feat: conf add FillDefault func

core/conf/config.go

@@ -13,12 +13,17 @@ import (
 	"github.com/zeromicro/go-zero/internal/encoding"
 )
 
-var loaders = map[string]func([]byte, any) error{
-	".json": LoadFromJsonBytes,
-	".toml": LoadFromTomlBytes,
-	".yaml": LoadFromYamlBytes,
-	".yml":  LoadFromYamlBytes,
-}
+const jsonTagKey = "json"
+
+var (
+	fillDefaultUnmarshaler = mapping.NewUnmarshaler(jsonTagKey, mapping.WithDefault())
+	loaders                = map[string]func([]byte, any) error{
+		".json": LoadFromJsonBytes,
+		".toml": LoadFromTomlBytes,
+		".yaml": LoadFromYamlBytes,
+		".yml":  LoadFromYamlBytes,
+	}
+)
 
 // children and mapField should not be both filled.
 // named fields and map cannot be bound to the same field name.
@@ -27,6 +32,11 @@ type fieldInfo struct {
 	mapField *fieldInfo
 }
 
+// FillDefault fills the default values for the given v.
+func FillDefault(v any) error {
+	return fillDefaultUnmarshaler.Unmarshal(map[string]any{}, v)
+}
+
 // Load loads config into v from file, .json, .yaml and .yml are acceptable.
 func Load(file string, v interface{}, opts ...Option) error {
 	content, err := os.ReadFile(file)

core/conf/config_test.go

@@ -1039,3 +1039,43 @@ func createTempFile(ext, text string) (string, error) {
 
 	return filename, nil
 }
+
+func TestFillDefaultUnmarshal(t *testing.T) {
+	t.Run("nil", func(t *testing.T) {
+		type St struct{}
+		err := FillDefault(St{})
+		assert.Error(t, err)
+	})
+
+	t.Run("not nil", func(t *testing.T) {
+		type St struct{}
+		err := FillDefault(&St{})
+		assert.NoError(t, err)
+	})
+
+	t.Run("default", func(t *testing.T) {
+		type St struct {
+			A string `json:",default=a"`
+			B string
+		}
+		var st St
+		err := FillDefault(&st)
+		assert.NoError(t, err)
+		assert.Equal(t, st.A, "a")
+	})
+
+	t.Run("env", func(t *testing.T) {
+		type St struct {
+			A string `json:",default=a"`
+			B string
+			C string `json:",env=TEST_C"`
+		}
+		t.Setenv("TEST_C", "c")
+
+		var st St
+		err := FillDefault(&st)
+		assert.NoError(t, err)
+		assert.Equal(t, st.A, "a")
+		assert.Equal(t, st.C, "c")
+	})
+}