From 8b1ca403b044329ba2c3e03eb08eede221f529f4 Mon Sep 17 00:00:00 2001
From: Gabriel Nordeborn <gabbe.nord@gmail.com>
Date: Thu, 22 May 2025 11:15:08 +0200
Subject: [PATCH 1/9] improve array <-> tuple error message by looking at what
 the user actually wrote

---
 compiler/bsc/rescript_compiler_main.ml        | 20 ++++++++
 compiler/ml/error_message_utils.ml            | 48 ++++++++++++++++++-
 compiler/ml/typecore.ml                       | 14 +++---
 compiler/ml/typecore.mli                      |  2 +-
 ...array_literal_passed_to_tuple.res.expected | 14 ++++++
 .../array_var_passed_to_tuple.res.expected    | 13 +++++
 .../array_literal_passed_to_tuple.res         |  5 ++
 .../fixtures/array_var_passed_to_tuple.res    |  7 +++
 8 files changed, 114 insertions(+), 9 deletions(-)
 create mode 100644 tests/build_tests/super_errors/expected/array_literal_passed_to_tuple.res.expected
 create mode 100644 tests/build_tests/super_errors/expected/array_var_passed_to_tuple.res.expected
 create mode 100644 tests/build_tests/super_errors/fixtures/array_literal_passed_to_tuple.res
 create mode 100644 tests/build_tests/super_errors/fixtures/array_var_passed_to_tuple.res

diff --git a/compiler/bsc/rescript_compiler_main.ml b/compiler/bsc/rescript_compiler_main.ml
index f9113c40b6..a7d9190b60 100644
--- a/compiler/bsc/rescript_compiler_main.ml
+++ b/compiler/bsc/rescript_compiler_main.ml
@@ -12,6 +12,26 @@
 
 let absname = ref false
 
+external to_comment : Res_comment.t -> Error_message_utils.comment = "%identity"
+external from_comment : Error_message_utils.comment -> Res_comment.t
+  = "%identity"
+
+let () =
+  Error_message_utils.parse_source :=
+    fun source ->
+      let res =
+        Res_driver.parse_implementation_from_source ~for_printer:false
+          ~display_filename:"<none>" ~source
+      in
+      (res.parsetree, res.comments |> List.map to_comment)
+
+let () =
+  Error_message_utils.reprint_source :=
+    fun parsetree comments ->
+      Res_printer.print_implementation parsetree
+        ~comments:(comments |> List.map from_comment)
+        ~width:80
+
 let set_abs_input_name sourcefile =
   let sourcefile =
     if !absname && Filename.is_relative sourcefile then
diff --git a/compiler/ml/error_message_utils.ml b/compiler/ml/error_message_utils.ml
index 31d8cafc3b..d652456350 100644
--- a/compiler/ml/error_message_utils.ml
+++ b/compiler/ml/error_message_utils.ml
@@ -1,6 +1,12 @@
 type extract_concrete_typedecl =
   Env.t -> Types.type_expr -> Path.t * Path.t * Types.type_declaration
 
+type comment
+let parse_source : (string -> Parsetree.structure * comment list) ref =
+  ref (fun _ -> ([], []))
+let reprint_source : (Parsetree.structure -> comment list -> string) ref =
+  ref (fun _ _ -> "")
+
 type type_clash_statement = FunctionCall
 type type_clash_context =
   | SetRecordField
@@ -62,7 +68,14 @@ let is_record_type ~extract_concrete_typedecl ~env ty =
     | _ -> false
   with _ -> false
 
-let print_extra_type_clash_help ~extract_concrete_typedecl ~env ppf
+let extract_location_string ~src (loc : Location.t) =
+  let start_pos = loc.loc_start in
+  let end_pos = loc.loc_end in
+  let start_offset = start_pos.pos_cnum in
+  let end_offset = end_pos.pos_cnum in
+  String.sub src start_offset (end_offset - start_offset)
+
+let print_extra_type_clash_help ~extract_concrete_typedecl ~env loc ppf
     (bottom_aliases : (Types.type_expr * Types.type_expr) option)
     type_clash_context =
   match (type_clash_context, bottom_aliases) with
@@ -185,6 +198,39 @@ let print_extra_type_clash_help ~extract_concrete_typedecl ~env ppf
   | _, Some ({Types.desc = Tconstr (p1, _, _)}, _)
     when Path.same p1 Predef.path_promise ->
     fprintf ppf "\n\n  - Did you mean to await this promise before using it?\n"
+  | _, Some ({Types.desc = Tconstr (p1, _, _)}, {Types.desc = Ttuple _})
+    when Path.same p1 Predef.path_array ->
+    let src = Ext_io.load_file loc.Location.loc_start.pos_fname in
+    let sub_src = extract_location_string ~src loc in
+    let parsed, comments = !parse_source sub_src in
+    let suggested_rewrite =
+      match parsed with
+      | [
+       ({
+          Parsetree.pstr_desc =
+            Pstr_eval (({pexp_desc = Pexp_array items} as exp), l);
+        } as str_item);
+      ] ->
+        Some
+          (!reprint_source
+             [
+               {
+                 str_item with
+                 pstr_desc =
+                   Pstr_eval ({exp with pexp_desc = Pexp_tuple items}, l);
+               };
+             ]
+             comments)
+      | _ -> None
+    in
+    fprintf ppf
+      "\n\n  - Fix this by passing a tuple instead of an array%s@{<info>%s@}\n"
+      (match suggested_rewrite with
+      | Some _ -> ", like: "
+      | None -> "")
+      (match suggested_rewrite with
+      | Some rewrite -> rewrite
+      | None -> "")
   | _ -> ()
 
 let type_clash_context_from_function sexp sfunct =
diff --git a/compiler/ml/typecore.ml b/compiler/ml/typecore.ml
index 7fb9472b9f..de48f4b2c7 100644
--- a/compiler/ml/typecore.ml
+++ b/compiler/ml/typecore.ml
@@ -728,7 +728,7 @@ let rec collect_missing_arguments env type1 type2 =
     | None -> None)
   | _ -> None
 
-let print_expr_type_clash ?type_clash_context env trace ppf =
+let print_expr_type_clash ?type_clash_context env loc trace ppf =
   (* this is the most frequent error. We should do whatever we can to provide
       specific guidance to this generic error before giving up *)
   let bottom_aliases_result = bottom_aliases trace in
@@ -785,7 +785,7 @@ let print_expr_type_clash ?type_clash_context env trace ppf =
       (function
         | ppf -> error_type_text ppf type_clash_context)
       (function ppf -> error_expected_type_text ppf type_clash_context);
-    print_extra_type_clash_help ~extract_concrete_typedecl ~env ppf
+    print_extra_type_clash_help ~extract_concrete_typedecl ~env loc ppf
       bottom_aliases_result type_clash_context;
     show_extra_help ppf env trace
 
