fix: Expect at least one artifact in verification

Fixes slsa-framework#425 introduces by slsa-framework#419

Signed-off-by: Mihai Maruseac <[email protected]>

Author: mihaimaruseac

cli/slsa-verifier/verify.go

@@ -33,6 +33,12 @@ func verifyArtifactCmd() *cobra.Command {
 
 	cmd := &cobra.Command{
 		Use:   "verify-artifact [flags] artifact [artifact..]",
+		Args: func(cmd *cobra.Command, args []string) error {
+			if len(args) < 1 {
+				return errors.New("expects at least one artifact")
+			}
+			return nil
+		},
 		Short: "Verifies SLSA provenance on artifact blobs given as arguments (assuming same provenance)",
 		RunE: func(cmd *cobra.Command, args []string) error {
 			v := verify.VerifyArtifactCommand{