Add support of nested struct in map store by pointer

cleanenv.go

@@ -331,6 +331,40 @@ func readStructMetadata(cfgRoot interface{}) ([]structMeta, error) {
 				separator string
 			)
 
+			// process structs in map (except of supported ones)
+			if fld := s.Field(idx); fld.Kind() == reflect.Map && validStructs[fld.Type().Elem()] == nil {
+				mapElem := fld.Type().Elem()
+
+				if mapElem.Kind() == reflect.Struct {
+					// I don't see a way to support structures in maps at the moment.
+					// Perhaps this requires a major change in library logic.
+					return nil, fmt.Errorf("struct in map value is not supported, use pointer to struct instead")
+				}
+
+				isPointerToStruct := mapElem.Kind() == reflect.Ptr && mapElem.Elem().Kind() == reflect.Struct
+				if isPointerToStruct {
+					// Map values are not addressable, and we can't pass them to cfgNode.
+					// So we need to create a new map with new struct values.
+					newMap := reflect.MakeMap(fld.Type())
+					for _, key := range fld.MapKeys() {
+						value := fld.MapIndex(key)
+						// unwrap pointer
+						if value.Kind() == reflect.Ptr {
+							value = value.Elem()
+						}
+
+						newStruct := reflect.New(value.Type()).Elem()
+						newStruct.Set(value)
+						newMap.SetMapIndex(key, newStruct.Addr())
+
+						prefix, _ := fType.Tag.Lookup(TagEnvPrefix)
+						cfgStack = append(cfgStack, cfgNode{newStruct.Addr().Interface(), sPrefix + prefix})
+					}
+					// replace old map with new one
+					fld.Set(newMap)
+				}
+			}
+
 			// process nested structure (except of supported ones)
 			if fld := s.Field(idx); fld.Kind() == reflect.Struct {
 				//skip unexported

cleanenv_test.go

@@ -1191,8 +1191,8 @@ func TestTimeLocation(t *testing.T) {
 func TestSkipUnexportedField(t *testing.T) {
 	conf := struct {
 		Database struct {
-			Host        string `yaml:"host" env:"DB_HOST" env-description:"Database host"`
-			Port        string `yaml:"port" env:"DB_PORT" env-description:"Database port"`
+			Host string `yaml:"host" env:"DB_HOST" env-description:"Database host"`
+			Port string `yaml:"port" env:"DB_PORT" env-description:"Database port"`
 		} `yaml:"database"`
 		server struct {
 			Host string `yaml:"host" env:"SRV_HOST,HOST" env-description:"Server host" env-default:"localhost"`
@@ -1210,3 +1210,59 @@ func TestSkipUnexportedField(t *testing.T) {
 		t.Fatal("expect value on exported fields")
 	}
 }
+
+func TestReadConfig_NestedStructInMap(t *testing.T) {
+	tmpFile, err := os.CreateTemp(t.TempDir(), "*.yaml")
+	if err != nil {
+		t.Fatal("create temp file:", err)
+	}
+
+	text := []byte(`
+children: 
+  first:
+    number: 1`)
+	if _, err = tmpFile.Write(text); err != nil {
+		t.Fatal("write to temp file:", err)
+	}
+
+	t.Run("nested pointer to struct", func(t *testing.T) {
+		type (
+			Child struct {
+				Number        int64 `yaml:"number"`
+				DefaultNumber int64 `yaml:"default_number" env-default:"10"`
+			}
+			Parent struct {
+				Children map[string]*Child `yaml:"children"`
+			}
+		)
+		expectedConfig := Parent{
+			Children: map[string]*Child{"first": {Number: 1, DefaultNumber: 10}},
+		}
+
+		var p Parent
+		if err = ReadConfig(tmpFile.Name(), &p); err != nil {
+			t.Fatal("read config:", err)
+		}
+		if err == nil && !reflect.DeepEqual(p, expectedConfig) {
+			t.Errorf("wrong data: %+v, want: %+v", p, expectedConfig)
+		}
+
+	})
+
+	t.Run("nested struct", func(t *testing.T) {
+		type (
+			Child struct {
+				Number        int64 `yaml:"number"`
+				DefaultNumber int64 `yaml:"default_number" env-default:"10"`
+			}
+			Parent struct {
+				Children map[string]Child `yaml:"children"`
+			}
+		)
+
+		var p Parent
+		if err = ReadConfig(tmpFile.Name(), &p); err == nil {
+			t.Error("expected error, got nil")
+		}
+	})
+}