@@ -4173,7 +4173,7 @@ let type_expr ppf typ =
   Printtyp.reset_and_mark_loops typ;
   Printtyp.type_expr ppf typ
 
-let report_error env ppf error =
+let report_error env loc ppf error =
   match error with
   | Polymorphic_label lid ->
     fprintf ppf "@[The record field %a is polymorphic.@ %s@]" longident lid
@@ -4237,7 +4237,7 @@ let report_error env ppf error =
   | Expr_type_clash (trace, type_clash_context) ->
     (* modified *)
     fprintf ppf "@[<v>";
-    print_expr_type_clash ?type_clash_context env trace ppf;
+    print_expr_type_clash ?type_clash_context env loc trace ppf;
     fprintf ppf "@]"
   | Apply_non_function typ -> (
     (* modified *)
@@ -4542,13 +4542,13 @@ let report_error env ppf error =
     fprintf ppf
       "Direct field access on a dict is not supported. Use Dict.get instead."
 
-let report_error env ppf err =
-  Printtyp.wrap_printing_env env (fun () -> report_error env ppf err)
+let report_error env loc ppf err =
+  Printtyp.wrap_printing_env env (fun () -> report_error env loc ppf err)
 
 let () =
   Location.register_error_of_exn (function
     | Error (loc, env, err) ->
-      Some (Location.error_of_printer loc (report_error env) err)
+      Some (Location.error_of_printer loc (report_error env loc) err)
     | Error_forward err -> Some err
     | _ -> None)
 
diff --git a/compiler/ml/typecore.mli b/compiler/ml/typecore.mli
index c11f557a2e..fef96830c2 100644
--- a/compiler/ml/typecore.mli
+++ b/compiler/ml/typecore.mli
@@ -108,7 +108,7 @@ type error =
 exception Error of Location.t * Env.t * error
 exception Error_forward of Location.error
 
-val report_error : Env.t -> formatter -> error -> unit
+val report_error : Env.t -> Location.t -> formatter -> error -> unit
 (* Deprecated.  Use Location.{error_of_exn, report_error}. *)
 
 (* Forward declaration, to be filled in by Typemod.type_module *)
diff --git a/tests/build_tests/super_errors/expected/array_literal_passed_to_tuple.res.expected b/tests/build_tests/super_errors/expected/array_literal_passed_to_tuple.res.expected
new file mode 100644
index 0000000000..5fe60abda3
--- /dev/null
+++ b/tests/build_tests/super_errors/expected/array_literal_passed_to_tuple.res.expected
@@ -0,0 +1,14 @@
+
+  We've found a bug for you!
+  /.../fixtures/array_literal_passed_to_tuple.res:5:17-34
+
+  3 │ }
+  4 │ 
+  5 │ let x = doStuff(["hello", "world"])
+  6 │ 
+
+  This has type: array<'a>
+  But it's expected to have type: (string, string)
+
+  - Fix this by passing a tuple instead of an array, like: ("hello", "world")
+
\ No newline at end of file
diff --git a/tests/build_tests/super_errors/expected/array_var_passed_to_tuple.res.expected b/tests/build_tests/super_errors/expected/array_var_passed_to_tuple.res.expected
new file mode 100644
index 0000000000..e75a50f376
--- /dev/null
+++ b/tests/build_tests/super_errors/expected/array_var_passed_to_tuple.res.expected
@@ -0,0 +1,13 @@
+
+  We've found a bug for you!
+  /.../fixtures/array_var_passed_to_tuple.res:7:17-18
+
+  5 │ let xx = ["hello", "world"]
+  6 │ 
+  7 │ let x = doStuff(xx)
+  8 │ 
+
+  This has type: array<string>
+  But this function argument is expecting: (string, string)
+
+  - Fix this by passing a tuple instead of an array
\ No newline at end of file
diff --git a/tests/build_tests/super_errors/fixtures/array_literal_passed_to_tuple.res b/tests/build_tests/super_errors/fixtures/array_literal_passed_to_tuple.res
new file mode 100644
index 0000000000..4b203b92ce
--- /dev/null
+++ b/tests/build_tests/super_errors/fixtures/array_literal_passed_to_tuple.res
@@ -0,0 +1,5 @@
+let doStuff = ((one, two)) => {
+  one ++ two
+}
+
+let x = doStuff(["hello", "world"])
diff --git a/tests/build_tests/super_errors/fixtures/array_var_passed_to_tuple.res b/tests/build_tests/super_errors/fixtures/array_var_passed_to_tuple.res
new file mode 100644
index 0000000000..7fee1bbc8b
--- /dev/null
+++ b/tests/build_tests/super_errors/fixtures/array_var_passed_to_tuple.res
@@ -0,0 +1,7 @@
+let doStuff = ((one, two)) => {
+  one ++ two
+}
+
+let xx = ["hello", "world"]
+
+let x = doStuff(xx)

From 6a28ea9a112ec26b9f5aeb517c58eb0162327f3b Mon Sep 17 00:00:00 2001
From: Gabriel Nordeborn <gabbe.nord@gmail.com>
Date: Thu, 22 May 2025 12:56:35 +0200
Subject: [PATCH 2/9] refactor

---
 compiler/bsc/rescript_compiler_main.ml | 19 ++++--
 compiler/ml/error_message_utils.ml     | 88 ++++++++++++++++----------
 2 files changed, 67 insertions(+), 40 deletions(-)

diff --git a/compiler/bsc/rescript_compiler_main.ml b/compiler/bsc/rescript_compiler_main.ml
index a7d9190b60..6b59a25360 100644
--- a/compiler/bsc/rescript_compiler_main.ml
+++ b/compiler/bsc/rescript_compiler_main.ml
@@ -12,24 +12,29 @@
 
 let absname = ref false
 
-external to_comment : Res_comment.t -> Error_message_utils.comment = "%identity"
-external from_comment : Error_message_utils.comment -> Res_comment.t
-  = "%identity"
+(* TODO: Maybe there's a better place to do this init. *)
+module Error_message_utils_support = struct
+  external to_comment : Res_comment.t -> Error_message_utils.Parser.comment
+    = "%identity"
+  external from_comment : Error_message_utils.Parser.comment -> Res_comment.t
+    = "%identity"
+end
 
 let () =
-  Error_message_utils.parse_source :=
+  Error_message_utils.Parser.parse_source :=
     fun source ->
       let res =
         Res_driver.parse_implementation_from_source ~for_printer:false
           ~display_filename:"<none>" ~source
       in
-      (res.parsetree, res.comments |> List.map to_comment)
+      ( res.parsetree,
+        res.comments |> List.map Error_message_utils_support.to_comment )
 
 let () =
-  Error_message_utils.reprint_source :=
+  Error_message_utils.Parser.reprint_source :=
     fun parsetree comments ->
       Res_printer.print_implementation parsetree
-        ~comments:(comments |> List.map from_comment)
+        ~comments:(comments |> List.map Error_message_utils_support.from_comment)
         ~width:80
 
 let set_abs_input_name sourcefile =
diff --git a/compiler/ml/error_message_utils.ml b/compiler/ml/error_message_utils.ml
index d652456350..4304d8c22d 100644
--- a/compiler/ml/error_message_utils.ml
+++ b/compiler/ml/error_message_utils.ml
@@ -1,11 +1,56 @@
 type extract_concrete_typedecl =
   Env.t -> Types.type_expr -> Path.t * Path.t * Types.type_declaration
 
