showcase error with one field record

Changes.md

@@ -30,6 +30,9 @@ Unreleased
     - `Dom.*`: we now ship a `melange.dom` library that includes the modules
       containing Node.js bindings. This library is included by default so the
       `Dom` module will always be available in Melange projects.
+- Disable warning 61 (`unboxable-type-in-prim-decl`) for externals generated by
+  `[@@deriving abstract]`
+  ([#641](https://github.com/melange-re/melange/pull/641),
 
 1.0.0 2023-05-31
 ---------------

ppx/ast_attributes.ml

@@ -394,3 +394,21 @@ let is_inline : attr -> bool =
  fun { attr_name = { txt; _ }; _ } -> txt = "bs.inline" || txt = "inline"
 
 let has_inline_payload (attrs : t) = Ext_list.find_first attrs is_inline
+
+(* We disable warning 61 in Melange externals since they're substantially
+   different from OCaml externals. This warning doesn't make sense for a JS
+   runtime *)
+let unboxable_type_in_prim_decl : Parsetree.attribute =
+  let open Ast_helper in
+  {
+    attr_name = { txt = "ocaml.warning"; loc = Location.none };
+    attr_payload =
+      PStr
+        [
+          Str.eval
+            (Exp.constant
+               (Pconst_string
+                  ("-unboxable-type-in-prim-decl", Location.none, None)));
+        ];
+    attr_loc = Location.none;
+  }

ppx/ast_attributes.mli

@@ -60,3 +60,4 @@ val rs_externals : t -> string list -> bool
 type as_const_payload = Int of int | Str of string | Js_literal_str of string
 
 val iter_process_bs_string_or_int_as : t -> as_const_payload option
+val unboxable_type_in_prim_decl : attr

ppx/ast_derive/ast_derive_abstract.ml

@@ -35,8 +35,8 @@ open Ast_helper
 let get_optional_attrs =
   [ Ast_attributes.bs_get; Ast_attributes.bs_return_undefined ]
 
-let get_attrs = [ Ast_attributes.bs_get_arity ]
-let set_attrs = [ Ast_attributes.bs_set ]
+let get_attrs = Ast_attributes.[ bs_get_arity; unboxable_type_in_prim_decl ]
+let set_attrs = Ast_attributes.[ bs_set; unboxable_type_in_prim_decl ]
 
 let get_pld_type pld_type ~attrs =
   let is_optional = Ast_attributes.has_bs_optional attrs in
@@ -142,7 +142,9 @@ let handleTdcl light (tdcl : Parsetree.type_declaration) :
             Ast_external_mk.pval_prim_of_option_labels labels has_optional_field
           in
           let myMaker =
-            Val.mk ~loc { loc; txt = type_name } ~prim:myPrims makeType
+            Val.mk ~loc { loc; txt = type_name }
+              ~attrs:[ Ast_attributes.unboxable_type_in_prim_decl ]
+              ~prim:myPrims makeType
           in
           myMaker :: setter_accessor )
   | Ptype_abstract | Ptype_variant _ | Ptype_open ->

ppx/ast_external.ml

@@ -24,24 +24,6 @@
 
 open Ppxlib
 
-(* We disable warning 61 in Melange externals since they're substantially
-   different from OCaml externals. This warning doesn't make sense for a JS
-   runtime *)
-let unboxable_type_in_prim_decl : Parsetree.attribute =
-  let open Ast_helper in
-  {
-    attr_name = { txt = "ocaml.warning"; loc = Location.none };
-    attr_payload =
-      PStr
-        [
-          Str.eval
-            (Exp.constant
-               (Pconst_string
-                  ("-unboxable-type-in-prim-decl", Location.none, None)));
-        ];
-    attr_loc = Location.none;
-  }
-
 let handleExternalInSig (self : Ast_traverse.map)
     (prim : Parsetree.value_description) (sigi : Parsetree.signature_item) :
     Parsetree.signature_item =
@@ -79,7 +61,8 @@ let handleExternalInSig (self : Ast_traverse.map)
               prim with
               pval_type;
               pval_prim = (if no_inline_cross_module then [] else pval_prim);
-              pval_attributes = unboxable_type_in_prim_decl :: pval_attributes;
+              pval_attributes =
+                Ast_attributes.unboxable_type_in_prim_decl :: pval_attributes;
             };
       }
 
@@ -120,7 +103,8 @@ let handleExternalInStru (self : Ast_traverse.map)
                 prim with
                 pval_type;
                 pval_prim;
-                pval_attributes = unboxable_type_in_prim_decl :: pval_attributes;
+                pval_attributes =
+                  Ast_attributes.unboxable_type_in_prim_decl :: pval_attributes;
               };
         }
       in

test/blackbox-tests/deriving-abstract-one-field.t

@@ -0,0 +1,34 @@
+Showcase an error with deriving abstract when the record has one field
+
+  $ . ./setup.sh
+
+  $ cat > dune-project <<EOF
+  > (lang dune 3.8)
+  > (using melange 0.1)
+  > EOF
+
+  $ cat > dune <<EOF
+  > (library
+  >  (modes melange)
+  >  (name x)
+  >  (preprocess
+  >   (pps melange.ppx)))
+  > EOF
+
+Record with two fields works fine
+
+  $ cat > x.ml <<EOF
+  > type chartDataItemType = { height: int; foo: string } [@@deriving abstract]
+  > EOF
+
+  $ dune build ./.x.objs/melange/x.cmj
+
+Record with one field crashes
+
+  $ dune clean
+
+  $ cat > x.ml <<EOF
+  > type chartDataItemType = { height: int; } [@@deriving abstract]
+  > EOF
+
+  $ dune build ./.x.objs/melange/x.cmj