cmd/cp: Add oci-layout-path flag

The oci-layout can't be used when the image
reference contains a slash ( see issue 1505). This
PR introduces a new oci-layout-path that
explicitly receives the path of the oci layout
fixing the parsing ambiguity.

The usage of this flag is:

oras cp --from-oci-layout-path <layout_path> <src> <dst>

Signed-off-by: Mauricio Vásquez <mauriciov@microsoft.com>

cmd/oras/internal/option/target.go

@@ -85,6 +85,7 @@ func (opts *Target) AnnotatedReference() string {
 func (opts *Target) applyFlagsWithPrefix(fs *pflag.FlagSet, prefix, description string) {
 	flagPrefix, notePrefix := applyPrefix(prefix, description)
 	fs.BoolVarP(&opts.IsOCILayout, flagPrefix+"oci-layout", "", false, "set "+notePrefix+"target as an OCI image layout")
+	fs.StringVar(&opts.Path, flagPrefix+"oci-layout-path", "", "set the path for the "+notePrefix+"OCI image layout target")
 }
 
 // ApplyFlagsWithPrefix applies flags to a command flag set with a prefix string.
@@ -96,13 +97,21 @@ func (opts *Target) ApplyFlagsWithPrefix(fs *pflag.FlagSet, prefix, description
 
 // Parse gets target options from user input.
 func (opts *Target) Parse(cmd *cobra.Command) error {
+	if opts.IsOCILayout && opts.Path != "" {
+		return fmt.Errorf("flag %q is not supported with %q", "oci-layout-path", "oci-layout")
+	}
+
 	switch {
 	case opts.IsOCILayout:
 		opts.Type = TargetTypeOCILayout
 		if len(opts.headerFlags) != 0 {
 			return errors.New("custom header flags cannot be used on an OCI image layout target")
 		}
 		return opts.parseOCILayoutReference()
+	case opts.Path != "":
+		opts.Type = TargetTypeOCILayout
+		opts.Reference = opts.RawReference
+		return nil
 	default:
 		opts.Type = TargetTypeRemote
 		if ref, err := registry.ParseReference(opts.RawReference); err != nil {

cmd/oras/internal/option/target_test.go

@@ -20,6 +20,7 @@ import (
 	"net/http"
 	"net/url"
 	"reflect"
+	"strings"
 	"testing"
 
 	"github.com/spf13/cobra"
@@ -28,6 +29,19 @@ import (
 	oerrors "oras.land/oras/cmd/oras/internal/errors"
 )
 
+func TestTarget_Parse_oci_path(t *testing.T) {
+	opts := Target{
+		Path:         "foo",
+		RawReference: "mocked/test",
+	}
+	if err := opts.Parse(nil); err != nil {
+		t.Errorf("Target.Parse() error = %v", err)
+	}
+	if opts.Type != TargetTypeOCILayout {
+		t.Errorf("Target.Parse() failed, got %q, want %q", opts.Type, TargetTypeOCILayout)
+	}
+}
+
 func TestTarget_Parse_oci(t *testing.T) {
 	opts := Target{IsOCILayout: true}
 	err := opts.Parse(nil)
@@ -39,6 +53,22 @@ func TestTarget_Parse_oci(t *testing.T) {
 	}
 }
 
+func TestTarget_Parse_oci_and_oci_path(t *testing.T) {
+	opts := Target{
+		IsOCILayout: true,
+		Path:        "foo",
+	}
+	cmd := &cobra.Command{}
+	ApplyFlags(&opts, cmd.Flags())
+	err := opts.Parse(cmd)
+	if err == nil {
+		t.Errorf("expect Target.Parse() to fail but not")
+	}
+	if !strings.Contains(err.Error(), "supported") {
+		t.Errorf("expect error message to contain 'supported' but not")
+	}
+}
+
 func TestTarget_Parse_remote(t *testing.T) {
 	opts := Target{
 		RawReference: "mocked/test",