A few years ago I tried making some contributions to the TLC codebase. It was definitely "academic code," lacking tests, reinvesting basic structured instead of using them from libraries, and largely the work of a single contributor with seemingly no code reviews for commits. I was motivated to try to help improve things and wanted to get a sense for what that would be like by sending a small PR to get a feeling for working with the code owners. They basically stonewalled me. It was odd.
There has definitely been a focus on improving developer onboarding in the past few years! If someone's PR is rejected now that can be considered a failure of the process, something to be fixed. I think when TLA+ was mostly a product of MSR this sort of thing could kind of fly (still unfortunate) but now that we're out in the wild with a foundation it's really a survival thing to not bounce willing contributors.
A few years ago I tried making some contributions to the TLC codebase. It was definitely "academic code," lacking tests, reinvesting basic structured instead of using them from libraries, and largely the work of a single contributor with seemingly no code reviews for commits. I was motivated to try to help improve things and wanted to get a sense for what that would be like by sending a small PR to get a feeling for working with the code owners. They basically stonewalled me. It was odd.