Lint `HashMap<T, ZST>` where ZST is any zero sized type

[oli-obk]

The user should be using HashSet<T> instead and magically create the ZSTs out of thin air when needed (since they are all the same value anyway).

[clarfonthey]

One exception I can think of for this: ZSTs not located in the same crate.

For example, if a dependency defines struct MyError(()) then this lint shouldn't trigger because the user can't necessarily create the value out of thin air, and it might not be a ZST in the future.

One example from libstd: https://doc.rust-lang.org/std/net/struct.AddrParseError.html

[korrat]

Hi, I would like to take a shot at this.

[ebroto]

Hey @korrat, it's all yours!

If you have any question, don't hesitate to ask here, in Zulip, or open a draft PR.