 
   src = fetchurl {

pkgs/build-support/ocaml/dune.nix

@@ -3,7 +3,7 @@
 { pname, version, nativeBuildInputs ? [], enableParallelBuilding ? true, ... }@args:
 
 let Dune =
-  let dune-version = args . duneVersion or (if args.useDune2 or true then "2" else "1"); in
+  let dune-version = args.duneVersion or "2"; in
   { "1" = dune_1; "2" = dune_2; "3" = dune_3; }."${dune-version}"
 ; in