Converter: make sure uncompressed digest annotation is set

Signed-off-by: Kohei Tokunaga <ktokunaga.mail@gmail.com>

cache/converter.go

@@ -191,16 +191,13 @@ func (c *conversion) convert(ctx context.Context, cs content.Store, desc ocispec
 	newDesc.MediaType = c.target.DefaultMediaType()
 	newDesc.Digest = info.Digest
 	newDesc.Size = info.Size
-	newDesc.Annotations = nil
+	newDesc.Annotations = map[string]string{labels.LabelUncompressed: diffID.Digest().String()}
 	if c.finalize != nil {
 		a, err := c.finalize(ctx, cs)
 		if err != nil {
 			return nil, errors.Wrapf(err, "failed finalize compression")
 		}
 		for k, v := range a {
-			if newDesc.Annotations == nil {
-				newDesc.Annotations = make(map[string]string)
-			}
 			newDesc.Annotations[k] = v
 		}
 	}

cache/manager_test.go

@@ -1115,6 +1115,8 @@ func TestConversion(t *testing.T) {
 						require.NoError(t, err, testName)
 					}
 					require.Equal(t, recreatedDesc.Digest, orgDesc.Digest, testName)
+					require.NotNil(t, recreatedDesc.Annotations)
+					require.Equal(t, recreatedDesc.Annotations["containerd.io/uncompressed"], orgDesc.Digest.String(), testName)
 					return nil
 				})
 			}