Support {} for empty record literals and types.

CHANGELOG.md

@@ -12,6 +12,11 @@
 
 # 10.1.0-alpha.2
 
+#### :rocket: New Feature
+
+- Add support for empty record literal `{}` for records where all fields are optional https://github.com/rescript-lang/rescript-compiler/pull/5658
+- Add support for empty record type (e.g. `type empty = {}`) https://github.com/rescript-lang/rescript-compiler/pull/5658
+
 #### :bug: Bug Fix
 
 - Fix printing of type declarations in error message where they would be considered recursive by default

jscomp/core/js_dump.ml

@@ -718,7 +718,7 @@ and expression_desc cxt ~(level : int) f x : cxt =
                 Js_op.Lit (Ext_ident.convert x))))
   (*name convention of Record is slight different from modules*)
   | Caml_block (el, mutable_flag, _, Blk_record { fields; record_repr }) -> (
-      if Ext_array.for_alli fields (fun i v -> string_of_int i = v) then
+      if Array.length fields <> 0 && Ext_array.for_alli fields (fun i v -> string_of_int i = v) then
         expression_desc cxt ~level f (Array (el, mutable_flag))
       else
         match record_repr with

jscomp/ml/typecore.ml

@@ -72,6 +72,7 @@ type error =
   | Unknown_literal of string * char
   | Illegal_letrec_pat
   | Labels_omitted of string list
+  | Empty_record_literal
 exception Error of Location.t * Env.t * error
 exception Error_forward of Location.error
 
@@ -298,7 +299,7 @@ let extract_option_type env ty =
 
 let extract_concrete_record env ty =
   match extract_concrete_typedecl env ty with
-    (p0, p, {type_kind=Type_record (fields, _)}) -> (p0, p, fields)
+    (p0, p, {type_kind=Type_record (fields, repr)}) -> (p0, p, fields, repr)
   | _ -> raise Not_found
 
 let extract_concrete_variant env ty =
@@ -1145,7 +1146,7 @@ and type_pat_aux ~constrs ~labels ~no_existentials ~mode ~explode ~env
       assert (lid_sp_list <> []);
       let opath, record_ty =
         try
-          let (p0, p,_) = extract_concrete_record !env expected_ty in
+          let (p0, p, _, _) = extract_concrete_record !env expected_ty in
           Some (p0, p), expected_ty
         with Not_found -> None, newvar ()
       in
@@ -2147,14 +2148,13 @@ and type_expect_ ?in_function ?(recarg=Rejected) env sexp ty_expected =
           exp_env = env }
       end
     | Pexp_record(lid_sexp_list, None) ->
-        assert (lid_sexp_list <> []);
-        let ty_record, opath =          
+        let ty_record, opath, fields, repr_opt =          
           match extract_concrete_record env ty_expected with
-          |  (p0, p,_) ->
+          |  (p0, p, fields, repr) ->
               (* XXX level may be wrong *)
-              ty_expected, Some (p0, p) 
+              ty_expected, Some (p0, p), fields, Some repr 
           | exception Not_found -> 
-               newvar (), None
+               newvar (), None, [], None
 
