It's a mixture of the two. Some of the borrowck errors are due to warts which we hope to eventually fix. Others are due to not-immediately-obvious issues with

It's a mixture of the two. Some of the borrowck errors are due to warts which we hope to eventually fix. Others are due to not-immediately-obvious issues with code. One of the most common borrowck complaints I've seen is about the fact that you can't have mutable and immutable aliases operating simultaneously, even if you don't have threads involved. There's a reason behind that (http://manishearth.github.io/blog/2015/05/17/the-problem-with-shared-mutability/ http://manishearth.github.io/blog/2015/05/17/the-problem-wit...).