fix: time.Duration slice type conversion (#1498)

* fix DurationSlice

* Fix typo

---------

Co-authored-by: Márk Sági-Kazár <sagikazarmark@users.noreply.github.com>

viper.go

@@ -928,6 +928,8 @@ func (v *Viper) Get(key string) interface{} {
 			return cast.ToStringSlice(val)
 		case []int:
 			return cast.ToIntSlice(val)
+		case []time.Duration:
+			return cast.ToDurationSlice(val)
 		}
 	}
 
@@ -1274,8 +1276,14 @@ func (v *Viper) find(lcaseKey string, flagDefault bool) interface{} {
 			s = strings.TrimSuffix(s, "]")
 			res, _ := readAsCSV(s)
 			return cast.ToIntSlice(res)
+		case "durationSlice":
+			s := strings.TrimPrefix(flag.ValueString(), "[")
+			s = strings.TrimSuffix(s, "]")
+			slice := strings.Split(s, ",")
+			return cast.ToDurationSlice(slice)
 		case "stringToString":
 			return stringToStringConv(flag.ValueString())
+
 		default:
 			return flag.ValueString()
 		}
@@ -1355,6 +1363,11 @@ func (v *Viper) find(lcaseKey string, flagDefault bool) interface{} {
 				return cast.ToIntSlice(res)
 			case "stringToString":
 				return stringToStringConv(flag.ValueString())
+			case "durationSlice":
+				s := strings.TrimPrefix(flag.ValueString(), "[")
+				s = strings.TrimSuffix(s, "]")
+				slice := strings.Split(s, ",")
+				return cast.ToDurationSlice(slice)
 			default:
 				return flag.ValueString()
 			}

viper_test.go

@@ -1094,6 +1094,28 @@ func TestBindPFlagsStringArray(t *testing.T) {
 	}
 }
 
+func TestSliceFlagsReturnCorrectType(t *testing.T) {
+	flagSet := pflag.NewFlagSet("test", pflag.ContinueOnError)
+	flagSet.IntSlice("int", []int{1, 2}, "")
+	flagSet.StringSlice("str", []string{"3", "4"}, "")
+	flagSet.DurationSlice("duration", []time.Duration{5 * time.Second}, "")
+
+	v := New()
+	v.BindPFlags(flagSet)
+
+	all := v.AllSettings()
+
+	if _, ok := all["int"].([]int); !ok {
+		t.Errorf("unexpected type %T expected []int", all["int"])
+	}
+	if _, ok := all["str"].([]string); !ok {
+		t.Errorf("unexpected type %T expected []string", all["str"])
+	}
+	if _, ok := all["duration"].([]time.Duration); !ok {
+		t.Errorf("unexpected type %T expected []time.Duration", all["duration"])
+	}
+}
+
 //nolint:dupl
 func TestBindPFlagsIntSlice(t *testing.T) {
 	tests := []struct {