Support @new @variadic (#5364)

* Support @new @variadic

Signed-off-by: Yuta Sato <[email protected]>

* [variadic-new] stage everything

Signed-off-by: Yuta Sato <[email protected]>

Co-authored-by: Yuta Sato <[email protected]>

Author: cannorin

Changes.md

@@ -4,6 +4,8 @@
 
 **Compiler**
 
+- #5364 support `@new @variadic`
+
 **Syntax**
 
 **Playground**

jscomp/core/lam_compile_external_call.ml

@@ -26,11 +26,15 @@
 
 module E = Js_exp_make
 
-let splice_fn_apply fn args =
+let splice_apply fn args =
   E.runtime_call Js_runtime_modules.caml_splice_call "spliceApply"
     [ fn; E.array Immutable args ]
 
-let splice_obj_fn_apply obj name args =
+let splice_new_apply fn args =
+  E.runtime_call Js_runtime_modules.caml_splice_call "spliceNewApply"
+    [ fn; E.array Immutable args ]
+
+let splice_obj_apply obj name args =
   E.runtime_call Js_runtime_modules.caml_splice_call "spliceObjApply"
     [ obj; E.str name; E.array Immutable args ]
 
@@ -253,7 +257,7 @@ let translate_ffi (cxt : Lam_compile_context.t) arg_types
       if splice then
         let args, eff, dynamic = assemble_args_has_splice arg_types args in
         add_eff eff
-          (if dynamic then splice_fn_apply fn args
+          (if dynamic then splice_apply fn args
           else E.call ~info:{ arity = Full; call_info = Call_na } fn args)
       else
         let args, eff = assemble_args_no_splice arg_types args in
@@ -265,13 +269,13 @@ let translate_ffi (cxt : Lam_compile_context.t) arg_types
         let args, eff, dynamic = assemble_args_has_splice arg_types args in
         (* TODO: fix in rest calling convention *)
         add_eff eff
-          (if dynamic then splice_fn_apply fn args
+          (if dynamic then splice_apply fn args
           else E.call ~info:{ arity = Full; call_info = Call_na } fn args)
       else
         let args, eff = assemble_args_no_splice arg_types args in
         (* TODO: fix in rest calling convention *)
         add_eff eff (E.call ~info:{ arity = Full; call_info = Call_na } fn args)
-  | Js_new { external_module_name = module_name; name = fn; scopes } ->
+  | Js_new { external_module_name = module_name; name = fn; splice; scopes } ->
       (* handle [@@new]*)
       (* This has some side effect, it will
          mark its identifier (If it has) as an object,
@@ -281,15 +285,25 @@ let translate_ffi (cxt : Lam_compile_context.t) arg_types
          TODO: we should propagate this property
          as much as we can(in alias table)
       *)
-      let args, eff = assemble_args_no_splice arg_types args in
-      let fn = translate_scoped_module_val module_name fn scopes in
-      add_eff eff
-        ((match cxt.continuation with
+      let mark () =
+        match cxt.continuation with
          | Declare (_, id) | Assign id ->
              (* Format.fprintf Format.err_formatter "%a@."Ident.print  id; *)
              Ext_ident.make_js_object id
-         | EffectCall _ | NeedValue _ -> ());
-         E.new_ fn args)
+        | EffectCall _ | NeedValue _ -> ()
+      in
+      if splice then
+        let args, eff, dynamic = assemble_args_has_splice arg_types args in
+        let fn = translate_scoped_module_val module_name fn scopes in
+        add_eff eff
+          (mark ();
+          if dynamic then splice_new_apply fn args
+          else E.new_ fn args)
+      else
+        let args, eff = assemble_args_no_splice arg_types args in
+        let fn = translate_scoped_module_val module_name fn scopes in
+        add_eff eff
+          (mark (); E.new_ fn args)
   | Js_send { splice; name; js_send_scopes } -> (
       match args with
       | self :: args ->
@@ -300,7 +314,7 @@ let translate_ffi (cxt : Lam_compile_context.t) arg_types
             let args, eff, dynamic = assemble_args_has_splice arg_types args in
             add_eff eff
               (let self = translate_scoped_access js_send_scopes self in
-               if dynamic then splice_obj_fn_apply self name args
+               if dynamic then splice_obj_apply self name args
                else
                  E.call
                    ~info:{ arity = Full; call_info = Call_na }