         in
         let lbl_exp_list =
@@ -2166,7 +2166,24 @@ and type_expect_ ?in_function ?(recarg=Rejected) env sexp ty_expected =
         in
         unify_exp_types loc env ty_record (instance env ty_expected);
         check_duplicates loc env lbl_exp_list;
-        let (_, { lbl_all = label_descriptions; lbl_repres = representation}, _) = List.hd lbl_exp_list in
+        let label_descriptions, representation = match lbl_exp_list, repr_opt with
+        | (_, { lbl_all = label_descriptions; lbl_repres = representation}, _) :: _, _ -> label_descriptions, representation
+        | [], Some (Record_optional_labels optional_labels as representation) when lid_sexp_list = [] ->
+            let filter_missing (ld : Types.label_declaration) =
+              let name = Ident.name ld.ld_id in
+              if List.mem name optional_labels then
+                None
+              else
+                Some name in
+            let labels_missing = fields |> List.filter_map filter_missing in
+            if labels_missing <> [] then
+              raise(Error(loc, env, Labels_missing labels_missing));
+            [||], representation
+        | [], _ ->
+          if fields = [] then
+            [||], Record_optional_labels []
+          else
+            raise(Error(loc, env, Empty_record_literal)) in
         let labels_missing = ref [] in
         let label_definitions =
           let matching_label lbl =
@@ -2205,7 +2222,7 @@ and type_expect_ ?in_function ?(recarg=Rejected) env sexp ty_expected =
       let ty_record, opath =
         let get_path ty =
           try
-            let (p0, p,_) = extract_concrete_record env ty in
+            let (p0, p, _, _) = extract_concrete_record env ty in
             (* XXX level may be wrong *)
             Some (p0, p) 
           with Not_found -> None
@@ -2803,7 +2820,7 @@ and type_label_access env srecord lid =
   let ty_exp = record.exp_type in
   let opath =
     try
-      let (p0, p,_) = extract_concrete_record env ty_exp in
+      let (p0, p, _, _) = extract_concrete_record env ty_exp in
       Some(p0, p)
     with Not_found -> None
   in
@@ -3805,9 +3822,11 @@ let report_error env ppf = function
   | Illegal_letrec_pat ->
       fprintf ppf
         "Only variables are allowed as left-hand side of `let rec'"
-  | Labels_omitted labels -> 
+  | Labels_omitted labels ->
       fprintf ppf  "For labeled funciton, labels %s were omitted in the application of this function." 
       (String.concat ", " labels)  
+  | Empty_record_literal ->
+      fprintf ppf  "Empty record literal {} should be type annotated or used in a record context."
 
 let super_report_error_no_wrap_printing_env = report_error
 

jscomp/ml/typecore.mli

@@ -108,6 +108,7 @@ type error =
   | Unknown_literal of string * char
   | Illegal_letrec_pat
   | Labels_omitted of string list
+  | Empty_record_literal
 exception Error of Location.t * Env.t * error
 exception Error_forward of Location.error
 

jscomp/ml/typedecl.ml

@@ -206,7 +206,6 @@ let make_params env params =
     List.map make_param params
 
 let transl_labels env closed lbls =
-  assert (lbls <> []);
   if !Config.bs_only then 
     match !Builtin_attributes.check_duplicated_labels lbls with 
     | None -> ()

jscomp/test/EmptyRecord.js

@@ -0,0 +1,18 @@
+'use strict';
+
+
+function construct(b) {
+  if (b) {
+    return {
+            n: 0
+          };
+  } else {
+    return {};
+  }
+}
+
+var er = {};
+
+exports.construct = construct;
+exports.er = er;
+/* No side effect */

jscomp/test/EmptyRecord.res

@@ -0,0 +1,10 @@
+type allOptRec = {n?: int, s?:string}
+
+let construct = (b) => b ? {n:0} : {}
+
+// let z = {}
+// Error: Empty record literal {} should be type annotated or used in a record context.
+
+type emptyrec = {}
+
+let er : emptyrec = {}

lib/4.06.1/unstable/js_compiler.ml

@@ -36048,7 +36048,6 @@ let make_params env params =
     List.map make_param params
 
 let transl_labels env closed lbls =
-  assert (lbls <> []);
   if !Config.bs_only then 
     match !Builtin_attributes.check_duplicated_labels lbls with 
     | None -> ()
@@ -38915,6 +38914,7 @@ type error =
   | Unknown_literal of string * char
   | Illegal_letrec_pat
   | Labels_omitted of string list
+  | Empty_record_literal
 exception Error of Location.t * Env.t * error
 exception Error_forward of Location.error
 
@@ -39021,6 +39021,7 @@ type error =
   | Unknown_literal of string * char
   | Illegal_letrec_pat
   | Labels_omitted of string list
+  | Empty_record_literal
 exception Error of Location.t * Env.t * error
 exception Error_forward of Location.error
 
