WIP: Add UnparsedInstanceWithReference

FIXME: write rationale here

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

image/unparsed.go

@@ -2,6 +2,8 @@ package image
 
 import (
 	"github.com/containers/image/v5/internal/image"
+	"github.com/containers/image/v5/internal/private"
+	"github.com/containers/image/v5/internal/unparsedimage"
 	"github.com/containers/image/v5/types"
 	"github.com/opencontainers/go-digest"
 )
@@ -17,3 +19,23 @@ type UnparsedImage = image.UnparsedImage
 func UnparsedInstance(src types.ImageSource, instanceDigest *digest.Digest) *UnparsedImage {
 	return image.UnparsedInstance(src, instanceDigest)
 }
+
+// unparsedWithRef wraps a private.UnparsedImage, claiming another replacementRef
+type unparsedWithRef struct {
+	private.UnparsedImage
+	ref types.ImageReference
+}
+
+func (uwr *unparsedWithRef) Reference() types.ImageReference {
+	return uwr.ref
+}
+
+// UnparsedInstanceWithReference returns a types.UnparsedImage for wrappedInstance which claims to be a replacementRef.
+// This is useful for combining image data with other reference values, e.g. to check signatures on a locally-pulled image
+// based on a remote-registry policy.
+func UnparsedInstanceWithReference(wrappedInstance types.UnparsedImage, replacementRef types.ImageReference) types.UnparsedImage {
+	return &unparsedWithRef{
+		UnparsedImage: unparsedimage.FromPublic(wrappedInstance),
+		ref:           replacementRef,
+	}
+}