test: add repro for ocaml#10264

This is only one part of the issue; the other part is more difficult to
test because it is related to `Modules.t` round-tripping correctly.

Signed-off-by: Etienne Millon <[email protected]>

src/dune_rules/module.mli

@@ -21,6 +21,8 @@ module Kind : sig
     | Root
 
   include Dune_lang.Conv.S with type t := t
+
+  val to_dyn : t -> Dyn.t
 end
 
 module Source : sig

test/expect-tests/module_tests.ml

@@ -0,0 +1,47 @@
+open Stdune
+module Kind = Dune_rules.Module.Kind
+
+(* See #10264 *)
+let%expect_test "Module.Kind encoding round trip" =
+  let module_name s = Dune_rules.Module_name.of_string s in
+  let test k =
+    let ast = Kind.encode k in
+    let sexp = Dune_sexp.Ast.add_loc ~loc:Loc.none ast in
+    let decoded =
+      match Dune_lang.Decoder.parse Kind.decode Univ_map.empty sexp with
+      | r -> Ok r
+      | exception e -> Error e
+    in
+    let dyn =
+      Dyn.record
+        [ "ast", Dyn.string (Dune_sexp.to_string ast)
+        ; "decoded", Or_exn.to_dyn Kind.to_dyn decoded
+        ]
+    in
+    Dune_tests_common.print_dyn dyn
+  in
+  test Impl;
+  [%expect {| { ast = "impl"; decoded = Ok Impl } |}];
+  test (Alias []);
+  [%expect {| { ast = "alias"; decoded = Ok Alias [] } |}];
+  test (Alias [ module_name "A" ]);
+  [%expect
+    {|
+    { ast = "(alias (A))"
+    ; decoded =
+        Error
+          "File \"<none>\", line 1, characters 0-0:\n\
+           Error: Atom or quoted string expected\n\
+           "
+    } |}];
+  test (Alias [ module_name "A"; module_name "B" ]);
+  [%expect
+    {|
+    { ast = "(alias (A B))"
+    ; decoded =
+        Error
+          "File \"<none>\", line 1, characters 0-0:\n\
+           Error: Atom or quoted string expected\n\
+           "
+    } |}]
+;;