-type comment
-let parse_source : (string -> Parsetree.structure * comment list) ref =
-  ref (fun _ -> ([], []))
-let reprint_source : (Parsetree.structure -> comment list -> string) ref =
-  ref (fun _ _ -> "")
+module Parser : sig
+  type comment
+
+  val parse_source : (string -> Parsetree.structure * comment list) ref
+
+  val reprint_source : (Parsetree.structure -> comment list -> string) ref
+
+  val parse_expr_at_loc :
+    Warnings.loc -> (Parsetree.expression * comment list) option
+
+  val reprint_expr_at_loc :
+    ?mapper:(Parsetree.expression -> Parsetree.expression option) ->
+    Warnings.loc ->
+    string option
+end = struct
+  type comment
+
+  let parse_source : (string -> Parsetree.structure * comment list) ref =
+    ref (fun _ -> ([], []))
+
+  let reprint_source : (Parsetree.structure -> comment list -> string) ref =
+    ref (fun _ _ -> "")
+
+  let extract_location_string ~src (loc : Location.t) =
+    let start_pos = loc.loc_start in
+    let end_pos = loc.loc_end in
+    let start_offset = start_pos.pos_cnum in
+    let end_offset = end_pos.pos_cnum in
+    String.sub src start_offset (end_offset - start_offset)
+
+  let parse_expr_at_loc loc =
+    (* TODO: Maybe cache later on *)
+    let src = Ext_io.load_file loc.Location.loc_start.pos_fname in
+    let sub_src = extract_location_string ~src loc in
+    let parsed, comments = !parse_source sub_src in
+    match parsed with
+    | [{Parsetree.pstr_desc = Pstr_eval (exp, _)}] -> Some (exp, comments)
+    | _ -> None
+
+  let wrap_in_structure exp =
+    [{Parsetree.pstr_desc = Pstr_eval (exp, []); pstr_loc = Location.none}]
+
+  let reprint_expr_at_loc ?(mapper = fun _ -> None) loc =
+    match parse_expr_at_loc loc with
+    | Some (exp, comments) -> (
+      match mapper exp with
+      | Some exp -> Some (!reprint_source (wrap_in_structure exp) comments)
+      | None -> None)
+    | None -> None
+end
 
 type type_clash_statement = FunctionCall
 type type_clash_context =
@@ -68,13 +113,6 @@ let is_record_type ~extract_concrete_typedecl ~env ty =
     | _ -> false
   with _ -> false
 
-let extract_location_string ~src (loc : Location.t) =
-  let start_pos = loc.loc_start in
-  let end_pos = loc.loc_end in
-  let start_offset = start_pos.pos_cnum in
-  let end_offset = end_pos.pos_cnum in
-  String.sub src start_offset (end_offset - start_offset)
-
 let print_extra_type_clash_help ~extract_concrete_typedecl ~env loc ppf
     (bottom_aliases : (Types.type_expr * Types.type_expr) option)
     type_clash_context =
@@ -200,28 +238,12 @@ let print_extra_type_clash_help ~extract_concrete_typedecl ~env loc ppf
     fprintf ppf "\n\n  - Did you mean to await this promise before using it?\n"
   | _, Some ({Types.desc = Tconstr (p1, _, _)}, {Types.desc = Ttuple _})
     when Path.same p1 Predef.path_array ->
-    let src = Ext_io.load_file loc.Location.loc_start.pos_fname in
-    let sub_src = extract_location_string ~src loc in
-    let parsed, comments = !parse_source sub_src in
     let suggested_rewrite =
-      match parsed with
-      | [
-       ({
-          Parsetree.pstr_desc =
-            Pstr_eval (({pexp_desc = Pexp_array items} as exp), l);
-        } as str_item);
-      ] ->
-        Some
-          (!reprint_source
-             [
-               {
-                 str_item with
-                 pstr_desc =
-                   Pstr_eval ({exp with pexp_desc = Pexp_tuple items}, l);
-               };
-             ]
-             comments)
-      | _ -> None
+      Parser.reprint_expr_at_loc loc ~mapper:(fun exp ->
+          match exp.Parsetree.pexp_desc with
+          | Pexp_array items ->
+            Some {exp with Parsetree.pexp_desc = Pexp_tuple items}
+          | _ -> None)
     in
     fprintf ppf
       "\n\n  - Fix this by passing a tuple instead of an array%s@{<info>%s@}\n"

From a8378e6a35396e745d4533a0bfd2908b2385de63 Mon Sep 17 00:00:00 2001
From: Gabriel Nordeborn <gabbe.nord@gmail.com>
Date: Thu, 22 May 2025 13:09:45 +0200
Subject: [PATCH 3/9] example of detecting and providing rewrite for ReScript
 object -> record

