manifest_list: inspect add fields from both OCIv1 and docker format

ManifestInspect should contain all known formats for a valid manifest
list as of now only supported formats are `OCIv1` and `Docker` so
inspect should support fields from `OCIv1` format as well. Following
commit adds a new field to inspect i.e `Annotations` from `OCIv1`.

Example output from podman
```console
podman manifest inspect test
{
    "schemaVersion": 2,
    "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
    "manifests": [
        {
            "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
            "size": 528,
            "digest": "sha256:9b2a28eb47540823042a2ba401386845089bb7b62a9637d55816132c4c3c36eb",
            "platform": {
                "architecture": "amd64",
                "os": "linux"
            },
            "annotations": {
                "annotationTest1": "annotationTest2"
            }
        }
    ]
}
```

Closes: https://github.com/containers/podman/issues/15069

Signed-off-by: Aditya R <arajan@redhat.com>

common/libimage/manifest_list.go

@@ -13,6 +13,7 @@ import (
 	"github.com/containers/image/v5/transports/alltransports"
 	"github.com/containers/image/v5/types"
 	"github.com/containers/storage"
+	structcopier "github.com/jinzhu/copier"
 	"github.com/opencontainers/go-digest"
 )
 
@@ -39,6 +40,28 @@ type ManifestList struct {
 	list manifests.List
 }
 
+// ManifestListDescriptor references a platform-specific manifest.
+// Contains exclusive field like `annotations` which is only present in
+// OCI spec and not in docker image spec.
+type ManifestListDescriptor struct {
+	manifest.Schema2Descriptor
+	Platform manifest.Schema2PlatformSpec `json:"platform"`
+	// Annotations contains arbitrary metadata for the image index.
+	Annotations map[string]string `json:"annotations,omitempty"`
+}
+
+// ManifestListData is a list of platform-specific manifests, specifically used to
+// generate output struct for `podman manifest inspect`. Reason for maintaining and
+// having this type is to ensure we can have a common type which contains exclusive
+// fields from both Docker manifest format and OCI manifest format.
+type ManifestListData struct {
+	SchemaVersion int                      `json:"schemaVersion"`
+	MediaType     string                   `json:"mediaType"`
+	Manifests     []ManifestListDescriptor `json:"manifests"`
+	// Annotations contains arbitrary metadata for the image index.
+	Annotations map[string]string `json:"annotations,omitempty"`
+}
+
 // ID returns the ID of the manifest list.
 func (m *ManifestList) ID() string {
 	return m.image.ID()
@@ -210,8 +233,21 @@ func (i *Image) IsManifestList(ctx context.Context) (bool, error) {
 }
 
 // Inspect returns a dockerized version of the manifest list.
-func (m *ManifestList) Inspect() (*manifest.Schema2List, error) {
-	return m.list.Docker(), nil
+func (m *ManifestList) Inspect() (*ManifestListData, error) {
+	inspectList := ManifestListData{}
+	dockerFormat := m.list.Docker()
+	err := structcopier.Copy(&inspectList, &dockerFormat)
+	if err != nil {
+		return &inspectList, err
+	}
+	// Get missing annotation field from OCIv1 Spec
+	// and populate inspect data.
+	ociFormat := m.list.OCIv1()
+	inspectList.Annotations = ociFormat.Annotations
+	for i, manifest := range ociFormat.Manifests {
+		inspectList.Manifests[i].Annotations = manifest.Annotations
+	}
+	return &inspectList, nil
 }
 
 // Options for adding a manifest list.

common/libimage/manifest_list_test.go

@@ -39,6 +39,44 @@ func TestCreateManifestList(t *testing.T) {
 	require.True(t, errors.Is(err, ErrNotAManifestList))
 }
 
+// Inspect must contain both formats i.e OCIv1 and docker
+func TestInspectManifestListWithAnnotations(t *testing.T) {
+	listName := "testinspect"
+	runtime, cleanup := testNewRuntime(t)
+	defer cleanup()
+	ctx := context.Background()
+
+	list, err := runtime.CreateManifestList(listName)
+	require.NoError(t, err)
+	require.NotNil(t, list)
+
+	manifestListOpts := &ManifestListAddOptions{All: true}
+	_, err = list.Add(ctx, "docker://busybox", manifestListOpts)
+	require.NoError(t, err)
+
+	list, err = runtime.LookupManifestList(listName)
+	require.NoError(t, err)
+	require.NotNil(t, list)
+
+	inspectReport, err := list.Inspect()
+	// get digest of the first instance
+	digest := inspectReport.Manifests[0].Digest
+	require.NoError(t, err)
+
+	annotateOptions := ManifestListAnnotateOptions{}
+	annotations := make(map[string]string)
+	annotations["hello"] = "world"
+	annotateOptions.Annotations = annotations
+
+	err = list.AnnotateInstance(digest, &annotateOptions)
+	require.NoError(t, err)
+	// Inspect list again
+	inspectReport, err = list.Inspect()
+	require.NoError(t, err)
+	// verify annotation
+	require.Equal(t, inspectReport.Manifests[0].Annotations, annotations)
+}
+
 // Following test ensure that `Tag` tags the manifest list instead of resolved image.
 // Both the tags should point to same image id
 func TestCreateAndTagManifestList(t *testing.T) {