Fix field error

Author: lpil

src/gleam/dynamic.gleam

@@ -437,8 +437,9 @@ if javascript {
 ///
 pub fn field(named name: a, of inner_type: Decoder(t)) -> Decoder(t) {
   fn(value) {
-    try value = decode_field(value, name)
-    inner_type(value)
+    value
+    |> decode_field(name)
+    |> result.then(inner_type)
     |> map_errors(push_path(_, name))
   }
 }

src/gleam_stdlib.erl

@@ -49,8 +49,10 @@ iodata_append(Iodata, String) -> [Iodata, String].
 
 identity(X) -> X.
 
-decode_error_msg(Expected, Data) ->
-    {error, [{decode_error, Expected, classify_dynamic(Data), []}]}.
+decode_error_msg(Expected, Data) when is_binary(Expected) ->
+    decode_error(Expected, classify_dynamic(Data)).
+decode_error(Expected, Got) when is_binary(Expected) andalso is_binary(Got) ->
+    {error, [{decode_error, Expected, Got, []}]}.
 
 classify_dynamic(X) when is_atom(X) -> <<"Atom">>;
 classify_dynamic(X) when is_binary(X) -> <<"String">>;
@@ -94,7 +96,8 @@ decode_list(Data) -> decode_error_msg(<<"List">>, Data).
 decode_field(Data, Key) ->
     case Data of
         #{Key := Value} -> {ok, Value};
-        _ -> decode_error_msg("object", Data)
+        _ -> 
+            decode_error(<<"field"/utf8>>, <<"nothing"/utf8>>)
     end.
 
 size_of_tuple(Data) -> tuple_size(Data).

src/gleam_stdlib.mjs

@@ -494,10 +494,12 @@ export function classify_dynamic(data) {
 }
 
 function decoder_error(expected, got) {
+  return decoder_error_no_classify(expected, classify_dynamic(got));
+}
+
+function decoder_error_no_classify(expected, got) {
   return new Error(
-    List.fromArray([
-      new DecodeError(expected, classify_dynamic(got), List.fromArray([])),
-    ])
+    List.fromArray([new DecodeError(expected, got, List.fromArray([]))])
   );
 }
 
@@ -560,7 +562,7 @@ export function decode_option(data, decoder) {
 }
 
 export function decode_field(value, name) {
-  let error = () => decoder_error("object", value);
+  let error = () => decoder_error_no_classify("field", "nothing");
   if (value instanceof Map) {
     let entry = value.get(name);
     return entry.isOk() ? entry : error();

test/gleam/dynamic_test.gleam

@@ -260,7 +260,7 @@ if javascript {
     |> dynamic.from
     |> dynamic.field("Nope", dynamic.int)
     |> should.equal(Error([
-      DecodeError(expected: "object", found: "Result", path: []),
+      DecodeError(expected: "field", found: "nothing", path: ["Nope"]),
     ]))
   }
 }
@@ -289,22 +289,30 @@ pub fn field_test() {
   |> map.insert("ok", 3)
   |> dynamic.from
   |> dynamic.field("ok", dynamic.string)
-  |> should.be_error
+  |> should.equal(Error([
+    DecodeError(expected: "String", found: "Int", path: ["ok"]),
+  ]))
 
   map.new()
   |> dynamic.from
   |> dynamic.field("ok", dynamic.int)
-  |> should.be_error
+  |> should.equal(Error([
+    DecodeError(expected: "field", found: "nothing", path: ["ok"]),
+  ]))
 
   1
   |> dynamic.from
   |> dynamic.field("ok", dynamic.int)
-  |> should.be_error
+  |> should.equal(Error([
+    DecodeError(expected: "field", found: "nothing", path: ["ok"]),
+  ]))
 
   []
   |> dynamic.from
   |> dynamic.field("ok", dynamic.int)
-  |> should.be_error
+  |> should.equal(Error([
+    DecodeError(expected: "field", found: "nothing", path: ["ok"]),
+  ]))
 }
 
 pub fn element_test() {