parser.Usage should also accept strings and fmt.Stringer

akamensky · akamensky · commit b8cd502bf8fd · 2018-11-21T23:04:49.000+08:00
diff --git a/argparse.go b/argparse.go
@@ -260,23 +260,32 @@ func (o *Command) Happened() bool {
 // Since Parser is a Command as well, they work in exactly same way. Meaning that usage string
 // can be retrieved for any level of commands. It will only include information about this Command,
 // its sub-commands, current Command arguments and arguments of all preceding commands (if any)
-func (o *Command) Usage(err interface{}) string {
+//
+// Accepts an interface that can be error, string or fmt.Stringer that will be prepended to a message.
+// All other interface types will be ignored
+func (o *Command) Usage(msg interface{}) string {
+	var result string
 	// Stay classy
 	maxWidth := 80
 	// List of arguments from all preceding commands
 	arguments := make([]*arg, 0)
 	// First get line of commands until root
 	var chain []string
 	current := o
-	if err != nil {
-		switch err.(type) {
+	if msg != nil {
+		switch msg.(type) {
 		case subCommandError:
-			fmt.Println(err.(error).Error())
-			if err.(subCommandError).cmd != nil {
-				return err.(subCommandError).cmd.Usage(nil)
+			result = fmt.Sprintf("%s\n", msg.(error).Error())
+			if msg.(subCommandError).cmd != nil {
+				result += msg.(subCommandError).cmd.Usage(nil)
 			}
+			return result
 		case error:
-			fmt.Println(err.(error).Error())
+			result = fmt.Sprintf("%s\n", msg.(error).Error())
+		case string:
+			result = fmt.Sprintf("%s\n", msg.(string))
+		case fmt.Stringer:
+			result = fmt.Sprintf("%s\n", msg.(fmt.Stringer).String())
 		}
 	}
 	for current != nil {
@@ -301,8 +310,8 @@ func (o *Command) Usage(err interface{}) string {
 		}
 	}
 
-	// Build result description
-	var result = "usage:"
+	// Build usage description
+	result += "usage:"
 	leftPadding := len("usage: " + chain[0] + "")
 	// Add preceding commands
 	for _, v := range chain {
diff --git a/argparse_test.go b/argparse_test.go
@@ -1099,3 +1099,56 @@ func TestFloatFail1(t *testing.T) {
 		return
 	}
 }
+
+var pUsageString = `test string
+usage: prog [-h|--help]
+
+            program description
+
+Arguments:
+
+  -h  --help  Print help information
+
+`
+
+func TestUsageString(t *testing.T) {
+	p := NewParser("prog", "program description")
+
+	p.Parse(os.Args)
+
+	usage := p.Usage("test string")
+
+	if usage != pUsageString {
+		t.Errorf("%s", usage)
+	}
+}
+
+type s string
+func (s s) String() string {
+	return string(s)
+}
+
+var pUsageStringer = `stringer message
+usage: prog [-h|--help]
+
+            program description
+
+Arguments:
+
+  -h  --help  Print help information
+
+`
+
+func TestUsageStringer(t *testing.T) {
+	p := NewParser("prog", "program description")
+
+	p.Parse(os.Args)
+
+	var msg s = "stringer message"
+
+	usage := p.Usage(msg)
+
+	if usage != pUsageStringer {
+		t.Errorf("%s", usage)
+	}
+}
