Go Reflection Get current field name but error on untyped string with mismatched types

Question content

type Issue struct {
  SysId  uuid.UUID  `json:"sysid" maelstrom:"required"`
}

func (i *Issue) Unmarshal(data []byte) error {
  err := json.Unmarshal(data, i)
  if err != nil {
    slog.Error(err.Error())
    return err
  }
  fields := reflect.ValueOf(i).Elem()
  for i := 0; i < fields.NumField(); i++ {
    maelstromTags := fields.Type().Field(i).Tag.Get("maelstrom")
    if strings.Contains(maelstromTags, "required") && fields.Field(i).IsZero() {
      return errors.New("Required field is missing." + fields.Field(i))
    }
  }
  return nil
}

In the above code, one line:

return errors.New("Required field is missing." + fields.Field(i))

I want to include the name of the current field in the error message.

This is the error I receive:

<code>
invalid operation: "Required field is missing." + fields.Field(i) (mismatched types untyped string and reflect.Value)
</code>

I also tried this:

return errors.New("Required field is missing." + fields.Field(i).String)

But I understand:

<code>
invalid operation: "Required field is missing." + fields.Field(i).String (mismatched types untyped string and func() string)
</code>

I also tried this:

return errors.New("Required field is missing." + string(fields.Field(i)))

But I understand:

<code>
cannot convert fields.Field(i) (value of type reflect.Value) to type string [InvalidConversion]
</code>

Can anyone point me in the right direction or provide a solution? Thanks!

Correct answer

Get StructField from the type. Get field name from StructField.

return fmt.Errorf("required field is missing: %s", fields.Type().Field(i).Name)

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