show field name for required and default check

Author: vgough

flagset.go

@@ -262,7 +262,7 @@ func (f *FlagSetFiller) processField(flagSet *flag.FlagSet, fieldRef any,
 	// Check for required tag and validate it doesn't conflict with default
 	_, hasRequiredTag := tag.Lookup(TagRequired)
 	if hasRequiredTag && hasDefaultTag {
-		return fmt.Errorf("field cannot be both required and have a default value")
+		return fmt.Errorf("field %q cannot be both required and have a default value", name)
 	}
 
 	var renamed string

flagset_test.go

@@ -1048,6 +1048,7 @@ func TestRequiredFieldWithDefault(t *testing.T) {
 	err := filler.Fill(&flagset, &config)
 	assert.Error(t, err)
 	assert.Contains(t, err.Error(), "cannot be both required and have a default")
+	assert.Contains(t, err.Error(), "\"Host\"")
 }
 
 func TestMultipleRequiredFields(t *testing.T) {