Don't emit f(undefined) when passing unit (). (#6459)

* RFC: don't emit f(undefined)

This changes code generation so it emits `f()` instead of `f(undefined)` when the function takes a single argument and its value is `undefined`.

* Track when undefined is coming from `()`.

* isUnit

* Update CHANGELOG.md

* Update jscomp/core/js_dump.ml

Co-authored-by: Christoph Knittel <ck@cca.io>

---------

Co-authored-by: Christoph Knittel <ck@cca.io>

Author: cristianoc

CHANGELOG.md

@@ -41,6 +41,7 @@
 - Add [`Deno`](https://deno.land/api?s=Deno) to reserved names, so that modules named `Deno` don't clash with the globally exposed `Deno` object. https://github.com/rescript-lang/rescript-compiler/pull/6428
 - Disable ESLint/TSLint on gentype outputs properly. https://github.com/rescript-lang/rescript-compiler/pull/6442
 - Improve `rescript` CLI to use `stdout`/`stderr` appropriately for help command's message. https://github.com/rescript-lang/rescript-compiler/pull/6439
+- Generate `f()` instead of `f(undefined)` for `f()` https://github.com/rescript-lang/rescript-compiler/pull/6459
 
 # 11.0.0-rc.4
 

jscomp/core/j.ml

@@ -159,7 +159,7 @@ and expression_desc =
   *)
   | Number of number
   | Object of property_map
-  | Undefined
+  | Undefined of {isUnit: bool}
   | Null
   | Await of expression
 

jscomp/core/js_analyzer.ml

@@ -82,7 +82,7 @@ let free_variables_of_expression st =
 
 let rec no_side_effect_expression_desc (x : J.expression_desc) =
   match x with
-  | Undefined | Null | Bool _ | Var _ -> true
+  | Undefined _ | Null | Bool _ | Var _ -> true
   | Fun _ -> true
   | Number _ -> true (* Can be refined later *)
   | Static_index (obj, (_name : string), (_pos : int32 option)) ->
@@ -153,7 +153,7 @@ let rec eq_expression ({ expression_desc = x0 } : J.expression)
     ({ expression_desc = y0 } : J.expression) =
   match x0 with
   | Null -> y0 = Null
-  | Undefined -> y0 = Undefined
+  | Undefined x -> y0 = Undefined x
   | Number (Int { i }) -> (
       match y0 with Number (Int { i = j }) -> i = j | _ -> false)
   | Number (Float _) -> false

jscomp/core/js_cmj_format.ml

@@ -113,7 +113,7 @@ let get_result midVal =
   match midVal.persistent_closed_lambda with
   | Some
       (Lconst
-        (Const_js_null | Const_js_undefined | Const_js_true | Const_js_false))
+        (Const_js_null | Const_js_undefined _ | Const_js_true | Const_js_false))
   | None ->
       midVal
   | Some _ ->

