Lint on const RUNTIME: tokio<Runtime>

[jyn514]

What it does

What does this lint do?

It errors on const tokio runtimes.

Categories (optional)

• Kind: Correctness
• Deny by default

What is the advantage of the recommended code over the original code

It avoids errors like the following:

Io(Custom { kind: Other, error: "reactor gone" })

const creates a new copy of the runtime every time it's used, while static uses the same runtime each time.
I was using this as RUNTIME.block_on(), which takes &mut, so possibly this could be expanded to any &mut use of a const.

Drawbacks

None.

Example

pub const RUNTIME: Lazy<Runtime> = Lazy::new(|| Runtime::new().unwrap());

should instead be

pub static RUNTIME: Lazy<Runtime> = Lazy::new(|| Runtime::new().unwrap());

[ebroto]

@jyn514 would const_item_mutation solve your use case? To be landed in 1.48.

[jyn514]

Yes it would! Thank you :D https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=5329dc009d37cefba58f5acaab8d4be7