Make command suggestion messages configurable.

args.go

@@ -33,7 +33,7 @@ func legacyArgs(cmd *Command, args []string) error {
 
 	// root command with subcommands, do subcommand checking.
 	if !cmd.HasParent() && len(args) > 0 {
-		return fmt.Errorf("unknown command %q for %q%s", args[0], cmd.CommandPath(), cmd.findSuggestions(args[0]))
+		return fmt.Errorf("unknown command %q for %q%s", args[0], cmd.CommandPath(), cmd.SuggestFunc()(args[0]))
 	}
 	return nil
 }
@@ -58,7 +58,7 @@ func OnlyValidArgs(cmd *Command, args []string) error {
 		}
 		for _, v := range args {
 			if !stringInSlice(v, validArgs) {
-				return fmt.Errorf("invalid argument %q for %q%s", v, cmd.CommandPath(), cmd.findSuggestions(args[0]))
+				return fmt.Errorf("invalid argument %q for %q%s", v, cmd.CommandPath(), cmd.SuggestFunc()(args[0]))
 			}
 		}
 	}

command.go

@@ -180,6 +180,8 @@ type Command struct {
 	helpCommand *Command
 	// helpCommandGroupID is the group id for the helpCommand
 	helpCommandGroupID string
+	// suggestFunc is suggest func defined by the user.
+	suggestFunc func(string) string
 
 	// completionCommandGroupID is the group id for the completion command
 	completionCommandGroupID string
@@ -340,6 +342,10 @@ func (c *Command) SetHelpCommandGroupID(groupID string) {
 	c.helpCommandGroupID = groupID
 }
 
+func (c *Command) SetSuggestFunc(f func(string) string) {
+	c.suggestFunc = f
+}
+
 // SetCompletionCommandGroupID sets the group id of the completion command.
 func (c *Command) SetCompletionCommandGroupID(groupID string) {
 	// completionCommandGroupID is used if no completion command is defined by the user
@@ -477,6 +483,18 @@ func (c *Command) Help() error {
 	return nil
 }
 
+// SuggestFunc returns either the function set by SetSuggestFunc for this command
+// or a parent, or it returns a function with default suggestion behavior.
+func (c *Command) SuggestFunc() func(string) string {
+	if c.suggestFunc != nil && !c.DisableSuggestions {
+		return c.suggestFunc
+	}
+	if c.HasParent() {
+		return c.Parent().SuggestFunc()
+	}
+	return c.findSuggestions
+}
+
 // UsageString returns usage string.
 func (c *Command) UsageString() string {
 	// Storing normal writers

command_test.go

@@ -1393,6 +1393,48 @@ func TestSuggestions(t *testing.T) {
 	}
 }
 
+func TestCustomSuggestions(t *testing.T) {
+	templateWithCustomSuggestions := "Error: unknown command \"%s\" for \"root\"\nSome custom suggestion.\n\nRun 'root --help' for usage.\n"
+	templateWithDefaultSuggestions := "Error: unknown command \"%s\" for \"root\"\n\nDid you mean this?\n\t%s\n\nRun 'root --help' for usage.\n"
+	templateWithoutSuggestions := "Error: unknown command \"%s\" for \"root\"\nRun 'root --help' for usage.\n"
+
+	for typo, suggestion := range map[string]string{"time": "times", "timse": "times"} {
+		for _, suggestionsDisabled := range []bool{true, false} {
+			for _, setCustomSuggest := range []bool{true, false} {
+				rootCmd := &Command{Use: "root", Run: emptyRun}
+				timesCmd := &Command{
+					Use: "times",
+					Run: emptyRun,
+				}
+				rootCmd.AddCommand(timesCmd)
+
+				rootCmd.DisableSuggestions = suggestionsDisabled
+
+				if setCustomSuggest {
+					rootCmd.SetSuggestFunc(func(a string) string {
+						return "\nSome custom suggestion.\n"
+					})
+				}
+
+				var expected string
+				if suggestionsDisabled {
+					expected = fmt.Sprintf(templateWithoutSuggestions, typo)
+				} else if setCustomSuggest {
+					expected = fmt.Sprintf(templateWithCustomSuggestions, typo)
+				} else {
+					expected = fmt.Sprintf(templateWithDefaultSuggestions, typo, suggestion)
+				}
+
+				output, _ := executeCommand(rootCmd, typo)
+
+				if output != expected {
+					t.Errorf("Unexpected response.\nExpected:\n %q\nGot:\n %q\n", expected, output)
+				}
+			}
+		}
+	}
+}
+
 func TestCaseInsensitive(t *testing.T) {
 	rootCmd := &Command{Use: "root", Run: emptyRun}
 	childCmd := &Command{Use: "child", Run: emptyRun, Aliases: []string{"alternative"}}