Detect named lifetimes that are effectively `'static`

What it does

Given a function that returns a borrow to a lifetime that isn't used in any parameter, give and explanation and suggest removing the named lifetime and making it 'static, as it is the only effective lifetime that will work:

fn foo<'a>() -> &'a str { todo!() }

Lint Name

hidden_static_lifetime

Category

suspicious, style, pedantic

Advantage

It makes the code easier to follow and is a good thing to teach users about.

Drawbacks

No response

Example

fn foo<'a>() -> &'a str { todo!() }

Could be written as:

fn foo() -> &'static str { todo!() }

Start with the linked Rust playground example and the issue's hidden_static_lifetime lint name. Trace how Clippy defines and tests similar suspicious or style lints, then verify the implementation explains the ineffective named lifetime and suggests the shown 'static form.