Detect named lifetimes that are effectively `'static`

[estebank]

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!() }

[lukaslueg]

Notice Box::leak():

/// Consumes and leaks the Box, returning a mutable reference, &'a mut T.
/// Note that the type T must outlive the chosen lifetime 'a. If the type
/// has only static references, or none at all, then this may be chosen to be 'static.
pub fn leak<'a>(b: Box<T, A>) -> &'a mut T where A: 'a

That is, in the face of generics, 'a is not necessarily 'static.

[blyxyas]

@rustbot claim