jscomp/core/js_dump.ml

@@ -160,7 +160,7 @@ let exp_need_paren (e : J.expression) =
   | Raw_js_code { code_info = Stmt _ }
   | Length _ | Call _ | Caml_block_tag _ | Seq _ | Static_index _ | Cond _
   | Bin _ | Is_null_or_undefined _ | String_index _ | Array_index _
-  | String_append _ | Var _ | Undefined | Null | Str _ | Array _
+  | String_append _ | Var _ | Undefined _ | Null | Str _ | Array _
   | Optional_block _ | Caml_block _ | FlatCall _ | Typeof _ | Number _
   | Js_not _ | Bool _ | New _ ->
       false
@@ -519,7 +519,7 @@ and expression_desc cxt ~(level : int) f x : cxt =
   | Null ->
       P.string f L.null;
       cxt
-  | Undefined ->
+  | Undefined _ ->
       P.string f L.undefined;
       cxt
   | Var v -> vident cxt f v
@@ -569,7 +569,14 @@ and expression_desc cxt ~(level : int) f x : cxt =
                           pp_function ~is_method ~return_unit ~async cxt f
                             ~fn_state:(No_name { single_arg = true })
                             params body env
-                      | _ -> arguments cxt f el)
+                      | _ ->
+                        let el = match el with
+                        | [e] when e.expression_desc = Undefined {isUnit = true} ->
+                          (* omit passing undefined when the call is f() *)
+                          []
+                        | _ ->
+                          el in
+                         arguments cxt f el)
               | _, _ ->
                   let len = List.length el in
                   if 1 <= len && len <= 8 then (
@@ -736,7 +743,7 @@ and expression_desc cxt ~(level : int) f x : cxt =
             let fields =
               Ext_list.array_list_filter_map fields el (fun f x ->
                   match x.expression_desc with
-                  | Undefined -> None
+                  | Undefined _ -> None
                   | _ -> Some (Js_op.Lit f, x))
             in
             expression_desc cxt ~level f (Object fields))
@@ -774,7 +781,7 @@ and expression_desc cxt ~(level : int) f x : cxt =
           | _ ->
             Ext_list.filter_map tails (fun (f, x) ->
               match x.expression_desc with
-              | Undefined when is_optional f -> None
+              | Undefined _ when is_optional f -> None
               | _ -> Some (f, x))
           in
         if untagged then
@@ -1176,7 +1183,7 @@ and statement_desc top cxt f (s : J.statement_desc) : cxt =
           in
           semi f;
           cxt
-      | Undefined ->
+      | Undefined _ ->
           return_sp f;
           semi f;
           cxt
@@ -1270,16 +1277,16 @@ and function_body (cxt : cxt) f ~return_unit (b : J.block) : unit =
       | If
           ( bool,
             then_,
-            [ { statement_desc = Return { expression_desc = Undefined } } ] ) ->
+            [ { statement_desc = Return { expression_desc = Undefined _ } } ] ) ->
           ignore
             (statement false cxt f
                { s with statement_desc = If (bool, then_, []) }
               : cxt)
-      | Return { expression_desc = Undefined } -> ()
+      | Return { expression_desc = Undefined _ } -> ()
       | Return exp when return_unit ->
           ignore (statement false cxt f (S.exp exp) : cxt)
       | _ -> ignore (statement false cxt f s : cxt))
-  | [ s; { statement_desc = Return { expression_desc = Undefined } } ] ->
+  | [ s; { statement_desc = Return { expression_desc = Undefined _ } } ] ->
       ignore (statement false cxt f s : cxt)
   | s :: r ->
       let cxt = statement false cxt f s in

jscomp/core/js_exp_make.ml

@@ -60,7 +60,7 @@ let var ?comment id : t = { expression_desc = Var (Id id); comment }
     Invariant: it should not call an external module .. *)
 
 let js_global ?comment (v : string) = var ?comment (Ext_ident.create_js v)
-let undefined : t = { expression_desc = Undefined; comment = None }
+let undefined : t = { expression_desc = Undefined {isUnit = false}; comment = None }
 let nil : t = { expression_desc = Null; comment = None }
 
 let call ?comment ~info e0 args : t =
@@ -183,7 +183,7 @@ let is_array  (e0 : t) : t =
 let new_ ?comment e0 args : t =
   { expression_desc = New (e0, Some args); comment }
 
-let unit : t = { expression_desc = Undefined; comment = None }
+let unit : t = { expression_desc = Undefined {isUnit = true}; comment = None }
 
 (* let math ?comment v args  : t =
    {comment ; expression_desc = Math(v,args)} *)
@@ -256,17 +256,17 @@ let dummy_obj ?comment (info : Lam_tag_info.t) : t =
 *)
 let rec seq ?comment (e0 : t) (e1 : t) : t =
   match (e0.expression_desc, e1.expression_desc) with
-  | ( ( Seq (a, { expression_desc = Number _ | Undefined })
-      | Seq ({ expression_desc = Number _ | Undefined }, a) ),
+  | ( ( Seq (a, { expression_desc = Number _ | Undefined _ })
+      | Seq ({ expression_desc = Number _ | Undefined _ }, a) ),
       _ ) ->
       seq ?comment a e1
-  | _, Seq ({ expression_desc = Number _ | Undefined }, a) ->
+  | _, Seq ({ expression_desc = Number _ | Undefined _ }, a) ->
       (* Return value could not be changed*)
       seq ?comment e0 a
-  | _, Seq (a, ({ expression_desc = Number _ | Undefined } as v)) ->
+  | _, Seq (a, ({ expression_desc = Number _ | Undefined _ } as v)) ->
       (* Return value could not be changed*)
       seq ?comment (seq e0 a) v
-  | (Number _ | Var _ | Undefined), _ -> e1
+  | (Number _ | Var _ | Undefined _), _ -> e1
   | _ -> { expression_desc = Seq (e0, e1); comment }
 
 let fuse_to_seq x xs = if xs = [] then x else Ext_list.fold_left xs x seq
@@ -567,22 +567,22 @@ let str_equal (txt0:string) (delim0:External_arg_spec.delim) txt1 delim1 =
 
