libpod/image: Use ParseNormalizedNamed in RepoDigests

Avoid generating
quay.io/openshift-release-dev/ocp-release@sha256@sha256:239... and
similar when the image name is already digest-based [1].  It's not
clear exactly how we get into this state, but as shown by the unit
tests, the new code handles this case correctly (while the previous
code does not).

[1]: https://github.com/containers/libpod/issues/2086

Signed-off-by: W. Trevor King <wking@tremily.us>

Closes: #2106
Approved by: rhatdan

libpod/image/image_test.go

@@ -9,6 +9,7 @@ import (
 	"testing"
 
 	"github.com/containers/storage"
+	"github.com/opencontainers/go-digest"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -192,6 +193,51 @@ func TestImage_MatchRepoTag(t *testing.T) {
 	cleanup(workdir, ir)
 }
 
+// TestImage_RepoDigests tests RepoDigest generation.
+func TestImage_RepoDigests(t *testing.T) {
+	dgst, err := digest.Parse("sha256:7173b809ca12ec5dee4506cd86be934c4596dd234ee82c0662eac04a8c2c71dc")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for _, test := range []struct {
+		name     string
+		names    []string
+		expected []string
+	}{
+		{
+			name:     "empty",
+			names:    []string{},
+			expected: nil,
+		},
+		{
+			name:     "tagged",
+			names:    []string{"docker.io/library/busybox:latest"},
+			expected: []string{"docker.io/library/busybox@sha256:7173b809ca12ec5dee4506cd86be934c4596dd234ee82c0662eac04a8c2c71dc"},
+		},
+		{
+			name:     "digest",
+			names:    []string{"docker.io/library/busybox@sha256:7173b809ca12ec5dee4506cd86be934c4596dd234ee82c0662eac04a8c2c71dc"},
+			expected: []string{"docker.io/library/busybox@sha256:7173b809ca12ec5dee4506cd86be934c4596dd234ee82c0662eac04a8c2c71dc"},
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			image := &Image{
+				image: &storage.Image{
+					Names:  test.names,
+					Digest: dgst,
+				},
+			}
+			actual, err := image.RepoDigests()
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			assert.Equal(t, test.expected, actual)
+		})
+	}
+}
+
 // Test_splitString tests the splitString function in image that
 // takes input and splits on / and returns the last array item
 func Test_splitString(t *testing.T) {