jscomp/frontend/ast_external_process.ml

@@ -800,12 +800,12 @@ let external_desc_of_non_obj (loc : Location.t) (st : external_desc)
    val_send = None;
    set_name = None;
    get_name = None;
-   splice = false;
+   splice;
    scopes;
    mk_obj = _;
    return_wrapper = _;
   } ->
-      Js_new { name; external_module_name; scopes }
+      Js_new { name; external_module_name; splice; scopes }
   | { new_name = Some _; _ } ->
       Bs_syntaxerr.err loc
         (Conflict_ffi_attribute "Attribute found that conflicts with %@new")

jscomp/frontend/external_ffi_types.ml

@@ -72,6 +72,7 @@ type external_spec =
   | Js_new of {
       name : string ;
       external_module_name : external_module_name option;
+      splice : bool ;
       scopes : string list;
     }
   | Js_set of { 
@@ -224,7 +225,7 @@ let check_ffi ?loc ffi : bool =
       -> 
       upgrade (is_package_relative_path external_module_name.bundle);
       check_external_module_name external_module_name
-    | Js_new {external_module_name ;  name; scopes = _}
+    | Js_new {external_module_name ;  name; splice = _; scopes = _}
     | Js_call {external_module_name ;  name ; splice = _; scopes = _ }
       ->
       Ext_option.iter external_module_name (fun external_module_name ->
@@ -266,10 +267,10 @@ let is_bs_primitive s =
 
 let () = Oprint.map_primitive_name := 
 
-# 272 "frontend/external_ffi_types.pp.ml"
+# 273 "frontend/external_ffi_types.pp.ml"
       String.escaped
 
-# 275 "frontend/external_ffi_types.pp.ml"
+# 276 "frontend/external_ffi_types.pp.ml"
 (* TODO:  better error message when version mismatch *)
 let from_string s : t =
   if is_bs_primitive s  then   

jscomp/frontend/external_ffi_types.mli

@@ -58,6 +58,7 @@ type external_spec =
   | Js_new of {
       name : string;
       external_module_name : external_module_name option;
+      splice : bool;
       scopes : string list;
     }
   | Js_set of { js_set_name : string; js_set_scopes : string list }

jscomp/frontend/external_ffi_types.pp.ml

@@ -71,6 +71,7 @@ type external_spec =
   | Js_new of {
       name : string ;
       external_module_name : external_module_name option;
+      splice : bool ;
       scopes : string list;
     }
   | Js_set of { 
@@ -223,7 +224,7 @@ let check_ffi ?loc ffi : bool =
       -> 
       upgrade (is_package_relative_path external_module_name.bundle);
       check_external_module_name external_module_name
-    | Js_new {external_module_name ;  name; scopes = _}
+    | Js_new {external_module_name ;  name; splice = _; scopes = _}
     | Js_call {external_module_name ;  name ; splice = _; scopes = _ }
       ->
       Ext_option.iter external_module_name (fun external_module_name ->

