Making the field name matching when merging respect the toml struct tag.

If the field has a toml struct tag, don't try fuzzy matching, thanks to
@ekini.

config.go

@@ -369,12 +369,29 @@ func PrintOutputConfig(name string) error {
 	return nil
 }
 
-// Used for fuzzy matching struct field names in FieldByNameFunc calls below
+// Find the field with a name matching fieldName, respecting the struct tag and ignoring case and underscores.
-func fieldMatch(field string) func(string) bool {
+// If no field is found, return the zero reflect.Value, which should be checked for with .IsValid().
-	return func(name string) bool {
+func findField(fieldName string, value reflect.Value) reflect.Value {
 	r := strings.NewReplacer("_", "")
-		return strings.ToLower(name) == strings.ToLower(r.Replace(field))
+	vType := value.Type()
+	for i := 0; i < vType.NumField(); i++ {
+		fieldType := vType.Field(i)
+
+		// if we have toml tag, use it
+		if tag := fieldType.Tag.Get("toml"); tag != "" {
+			if tag == "-" { // omit
+				continue
 			}
+			if tag == fieldName {
+				return value.Field(i)
+			}
+		} else {
+			if strings.ToLower(fieldType.Name) == strings.ToLower(r.Replace(fieldName)) {
+				return value.Field(i)
+			}
+		}
+	}
+	return reflect.Value{}
 }
 
 // A very limited merge. Merges the fields named in the fields parameter, replacing most values, but appending to arrays.
@@ -388,15 +405,15 @@ func mergeStruct(base, overlay interface{}, fields []string) error {
 		return fmt.Errorf("Tried to merge two different types: %v and %v", baseValue.Type(), overlayValue.Type())
 	}
 	for _, field := range fields {
-		overlayFieldValue := overlayValue.FieldByNameFunc(fieldMatch(field))
+		overlayFieldValue := findField(field, overlayValue)
 		if !overlayFieldValue.IsValid() {
 			return fmt.Errorf("could not find field in %v matching %v", overlayValue.Type(), field)
 		}
+		baseFieldValue := findField(field, baseValue)
 		if overlayFieldValue.Kind() == reflect.Slice {
-			baseFieldValue := baseValue.FieldByNameFunc(fieldMatch(field))
 			baseFieldValue.Set(reflect.AppendSlice(baseFieldValue, overlayFieldValue))
 		} else {
-			baseValue.FieldByNameFunc(fieldMatch(field)).Set(overlayFieldValue)
+			baseFieldValue.Set(overlayFieldValue)
 		}
 	}
 	return nil

config_test.go

@@ -16,22 +16,6 @@ import (
 	"github.com/stretchr/testify/suite"
 )
 
-func TestConfig_fieldMatch(t *testing.T) {
-	assert := assert.New(t)
-
-	matchFunc := fieldMatch("testfield")
-	assert.True(matchFunc("testField"), "testfield should match testField")
-	assert.True(matchFunc("TestField"), "testfield should match TestField")
-	assert.True(matchFunc("TESTFIELD"), "testfield should match TESTFIELD")
-	assert.False(matchFunc("OtherField"), "testfield should not match OtherField")
-
-	matchFunc = fieldMatch("test_field")
-	assert.True(matchFunc("testField"), "test_field should match testField")
-	assert.True(matchFunc("TestField"), "test_field should match TestField")
-	assert.True(matchFunc("TESTFIELD"), "test_field should match TESTFIELD")
-	assert.False(matchFunc("OtherField"), "test_field should not match OtherField")
-}
-
 type subTest struct {
 	AField       string
 	AnotherField int
@@ -40,7 +24,7 @@ type test struct {
 	StringField     string
 	IntegerField    int
 	FloatField      float32
-	BooleanField    bool
+	BooleansField   bool `toml:"boolean_field"`
 	DatetimeField   time.Time
 	ArrayField      []string
 	TableArrayField []subTest
@@ -67,7 +51,7 @@ func (s *MergeStructSuite) SetupTest() {
 		StringField:   "one",
 		IntegerField:  1,
 		FloatField:    1.1,
-		BooleanField:  false,
+		BooleansField: false,
 		DatetimeField: time.Date(1963, time.August, 28, 17, 0, 0, 0, time.UTC),
 		ArrayField:    []string{"one", "two", "three"},
 		TableArrayField: []subTest{
@@ -85,7 +69,7 @@ func (s *MergeStructSuite) SetupTest() {
 		StringField:   "two",
 		IntegerField:  2,
 		FloatField:    2.2,
-		BooleanField:  true,
+		BooleansField: true,
 		DatetimeField: time.Date(1965, time.March, 25, 17, 0, 0, 0, time.UTC),
 		ArrayField:    []string{"four", "five", "six"},
 		TableArrayField: []subTest{
@@ -114,7 +98,7 @@ func (s *MergeStructSuite) TestFullMerge() {
 		StringField:   "two",
 		IntegerField:  2,
 		FloatField:    2.2,
-		BooleanField:  true,
+		BooleansField: true,
 		DatetimeField: time.Date(1965, time.March, 25, 17, 0, 0, 0, time.UTC),
 		ArrayField:    []string{"one", "two", "three", "four", "five", "six"},
 		TableArrayField: []subTest{
@@ -149,7 +133,7 @@ func (s *MergeStructSuite) TestPartialMergeWithoutSlices() {
 		StringField:   "two",
 		IntegerField:  1,
 		FloatField:    2.2,
-		BooleanField:  false,
+		BooleansField: false,
 		DatetimeField: time.Date(1965, time.March, 25, 17, 0, 0, 0, time.UTC),
 		ArrayField:    []string{"one", "two", "three"},
 		TableArrayField: []subTest{
@@ -176,7 +160,7 @@ func (s *MergeStructSuite) TestPartialMergeWithSlices() {
 		StringField:   "two",
 		IntegerField:  1,
 		FloatField:    2.2,
-		BooleanField:  false,
+		BooleansField: false,
 		DatetimeField: time.Date(1965, time.March, 25, 17, 0, 0, 0, time.UTC),
 		ArrayField:    []string{"one", "two", "three"},
 		TableArrayField: []subTest{