Implement scanning of version flag in specs for usage generation

usage.go

@@ -62,29 +62,39 @@ func (p *Parser) WriteUsageForSubcommand(w io.Writer, subcommand ...string) erro
 // writeUsageForSubcommand writes usage information for the given subcommand
 func (p *Parser) writeUsageForSubcommand(w io.Writer, cmd *command) {
 	var positionals, longOptions, shortOptions []*spec
+	var hasVersionOption bool
 	for _, spec := range cmd.specs {
 		switch {
 		case spec.positional:
 			positionals = append(positionals, spec)
 		case spec.long != "":
 			longOptions = append(longOptions, spec)
+			if spec.long == "version" {
+				hasVersionOption = true
+			}
 		case spec.short != "":
 			shortOptions = append(shortOptions, spec)
 		}
 	}
 
-	if p.version != "" {
-		fmt.Fprintln(w, p.version)
-	}
-
 	// make a list of ancestor commands so that we print with full context
+	// also determine if any ancestor has a version option spec
 	var ancestors []string
 	ancestor := cmd
 	for ancestor != nil {
+		for _, spec := range ancestor.specs {
+			if spec.long == "version" {
+				hasVersionOption = true
+			}
+		}
 		ancestors = append(ancestors, ancestor.name)
 		ancestor = ancestor.parent
 	}
 
+	if !hasVersionOption && p.version != "" {
+		fmt.Fprintln(w, p.version)
+	}
+
 	// print the beginning of the usage string
 	fmt.Fprint(w, "Usage:")
 	for i := len(ancestors) - 1; i >= 0; i-- {