*: fix modernise failures

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

Author: cyphar

cmd/umoci/utils_ux.go

@@ -182,14 +182,10 @@ func uxImage(cmd cli.Command) cli.Command {
 		if ctx.IsSet("image") {
 			image := ctx.String("image")
 
-			var dir, tag string
-			sep := strings.Index(image, ":")
-			if sep == -1 {
+			dir, tag, ok := strings.Cut(image, ":")
+			if !ok {
 				dir = image
 				tag = "latest"
-			} else {
-				dir = image[:sep]
-				tag = image[sep+1:]
 			}
 
 			// Verify directory value.

oci/casext/map.go

@@ -31,7 +31,7 @@ import (
 // Used by walkState.mark() to determine which struct members are descriptors to
 // recurse into them. We aren't interested in struct members which are not
 // either a slice of ispec.Descriptor or ispec.Descriptor themselves.
-var descriptorType = reflect.TypeOf(ispec.Descriptor{})
+var descriptorType = reflect.TypeFor[ispec.Descriptor]()
 
 // DescriptorMapFunc is a function that is used to provide a mapping between
 // different descriptor values with MapDescriptors. It will not be called

oci/casext/mediatype/compress.go

@@ -40,8 +40,6 @@ const (
 // should only be used for OCI media-types, where this behaviour is
 // well-defined.
 func SplitMediaTypeSuffix(mediaType string) (baseType, suffix string) {
-	if suffixStart := strings.Index(mediaType, "+"); suffixStart >= 0 {
-		return mediaType[:suffixStart], mediaType[suffixStart+1:]
-	}
-	return mediaType, ""
+	baseType, suffix, _ = strings.Cut(mediaType, "+")
+	return baseType, suffix
 }