cmd/create: pkg/utils: Fix wrong use of regexp.MatchString return value

The regexp.MatchString [1] API returns an error only when the regular
expression is faulty, and the boolean return value tells if a match was
found. In this case, the regular expression is baked into the code as a
string literal. So, unless there's a programmer error, it should always
be valid.

Fallout dd947016b3

[1] https://golang.org/pkg/regexp/#MatchString

https://github.com/containers/toolbox/pull/825

src/cmd/create.go

@@ -669,7 +669,7 @@ func isPathReadWrite(path string) (bool, error) {
 }
 
 func pullImage(image, release string) (bool, error) {
-	if _, err := utils.ImageReferenceCanBeID(image); err == nil {
+	if ok := utils.ImageReferenceCanBeID(image); ok {
 		logrus.Debugf("Looking for image %s", image)
 
 		if _, err := podman.ImageExists(image); err == nil {

src/pkg/utils/utils.go

@@ -500,9 +500,12 @@ func HumanDuration(duration int64) string {
 }
 
 // ImageReferenceCanBeID checks if 'image' might be the ID of an image
-func ImageReferenceCanBeID(image string) (bool, error) {
+func ImageReferenceCanBeID(image string) bool {
 	matched, err := regexp.MatchString("^[a-f0-9]\\{6,64\\}$", image)
-	return matched, err
+	if err != nil {
+		panic("regular expression for ID reference matching is invalid")
+	}
+	return matched
 }
 
 func ImageReferenceGetBasename(image string) string {