Align shared debug help and completion

internal/cobra/parse.go

@@ -252,7 +252,7 @@ func displayCommandPath(rootName string, path []string) string {
 	return strings.Join(parts, " ")
 }
 
-// UsageLine returns Cobra's usage line for an exact path on this session.
+// UsageLine returns usage for an exact path on this session.
 func (session *Session) UsageLine(path []string) (string, *commandmeta.Failure) {
 	if session == nil || session.root == nil {
 		return "", &commandmeta.Failure{Message: "command tree is nil"}
@@ -267,6 +267,22 @@ func (session *Session) UsageLine(path []string) (string, *commandmeta.Failure)
 	if selected.HasSubCommands() {
 		line += " [command]"
 	}
+	for _, flag := range declaration.Flags {
+		if flag.Name != "debug" || !flag.Boolean {
+			continue
+		}
+		for _, effective := range commandmeta.EffectiveFlags(declaration.Flags, declaration.CoreFlags) {
+			if effective.Name == "debug" {
+				spelling := "--debug"
+				if effective.Short != "" {
+					spelling = "-" + effective.Short + ", " + spelling
+				}
+				line += "\n  " + spelling + "  " + flagUsage(effective)
+				break
+			}
+		}
+		break
+	}
 	return line, nil
 }