Lint for redundant lifetimes.

[eddyb]

Sometimes refactorings can leave behind needlessly generic functions, like in this case:

fn foo<'a>(foo: &'a Foo<'a>) {...}

becomes

type Foo<'a> = &'a FooStruct<'a>;
fn foo<'a>(foo: Foo<'a>) {...}

If the lifetime 'a is not used anywhere else in foo, it isn't any different from an anonymous lifetime.

[huonw]

At the very least fn foo<'a>(foo: int) { ... } could be warned about, since 'a is declared but not used.

[steveklabnik]

Full example:

struct Foo<'a>;
fn foo<'a>(foo: &'a Foo<'a>) { }

fn main() {}

This is an error as of pre-1.0, so I think this can be closed?

[eddyb]

@Toby-s No, @steveklabnik's example is unrelated to the actual issue.

@eddyb thanks.

Full example:

struct FooStruct<'a> {
    val: &'a u8,
}

type Foo<'a> = &'a FooStruct<'a>;
fn foo<'a>(foo: Foo<'a>) { } // could be: fn foo(foo: Foo) { }

fn main() { }

[jonas-schievink]

Doesn't clippy have a Lint for non-elided lifetimes?

[steveklabnik]

Since new lints have a big impact on users of rustc, the policy is that they should go through the RFC process like other user-facing changes. As such, I'm going to give this one a close, but if anyone comes across this ticket and wants this lint, consider adding it to clippy and/or writing up an RFC. Thanks!