Restrict the name when there's only one package

it should always be the same as the project name

Signed-off-by: Rudi Grinberg <rudi.grinberg@gmail.com>

src/dune_project.ml

@@ -614,15 +614,24 @@ let parse ~dir ~lang ~packages ~file =
      let allow_approx_merlin =
        Option.value ~default:false allow_approx_merlin in
      let packages =
+       begin match dune_defined_packages, name with
+       | [loc, p], Named name ->
+         if Package.Name.to_string p.name <> name then
+           of_sexp_errorf loc
+             "when a single package is defined, it must have the same \
+              name as the project name: %s" name;
+       | _, _ -> ()
+       end;
        match
-        dune_defined_packages
-        |> Package.Name.Map.of_list_map
-             ~f:(fun (_loc, (p : Package.t)) -> p.name, p)
+         dune_defined_packages
+         |> Package.Name.Map.of_list_map
+              ~f:(fun (_loc, (p : Package.t)) -> p.name, p)
        with
        | Error (p, (_, _), (loc, _)) ->
          of_sexp_errorf loc "package %s is already defined"
            (Package.Name.to_string p)
-       | Ok d -> Package.Name.Map.superpose packages d
+       | Ok d ->
+         Package.Name.Map.superpose packages d
      in
      { name
      ; root = dir