fix: error message for trust policy

cmd/notation/policy/import.go

@@ -42,7 +42,12 @@ func importCmd() *cobra.Command {
 Example - Import trust policy configuration from a file:
   notation policy import my_policy.json
 `,
-		Args: cobra.ExactArgs(1),
+		Args: func(cmd *cobra.Command, args []string) error {
+			if len(args) != 1 {
+				return fmt.Errorf("requires 1 argument but received %d.\nUsage: notation policy import <path-to-policy.json>\nPlease specify a trust policy file as the argument", len(args))
+			}
+			return nil
+		},
 		RunE: func(cmd *cobra.Command, args []string) error {
 			opts.filePath = args[0]
 			return runImport(cmd, opts)
@@ -71,7 +76,7 @@ func runImport(command *cobra.Command, opts importOpts) error {
 	// optional confirmation
 	if !opts.force {
 		if _, err := trustpolicy.LoadDocument(); err == nil {
-			confirmed, err := cmdutil.AskForConfirmation(os.Stdin, "Existing trust policy configuration found, do you want to overwrite it?", opts.force)
+			confirmed, err := cmdutil.AskForConfirmation(os.Stdin, "The trust policy configuration already exists, do you want to overwrite it?", opts.force)
 			if err != nil {
 				return err
 			}

cmd/notation/policy/show.go

@@ -59,7 +59,10 @@
 	// core process
 	policyJSON, err := os.ReadFile(policyPath)
 	if err != nil {
-		return fmt.Errorf("failed to load trust policy configuration, you may import one via `notation policy import <path-to-policy.json>`: %w", err)
+		if os.IsNotExist(err) {
+			return fmt.Errorf("failed to show trust policy configuration because the trust policy file does not exist.\nYou may import one via `notation policy import <path-to-policy.json>`")
+		}
+		return fmt.Errorf("failed to load trust policy configuration: %w", err)
 	}
 	var doc trustpolicy.Document
 	if err = json.Unmarshal(policyJSON, &doc); err == nil {

test/e2e/suite/command/policy.go

@@ -30,7 +30,7 @@ var _ = Describe("trust policy maintainer", func() {
 			Host(Opts(), func(notation *utils.ExecOpts, artifact *Artifact, vhost *utils.VirtualHost) {
 				notation.ExpectFailure().
 					Exec("policy", "show").
-					MatchErrKeyWords("failed to load trust policy configuration", "notation policy import")
+					MatchErrKeyWords("failed to show trust policy configuration", "notation policy import")
 			})
 		})