---
 compiler/ml/error_message_utils.ml            | 35 +++++++++++++++----
 ..._passed_when_record_expected.res.expected} | 12 ++++---
 ...t_literal_passed_when_record_expected.res} |  0
 3 files changed, 36 insertions(+), 11 deletions(-)
 rename tests/build_tests/super_errors/expected/{object_passed_when_record_expected.res.expected => object_literal_passed_when_record_expected.res.expected} (51%)
 rename tests/build_tests/super_errors/fixtures/{object_passed_when_record_expected.res => object_literal_passed_when_record_expected.res} (100%)

diff --git a/compiler/ml/error_message_utils.ml b/compiler/ml/error_message_utils.ml
index 4304d8c22d..5c9097a3f7 100644
--- a/compiler/ml/error_message_utils.ml
+++ b/compiler/ml/error_message_utils.ml
@@ -227,12 +227,35 @@ let print_extra_type_clash_help ~extract_concrete_typedecl ~env loc ppf
   | _, Some ({desc = Tobject _}, ({Types.desc = Tconstr _} as t1))
     when is_record_type ~extract_concrete_typedecl ~env t1 ->
     fprintf ppf
-      "\n\n\
-      \  You're passing a @{<error>ReScript object@} where a @{<info>record@} \
-       is expected. \n\n\
-      \  - Did you mean to pass a record instead of an object? Objects are \
-       written with quoted keys, and records with unquoted keys. Remove the \
-       quotes from the object keys to pass it as a record instead of object. \n\n"
+      "@,\
+       @,\
+       You're passing a @{<error>ReScript object@} where a @{<info>record@} is \
+       expected. Objects are written with quoted keys, and records with \
+       unquoted keys.";
+
+    let suggested_rewrite =
+      Parser.reprint_expr_at_loc loc ~mapper:(fun exp ->
+          match exp.Parsetree.pexp_desc with
+          | Pexp_extension
+              ( {txt = "obj"},
+                PStr
+                  [
+                    {
+                      pstr_desc =
+                        Pstr_eval (({pexp_desc = Pexp_record _} as record), _);
+                    };
+                  ] ) ->
+            Some record
+          | _ -> None)
+    in
+    fprintf ppf
+      "@,\
+       @,\
+       Possible solutions: @,\
+       - Rewrite the object to a record, like: @{<info>%s@}@,"
+      (match suggested_rewrite with
+      | Some rewrite -> rewrite
+      | None -> "")
   | _, Some ({Types.desc = Tconstr (p1, _, _)}, _)
     when Path.same p1 Predef.path_promise ->
     fprintf ppf "\n\n  - Did you mean to await this promise before using it?\n"
diff --git a/tests/build_tests/super_errors/expected/object_passed_when_record_expected.res.expected b/tests/build_tests/super_errors/expected/object_literal_passed_when_record_expected.res.expected
similarity index 51%
rename from tests/build_tests/super_errors/expected/object_passed_when_record_expected.res.expected
rename to tests/build_tests/super_errors/expected/object_literal_passed_when_record_expected.res.expected
index be09067202..b69288a686 100644
--- a/tests/build_tests/super_errors/expected/object_passed_when_record_expected.res.expected
+++ b/tests/build_tests/super_errors/expected/object_literal_passed_when_record_expected.res.expected
@@ -1,6 +1,6 @@
 
   We've found a bug for you!
-  /.../fixtures/object_passed_when_record_expected.res:4:14-26
+  /.../fixtures/object_literal_passed_when_record_expected.res:4:14-26
 
   2 │ type xx = array<x>
   3 │ 
@@ -9,7 +9,9 @@
 
   This has type: {"one": bool}
   But it's expected to have type: x
-
-  You're passing a ReScript object where a record is expected. 
-
-  - Did you mean to pass a record instead of an object? Objects are written with quoted keys, and records with unquoted keys. Remove the quotes from the object keys to pass it as a record instead of object.
\ No newline at end of file
+  
+  You're passing a ReScript object where a record is expected. Objects are written with quoted keys, and records with unquoted keys.
+  
+  Possible solutions: 
+  - Rewrite the object to a record, like: {one: true}
+
\ No newline at end of file
diff --git a/tests/build_tests/super_errors/fixtures/object_passed_when_record_expected.res b/tests/build_tests/super_errors/fixtures/object_literal_passed_when_record_expected.res
similarity index 100%
rename from tests/build_tests/super_errors/fixtures/object_passed_when_record_expected.res
rename to tests/build_tests/super_errors/fixtures/object_literal_passed_when_record_expected.res

From fa7e4836aebda204c5a0d983e7dd4728175f2c65 Mon Sep 17 00:00:00 2001
From: Gabriel Nordeborn <gabbe.nord@gmail.com>
Date: Thu, 22 May 2025 13:24:05 +0200
Subject: [PATCH 4/9] remove Belt prefix

---
 compiler/ml/error_message_utils.ml                          | 6 +++---
 .../super_errors/expected/math_operator_float.res.expected  | 2 +-
 .../super_errors/expected/primitives7.res.expected          | 2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/compiler/ml/error_message_utils.ml b/compiler/ml/error_message_utils.ml
index 5c9097a3f7..c6e8663514 100644
--- a/compiler/ml/error_message_utils.ml
+++ b/compiler/ml/error_message_utils.ml
@@ -155,8 +155,8 @@ let print_extra_type_clash_help ~extract_concrete_typedecl ~env loc ppf
          you cannot %s a float and an int without converting between the two.\n\n\
         \  Possible solutions:\n\
         \  - Ensure all values in this calculation has the type @{<info>%s@}. \
-         You can convert between floats and ints via \
-         @{<info>Belt.Float.toInt@} and @{<info>Belt.Int.fromFloat@}."
+         You can convert between floats and ints via @{<info>Float.toInt@} and \
+         @{<info>Int.fromFloat@}."
         operator_text
         (if for_float then "float" else "int"));
     match (is_constant, bottom_aliases) with
@@ -204,7 +204,7 @@ let print_extra_type_clash_help ~extract_concrete_typedecl ~env loc ppf
       "\n\n\
       \  Possible solutions:\n\
       \  - Unwrap the option to its underlying value using \
-       `yourValue->Belt.Option.getWithDefault(someDefaultValue)`"
+       `yourValue->Option.getOr(someDefaultValue)`"
   | Some ComparisonOperator, _ ->
     fprintf ppf "\n\n  You can only compare things of the same type."
   | Some ArrayValue, _ ->
diff --git a/tests/build_tests/super_errors/expected/math_operator_float.res.expected b/tests/build_tests/super_errors/expected/math_operator_float.res.expected
index 640e57a500..28b4a7e7ec 100644
--- a/tests/build_tests/super_errors/expected/math_operator_float.res.expected
+++ b/tests/build_tests/super_errors/expected/math_operator_float.res.expected
@@ -13,7 +13,7 @@
   Floats and ints have their own mathematical operators. This means you cannot add a float and an int without converting between the two.
 
   Possible solutions:
-  - Ensure all values in this calculation has the type float. You can convert between floats and ints via Belt.Float.toInt and Belt.Int.fromFloat.
+  - Ensure all values in this calculation has the type float. You can convert between floats and ints via Float.toInt and Int.fromFloat.
   - Change the operator to +, which works on int
   
   You can convert int to float with Int.toFloat.
diff --git a/tests/build_tests/super_errors/expected/primitives7.res.expected b/tests/build_tests/super_errors/expected/primitives7.res.expected
index a6fe42b223..6f5cd351a3 100644
--- a/tests/build_tests/super_errors/expected/primitives7.res.expected
+++ b/tests/build_tests/super_errors/expected/primitives7.res.expected
@@ -13,7 +13,7 @@
   Floats and ints have their own mathematical operators. This means you cannot add a float and an int without converting between the two.
 
