When I first came across the issue described in the previous post, I was baffled. I tried to reduce the problem, but whenever I tried to manually copy out bits I thought could be the problem, the problem went away. The “building up” solution not working, I started to try at the “breaking down” solution, starting from the full code that demonstrated the problem and deleting irrelevant code. But this was in a file more than a thousand lines long, and the broken code had many dependencies on other parts of this file, making stripping it down difficult.
But I had a tool in my toolbox that could help. I’ve been a fan of delta debugging for a long time. With delta debugging, you define an “interestingness” criterion, and provide this, along with a large but interesting input to a reducer tool, and it will attempt to reduce the code to the smallest example that is still interesting per the provided criterion.