Fixing a Hidden Infinite Loop in Robot Framework's TypeInfoParser: A Deep Dive

Introduction Robot Framework is one of the most widely adopted open-source test automation frameworks in the world, used by thousands of engineering teams-including those in government, healthcare, and regulated industries. While contributing to its codebase, I discovered a critical bug in the TypeInfoParser that caused either a silent UnboundLocalError crash or an infinite loop when parsing certain type parameter expressions like list[int | str]. This post walks through the diagnosis, root caus