Support map[T]encoding.TextUnmarshaler

env.go

@@ -699,9 +699,35 @@ func handleMap(field reflect.Value, value string, sf reflect.StructField, funcMa
 	elemType := sf.Type.Elem()
 	elemParserFunc, ok := funcMap[elemType]
 	if !ok {
-		elemParserFunc, ok = defaultBuiltInParsers[elemType.Kind()]
-		if !ok {
-			return newNoParserError(sf)
+		rawType := elemType
+		isPtr := reflect.Ptr == rawType.Kind()
+
+		if isPtr {
+			rawType = rawType.Elem()
+		}
+
+		if _, ok := reflect.New(rawType).Interface().(encoding.TextUnmarshaler); ok {
+			if isPtr {
+				elemParserFunc = func(v string) (any, error) {
+					ptr := reflect.New(rawType)
+					unmarshaler := ptr.Interface().(encoding.TextUnmarshaler)
+					err := unmarshaler.UnmarshalText([]byte(v))
+
+					return unmarshaler, err
+				}
+			} else {
+				elemParserFunc = func(v string) (any, error) {
+					ptr := reflect.New(rawType)
+					err := ptr.Interface().(encoding.TextUnmarshaler).UnmarshalText([]byte(v))
+
+					return ptr.Elem().Interface(), err
+				}
+			}
+		} else {
+			elemParserFunc, ok = defaultBuiltInParsers[elemType.Kind()]
+			if !ok {
+				return newNoParserError(sf)
+			}
 		}
 	}
 

env_test.go

@@ -456,6 +456,34 @@ func TestParsesEnvInvalidMap(t *testing.T) {
 	isTrue(t, errors.Is(err, ParseError{}))
 }
 
+func TestParseMapOfUnmarshalerValues(t *testing.T) {
+	type mapOfUnmarshaler map[string]unmarshaler
+
+	type config struct {
+		Durations mapOfUnmarshaler `env:"DURATIONS"`
+	}
+
+	t.Setenv("DURATIONS", "year:8760h")
+
+	var cfg config
+	isNoErr(t, Parse(&cfg))
+	isEqual(t, mapOfUnmarshaler{"year": {Duration: 365 * 24 * time.Hour}}, cfg.Durations)
+}
+
+func TestParseMapOfUnmarshalerPtrs(t *testing.T) {
+	type mapOfUnmarshaler map[string]*unmarshaler
+
+	type config struct {
+		Durations mapOfUnmarshaler `env:"DURATIONS"`
+	}
+
+	t.Setenv("DURATIONS", "year:8760h")
+
+	var cfg config
+	isNoErr(t, Parse(&cfg))
+	isEqual(t, mapOfUnmarshaler{"year": {Duration: 365 * 24 * time.Hour}}, cfg.Durations)
+}
+
 func TestParseCustomMapType(t *testing.T) {
 	type custommap map[string]bool