jscomp/main/builtin_cmi_datasets.ml

@@ -1,4 +1,4 @@
-(* f9d475089045bd1c017bc432cb172197 *) 
+(* 6315eecf577934fb71f2fee59c91a9c2 *) 
 let module_names : string array = Obj.magic (
 "Js" (* 23 *),
 "Arg" (* 217 *),
@@ -25,7 +25,7 @@ let module_names : string array = Obj.magic (
 "Buffer" (* 531 *),
 "Digest" (* 153 *),
 "Genlex" (* 44 *),
-"Js_exn" (* 950 *),
+"Js_exn" (* 957 *),
 "Js_int" (* 116 *),
 "Js_obj" (* 23 *),
 "Lexing" (* 807 *),
@@ -151,7 +151,7 @@ let module_data : string array = Obj.magic (
 (* Buffer *)"\132\149\166\190\000\000\001\255\000\000\000\140\000\000\001\216\000\000\001\188\160\b\000\000P\000\176#nth\144\160\160B@@@\176#sub\144\160\160C@@@\176$blit\144\160\160E@@@\176%clear\144\160\160A@@\144\148\192A\160\176\001\004\007!b@@\151\176\162A\144(position\160\144\004\t\160\146\160\025_i\000\000\000\000\000@@\176\1924stdlib-406/buffer.mlv\001\007\212\001\007\226\192\004\002v\001\007\212\001\007\241@\192B@@A\176%reset\144\160\160A@@@\176&create\144\160\160A@@@\176&length\144\160\160A@@\144\148\192A\160\176\001\004\005!b@@\151\176\161A\160\004%A\160\144\004\b@\176\192\004 t\001\007\185\001\007\200\192\004!t\001\007\185\001\007\210@\192B@@@\176(add_char\144\160\160B@@@\176(contents\144\160\160A@@@\176(to_bytes\144\160\160A@@@\176(truncate\144\160\160B@@@\176)add_bytes\144\160\160B@@@\176*add_buffer\144\160\160B@@@\176*add_string\144\160\160B@@@\176,add_subbytes\144\160\160D@@@\176-add_substring\144\160\160D@@@\176.add_substitute\144\160\160C@@@\176/add_utf_8_uchar\144\160\160B@@@\1762add_utf_16be_uchar\144\160\160B@@@\1762add_utf_16le_uchar\144\160\160B@@@A",
 (* Digest *)"\132\149\166\190\000\000\000\133\000\000\000*\000\000\000\135\000\000\000\127\160\b\000\000 \000\176%bytes\144\160\160A@@@\176%equal\144\160\160B@@@\176&string\144\160\160A@@@\176&to_hex\144\160\160A@@@\176'compare\144\160\160B@@@\176(from_hex\144\160\160A@@@\176(subbytes\144\160\160C@@@\176)substring\144\160\160C@@@A",
 (* Genlex *)"\132\149\166\190\000\000\000\024\000\000\000\b\000\000\000\024\000\000\000\023\160\144\176*make_lexer\144\160\160A\160A@@@A",
-(* Js_exn *)"\132\149\166\190\000\000\003\162\000\000\000\214\000\000\003\002\000\000\002\227\160\240\176*raiseError\144\160\160A@A\144\148\192A\160\176\001\003\246#str@@\151\176D\160\151\176\180%Error\160\160AA@\182%Error@@\160\144\004\015@\176\1920others/js_exn.mlt\001\007\140\001\007\160\192\004\002t\001\007\140\001\007\173@@\176\192\004\004t\001\007\140\001\007\142\192\004\005t\001\007\140\001\007\189@\192B@@@\176-raiseUriError\144\160\160A@A\144\148\192A\160\176\001\004\014#str@@\151\176D\160\151\176\180(URIError\160\004 @\182(URIError@@\160\144\004\014@\176\192\004\031\000Y\001\011\143\001\011\162\192\004 \000Y\001\011\143\001\011\180@@\176\192\004\"\000Y\001\011\143\001\011\145\192\004#\000Y\001\011\143\001\011\181@\192B@@@\176.raiseEvalError\144\160\160A@A\144\148\192A\160\176\001\003\250#str@@\151\176D\160\151\176\180)EvalError\160\004>@\182)EvalError@@\160\144\004\014@\176\192\004=z\001\b1\001\bE\192\004>z\001\b1\001\bV@@\176\192\004@z\001\b1\001\b3\192\004Az\001\b1\001\bk@\192B@@@\176.raiseTypeError\144\160\160A@A\144\148\192A\160\176\001\004\n#str@@\151\176D\160\151\176\180)TypeError\160\004\\@\182)TypeError@@\160\144\004\014@\176\192\004[\000S\001\n\249\001\011\012\192\004\\\000S\001\n\249\001\011\031@@\176\192\004^\000S\001\n\249\001\n\251\192\004_\000S\001\n\249\001\011 @\192B@@@\176/raiseRangeError\144\160\160A@A\144\148\192A\160\176\001\003\254#str@@\151\176D\160\151\176\180*RangeError\160\004z@\182*RangeError@@\160\144\004\014@\176\192\004y\000@\001\b\229\001\b\249\192\004z\000@\001\b\229\001\t\011@@\176\192\004|\000@\001\b\229\001\b\231\192\004}\000@\001\b\229\001\t!@\192B@@@\1760raiseSyntaxError\144\160\160A@A\144\148\192A\160\176\001\004\006#str@@\151\176D\160\151\176\180+SyntaxError\160\004\152@\182+SyntaxError@@\160\144\004\014@\176\192\004\151\000M\001\n\\\001\no\192\004\152\000M\001\n\\\001\n\132@@\176\192\004\154\000M\001\n\\\001\n^\192\004\155\000M\001\n\\\001\n\133@\192B@@@\1763raiseReferenceError\144\160\160A@A\144\148\192A\160\176\001\004\002#str@@\151\176D\160\151\176\180.ReferenceError\160\004\182@\182.ReferenceError@@\160\144\004\014@\176\192\004\181\000G\001\t\177\001\t\196\192\004\182\000G\001\t\177\001\t\220@@\176\192\004\184\000G\001\t\177\001\t\179\192\004\185\000G\001\t\177\001\t\221@\192B@@@A",