 let rec triple_equal ?comment (e0 : t) (e1 : t) : t =
   match (e0.expression_desc, e1.expression_desc) with
-  | ( (Null | Undefined),
+  | ( (Null | Undefined _),
       (Bool _ | Number _ | Typeof _ | Fun _ | Array _ | Caml_block _) )
     when no_side_effect e1 ->
       false_
   | ( (Bool _ | Number _ | Typeof _ | Fun _ | Array _ | Caml_block _),
-      (Null | Undefined) )
+      (Null | Undefined _) )
     when no_side_effect e0 ->
       false_
   | Number (Int { i = i0; _ }), Number (Int { i = i1; _ }) -> bool (i0 = i1)
   | Optional_block (a, _), Optional_block (b, _) -> triple_equal ?comment a b
-  | Undefined, Optional_block _
-  | Optional_block _, Undefined
-  | Null, Undefined
-  | Undefined, Null ->
+  | Undefined _, Optional_block _
+  | Optional_block _, Undefined _
+  | Null, Undefined _
+  | Undefined _, Null ->
       false_
-  | Null, Null | Undefined, Undefined -> true_
+  | Null, Null | Undefined _, Undefined _ -> true_
   | _ -> { expression_desc = Bin (EqEqEq, e0, e1); comment }
 
 let bin ?comment (op : J.binop) (e0 : t) (e1 : t) : t =
@@ -654,7 +654,7 @@ let and_ ?comment (e1 : t) (e2 : t) : t =
   | Var i, Bin (And, l, ({ expression_desc = Var j; _ } as r))
     when Js_op_util.same_vident i j ->
       { e2 with expression_desc = Bin (And, r, l) }
-  | ( Bin (NotEqEq, { expression_desc = Var i }, { expression_desc = Undefined }),
+  | ( Bin (NotEqEq, { expression_desc = Var i }, { expression_desc = Undefined _ }),
       Bin
         ( EqEqEq,
           { expression_desc = Var j },
@@ -702,7 +702,7 @@ let not (e : t) : t =
 
 let not_empty_branch (x : t) =
   match x.expression_desc with
-  | Number (Int { i = 0l }) | Undefined -> false
+  | Number (Int { i = 0l }) | Undefined _ -> false
   | _ -> true
 
 let rec econd ?comment (pred : t) (ifso : t) (ifnot : t) : t =
@@ -735,8 +735,8 @@ let rec econd ?comment (pred : t) (ifso : t) (ifnot : t) : t =
       econd (or_ pred (not pred1)) ifso ifso1
   | Js_not e, _, _ when not_empty_branch ifnot -> econd ?comment e ifnot ifso
   | ( _,
-      Seq (a, { expression_desc = Undefined }),
-      Seq (b, { expression_desc = Undefined }) ) ->
+      Seq (a, { expression_desc = Undefined _ }),
+      Seq (b, { expression_desc = Undefined _ }) ) ->
       seq (econd ?comment pred a b) undefined
   | _ ->
       if Js_analyzer.eq_expression ifso ifnot then
@@ -746,7 +746,7 @@ let rec econd ?comment (pred : t) (ifso : t) (ifnot : t) : t =
 let rec float_equal ?comment (e0 : t) (e1 : t) : t =
   match (e0.expression_desc, e1.expression_desc) with
   | Number (Int { i = i0; _ }), Number (Int { i = i1 }) -> bool (i0 = i1)
-  | Undefined, Undefined -> true_
+  | Undefined _, Undefined _ -> true_
   (* | (Bin(Bor,
          {expression_desc = Number(Int {i = 0l; _})},
          ({expression_desc = Caml_block_tag _; _} as a ))
@@ -983,11 +983,11 @@ let rec int_comp (cmp : Lam_compat.comparison) ?comment (e0 : t) (e1 : t) =
               args,
               call_info );
       }
-  | Ceq, Optional_block _, Undefined | Ceq, Undefined, Optional_block _ ->
+  | Ceq, Optional_block _, Undefined _ | Ceq, Undefined _, Optional_block _ ->
       false_
   | Ceq, _, _ -> int_equal e0 e1
-  | Cneq, Optional_block _, Undefined
-  | Cneq, Undefined, Optional_block _
+  | Cneq, Optional_block _, Undefined _
+  | Cneq, Undefined _, Optional_block _
   | Cneq, Caml_block _, Number _
   | Cneq, Number _, Caml_block _ ->
       true_
@@ -1281,36 +1281,36 @@ let is_null ?comment (x : t) = triple_equal ?comment x nil
 let is_undef ?comment x = triple_equal ?comment x undefined
 
