graphics: Forbid nil at ReplacePixels explicitly

image.go

@@ -15,6 +15,7 @@
 package ebiten
 
 import (
+	"fmt"
 	"image"
 	"image/color"
 	"math"
@@ -616,6 +617,10 @@ func (i *Image) ReplacePixels(p []byte) error {
 	if i.isSubimage() {
 		panic("render to a subimage is not implemented")
 	}
+	s := i.Bounds().Size()
+	if l := 4 * s.X * s.Y; len(p) != l {
+		panic(fmt.Sprintf("ebiten: len(p) was %d but must be %d", len(p), l))
+	}
 	i.mipmap.original().ReplacePixels(p)
 	i.disposeMipmaps()
 	return nil

image_test.go

@@ -368,6 +368,22 @@ func TestImageReplacePixels(t *testing.T) {
 	}
 }
 
+func TestImageReplacePixelsNil(t *testing.T) {
+	defer func() {
+		if r := recover(); r == nil {
+			t.Errorf("ReplacePixels(nil) must panic")
+		}
+	}()
+
+	img, err := NewImage(16, 16, FilterNearest)
+	if err != nil {
+		t.Fatal(err)
+		return
+	}
+	img.Fill(color.White)
+	img.ReplacePixels(nil)
+}
+
 func TestImageDispose(t *testing.T) {
 	img, err := NewImage(16, 16, FilterNearest)
 	if err != nil {
@@ -799,7 +815,7 @@ func TestImageSize4096(t *testing.T) {
 func TestImageCopy(t *testing.T) {
 	defer func() {
 		if r := recover(); r == nil {
-			t.Errorf("copying image and using it should panic")
+			t.Errorf("copying image and using it must panic")
 		}
 	}()
 

internal/shareable/shareable.go

@@ -15,7 +15,6 @@
 package shareable
 
 import (
-	"fmt"
 	"image"
 	"image/color"
 	"runtime"
@@ -259,7 +258,7 @@ func (i *Image) replacePixels(p []byte) {
 	x, y, w, h := i.region()
 	if p != nil {
 		if l := 4 * w * h; len(p) != l {
-			panic(fmt.Sprintf("shareable: len(p) was %d but must be %d", len(p), l))
+			panic("not reached")
 		}
 	}
 	i.backend.restorable.ReplacePixels(p, x, y, w, h)