+(* Js_exn *)"\132\149\166\190\000\000\003\169\000\000\000\214\000\000\003\t\000\000\002\234\160\240\176*raiseError\144\160\160A@A\144\148\192A\160\176\001\003\246#str@@\151\176D\160\151\176\180%Error\160\160AA@\198%Error@@@\160\144\004\015@\176\1920others/js_exn.mlt\001\007\140\001\007\160\192\004\002t\001\007\140\001\007\173@@\176\192\004\004t\001\007\140\001\007\142\192\004\005t\001\007\140\001\007\189@\192B@@@\176-raiseUriError\144\160\160A@A\144\148\192A\160\176\001\004\014#str@@\151\176D\160\151\176\180(URIError\160\004 @\198(URIError@@@\160\144\004\014@\176\192\004\031\000Y\001\011\143\001\011\162\192\004 \000Y\001\011\143\001\011\180@@\176\192\004\"\000Y\001\011\143\001\011\145\192\004#\000Y\001\011\143\001\011\181@\192B@@@\176.raiseEvalError\144\160\160A@A\144\148\192A\160\176\001\003\250#str@@\151\176D\160\151\176\180)EvalError\160\004>@\198)EvalError@@@\160\144\004\014@\176\192\004=z\001\b1\001\bE\192\004>z\001\b1\001\bV@@\176\192\004@z\001\b1\001\b3\192\004Az\001\b1\001\bk@\192B@@@\176.raiseTypeError\144\160\160A@A\144\148\192A\160\176\001\004\n#str@@\151\176D\160\151\176\180)TypeError\160\004\\@\198)TypeError@@@\160\144\004\014@\176\192\004[\000S\001\n\249\001\011\012\192\004\\\000S\001\n\249\001\011\031@@\176\192\004^\000S\001\n\249\001\n\251\192\004_\000S\001\n\249\001\011 @\192B@@@\176/raiseRangeError\144\160\160A@A\144\148\192A\160\176\001\003\254#str@@\151\176D\160\151\176\180*RangeError\160\004z@\198*RangeError@@@\160\144\004\014@\176\192\004y\000@\001\b\229\001\b\249\192\004z\000@\001\b\229\001\t\011@@\176\192\004|\000@\001\b\229\001\b\231\192\004}\000@\001\b\229\001\t!@\192B@@@\1760raiseSyntaxError\144\160\160A@A\144\148\192A\160\176\001\004\006#str@@\151\176D\160\151\176\180+SyntaxError\160\004\152@\198+SyntaxError@@@\160\144\004\014@\176\192\004\151\000M\001\n\\\001\no\192\004\152\000M\001\n\\\001\n\132@@\176\192\004\154\000M\001\n\\\001\n^\192\004\155\000M\001\n\\\001\n\133@\192B@@@\1763raiseReferenceError\144\160\160A@A\144\148\192A\160\176\001\004\002#str@@\151\176D\160\151\176\180.ReferenceError\160\004\182@\198.ReferenceError@@@\160\144\004\014@\176\192\004\181\000G\001\t\177\001\t\196\192\004\182\000G\001\t\177\001\t\220@@\176\192\004\184\000G\001\t\177\001\t\179\192\004\185\000G\001\t\177\001\t\221@\192B@@@A",
 (* Js_int *)"\132\149\166\190\000\000\000`\000\000\000\028\000\000\000Z\000\000\000W\160\144\176%equal\144\160\160B@@\144\148\192B\160\176\001\003\242!x@\160\176\001\003\243!y@@\151\176\152@\160\144\004\n\160\144\004\t@\176\1920others/js_int.ml\001\000\168\001\023\219\001\023\242\192\004\002\001\000\168\001\023\219\001\023\247@\192B@@@A",
 (* Js_obj *)"\132\149\166\190\000\000\000\003\000\000\000\001\000\000\000\003\000\000\000\003\160\128A",
 (* Lexing *)"\132\149\166\190\000\000\003\019\000\000\000\192\000\000\002\153\000\000\002v\160\b\000\000@\000\176&engine\144\160\160C@@@\176&lexeme\144\160\160A@@@\176(new_line\144\160\160A@@@\176*lexeme_end\144\160\160A@@\144\148\192A\160\176\001\004@&lexbuf@@\151\176\161C\160(pos_cnum@\160\151\176\161K\160*lex_curr_pA\160\144\004\015@\176\1924stdlib-406/lexing.ml\001\000\210\001\026\178\001\026\202\192\004\002\001\000\210\001\026\178\001\026\219@@\176\004\004\192\004\004\001\000\210\001\026\178\001\026\228@\192B@@@\176*new_engine\144\160\160C@@@\176*sub_lexeme\144\160\160C@@@\176+flush_input\144\160\160A@@@\176+from_string\144\160\160A@@@\176+lexeme_char\144\160\160B@@@\176,lexeme_end_p\144\160\160A@@\144\148\192A\160\176\001\004D&lexbuf@@\151\176\161K\160\0042A\160\144\004\b@\176\192\0041\001\000\213\001\027\021\001\027/\192\0042\001\000\213\001\027\021\001\027@@\192B@@@\176,lexeme_start\144\160\160A@@\144\148\192A\160\176\001\004>&lexbuf@@\151\176\161C\160\004M@\160\151\176\161J\160+lex_start_pA\160\144\004\014@\176\192\004L\001\000\209\001\026|\001\026\150\192\004M\001\000\209\001\026|\001\026\168@@\176\004\003\192\004O\001\000\209\001\026|\001\026\177@\192B@@@\176-from_function\144\160\160A@@@\176.lexeme_start_p\144\160\160A@@\144\148\192A\160\176\001\004B&lexbuf@@\151\176\161J\160\004\029A\160\144\004\b@\176\192\004h\001\000\212\001\026\230\001\027\002\192\004i\001\000\212\001\026\230\001\027\020@\192B@@@\176.sub_lexeme_opt\144\160\160C@@@\176/sub_lexeme_char\144\160\160B@@\144\148\192B\160\176\001\0045&lexbuf@\160\176\001\0046!i@@\151\176d\160\151\176\161A\160*lex_bufferA\160\144\004\015@\176\192\004\137\001\000\197\001\025z\001\025\163\192\004\138\001\000\197\001\025z\001\025\180@\160\144\004\017@\176\192\004\142\001\000\197\001\025z\001\025\153\192\004\143\001\000\197\001\025z\001\025\182@\192B@@@\1763sub_lexeme_char_opt\144\160\160B@@@A",

