fix(ids): %x formatting of ID and ShortID

ids/format.go

@@ -0,0 +1,48 @@
+// Copyright (C) 2019-2024, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package ids
+
+import "fmt"
+
+var _ = []fmt.Formatter{ID{}, ShortID{}}
+
+// Format implements the [fmt.Formatter] interface.
+func (id ID) Format(s fmt.State, verb rune) {
+	format(s, verb, id)
+}
+
+// Format implements the [fmt.Formatter] interface.
+func (id ShortID) Format(s fmt.State, verb rune) {
+	format(s, verb, id)
+}
+
+type idForFormatting interface {
+	String() string
+	Hex() string
+}
+
+// format implements the [fmt.Formatter] interface for [ID] and [ShortID].
+func format[T interface {
+	idForFormatting
+	ID | ShortID
+}](s fmt.State, verb rune, id T) {
+	switch verb {
+	case 'x':
+		if s.Flag('#') {
+			s.Write([]byte("0x")) //nolint:errcheck // [fmt.Formatter] doesn't allow for returning errors, and the implementation of [fmt.State] always returns nil on Write()
+		}
+		s.Write([]byte(id.Hex())) //nolint:errcheck // See above
+
+	case 'q':
+		str := id.String()
+		buf := make([]byte, len(str)+2)
+		buf[0] = '"'
+		buf[len(buf)-1] = '"'
+		copy(buf[1:], str)
+		s.Write(buf) //nolint:errcheck // See above
+
+	default:
+		s.Write([]byte(id.String())) //nolint:errcheck // See above
+	}
+}

ids/format_test.go

@@ -0,0 +1,55 @@
+// Copyright (C) 2019-2024, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package ids
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestFormat(t *testing.T) {
+	type test struct {
+		id   idForFormatting
+		want map[string]string // format -> output
+	}
+	makeTestCase := func(id idForFormatting) test {
+		return test{
+			id: id,
+			want: map[string]string{
+				"%v":  id.String(),
+				"%s":  id.String(),
+				"%q":  `"` + id.String() + `"`,
+				"%x":  id.Hex(),
+				"%#x": `0x` + id.Hex(),
+			},
+		}
+	}
+
+	tests := []test{
+		makeTestCase(ID{}),
+		makeTestCase(GenerateTestID()),
+		makeTestCase(GenerateTestID()),
+		makeTestCase(ShortID{}),
+		makeTestCase(GenerateTestShortID()),
+		makeTestCase(GenerateTestShortID()),
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.id.String(), func(t *testing.T) {
+			for format, want := range tt.want {
+				if got := fmt.Sprintf(format, tt.id); got != want {
+					//nolint:forbidigo // require.Equal() is inappropriate as it unnecessarily stops future tests and `assert.Equal()` isn't allowed
+					t.Errorf("fmt.Sprintf(%q, %T) got %q; want %q", format, tt.id, got, want)
+				}
+			}
+		})
+	}
+}
+
+func BenchmarkFormat(*testing.B) {
+	// %q uses a []byte so this is just to demonstrate that it's on the stack
+	// otherwise someone, not naming any names, might want to "fix" it.
+	_ = fmt.Sprintf("%q", ID{})
+	_ = fmt.Sprintf("%q", ShortID{})
+}