I’ll not elaborate the points already made on why it would make sense to default the language version to the toolchain version, but just add two more minor point in favor of that:
- If we want people to migrate to the latest language version defaulting to it is crucial over time as we’d expect usage of swift to grow
- More importantly, it would set a strange precedent for future major language versions. If we’d default to swift 5 for the swift 6 toolchain, what should be the default for the swift 7 toolchain (and why?). Much clearer to link those and provide the escape hatches for migration outlined above.