jscomp/main/builtin_cmj_datasets.ml

@@ -38,6 +38,21 @@ let spliceApply : obj -> obj -> obj = [%raw{|function(fn,args){
   return fn.apply(null,applied)
 }|}] 
 
+let spliceNewApply : obj -> obj -> obj = [%raw{|function (ctor,args){
+  var i, argLen;
+  argLen = args.length
+  var applied = [null] // Function.prototype.bind.apply(fn, args) requires the first element in `args` to be `null`
+  for(i = 0; i < argLen - 1; ++i){
+    applied.push(args[i])
+  }
+  var lastOne = args[argLen - 1]
+  for(i = 0; i < lastOne.length; ++i ){
+    applied.push(lastOne[i])
+  }
+  var C = Function.prototype.bind.apply(ctor, applied)
+  return new C()
+}|}]
+
 let spliceObjApply : obj -> obj -> obj -> obj = [%raw{|function(obj,name,args){
   var i, argLen; 
   argLen = args.length

jscomp/runtime/caml_splice_call.ml

@@ -27,4 +27,6 @@ type obj = Obj.t
 
 val spliceApply : obj -> obj -> obj
 
+val spliceNewApply : obj -> obj -> obj
+
 val spliceObjApply : obj -> obj -> obj -> obj

jscomp/runtime/caml_splice_call.mli

@@ -64,11 +64,80 @@ dynamic([
       3
     ]);
 
-var a$1 = [];
+var a$1 = new Array(1, 2, 3, 4);
 
