Add support for empty record type.

Author: cristianoc

CHANGELOG.md

@@ -15,6 +15,7 @@
 #### :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
 

jscomp/ml/typecore.ml

@@ -2179,7 +2179,11 @@ and type_expect_ ?in_function ?(recarg=Rejected) env sexp ty_expected =
             if labels_missing <> [] then
               raise(Error(loc, env, Labels_missing labels_missing));
             [||], representation
-        | [], _ -> raise(Error(loc, env, Empty_record_literal)) in
+        | [], _ ->
+          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 =

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 = {}

jscomp/test/build.ninja

@@ -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 -> ()
@@ -41129,7 +41128,11 @@ and type_expect_ ?in_function ?(recarg=Rejected) env sexp ty_expected =
             if labels_missing <> [] then
               raise(Error(loc, env, Labels_missing labels_missing));
             [||], representation
-        | [], _ -> raise(Error(loc, env, Empty_record_literal)) in
+        | [], _ ->
+          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 =

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 -> ()
@@ -41129,7 +41128,11 @@ and type_expect_ ?in_function ?(recarg=Rejected) env sexp ty_expected =
             if labels_missing <> [] then
               raise(Error(loc, env, Labels_missing labels_missing));
             [||], representation
-        | [], _ -> raise(Error(loc, env, Empty_record_literal)) in
+        | [], _ ->
+          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 =
@@ -287722,13 +287725,6 @@ and parseRecordOrObjectDecl p =
           :: parseCommaDelimitedRegion ~grammar:Grammar.FieldDeclarations
                ~closing:Rbrace ~f:parseFieldDeclarationRegion p
       in
-      let () =
-        match fields with
-        | [] ->
-          Parser.err ~startPos p
-            (Diagnostics.message "A record needs at least one field")
-        | _ -> ()
-      in
       Parser.expect Rbrace p;
       Parser.eatBreadcrumb p;
       (None, Asttypes.Public, Parsetree.Ptype_record fields))

lib/4.06.1/unstable/js_playground_compiler.ml

@@ -212435,7 +212435,6 @@ let make_params env params =
     List.map make_param params
 
 let transl_labels env closed lbls =
-  assert (lbls <> []);
   if true then 
     match !Builtin_attributes.check_duplicated_labels lbls with 
     | None -> ()
@@ -217516,7 +217515,11 @@ and type_expect_ ?in_function ?(recarg=Rejected) env sexp ty_expected =
             if labels_missing <> [] then
               raise(Error(loc, env, Labels_missing labels_missing));
             [||], representation
-        | [], _ -> raise(Error(loc, env, Empty_record_literal)) in
+        | [], _ ->
+          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 =
@@ -301246,13 +301249,6 @@ and parseRecordOrObjectDecl p =
           :: parseCommaDelimitedRegion ~grammar:Grammar.FieldDeclarations
                ~closing:Rbrace ~f:parseFieldDeclarationRegion p
       in
-      let () =
-        match fields with
-        | [] ->
-          Parser.err ~startPos p
-            (Diagnostics.message "A record needs at least one field")
-        | _ -> ()
-      in
       Parser.expect Rbrace p;
       Parser.eatBreadcrumb p;
       (None, Asttypes.Public, Parsetree.Ptype_record fields))