codec: fix omitempty when array has all zero values (even if len != 0)

An array is empty if it has all zero values (even if len != 0)

Previously, we treated an array as empty only if len == 0. That is incorrect.

Instead, an array is empty if it is equal to its zero value.

This is now honored, making omitEmpty work effectively for arrays also.

codec/helper_not_unsafe.go

@@ -114,8 +114,19 @@ func isEmptyValue(v reflect.Value, tinfos *TypeInfos, recursive bool) bool {
 	switch v.Kind() {
 	case reflect.Invalid:
 		return true
-	case reflect.Array, reflect.String:
+	case reflect.String:
 		return v.Len() == 0
+	case reflect.Array:
+		// zero := reflect.Zero(v.Type().Elem())
+		// can I just check if the whole value is equal to zeros? seems not.
+		// can I just check if the whole value is equal to its zero value? no.
+		// Well, then we check if each value is empty without recursive.
+		for i, vlen := 0, v.Len(); i < vlen; i++ {
+			if !isEmptyValue(v.Index(i), tinfos, false) {
+				return false
+			}
+		}
+		return true
 	case reflect.Map, reflect.Slice, reflect.Chan:
 		return v.IsNil() || v.Len() == 0
 	case reflect.Bool:

codec/helper_unsafe.go

@@ -463,7 +463,11 @@ func isEmptyValueFallbackRecur(urv *unsafeReflectValue, v reflect.Value, tinfos
 	case reflect.Map:
 		return urv.ptr == nil || len_map(rvRefPtr(urv)) == 0
 	case reflect.Array:
-		return v.Len() == 0
+		return v.Len() == 0 ||
+			urv.ptr == nil ||
+			urv.typ == nil ||
+			rtsize2(urv.typ) == 0 ||
+			unsafeCmpZero(urv.ptr, int(rtsize2(urv.typ)))
 	}
 	return false
 }