-a$1.push(1, 2, 3, 4);
+eq("File \"splice_test.ml\", line 49, characters 5-12", a$1, [
+      1,
+      2,
+      3,
+      4
+    ]);
+
+function dynamicNew(arr) {
+  var a = Caml_splice_call.spliceNewApply(Array, [
+        1,
+        2,
+        arr
+      ]);
+  eq("File \"splice_test.ml\", line 53, characters 5-12", a, Caml_array.concat({
+            hd: [
+              1,
+              2
+            ],
+            tl: {
+              hd: arr,
+              tl: /* [] */0
+            }
+          }));
+}
+
+dynamicNew([
+      3,
+      4
+    ]);
+
+dynamicNew([]);
+
+dynamicNew([
+      1,
+      3
+    ]);
+
+class Foo {
+  constructor(...names) {
+    this.names = names;
+  }
+}
+;
+
+var f = new Foo("a", "b", "c");
+
+eq("File \"splice_test.ml\", line 74, characters 5-12", f.names, [
+      "a",
+      "b",
+      "c"
+    ]);
+
+function dynamicFoo(arr) {
+  var f = Caml_splice_call.spliceNewApply(Foo, [arr]);
+  eq("File \"splice_test.ml\", line 78, characters 5-12", f.names, arr);
+}
+
+dynamicFoo([]);
+
+dynamicFoo(["a"]);
+
+dynamicFoo([
+      "a",
+      "b",
+      "c"
+    ]);
+
+var a$2 = [];
+
+a$2.push(1, 2, 3, 4);
 
-eq("File \"splice_test.ml\", line 51, characters 7-14", a$1, [
+eq("File \"splice_test.ml\", line 95, characters 7-14", a$2, [
       1,
       2,
       3,
@@ -81,7 +150,7 @@ function dynamic$1(arr) {
         1,
         arr
       ]);
-  eq("File \"splice_test.ml\", line 56, characters 7-14", a, Caml_array.concat({
+  eq("File \"splice_test.ml\", line 100, characters 7-14", a, Caml_array.concat({
             hd: [1],
             tl: {
               hd: arr,
@@ -115,11 +184,11 @@ function f1(c) {
             ]);
 }
 
-eq("File \"splice_test.ml\", line 67, characters 6-13", Math.max(1, 2, 3), 3);
+eq("File \"splice_test.ml\", line 111, characters 6-13", Math.max(1, 2, 3), 3);
 
-eq("File \"splice_test.ml\", line 68, characters 6-13", Math.max(1), 1);
+eq("File \"splice_test.ml\", line 112, characters 6-13", Math.max(1), 1);
 
-eq("File \"splice_test.ml\", line 69, characters 6-13", Math.max(1, 1, 2, 3, 4, 5, 2, 3), 5);
+eq("File \"splice_test.ml\", line 113, characters 6-13", Math.max(1, 1, 2, 3, 4, 5, 2, 3), 5);
 
 Mt.from_pair_suites("splice_test.ml", suites.contents);
 
@@ -129,6 +198,8 @@ exports.eq = eq;
 exports.Caml_splice_call = Caml_splice_call$1;
 exports.f00 = f00;
 exports.dynamic = dynamic;
+exports.dynamicNew = dynamicNew;
+exports.dynamicFoo = dynamicFoo;
 exports.Pipe = Pipe;
 exports.f1 = f1;
 /*  Not a pure module */

jscomp/test/splice_test.js

@@ -37,6 +37,50 @@ let dynamic arr =
 ;; dynamic [||]
 ;; dynamic [|1;1;3|]
 
+(* Array constructor with a single parameter `x`
+   just makes an array with its length set to `x`,
+   so at least two parameters are needed
+*)
+external newArr : int -> int -> int array -> int array = "Array"
+  [@@bs.splice] [@@bs.new]
+
+let () =
+  let a = newArr 1 2 [|3;4|] in
+  eq __LOC__ a [|1;2;3;4|]
+
+let dynamicNew arr =
+  let a = newArr 1 2 arr in
+  eq __LOC__ a (Array.concat [[|1; 2|]; arr])
+
+;; dynamicNew [|3;4|]
+;; dynamicNew [||]
+;; dynamicNew [|1;3|]
+
+[%%raw{|
+class Foo {
+  constructor(...names) {
+    this.names = names;
+  }
+}
+|}]
+
+type foo
+
+external newFoo : string array -> foo = "Foo" [@@bs.splice] [@@bs.new]
+external fooNames : foo -> string array = "names" [@@get]
+
+let () =
+  let f = newFoo [|"a";"b";"c"|] in
+  eq __LOC__ (fooNames f) [|"a";"b";"c"|]
+
+let dynamicFoo arr =
+  let f = newFoo arr in
+  eq __LOC__ (fooNames f) arr
+
+;; dynamicFoo [||]
+;; dynamicFoo [|"a"|]
+;; dynamicFoo [|"a";"b";"c"|]
+
 module Pipe = struct
   external push :  int array -> int -> int array -> unit = 
     "push" [@@send] [@@bs.splice]