Specialize uses of new dict literal to direct JS object creation

CHANGELOG.md

@@ -16,6 +16,7 @@
 
 - Allow coercing polyvariants to variants when we can guarantee that the runtime representation matches. https://github.com/rescript-lang/rescript-compiler/pull/6981
 - Add new dict literal syntax (`dict{"foo": "bar"}`). https://github.com/rescript-lang/rescript-compiler/pull/6774
+- Optimize usage of the new dict literal syntax to emit an actual JS object literal. https://github.com/rescript-lang/rescript-compiler/pull/6538
 
 #### :nail_care: Polish
 
@@ -2618,4 +2619,4 @@ Features:
 
 # 1.0.0
 
-Initial release
+Initial release

jscomp/core/lam_dispatch_primitive.ml

@@ -264,6 +264,17 @@ let translate loc (prim_name : string) (args : J.expression list) : J.expression
       match args with
       | [e] -> {e with expression_desc = Await e}
       | _ -> assert false)
+  | "?create_dict" -> (
+    match args with
+    | [{expression_desc = Array (items, _)}] ->
+        E.obj
+        (items
+        |> List.filter_map (fun (exp : J.expression) ->
+                match exp.expression_desc with
+                | Caml_block ([{expression_desc = Str {txt}}; expr], _, _, _) ->
+                    Some (Js_op.Lit txt, expr)
+                | _ -> None))
+    | _ -> assert false)
   | missing_impl ->
     let msg = Warnings.message (Bs_unimplemented_primitive missing_impl) in
     Location.raise_errorf ~loc "%s" msg

jscomp/others/js_dict.res

@@ -122,3 +122,5 @@ let map = (f, source) => {
   }
   target
 }
+
+external unsafe_create: array<(string, 'a)> => dict<'a> = "?create_dict"

jscomp/others/js_dict.resi

@@ -171,3 +171,5 @@ salePrices == Js.Dict.fromList(list{("pen", 0.90), ("book", 4.50), ("stapler", 6
 ```
 */
 let map: ('a => 'b, t<'a>) => t<'b>
+
+external unsafe_create: array<(string, 'a)> => dict<'a> = "?create_dict"

jscomp/syntax/src/res_comments_table.ml

@@ -1352,7 +1352,7 @@ and walk_expression expr t comments =
               {
                 txt =
                   Longident.Ldot
-                    (Longident.Ldot (Lident "Js", "Dict"), "fromArray");
+                    (Longident.Ldot (Lident "Js", "Dict"), "unsafe_create");
               };
         },
         [(Nolabel, key_values)] )

jscomp/syntax/src/res_core.ml

@@ -3947,7 +3947,7 @@ and parse_dict_expr ~start_pos p =
     (Ast_helper.Exp.ident ~loc
        (Location.mkloc
           (Longident.Ldot
-             (Longident.Ldot (Longident.Lident "Js", "Dict"), "fromArray"))
+             (Longident.Ldot (Longident.Lident "Js", "Dict"), "unsafe_create"))
           loc))
     [(Asttypes.Nolabel, Ast_helper.Exp.array ~loc key_value_pairs)]
 

jscomp/syntax/src/res_printer.ml

@@ -4081,7 +4081,7 @@ and print_pexp_apply ~state expr cmt_tbl =
               {
                 txt =
                   Longident.Ldot
-                    (Longident.Ldot (Lident "Js", "Dict"), "fromArray");
+                    (Longident.Ldot (Lident "Js", "Dict"), "unsafe_create");
               };
         },
         [(Nolabel, key_values)] )

jscomp/syntax/tests/parsing/grammar/expressions/expected/dict.res.txt

@@ -1,7 +1,7 @@
-let x = Js.Dict.fromArray [||]
-let x = Js.Dict.fromArray [|("foo", {js|bar|js})|]
-let x = Js.Dict.fromArray [|("foo", {js|bar|js});("bar", {js|baz|js})|]
+let x = Js.Dict.unsafe_create [||]
+let x = Js.Dict.unsafe_create [|("foo", {js|bar|js})|]
+let x = Js.Dict.unsafe_create [|("foo", {js|bar|js});("bar", {js|baz|js})|]
 let baz = {js|foo|js}
 let x =
-  Js.Dict.fromArray
+  Js.Dict.unsafe_create
     [|("foo", {js|bar|js});("bar", {js|baz|js});("baz", baz)|]

jscomp/syntax/tests/printer/expr/expected/dict.res.txt

@@ -17,14 +17,10 @@ let x = dict{
   "baz": baz,
 }
 
-let x = dict{"foo": "bar", "bar": "baz"}
-let x = dict{"foo": "bar", "bar": "baz", "baz": baz}
+let x = Js.Dict.fromArray([("foo", "bar"), ("bar", "baz")])
+let x = Js.Dict.fromArray([("foo", "bar"), ("bar", "baz"), ("baz", baz)])
 
-let x = dict{
-  "foo": "bar",
-  "bar": "baz",
-  "baz": baz,
-}
+let x = Js.Dict.fromArray([("foo", "bar"), ("bar", "baz"), ("baz", baz)])
 
 // comments
 let x = dict{/* foo */ "foo": "bar"}
@@ -64,22 +60,30 @@ let x = dict{
   "baz": baz /* bar */,
 }
 
-let x = dict{/* foo */ "foo": "bar", /* bar */ "bar": "baz"}
-let x = dict{/* foo */ "foo": "bar", /* bar */ "bar": "baz", /* baz */ "baz": baz}
-let x = dict{"foo": /* foo */ "bar", "bar": /* bar */ "baz", "baz": /* baz */ baz}
-let x = dict{"foo": "bar" /* foo */, "bar": "baz" /* bar */, "baz": baz /* baz */}
+let x = Js.Dict.fromArray([/* foo */ ("foo", "bar"), /* bar */ ("bar", "baz")])
+let x = Js.Dict.fromArray([
+  (/* foo */ "foo", "bar"),
+  (/* bar */ "bar", "baz"),
+  (/* baz */ "baz", baz),
+])
+let x = Js.Dict.fromArray([
+  ("foo", /* foo */ "bar"),
+  ("bar", /* bar */ "baz"),
+  ("baz", /* baz */ baz),
+])
+let x = Js.Dict.fromArray([
+  ("foo", "bar" /* foo */),
+  ("bar", "baz" /* bar */),
+  ("baz", baz /* baz */),
+])
 
-let x = dict{
+let x = Js.Dict.fromArray([
   // foo
-  "foo": "bar",
+  ("foo", "bar"),
   // bar
-  "bar": "baz",
+  ("bar", "baz"),
   // baz
-  "baz": baz,
-}
+  ("baz", baz),
+])
 
-let x = dict{
-  "foo": "bar", // foo
-  "bar": "baz", // bar
-  "baz": baz, // baz
-}
+let x = Js.Dict.fromArray([("foo", "bar"), ("bar", "baz"), ("baz", baz)]) // foo // bar // baz

jscomp/test/DictTests.res

@@ -0,0 +1,8 @@
+let someString = "hello"
+
+let createdDict = dict{
+  "name": "hello",
+  "age": "what",
+  "more": "stuff",
+  "otherStr": someString,
+}