-i cache #3045Description
I've noticed that many people initially run plain mypy and then start using mypy -i but find that the first such run is not any faster than a plain run. This is understandable because it needs to warm the cache first.
We could alleviate this issue by just always writing the cache (perhaps allowing this feature to be turned off for special scenarios but having it on by default). This might cost a little bit of extra run time -- IIRC I once measured the cost of writing the cache and it was in the 5-10% range.