feat(civil): add IsEmpty function to time, date and datetime (#4728)

Fixes: #4727

civil/civil.go

@@ -107,6 +107,11 @@ func (d1 Date) After(d2 Date) bool {
 	return d2.Before(d1)
 }
 
+// IsZero reports whether date fields are set to their default value.
+func (d Date) IsZero() bool {
+	return (d.Year == 0) && (int(d.Month) == 0) && (d.Day == 0)
+}
+
 // MarshalText implements the encoding.TextMarshaler interface.
 // The output is the result of d.String().
 func (d Date) MarshalText() ([]byte, error) {
@@ -175,6 +180,11 @@ func (t Time) IsValid() bool {
 	return TimeOf(tm) == t
 }
 
+// IsZero reports whether time fields are set to their default value.
+func (t Time) IsZero() bool {
+	return (t.Hour == 0) && (t.Minute == 0) && (t.Second == 0) && (t.Nanosecond == 0)
+}
+
 // MarshalText implements the encoding.TextMarshaler interface.
 // The output is the result of t.String().
 func (t Time) MarshalText() ([]byte, error) {
@@ -262,6 +272,11 @@ func (dt1 DateTime) After(dt2 DateTime) bool {
 	return dt2.Before(dt1)
 }
 
+// IsZero reports whether datetime fields are set to their default value.
+func (dt DateTime) IsZero() bool {
+	return dt.Date.IsZero() && dt.Time.IsZero()
+}
+
 // MarshalText implements the encoding.TextMarshaler interface.
 // The output is the result of dt.String().
 func (dt DateTime) MarshalText() ([]byte, error) {

civil/civil_test.go

@@ -193,6 +193,24 @@ func TestDateAfter(t *testing.T) {
 	}
 }
 
+func TestDateIsZero(t *testing.T) {
+	for _, test := range []struct {
+		date Date
+		want bool
+	}{
+		{Date{2000, 2, 29}, false},
+		{Date{10000, 12, 31}, false},
+		{Date{-1, 0, 0}, false},
+		{Date{0, 0, 0}, true},
+		{Date{}, true},
+	} {
+		got := test.date.IsZero()
+		if got != test.want {
+			t.Errorf("%#v: got %t, want %t", test.date, got, test.want)
+		}
+	}
+}
+
 func TestTimeToString(t *testing.T) {
 	for _, test := range []struct {
 		str       string
@@ -260,6 +278,24 @@ func TestTimeIsValid(t *testing.T) {
 	}
 }
 
+func TestTimeIsZero(t *testing.T) {
+	for _, test := range []struct {
+		time Time
+		want bool
+	}{
+		{Time{0, 0, 0, 0}, true},
+		{Time{}, true},
+		{Time{0, 0, 0, 1}, false},
+		{Time{-1, 0, 0, 0}, false},
+		{Time{0, -1, 0, 0}, false},
+	} {
+		got := test.time.IsZero()
+		if got != test.want {
+			t.Errorf("%#v: got %t, want %t", test.time, got, test.want)
+		}
+	}
+}
+
 func TestDateTimeToString(t *testing.T) {
 	for _, test := range []struct {
 		str       string
@@ -383,6 +419,28 @@ func TestDateTimeAfter(t *testing.T) {
 	}
 }
 
+func TestDateTimeIsZero(t *testing.T) {
+	for _, test := range []struct {
+		dt   DateTime
+		want bool
+	}{
+		{DateTime{Date{2016, 3, 20}, Time{0, 0, 0, 0}}, false},
+		{DateTime{Date{}, Time{5, 44, 20, 0}}, false},
+		{DateTime{Date{2016, 3, 20}, Time{}}, false},
+		{DateTime{Date{0, 0, 0}, Time{5, 16, 47, 2}}, false},
+		{DateTime{Date{2021, 9, 5}, Time{9, 30, 51, 6}}, false},
+		{DateTime{Date{}, Time{}}, true},
+		{DateTime{Date{0, 0, 0}, Time{0, 0, 0, 0}}, true},
+		{DateTime{Date{}, Time{0, 0, 0, 0}}, true},
+		{DateTime{Date{0, 0, 0}, Time{}}, true},
+	} {
+		got := test.dt.IsZero()
+		if got != test.want {
+			t.Errorf("%#v: got %t, want %t", test.dt, got, test.want)
+		}
+	}
+}
+
 func TestMarshalJSON(t *testing.T) {
 	for _, test := range []struct {
 		value interface{}