Strange interaction between matching and lifetimes

[justhsu]

I ran into some baffling issues when matching on a mutable reference and assigning to the mutable reference in the match arms. It seems that the inferred lifetime bound escapes the match. Playpen:

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=4428e0752f518ba02ed12c77560d8afb

I tried three ways of matching on a borrowed value list.0. The first two work only without the "if true" block (1b, 1c). Should an if-block affect the inferred lifetime of the borrow of list.0?

The last method does not work with (3a) or without (3b) the if-block, but I am still confused: why is list.0 still borrowed after the match? Is this expected behavior?

I would expect all six variants to be accepted by the borrow checker, and I'm confused about why only two of them are.