Brush up a few object related error messages

CHANGELOG.md

@@ -22,6 +22,7 @@
 #### :nail_care: Polish
 
 - Better error message for when trying to await something that is not a promise. https://github.com/rescript-lang/rescript/pull/7561
+- Better error messages for object field missing and object field type mismatches. https://github.com/rescript-lang/rescript/pull/7580
 
 #### :house: Internal
 

compiler/ml/printtyp.ml

@@ -1352,13 +1352,29 @@ let explanation unif t3 t4 ppf =
     fprintf ppf "@,Self type cannot be unified with a closed object type"
   | _, Tfield (lab, _, _, _) when lab = dummy_method ->
     fprintf ppf "@,Self type cannot be unified with a closed object type"
-  | Tfield (l, _, _, {desc = Tnil}), Tfield (l', _, _, {desc = Tnil})
+  | Tfield (l, _, f1, {desc = Tnil}), Tfield (l', _, f2, {desc = Tnil})
     when l = l' ->
-    fprintf ppf "@,Types for method %s are incompatible" l
-  | (Tnil | Tconstr _), Tfield (l, _, _, _) ->
-    fprintf ppf "@,@[The first object type has no field %s@]" l
-  | Tfield (l, _, _, _), (Tnil | Tconstr _) ->
-    fprintf ppf "@,@[The second object type has no field %s@]" l
+    fprintf ppf
+      "@,\
+       @,\
+       Types for field @{<info>\"%s\"@} are incompatible:@,\
+       Field @{<info>\"%s\"@} in the passed object has type @{<error>%a@}, but \
+       is expected to have type @{<info>%a@}."
+      l l type_expr f1 type_expr f2
+  | (Tnil | Tconstr _), Tfield (l, _, f1, _) ->
+    fprintf ppf
+      "@,\
+       @,\
+       @[The first object is expected to have a field @{<info>\"%s\"@} of type \
+       @{<info>%a@}, but it does not.@]"
+      l type_expr f1
+  | Tfield (l, _, f1, _), (Tnil | Tconstr _) ->
+    fprintf ppf
+      "@,\
+       @,\
+       @[The second object is expected to have a field @{<info>\"%s\"@} of \
+       type @{<info>%a@}, but it does not.@]"
+      l type_expr f1
   | Tnil, Tconstr _ | Tconstr _, Tnil ->
     fprintf ppf
       "@,@[The %s object type has an abstract row, it cannot be closed@]"

tests/build_tests/super_errors/expected/object_field_mismatch.res.expected

@@ -0,0 +1,18 @@
+
+  We've found a bug for you!
+  /.../fixtures/object_field_mismatch.res:11:20-22
+
+   9 │   }
+  10 │ 
+  11 │   let _ = doStuff(~ctx)
+  12 │ }
+  13 │ 
+
+  This has type: {"multiply": (string, string) => string}
+  But this function argument ~ctx is expecting:
+    {.."multiply": (int, int) => int}
+
+  Types for field "multiply" are incompatible:
+  Field "multiply" in the passed object has type (string, string) => string, but is expected to have type (int, int) => int.
+
+  You can convert string to int with Int.fromString.

tests/build_tests/super_errors/expected/object_field_missing.res.expected

@@ -0,0 +1,15 @@
+
+  We've found a bug for you!
+  /.../fixtures/object_field_missing.res:11:20-22
+
+   9 │   }
+  10 │ 
+  11 │   let _ = doStuff(~ctx)
+  12 │ }
+  13 │ 
+
+  This has type: {"log": (string, string) => string}
+  But this function argument ~ctx is expecting:
+    {.."multiply": (int, int) => int}
+
+  The first object is expected to have a field "multiply" of type (int, int) => int, but it does not.

tests/build_tests/super_errors/fixtures/object_field_mismatch.res

@@ -0,0 +1,12 @@
+let doStuff = (~ctx) => {
+  let multiply: (int, int) => int = ctx["multiply"]
+  multiply(1, 2)
+}
+
+let main = () => {
+  let ctx = {
+    "multiply": (a, b) => a ++ b,
+  }
+
+  let _ = doStuff(~ctx)
+}

tests/build_tests/super_errors/fixtures/object_field_missing.res

@@ -0,0 +1,12 @@
+let doStuff = (~ctx) => {
+  let multiply: (int, int) => int = ctx["multiply"]
+  multiply(1, 2)
+}
+
+let main = () => {
+  let ctx = {
+    "log": (a, b) => a ++ b,
+  }
+
+  let _ = doStuff(~ctx)
+}