Revert "Always produce OCI images and indexes (ko-build#449)"

This reverts commit 465eca2.

This breaks pushing to quay.io.

pkg/build/gobuild.go

@@ -701,9 +701,6 @@ func (g *gobuild) configForImportPath(ip string) Config {
 func (g *gobuild) buildOne(ctx context.Context, refStr string, base v1.Image, platform *v1.Platform) (v1.Image, error) {
 	ref := newRef(refStr)
 
-	// Always produce OCI images, even if the base image isn't an OCI image.
-	base = mutate.MediaType(base, types.OCIManifestSchema1)
-
 	cf, err := base.ConfigFile()
 	if err != nil {
 		return nil, err
@@ -880,15 +877,16 @@ func (g *gobuild) Build(ctx context.Context, s string) (Result, error) {
 	}
 
 	// Annotate the image or index with base image information.
-	// If the result is an Index, it should be an OCI index that supports
-	// annotations.
-	anns := map[string]string{
-		specsv1.AnnotationBaseImageDigest: baseDigest.String(),
-	}
-	if _, ok := baseRef.(name.Tag); ok {
-		anns[specsv1.AnnotationBaseImageName] = baseRef.Name()
+	// (Docker manifest lists don't support annotations)
+	if mt != types.DockerManifestList {
+		anns := map[string]string{
+			specsv1.AnnotationBaseImageDigest: baseDigest.String(),
+		}
+		if _, ok := baseRef.(name.Tag); ok {
+			anns[specsv1.AnnotationBaseImageName] = baseRef.Name()
+		}
+		res = mutate.Annotations(res, anns).(Result)
 	}
-	res = mutate.Annotations(res, anns).(Result)
 
 	return res, nil
 }
@@ -924,13 +922,18 @@ func (g *gobuild) buildAll(ctx context.Context, ref string, baseIndex v1.ImageIn
 			Add: img,
 			Descriptor: v1.Descriptor{
 				URLs:        desc.URLs,
+				MediaType:   desc.MediaType,
 				Annotations: desc.Annotations,
 				Platform:    desc.Platform,
 			},
 		})
 	}
 
-	idx := mutate.IndexMediaType(mutate.AppendManifests(empty.Index, adds...), types.OCIImageIndex)
+	baseType, err := baseIndex.MediaType()
+	if err != nil {
+		return nil, err
+	}
+	idx := mutate.IndexMediaType(mutate.AppendManifests(empty.Index, adds...), baseType)
 
 	return idx, nil
 }

pkg/build/gobuild_test.go

@@ -36,7 +36,6 @@ import (
 	"github.com/google/go-containerregistry/pkg/v1/empty"
 	"github.com/google/go-containerregistry/pkg/v1/mutate"
 	"github.com/google/go-containerregistry/pkg/v1/random"
-	"github.com/google/go-containerregistry/pkg/v1/types"
 	specsv1 "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
@@ -421,17 +420,6 @@ func TestGoBuildNoKoData(t *testing.T) {
 			t.Errorf("created = %v, want %v", actual, creationTime)
 		}
 	})
-
-	t.Run("check OCI media type", func(t *testing.T) {
-		mt, err := img.MediaType()
-		if err != nil {
-			t.Errorf("MediaType() = %v", err)
-		}
-
-		if got, want := mt, types.OCIManifestSchema1; got != want {
-			t.Errorf("mediaType = %v, want %v", got, want)
-		}
-	})
 }
 
 func validateImage(t *testing.T, img v1.Image, baseLayers int64, creationTime v1.Time, checkAnnotations bool) {
@@ -743,23 +731,6 @@ func TestGoBuildIndex(t *testing.T) {
 			t.Errorf("Digest mismatch: %s != %s", d1, d2)
 		}
 	})
-
-	t.Run("check OCI media type", func(t *testing.T) {
-		mt, err := idx.MediaType()
-		if err != nil {
-			t.Fatalf("MediaType() = %v", err)
-		}
-
-		if got, want := mt, types.OCIImageIndex; got != want {
-			t.Errorf("mediaType = %v, want %v", got, want)
-		}
-
-		for i, mf := range im.Manifests {
-			if got, want := mf.MediaType, types.OCIManifestSchema1; got != want {
-				t.Errorf("manifest[%d] mediaType = %s, want %s", i, got, want)
-			}
-		}
-	})
 }
 
 func TestNestedIndex(t *testing.T) {