   Possible solutions:
-  - Ensure all values in this calculation has the type float. You can convert between floats and ints via Belt.Float.toInt and Belt.Int.fromFloat.
+  - Ensure all values in this calculation has the type float. You can convert between floats and ints via Float.toInt and Int.fromFloat.
   - Change the operator to +, which works on int
   
   You can convert int to float with Int.toFloat.

From 991dfb616f70193f77c5aa98f3fc70b64b847696 Mon Sep 17 00:00:00 2001
From: Gabriel Nordeborn <gabbe.nord@gmail.com>
Date: Thu, 22 May 2025 14:37:07 +0200
Subject: [PATCH 5/9] add dedicated JSX element type mismatch errors

---
 compiler/bsc/rescript_compiler_main.ml        | 38 +++++++------
 compiler/ml/error_message_utils.ml            | 53 +++++++++++++++++++
 ...x_type_mismatch_array_element.res.expected | 13 +++++
 .../jsx_type_mismatch_array_raw.res.expected  | 13 +++++
 .../jsx_type_mismatch_float.res.expected      | 13 +++++
 .../jsx_type_mismatch_int.res.expected        | 13 +++++
 .../jsx_type_mismatch_string.res.expected     | 13 +++++
 .../jsx_type_mismatch_array_element.res       | 19 +++++++
 .../fixtures/jsx_type_mismatch_array_raw.res  | 17 ++++++
 .../fixtures/jsx_type_mismatch_float.res      | 17 ++++++
 .../fixtures/jsx_type_mismatch_int.res        | 17 ++++++
 .../fixtures/jsx_type_mismatch_string.res     | 17 ++++++
 12 files changed, 226 insertions(+), 17 deletions(-)
 create mode 100644 tests/build_tests/super_errors/expected/jsx_type_mismatch_array_element.res.expected
 create mode 100644 tests/build_tests/super_errors/expected/jsx_type_mismatch_array_raw.res.expected
 create mode 100644 tests/build_tests/super_errors/expected/jsx_type_mismatch_float.res.expected
 create mode 100644 tests/build_tests/super_errors/expected/jsx_type_mismatch_int.res.expected
 create mode 100644 tests/build_tests/super_errors/expected/jsx_type_mismatch_string.res.expected
 create mode 100644 tests/build_tests/super_errors/fixtures/jsx_type_mismatch_array_element.res
 create mode 100644 tests/build_tests/super_errors/fixtures/jsx_type_mismatch_array_raw.res
 create mode 100644 tests/build_tests/super_errors/fixtures/jsx_type_mismatch_float.res
 create mode 100644 tests/build_tests/super_errors/fixtures/jsx_type_mismatch_int.res
 create mode 100644 tests/build_tests/super_errors/fixtures/jsx_type_mismatch_string.res

diff --git a/compiler/bsc/rescript_compiler_main.ml b/compiler/bsc/rescript_compiler_main.ml
index 6b59a25360..52f4b85651 100644
--- a/compiler/bsc/rescript_compiler_main.ml
+++ b/compiler/bsc/rescript_compiler_main.ml
@@ -12,30 +12,33 @@
 
 let absname = ref false
 
-(* TODO: Maybe there's a better place to do this init. *)
 module Error_message_utils_support = struct
   external to_comment : Res_comment.t -> Error_message_utils.Parser.comment
     = "%identity"
   external from_comment : Error_message_utils.Parser.comment -> Res_comment.t
     = "%identity"
-end
 
-let () =
-  Error_message_utils.Parser.parse_source :=
-    fun source ->
-      let res =
-        Res_driver.parse_implementation_from_source ~for_printer:false
-          ~display_filename:"<none>" ~source
-      in
-      ( res.parsetree,
-        res.comments |> List.map Error_message_utils_support.to_comment )
+  let setup () =
+    (Error_message_utils.Parser.parse_source :=
+       fun source ->
+         let res =
+           Res_driver.parse_implementation_from_source ~for_printer:false
+             ~display_filename:"<none>" ~source
+         in
+         (res.parsetree, res.comments |> List.map to_comment));
 
-let () =
-  Error_message_utils.Parser.reprint_source :=
-    fun parsetree comments ->
-      Res_printer.print_implementation parsetree
-        ~comments:(comments |> List.map Error_message_utils_support.from_comment)
-        ~width:80
+    (Error_message_utils.Parser.reprint_source :=
+       fun parsetree comments ->
+         Res_printer.print_implementation parsetree
+           ~comments:(comments |> List.map from_comment)
+           ~width:80);
+
+    Error_message_utils.configured_jsx_module :=
+      Some
+        (match !Js_config.jsx_module with
+        | React -> "React"
+        | Generic {module_name} -> module_name)
+end
 
 let set_abs_input_name sourcefile =
   let sourcefile =
@@ -66,6 +69,7 @@ let process_file sourcefile ?kind ppf =
      properly
   *)
   setup_outcome_printer ();
+  Error_message_utils_support.setup ();
   let kind =
     match kind with
     | None ->
diff --git a/compiler/ml/error_message_utils.ml b/compiler/ml/error_message_utils.ml
index c6e8663514..e16d635aaf 100644
--- a/compiler/ml/error_message_utils.ml
+++ b/compiler/ml/error_message_utils.ml
@@ -1,6 +1,13 @@
 type extract_concrete_typedecl =
   Env.t -> Types.type_expr -> Path.t * Path.t * Types.type_declaration
 
+let configured_jsx_module : string option ref = ref None
+
+let with_configured_jsx_module s =
+  match !configured_jsx_module with
+  | None -> s
+  | Some module_name -> module_name ^ "." ^ s
+
 module Parser : sig
   type comment
 