 let for_sure_js_null_undefined (x : t) =
-  match x.expression_desc with Null | Undefined -> true | _ -> false
+  match x.expression_desc with Null | Undefined _ -> true | _ -> false
 
 let is_null_undefined ?comment (x : t) : t =
   match x.expression_desc with
-  | Null | Undefined -> true_
+  | Null | Undefined _ -> true_
   | Number _ | Array _ | Caml_block _ -> false_
   | _ -> { comment; expression_desc = Is_null_or_undefined x }
 
 let eq_null_undefined_boolean ?comment (a : t) (b : t) =
   match (a.expression_desc, b.expression_desc) with
-  | ( (Null | Undefined),
+  | ( (Null | Undefined _),
       (Bool _ | Number _ | Typeof _ | Fun _ | Array _ | Caml_block _) ) ->
       false_
   | ( (Bool _ | Number _ | Typeof _ | Fun _ | Array _ | Caml_block _),
-      (Null | Undefined) ) ->
+      (Null | Undefined _) ) ->
       false_
-  | Null, Undefined | Undefined, Null -> false_
-  | Null, Null | Undefined, Undefined -> true_
+  | Null, Undefined _ | Undefined _, Null -> false_
+  | Null, Null | Undefined _, Undefined _ -> true_
   | _ -> { expression_desc = Bin (EqEqEq, a, b); comment }
 
 let neq_null_undefined_boolean ?comment (a : t) (b : t) =
   match (a.expression_desc, b.expression_desc) with
-  | ( (Null | Undefined),
+  | ( (Null | Undefined _),
       (Bool _ | Number _ | Typeof _ | Fun _ | Array _ | Caml_block _) ) ->
       true_
   | ( (Bool _ | Number _ | Typeof _ | Fun _ | Array _ | Caml_block _),
-      (Null | Undefined) ) ->
+      (Null | Undefined _) ) ->
       true_
-  | Null, Null | Undefined, Undefined -> false_
-  | Null, Undefined | Undefined, Null -> true_
+  | Null, Null | Undefined _, Undefined _ -> false_
+  | Null, Undefined _ | Undefined _, Null -> true_
   | _ -> { expression_desc = Bin (NotEqEq, a, b); comment }
 
 (** TODO: in the future add a flag

jscomp/core/js_fold.ml

@@ -169,7 +169,7 @@ class fold =
       | Object _x0 ->
           let _self = _self#property_map _x0 in
           _self
-      | Undefined -> _self
+      | Undefined _ -> _self
       | Null -> _self
       | Await _x0 ->
         let _self = _self#expression _x0 in

jscomp/core/js_of_lam_option.ml

@@ -36,7 +36,9 @@ type option_unwrap_time = Static_unwrapped | Runtime_maybe_unwrapped
 *)
 let none : J.expression = E.undefined
 
-let is_none_static (arg : J.expression_desc) = arg = Undefined
+let is_none_static (arg : J.expression_desc) = match arg with
+  | Undefined _ -> true
+  | _ -> false
 
 let is_not_none (e : J.expression) : J.expression =
   let desc = e.expression_desc in

jscomp/core/js_pass_flatten_and_mark_dead.ml

@@ -192,7 +192,7 @@ let subst_map (substitution : J.expression Hash_ident.t) =
             let _, e, bindings =
               Ext_list.fold_left ls (0, [], []) (fun (i, e, acc) x ->
                   match x.expression_desc with
-                  | Var _ | Number _ | Str _ | J.Bool _ | Undefined ->
+                  | Var _ | Number _ | Str _ | J.Bool _ | Undefined _ ->
                       (* TODO: check the optimization *)
                       (i + 1, x :: e, acc)
                   | _ ->
@@ -257,7 +257,7 @@ let subst_map (substitution : J.expression Hash_ident.t) =
                 match Ext_list.nth_opt ls (Int32.to_int i) with
                 | Some
                     ({
-                       expression_desc = J.Var _ | Number _ | Str _ | Undefined;
+                       expression_desc = J.Var _ | Number _ | Str _ | Undefined _;
                      } as x) ->
                     x
                 | None | Some _ -> super.expression self x)

jscomp/core/js_record_fold.ml

@@ -175,7 +175,7 @@ let expression_desc : 'a. ('a, expression_desc) fn =
   | Object _x0 ->
       let st = property_map _self st _x0 in
       st
-  | Undefined -> st
+  | Undefined _ -> st
   | Null -> st
   | Await _x0 ->
     let st = _self.expression _self st _x0 in