Don't use imageParts.assemble when pulling from a qualified name

CHANGES BEHAVIOR.

If the name is qualified, instead of decomposing it into components and
re-assembling, just use the input name unmodified:
- For name:tag values, .assemble() just recreates the input.
- For untagged values, .assemble() adds ":latest"; we keep
  the input as is, but both docker.ParseReference and storage.Transport.ParseStoreReference
  use reference.TagNameOnly() already.
- For digested references, .assemble() adds ":none", but
  the code was already bypassing .assemble() on that path
  already - for the source reference.  For the destination,
  this replaces a :none destination with a the @digest reference,
  as expected.

Note that while decompose() has already parsed the input,
it (intentionally) bypassed the docker.io/library normalization;
therefore we parse the input again (via docker.ParseReference) to ensure
that the reference is normalized.

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

libpod/image/pull.go

@@ -284,24 +284,13 @@ func (ir *Runtime) pullGoalFromPossiblyUnqualifiedName(inputName string) (*pullG
 		return nil, err
 	}
 	if decomposedImage.hasRegistry {
-		var imageName, destName string
+		srcRef, err := docker.ParseReference("//" + inputName)
-		if hasShaInInputName(inputName) {
-			imageName = inputName
-		} else {
-			imageName = decomposedImage.assemble()
-		}
-		srcRef, err := docker.ParseReference("//" + imageName)
 		if err != nil {
 			return nil, errors.Wrapf(err, "unable to parse '%s'", inputName)
 		}
-		if hasShaInInputName(inputName) {
+		destRef, err := is.Transport.ParseStoreReference(ir.store, inputName)
-			destName = decomposedImage.assemble()
-		} else {
-			destName = inputName
-		}
-		destRef, err := is.Transport.ParseStoreReference(ir.store, destName)
 		if err != nil {
-			return nil, errors.Wrapf(err, "error parsing dest reference name %#v", destName)
+			return nil, errors.Wrapf(err, "error parsing dest reference name %#v", inputName)
 		}
 		ps := pullRefPair{
 			image:  inputName,

libpod/image/pull_test.go

@@ -324,8 +324,7 @@ func TestPullGoalFromPossiblyUnqualifiedName(t *testing.T) {
 		{ // Qualified example.com, name@digest.
 			"example.com/ns/busybox" + digestSuffix,
 			[]pullRefStrings{{"example.com/ns/busybox" + digestSuffix, "docker://example.com/ns/busybox" + digestSuffix,
-				// FIXME?! Why is .dstName dropping the digest, and adding :none?!
+				"example.com/ns/busybox" + digestSuffix}},
-				"example.com/ns/busybox:none"}},
 			false,
 		},
 		// Qualified example.com, name:tag@digest.  This code is happy to try, but .srcRef parsing currently rejects such input.