Reuse the declaration validation path across siblings

command.go

@@ -443,42 +443,46 @@ func validateCommandDeclaration(command Command) error {
 
 func validateCommandPlacement(command Command) error {
 	var issues []error
-	collectDeclarationIssues(command, nil, true, &issues)
+	// Keep the grown slice header across recursive calls so siblings reuse capacity.
+	var path []string
+	var collectDeclarationIssues func(Command, bool)
+	collectDeclarationIssues = func(command Command, root bool) {
+		if command.record == nil {
+			issues = append(issues, errors.New("invalid zero command declaration"))
+			return
+		}
+		record := command.record
+		length := len(path)
+		path = append(path, record.name)
+		defer func() { path = path[:length] }()
+		var label string
+		if len(record.issues) > 0 || (record.rootOnly && !root) {
+			label = commandpath.Path(path).String()
+		}
+		for _, issue := range record.issues {
+			if label != "" {
+				issues = append(issues, fmt.Errorf("command %q: %w", label, issue))
+			} else {
+				issues = append(issues, issue)
+			}
+		}
+		if record.rootOnly && !root {
+			issues = append(issues, fmt.Errorf("root-only command %q is nested beneath another command", label))
+		}
+		if record.invalid || record.absent {
+			return
+		}
+		for _, child := range record.children {
+			if child.record == nil {
+				continue
+			}
+			collectDeclarationIssues(child, false)
+		}
+	}
+	collectDeclarationIssues(command, true)
 	return errors.Join(issues...)
 }
 
-func collectDeclarationIssues(command Command, parents []string, root bool, issues *[]error) {
-	if command.record == nil {
-		*issues = append(*issues, errors.New("invalid zero command declaration"))
-		return
-	}
-	record := command.record
-	path := append(parents, record.name)
-	var label string
-	if len(record.issues) > 0 || (record.rootOnly && !root) {
-		label = commandpath.Path(path).String()
-	}
-	for _, issue := range record.issues {
-		if label != "" {
-			*issues = append(*issues, fmt.Errorf("command %q: %w", label, issue))
-		} else {
-			*issues = append(*issues, issue)
-		}
-	}
-	if record.rootOnly && !root {
-		*issues = append(*issues, fmt.Errorf("root-only command %q is nested beneath another command", label))
-	}
-	if record.invalid || record.absent {
-		return
-	}
-	for _, child := range record.children {
-		if child.record == nil {
-			continue
-		}
-		collectDeclarationIssues(child, path, false, issues)
-	}
-}
-
 func validateCommandName(name string) error {
 	return commandpath.ValidateComponent(name)
 }