@@ -276,6 +283,52 @@ let print_extra_type_clash_help ~extract_concrete_typedecl ~env loc ppf
       (match suggested_rewrite with
       | Some rewrite -> rewrite
       | None -> "")
+  | ( _,
+      Some
+        ( {desc = Tconstr (p, type_params, _)},
+          {desc = Tconstr (Pdot (Pident {name = "Jsx"}, "element", _), _, _)} )
+    ) -> (
+    (* Looking for a JSX element but got something else *)
+    let is_jsx_element ty =
+      match Ctype.expand_head env ty with
+      | {desc = Tconstr (Pdot (Pident {name = "Jsx"}, "element", _), _, _)} ->
+        true
+      | _ -> false
+    in
+
+    let print_jsx_msg ?(extra = "") name target_fn =
+      fprintf ppf
+        "@,\
+         @,\
+         In JSX, all content must be JSX elements. You can convert %s to a JSX \
+         element with @{<info>%s@}%s.@,"
+        name target_fn extra
+    in
+
+    match type_params with
+    | _ when Path.same p Predef.path_int ->
+      print_jsx_msg "int" (with_configured_jsx_module "int")
+    | _ when Path.same p Predef.path_string ->
+      print_jsx_msg "string" (with_configured_jsx_module "string")
+    | _ when Path.same p Predef.path_float ->
+      print_jsx_msg "float" (with_configured_jsx_module "float")
+    | [tp] when Path.same p Predef.path_array && is_jsx_element tp ->
+      print_jsx_msg
+        ~extra:
+          (" (for example by using a pipe: ->"
+          ^ with_configured_jsx_module "array"
+          ^ ".")
+        "array"
+        (with_configured_jsx_module "array")
+    | [_] when Path.same p Predef.path_array ->
+      fprintf ppf
+        "@,\
+         @,\
+         You need to convert each item in this array to a JSX element first, \
+         then use @{<info>%s@} to convert the array of JSX elements into a \
+         single JSX element.@,"
+        (with_configured_jsx_module "array")
+    | _ -> ())
   | _ -> ()
 
 let type_clash_context_from_function sexp sfunct =
diff --git a/tests/build_tests/super_errors/expected/jsx_type_mismatch_array_element.res.expected b/tests/build_tests/super_errors/expected/jsx_type_mismatch_array_element.res.expected
new file mode 100644
index 0000000000..1cf8426d78
--- /dev/null
+++ b/tests/build_tests/super_errors/expected/jsx_type_mismatch_array_element.res.expected
@@ -0,0 +1,13 @@
+
+  We've found a bug for you!
+  /.../fixtures/jsx_type_mismatch_array_element.res:19:13-30
+
+  17 │ }
+  18 │ 
+  19 │ let x = <> {[React.string("")]} </>
+  20 │ 
+
+  This has type: array<'a>
+  But it's expected to have type: React.element (defined as Jsx.element)
+  
+  You need to convert each item in this array to a JSX element first, then use React.array to convert the array of JSX elements into a single JSX element.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors/expected/jsx_type_mismatch_array_raw.res.expected b/tests/build_tests/super_errors/expected/jsx_type_mismatch_array_raw.res.expected
new file mode 100644
index 0000000000..1eb1d4870d
--- /dev/null
+++ b/tests/build_tests/super_errors/expected/jsx_type_mismatch_array_raw.res.expected
@@ -0,0 +1,13 @@
+
+  We've found a bug for you!
+  /.../fixtures/jsx_type_mismatch_array_raw.res:17:13-16
+
+  15 │ }
+  16 │ 
+  17 │ let x = <> {[""]} </>
+  18 │ 
+
+  This has type: array<'a>
+  But it's expected to have type: React.element (defined as Jsx.element)
+  
+  You need to convert each item in this array to a JSX element first, then use React.array to convert the array of JSX elements into a single JSX element.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors/expected/jsx_type_mismatch_float.res.expected b/tests/build_tests/super_errors/expected/jsx_type_mismatch_float.res.expected
new file mode 100644
index 0000000000..af4279bd52
--- /dev/null
+++ b/tests/build_tests/super_errors/expected/jsx_type_mismatch_float.res.expected
@@ -0,0 +1,13 @@
+
+  We've found a bug for you!
+  /.../fixtures/jsx_type_mismatch_float.res:17:13-14
+
+  15 │ }
+  16 │ 
+  17 │ let x = <> {1.} </>
+  18 │ 
+
+  This has type: float
+  But it's expected to have type: React.element (defined as Jsx.element)
+  
+  In JSX, all content must be JSX elements. You can convert float to a JSX element with React.float.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors/expected/jsx_type_mismatch_int.res.expected b/tests/build_tests/super_errors/expected/jsx_type_mismatch_int.res.expected
new file mode 100644
index 0000000000..5a43157d03
--- /dev/null
+++ b/tests/build_tests/super_errors/expected/jsx_type_mismatch_int.res.expected
@@ -0,0 +1,13 @@
+
+  We've found a bug for you!
+  /.../fixtures/jsx_type_mismatch_int.res:17:13
+
+  15 │ }
+  16 │ 
+  17 │ let x = <> {1} </>
+  18 │ 
+
+  This has type: int
+  But it's expected to have type: React.element (defined as Jsx.element)
+  
+  In JSX, all content must be JSX elements. You can convert int to a JSX element with React.int.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors/expected/jsx_type_mismatch_string.res.expected b/tests/build_tests/super_errors/expected/jsx_type_mismatch_string.res.expected
new file mode 100644
index 0000000000..10d1d64dc7
--- /dev/null
+++ b/tests/build_tests/super_errors/expected/jsx_type_mismatch_string.res.expected
@@ -0,0 +1,13 @@
+
+  We've found a bug for you!
+  /.../fixtures/jsx_type_mismatch_string.res:17:13-14
+
+  15 │ }
+  16 │ 
+  17 │ let x = <> {""} </>
+  18 │ 
+
+  This has type: string
+  But it's expected to have type: React.element (defined as Jsx.element)
+  
+  In JSX, all content must be JSX elements. You can convert string to a JSX element with React.string.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_array_element.res b/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_array_element.res
new file mode 100644
index 0000000000..cebe870397
--- /dev/null
+++ b/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_array_element.res
@@ -0,0 +1,19 @@
+@@config({
+  flags: ["-bs-jsx", "4"],
+})
+
+module React = {
+  type element = Jsx.element
+  type componentLike<'props, 'return> = 'props => 'return
+  type component<'props> = Jsx.component<'props>
+
+  @module("react/jsx-runtime")
+  external jsx: (component<'props>, 'props) => element = "jsx"
+
+  type fragmentProps = {children?: element}
+  @module("react/jsx-runtime") external jsxFragment: component<fragmentProps> = "Fragment"
+
+  external string: string => element = "%identity"
+}
+
+let x = <> {[React.string("")]} </>
diff --git a/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_array_raw.res b/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_array_raw.res
new file mode 100644
index 0000000000..3a3c531b50
--- /dev/null
+++ b/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_array_raw.res
@@ -0,0 +1,17 @@
+@@config({
+  flags: ["-bs-jsx", "4"],
+})
+
+module React = {
+  type element = Jsx.element
+  type componentLike<'props, 'return> = 'props => 'return
+  type component<'props> = Jsx.component<'props>
+
+  @module("react/jsx-runtime")
+  external jsx: (component<'props>, 'props) => element = "jsx"
+
+  type fragmentProps = {children?: element}
+  @module("react/jsx-runtime") external jsxFragment: component<fragmentProps> = "Fragment"
+}
+
+let x = <> {[""]} </>
diff --git a/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_float.res b/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_float.res
new file mode 100644
index 0000000000..208eacac39
--- /dev/null
+++ b/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_float.res
@@ -0,0 +1,17 @@
+@@config({
+  flags: ["-bs-jsx", "4"],
+})
+
+module React = {
+  type element = Jsx.element
+  type componentLike<'props, 'return> = 'props => 'return
+  type component<'props> = Jsx.component<'props>
+
+  @module("react/jsx-runtime")
+  external jsx: (component<'props>, 'props) => element = "jsx"
+
+  type fragmentProps = {children?: element}
+  @module("react/jsx-runtime") external jsxFragment: component<fragmentProps> = "Fragment"
+}
+
+let x = <> {1.} </>
diff --git a/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_int.res b/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_int.res
new file mode 100644
index 0000000000..6836a4865d
--- /dev/null
+++ b/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_int.res
@@ -0,0 +1,17 @@
+@@config({
+  flags: ["-bs-jsx", "4"],
+})
+
+module React = {
+  type element = Jsx.element
+  type componentLike<'props, 'return> = 'props => 'return
+  type component<'props> = Jsx.component<'props>
+
+  @module("react/jsx-runtime")
+  external jsx: (component<'props>, 'props) => element = "jsx"
+
+  type fragmentProps = {children?: element}
+  @module("react/jsx-runtime") external jsxFragment: component<fragmentProps> = "Fragment"
+}
+
+let x = <> {1} </>
diff --git a/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_string.res b/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_string.res
new file mode 100644
index 0000000000..55ec5786e6
--- /dev/null
+++ b/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_string.res
@@ -0,0 +1,17 @@
+@@config({
+  flags: ["-bs-jsx", "4"],
+})
+
+module React = {
+  type element = Jsx.element
+  type componentLike<'props, 'return> = 'props => 'return
+  type component<'props> = Jsx.component<'props>
+
+  @module("react/jsx-runtime")
+  external jsx: (component<'props>, 'props) => element = "jsx"
+
+  type fragmentProps = {children?: element}
+  @module("react/jsx-runtime") external jsxFragment: component<fragmentProps> = "Fragment"
+}
+
+let x = <> {""} </>

