EnumVariant/Enum<T>: Data race allowed on T

[kuzeyardabulut]

Hi,
I found a memory-safety/soundness issue in this crate while scanning Rust code for potential vulnerabilities. This PR contains a fix for the issue.

Issue Description

EnumVariant<T> unconditionally implements Sync. This allows users to create data races on T: !Sync. Such data races can lead to undefined behavior.

wezterm/luahelper/src/enumctor.rs

Line 17 in a7c6ea8

unsafe impl<T> Send for EnumVariant<T> {}

same

wezterm/luahelper/src/enumctor.rs

Line 102 in a7c6ea8

unsafe impl<T> Send for Enum<T> {}

[wez]

FWIW, neither of those data types actually store an actual concrete instance of T; T is a present for its type signature only via a PhantomData, so I don't believe that there is really a race condition here, as it mentioned in the comments above the unsafe impl.

[kuzeyardabulut]

FWIW, neither of those data types actually store an actual concrete instance of T; T is a present for its type signature only via a PhantomData, so I don't believe that there is really a race condition here, as it mentioned in the comments above the unsafe impl.