feat: allow config to unmarshal regexes as strings

config/config.go

@@ -5,6 +5,8 @@ import (
 	"io"
 	"io/fs"
 	"os"
+	"reflect"
+	"regexp"
 	"strings"
 
 	"github.com/moov-io/base/log"
@@ -125,4 +127,14 @@ func LoadEnvironmentFile(logger log.Logger, envVar string, v *viper.Viper) error
 func overwriteConfig(cfg *mapstructure.DecoderConfig) {
 	cfg.ErrorUnused = true
 	cfg.ZeroFields = true
+
+	cfg.DecodeHook = func(t1 reflect.Type, t2 reflect.Type, value interface{}) (interface{}, error) {
+		decodingRegex := t2.String() == "regexp.Regexp"
+		if decodingRegex {
+			if stringValue, ok := value.(string); ok {
+				return regexp.Compile(stringValue)
+			}
+		}
+		return value, nil
+	}
 }

config/config_test.go

@@ -2,6 +2,7 @@ package config_test
 
 import (
 	"path/filepath"
+	"regexp"
 	"testing"
 
 	"github.com/moov-io/base"
@@ -22,6 +23,8 @@ type ConfigModel struct {
 	Zero    string
 
 	Widgets map[string]Widget
+
+	Search SearchConfig
 }
 
 type Widget struct {
@@ -47,6 +50,10 @@ type Nested3 struct {
 	Value string
 }
 
+type SearchConfig struct {
+	Patterns []*regexp.Regexp
+}
+
 func Test_Load(t *testing.T) {
 	t.Setenv(config.APP_CONFIG, filepath.Join("..", "configs", "config.app.yml"))
 	t.Setenv(config.APP_CONFIG_SECRETS, filepath.Join("..", "configs", "config.secrets.yml"))
@@ -135,3 +142,18 @@ func Test_WidgetsConfig(t *testing.T) {
 	require.Equal(t, "p2", w.Credentials.Password)
 	require.Equal(t, "v1", w.Nested.Nested2.Nested3.Value)
 }
+
+func Test_ReadRegexp(t *testing.T) {
+	t.Setenv(config.APP_CONFIG, filepath.Join("testdata", "with-regexp.yml"))
+	t.Setenv(config.APP_CONFIG_SECRETS, "")
+
+	cfg := &GlobalConfigModel{}
+
+	service := config.NewService(log.NewDefaultLogger())
+	err := service.LoadFromFS(cfg, base.ConfigDefaults)
+	require.Nil(t, err)
+
+	patterns := cfg.Config.Search.Patterns
+	require.Len(t, patterns, 1)
+	require.Equal(t, "a(b+)c", patterns[0].String())
+}

config/testdata/with-regexp.yml

@@ -0,0 +1,4 @@
+Config:
+  Search:
+    Patterns:
+      - "a(b+)c"