From 9f03508f47bf89bbf58658cdc44d5f10232f76f2 Mon Sep 17 00:00:00 2001
From: Gabriel Nordeborn <gabbe.nord@gmail.com>
Date: Thu, 22 May 2025 14:46:12 +0200
Subject: [PATCH 6/9] note that you need to unwrap options in JSX

---
 compiler/ml/error_message_utils.ml              | 14 +++++++++++++-
 .../jsx_type_mismatch_option.res.expected       | 14 ++++++++++++++
 .../fixtures/jsx_type_mismatch_option.res       | 17 +++++++++++++++++
 3 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 tests/build_tests/super_errors/expected/jsx_type_mismatch_option.res.expected
 create mode 100644 tests/build_tests/super_errors/fixtures/jsx_type_mismatch_option.res

diff --git a/compiler/ml/error_message_utils.ml b/compiler/ml/error_message_utils.ml
index e16d635aaf..890675a391 100644
--- a/compiler/ml/error_message_utils.ml
+++ b/compiler/ml/error_message_utils.ml
@@ -259,7 +259,10 @@ let print_extra_type_clash_help ~extract_concrete_typedecl ~env loc ppf
       "@,\
        @,\
        Possible solutions: @,\
-       - Rewrite the object to a record, like: @{<info>%s@}@,"
+       - Rewrite the object to a record%s@{<info>%s@}@,"
+      (match suggested_rewrite with
+      | Some _ -> ", like: "
+      | None -> "")
       (match suggested_rewrite with
       | Some rewrite -> rewrite
       | None -> "")
@@ -312,6 +315,15 @@ let print_extra_type_clash_help ~extract_concrete_typedecl ~env loc ppf
       print_jsx_msg "string" (with_configured_jsx_module "string")
     | _ when Path.same p Predef.path_float ->
       print_jsx_msg "float" (with_configured_jsx_module "float")
+    | [_] when Path.same p Predef.path_option ->
+      fprintf ppf
+        "@,\
+         @,\
+         You need to unwrap this option to its underlying value first, then \
+         turn that value into a JSX element.@,\
+         For @{<info>None@}, you can use @{<info>%s@} to output nothing into \
+         JSX.@,"
+        (with_configured_jsx_module "null")
     | [tp] when Path.same p Predef.path_array && is_jsx_element tp ->
       print_jsx_msg
         ~extra:
diff --git a/tests/build_tests/super_errors/expected/jsx_type_mismatch_option.res.expected b/tests/build_tests/super_errors/expected/jsx_type_mismatch_option.res.expected
new file mode 100644
index 0000000000..fee1ae03c6
--- /dev/null
+++ b/tests/build_tests/super_errors/expected/jsx_type_mismatch_option.res.expected
@@ -0,0 +1,14 @@
+
+  We've found a bug for you!
+  /.../fixtures/jsx_type_mismatch_option.res:17:13-16
+
+  15 │ }
+  16 │ 
+  17 │ let x = <> {None} </>
+  18 │ 
+
+  This has type: option<'a>
+  But it's expected to have type: React.element (defined as Jsx.element)
+  
+  You need to unwrap this option to its underlying value first, then turn that value into a JSX element.
+  For None, you can use React.null to output nothing into JSX.
\ No newline at end of file
diff --git a/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_option.res b/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_option.res
new file mode 100644
index 0000000000..334d11978c
--- /dev/null
+++ b/tests/build_tests/super_errors/fixtures/jsx_type_mismatch_option.res
@@ -0,0 +1,17 @@
+@@config({
+  flags: ["-bs-jsx", "4"],
+})
+
+module React = {
+  type element = Jsx.element
+  type componentLike<'props, 'return> = 'props => 'return
+  type component<'props> = Jsx.component<'props>
+
+  @module("react/jsx-runtime")
+  external jsx: (component<'props>, 'props) => element = "jsx"
+
+  type fragmentProps = {children?: element}
+  @module("react/jsx-runtime") external jsxFragment: component<fragmentProps> = "Fragment"
+}
+
+let x = <> {None} </>

From 4f302256d1af674579096ad87272cea340e08324 Mon Sep 17 00:00:00 2001
From: Gabriel Nordeborn <gabbe.nord@gmail.com>
Date: Thu, 22 May 2025 16:43:04 +0200
Subject: [PATCH 7/9] fix

