Implement Format on rat

See gohugoio/hugo#12718

Author: bep

helpers.go

@@ -110,6 +110,15 @@ func (r rat[T]) String() string {
 	return fmt.Sprintf("%d/%d", r.num, r.den)
 }
 
+func (r rat[T]) Format(w fmt.State, v rune) {
+	switch v {
+	case 'f':
+		fmt.Fprintf(w, "%f", r.Float64())
+	default:
+		fmt.Fprintf(w, "%s", r.String())
+	}
+}
+
 func (r *rat[T]) UnmarshalText(text []byte) error {
 	s := string(text)
 	if !strings.Contains(s, "/") {

helpers_test.go

@@ -5,6 +5,7 @@ package imagemeta
 
 import (
 	"encoding"
+	"fmt"
 	"testing"
 
 	qt "github.com/frankban/quicktest"
@@ -106,4 +107,12 @@ func TestRat(t *testing.T) {
 		ru, _ = NewRat[uint32](4, 1)
 		c.Assert(ru.String(), qt.Equals, "4")
 	})
+
+	c.Run("Format", func(c *qt.C) {
+		ru, _ := NewRat[uint32](1, 3)
+		s := fmt.Sprintf("%.2f", ru)
+		c.Assert(s, qt.Equals, "0.333333")
+		s = fmt.Sprintf("%s", ru)
+		c.Assert(s, qt.Equals, "1/3")
+	})
 }