internal/png: update with Go 1.22

internal/png/gen.go

@@ -24,6 +24,9 @@ import (
 	"go/token"
 	"os"
 	"path/filepath"
+	"regexp"
+	"runtime"
+	"strconv"
 	"strings"
 
 	exec "golang.org/x/sys/execabs"
@@ -47,6 +50,20 @@ func pngFiles() ([]string, error) {
 }
 
 func run() error {
+	reVer := regexp.MustCompile(`^go1\.(\d+)(\.\d+)?$`)
+	verStr := runtime.Version()
+	m := reVer.FindStringSubmatch(verStr)
+	if m == nil {
+		return fmt.Errorf("png: unexpected Go version: %s", verStr)
+	}
+	ver, err := strconv.Atoi(m[1])
+	if err != nil {
+		return err
+	}
+	if ver < 22 {
+		return fmt.Errorf("png: use Go 1.22 or newer")
+	}
+
 	dir, err := pngDir()
 	if err != nil {
 		return err
@@ -115,6 +132,18 @@ func run() error {
 		fmt.Fprintln(out, "// Code generated by gen.go. DO NOT EDIT.")
 		fmt.Fprintln(out)
 		format.Node(out, fset, tree)
+
+		if f == "reader.go" {
+			// The min function was removed as of Go 1.22, but this is needed for old Go.
+			// TODO: Remove this when Go 1.21 is the minimum supported version.
+			fmt.Fprintln(out, `
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}`)
+		}
 	}
 	return nil
 }

internal/png/stdlibreader.go

@@ -138,13 +138,6 @@ type UnsupportedError string
 
 func (e UnsupportedError) Error() string { return "png: unsupported feature: " + string(e) }
 
-func min(a, b int) int {
-	if a < b {
-		return a
-	}
-	return b
-}
-
 func (d *decoder) parseIHDR(length uint32) error {
 	if length != 13 {
 		return FormatError("bad IHDR length")
@@ -973,7 +966,7 @@ func (d *decoder) checkHeader() error {
 	return nil
 }
 
-// Decode reads a PNG image from r and returns it as an image.Image.
+// Decode reads a PNG image from r and returns it as an [image.Image].
 // The type of Image returned depends on the PNG contents.
 func Decode(r io.Reader) (image.Image, error) {
 	d := &decoder{
@@ -1061,3 +1054,10 @@ func DecodeConfig(r io.Reader) (image.Config, error) {
 func init() {
 
 }
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}

internal/png/stdlibwriter.go

@@ -27,7 +27,7 @@ type Encoder struct {
 }
 
 // EncoderBufferPool is an interface for getting and returning temporary
-// instances of the EncoderBuffer struct. This can be used to reuse buffers
+// instances of the [EncoderBuffer] struct. This can be used to reuse buffers
 // when encoding multiple images.
 type EncoderBufferPool interface {
 	Get() *EncoderBuffer
@@ -192,7 +192,7 @@ func (e *encoder) writePLTEAndTRNS(p color.Palette) {
 
 // An encoder is an io.Writer that satisfies writes by writing PNG IDAT chunks,
 // including an 8-byte header and 4-byte CRC checksum per Write call. Such calls
-// should be relatively infrequent, since writeIDATs uses a bufio.Writer.
+// should be relatively infrequent, since writeIDATs uses a [bufio.Writer].
 //
 // This method should only be called from writeIDATs (via writeImage).
 // No other code should treat an encoder as an io.Writer.
@@ -588,7 +588,7 @@ func levelToZlib(l CompressionLevel) int {
 func (e *encoder) writeIEND() { e.writeChunk(nil, "IEND") }
 
 // Encode writes the Image m to w in PNG format. Any Image may be
-// encoded, but images that are not image.NRGBA might be encoded lossily.
+// encoded, but images that are not [image.NRGBA] might be encoded lossily.
 func Encode(w io.Writer, m image.Image) error {
 	var e Encoder
 	return e.Encode(w, m)