@@ -39247,7 +39248,7 @@ let extract_option_type env ty =
 
 let extract_concrete_record env ty =
   match extract_concrete_typedecl env ty with
-    (p0, p, {type_kind=Type_record (fields, _)}) -> (p0, p, fields)
+    (p0, p, {type_kind=Type_record (fields, repr)}) -> (p0, p, fields, repr)
   | _ -> raise Not_found
 
 let extract_concrete_variant env ty =
@@ -40094,7 +40095,7 @@ and type_pat_aux ~constrs ~labels ~no_existentials ~mode ~explode ~env
       assert (lid_sp_list <> []);
       let opath, record_ty =
         try
-          let (p0, p,_) = extract_concrete_record !env expected_ty in
+          let (p0, p, _, _) = extract_concrete_record !env expected_ty in
           Some (p0, p), expected_ty
         with Not_found -> None, newvar ()
       in
@@ -41096,14 +41097,13 @@ and type_expect_ ?in_function ?(recarg=Rejected) env sexp ty_expected =
           exp_env = env }
       end
     | Pexp_record(lid_sexp_list, None) ->
-        assert (lid_sexp_list <> []);
-        let ty_record, opath =          
+        let ty_record, opath, fields, repr_opt =          
           match extract_concrete_record env ty_expected with
-          |  (p0, p,_) ->
+          |  (p0, p, fields, repr) ->
               (* XXX level may be wrong *)
-              ty_expected, Some (p0, p) 
+              ty_expected, Some (p0, p), fields, Some repr 
           | exception Not_found -> 
-               newvar (), None
+               newvar (), None, [], None
 
         in
         let lbl_exp_list =
@@ -41115,7 +41115,24 @@ and type_expect_ ?in_function ?(recarg=Rejected) env sexp ty_expected =
         in
         unify_exp_types loc env ty_record (instance env ty_expected);
         check_duplicates loc env lbl_exp_list;
-        let (_, { lbl_all = label_descriptions; lbl_repres = representation}, _) = List.hd lbl_exp_list in
+        let label_descriptions, representation = match lbl_exp_list, repr_opt with
+        | (_, { lbl_all = label_descriptions; lbl_repres = representation}, _) :: _, _ -> label_descriptions, representation
+        | [], Some (Record_optional_labels optional_labels as representation) when lid_sexp_list = [] ->
+            let filter_missing (ld : Types.label_declaration) =
+              let name = Ident.name ld.ld_id in
+              if List.mem name optional_labels then
+                None
+              else
+                Some name in
+            let labels_missing = fields |> List.filter_map filter_missing in
+            if labels_missing <> [] then
+              raise(Error(loc, env, Labels_missing labels_missing));
+            [||], representation
+        | [], _ ->
+          if fields = [] then
+            [||], Record_optional_labels []
+          else
+            raise(Error(loc, env, Empty_record_literal)) in
         let labels_missing = ref [] in
         let label_definitions =
           let matching_label lbl =
@@ -41154,7 +41171,7 @@ and type_expect_ ?in_function ?(recarg=Rejected) env sexp ty_expected =
       let ty_record, opath =
         let get_path ty =
           try
-            let (p0, p,_) = extract_concrete_record env ty in
+            let (p0, p, _, _) = extract_concrete_record env ty in
             (* XXX level may be wrong *)
             Some (p0, p) 
           with Not_found -> None
@@ -41752,7 +41769,7 @@ and type_label_access env srecord lid =
   let ty_exp = record.exp_type in
   let opath =
     try
-      let (p0, p,_) = extract_concrete_record env ty_exp in
+      let (p0, p, _, _) = extract_concrete_record env ty_exp in
       Some(p0, p)
     with Not_found -> None
   in
@@ -42754,9 +42771,11 @@ let report_error env ppf = function
   | Illegal_letrec_pat ->
       fprintf ppf
         "Only variables are allowed as left-hand side of `let rec'"
-  | Labels_omitted labels -> 
+  | Labels_omitted labels ->
       fprintf ppf  "For labeled funciton, labels %s were omitted in the application of this function." 
       (String.concat ", " labels)  
+  | Empty_record_literal ->
+      fprintf ppf  "Empty record literal {} should be type annotated or used in a record context."
 
 let super_report_error_no_wrap_printing_env = report_error
 
@@ -79689,7 +79708,7 @@ and expression_desc cxt ~(level : int) f x : cxt =
                 Js_op.Lit (Ext_ident.convert x))))
   (*name convention of Record is slight different from modules*)
   | Caml_block (el, mutable_flag, _, Blk_record { fields; record_repr }) -> (
-      if Ext_array.for_alli fields (fun i v -> string_of_int i = v) then
+      if Array.length fields <> 0 && Ext_array.for_alli fields (fun i v -> string_of_int i = v) then
         expression_desc cxt ~level f (Array (el, mutable_flag))
       else
         match record_repr with