(Author here)

The funniest part is that this ugly hack kept working across platforms for many years; whereas when somebody else implemented a "proper" integration with the clang / llvm API, their solution proved to be extremely fragile. The API wasn't stable between compiler versions, and because it wasn't really used much, it had all kinds of bugs, including being outright unusable at times.

Also, most distros packaged clang in a way that made it impossible to compile the plugin, because of missing or mismatched headers, missing companions tools, etc. So you had to download and rebuild the whole compiler, which took hours (and that's if you didn't get stuck in a dependency hell).

So yeah, this was very much a lesson in "worse is better".