feat: Display CLI usage on user error (#819)

cli/blocks_get.go

@@ -27,10 +27,7 @@ var getCmd = &cobra.Command{
 	Short: "Get a block by its CID from the blockstore.",
 	RunE: func(cmd *cobra.Command, args []string) (err error) {
 		if len(args) != 1 {
-			if err = cmd.Usage(); err != nil {
-				return err
-			}
-			return errors.New("get requires a CID argument")
+			return errors.New("missing argument: CID")
 		}
 		cid := args[0]
 

cli/cli.go

@@ -32,6 +32,16 @@ import (
 
 const badgerDatastoreName = "badger"
 
+// List of cobra errors indicating an error occurred in the way the command was invoked.
+// They are subject to change with new versions of cobra.
+var usageErrors = []string{
+	"flag needs an argument",
+	"invalid syntax",
+	"unknown flag",
+	"unknown shorthand flag",
+	"missing argument", // custom to defradb
+}
+
 var log = logging.MustNewLogger("defra.cli")
 
 var cfg = config.DefaultConfig()
@@ -45,7 +55,16 @@ func Execute() {
 	rootCmd.SetOut(os.Stdout)
 	err := rootCmd.ExecuteContext(ctx)
 	if err != nil {
-		log.FeedbackError(ctx, fmt.Sprintf("%s", err))
+		for _, cobraError := range usageErrors {
+			if strings.HasPrefix(err.Error(), cobraError) {
+				log.FeedbackErrorE(ctx, "Usage error", err)
+				if usageErr := rootCmd.Usage(); usageErr != nil {
+					log.FeedbackFatalE(ctx, "error displaying usage help", usageErr)
+				}
+				os.Exit(1)
+			}
+		}
+		log.FeedbackFatalE(ctx, "Execution error", err)
 	}
 }