This very post is a good example. Typescript has destructuring and control-flow analysis/refinement. But as you can see from the issues that are fixed by this PR, these two things haven't worked together very well.

This comes from trying to fix 1) compiler errors in conditions where the code is safe but the compiler can't understand that and 2) destructuring products/co-products.

Even if both features work on their own and help in certain cases, combining them leads to undesired results.