---
 compiler/ml/error_message_utils.ml                              | 2 +-
 .../super_errors/expected/math_operator_float.res.expected      | 2 +-
 .../build_tests/super_errors/expected/primitives7.res.expected  | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/compiler/ml/error_message_utils.ml b/compiler/ml/error_message_utils.ml
index 890675a391..b8eac99181 100644
--- a/compiler/ml/error_message_utils.ml
+++ b/compiler/ml/error_message_utils.ml
@@ -161,7 +161,7 @@ let print_extra_type_clash_help ~extract_concrete_typedecl ~env loc ppf
         \  Floats and ints have their own mathematical operators. This means \
          you cannot %s a float and an int without converting between the two.\n\n\
         \  Possible solutions:\n\
-        \  - Ensure all values in this calculation has the type @{<info>%s@}. \
+        \  - Ensure all values in this calculation have the type @{<info>%s@}. \
          You can convert between floats and ints via @{<info>Float.toInt@} and \
          @{<info>Int.fromFloat@}."
         operator_text
diff --git a/tests/build_tests/super_errors/expected/math_operator_float.res.expected b/tests/build_tests/super_errors/expected/math_operator_float.res.expected
index 28b4a7e7ec..fe5df9c95c 100644
--- a/tests/build_tests/super_errors/expected/math_operator_float.res.expected
+++ b/tests/build_tests/super_errors/expected/math_operator_float.res.expected
@@ -13,7 +13,7 @@
   Floats and ints have their own mathematical operators. This means you cannot add a float and an int without converting between the two.
 
   Possible solutions:
-  - Ensure all values in this calculation has the type float. You can convert between floats and ints via Float.toInt and Int.fromFloat.
+  - Ensure all values in this calculation have the type float. You can convert between floats and ints via Float.toInt and Int.fromFloat.
   - Change the operator to +, which works on int
   
   You can convert int to float with Int.toFloat.
diff --git a/tests/build_tests/super_errors/expected/primitives7.res.expected b/tests/build_tests/super_errors/expected/primitives7.res.expected
index 6f5cd351a3..bfe3cce7c0 100644
--- a/tests/build_tests/super_errors/expected/primitives7.res.expected
+++ b/tests/build_tests/super_errors/expected/primitives7.res.expected
@@ -13,7 +13,7 @@
   Floats and ints have their own mathematical operators. This means you cannot add a float and an int without converting between the two.
 
   Possible solutions:
-  - Ensure all values in this calculation has the type float. You can convert between floats and ints via Float.toInt and Int.fromFloat.
+  - Ensure all values in this calculation have the type float. You can convert between floats and ints via Float.toInt and Int.fromFloat.
   - Change the operator to +, which works on int
   
   You can convert int to float with Int.toFloat.

From aa1856a0e3675cafe8cc2495b18da0ec9c6e8668 Mon Sep 17 00:00:00 2001
From: Gabriel Nordeborn <gabbe.nord@gmail.com>
Date: Thu, 22 May 2025 18:05:45 +0200
Subject: [PATCH 8/9] add simple error message indicating dict syntax

---
 compiler/ml/error_message_utils.ml                  |  4 ++++
 .../super_errors/expected/dict_helper.res.expected  | 13 +++++++++++++
 .../super_errors/fixtures/dict_helper.res           |  3 +++
 3 files changed, 20 insertions(+)
 create mode 100644 tests/build_tests/super_errors/expected/dict_helper.res.expected
 create mode 100644 tests/build_tests/super_errors/fixtures/dict_helper.res

diff --git a/compiler/ml/error_message_utils.ml b/compiler/ml/error_message_utils.ml
index b8eac99181..ebc138284f 100644
--- a/compiler/ml/error_message_utils.ml
+++ b/compiler/ml/error_message_utils.ml
@@ -223,6 +223,10 @@ let print_extra_type_clash_help ~extract_concrete_typedecl ~env loc ppf
       \  - Use a tuple, if your array is of fixed length. Tuples can mix types \
        freely, and compiles to a JavaScript array. Example of a tuple: `let \
        myTuple = (10, \"hello\", 15.5, true)"
+  | _, Some (_, {desc = Tconstr (p2, _, _)}) when Path.same Predef.path_dict p2
+    ->
+    fprintf ppf
+      "@,@,Dicts are written like: @{<info>dict{\"a\": 1, \"b\": 2}@}@,"
   | _, Some ({Types.desc = Tconstr (_p1, _, _)}, {desc = Tconstr (p2, _, _)})
     when Path.same Predef.path_unit p2 ->
     fprintf ppf
diff --git a/tests/build_tests/super_errors/expected/dict_helper.res.expected b/tests/build_tests/super_errors/expected/dict_helper.res.expected
new file mode 100644
index 0000000000..b2e35e89b7
--- /dev/null
+++ b/tests/build_tests/super_errors/expected/dict_helper.res.expected
@@ -0,0 +1,13 @@
+
+  We've found a bug for you!
+  /.../fixtures/dict_helper.res:3:11-23
+
+  1 │ external takesDict: dict<string> => unit = "takesDict"
+  2 │ 
+  3 │ takesDict({"test": "1"})
+  4 │ 
+
+  This has type: {"test": string}
+  But it's expected to have type: dict<string>
+  
+  Dicts are written like: dict{"a": 1, "b": 2}
\ No newline at end of file
diff --git a/tests/build_tests/super_errors/fixtures/dict_helper.res b/tests/build_tests/super_errors/fixtures/dict_helper.res
new file mode 100644
index 0000000000..85e2ba4fea
--- /dev/null
+++ b/tests/build_tests/super_errors/fixtures/dict_helper.res
@@ -0,0 +1,3 @@
+external takesDict: dict<string> => unit = "takesDict"
+
+takesDict({"test": "1"})

From 2f2dcb74a1b687837c2a3939575fa60f8b978604 Mon Sep 17 00:00:00 2001
From: Gabriel Nordeborn <gabbe.nord@gmail.com>
Date: Thu, 22 May 2025 18:16:05 +0200
Subject: [PATCH 9/9] changelog

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9a5998097a..b44e383e83 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,7 @@
 - Suggest awaiting promise before using it when types mismatch. https://github.com/rescript-lang/rescript/pull/7498
 - Complete from `RegExp` stdlib module for regexes. https://github.com/rescript-lang/rescript/pull/7425
 - Allow oneliner formatting when including module with single type alias. https://github.com/rescript-lang/rescript/pull/7502
+- Improve error messages for JSX type mismatches, passing objects where record is expected, passing array literal where tuple is expected, and more. https://github.com/rescript-lang/rescript/pull/7500
 
 # 12.0.0-alpha.13