Elision in method can take 'static from self, perhaps surprising

@aturon

rustc currently compiles the following with no warnings or errors:

struct Foo;

impl Foo {
    pub fn get_mut(&'static self, x: &mut u8) -> &mut u8 {
        unsafe { &mut *(x as *mut _) }
    }
}

However, attempting to make this function safe reveals that the elided lifetime of x isn't the lifetime in the return type-- it's instead copying over the 'static lifetime into the return type! Rustdoc actually documents that the signature of this method is fn get_mut(&'static self, x: &mut u8) -> &'static mut u8.

The following code produces an error:

struct Foo;

impl Foo {
    pub fn get_mut(&'static self, x: &mut u8) -> &mut u8 {
        x
    }
}

error[E0312]: lifetime of reference outlives lifetime of borrowed content...
 --> src/main.rs:7:9
  |
7 |         x
  |         ^
  |
  = note: ...the reference is valid for the static lifetime...
note: ...but the borrowed content is only valid for the anonymous lifetime #1 defined on the method body at 6:5
 --> src/main.rs:6:5
  |
6 | /     pub fn get_mut(&'static self, x: &mut u8) -> &mut u8 {
7 | |         x
8 | |     }
  | |_____^

error: aborting due to previous error

error: Could not compile `playground`.

This seems like it could be fixed by disallowing elision in this case via a lint.

cc @aturon

@nikomatsakis

Sounds like a case of "disallow elided lifetimes that refer to explicit lifetimes", I recall @nikomatsakis being in favor of forbidding this.

I agree this is undesirable, but as @leodasvacas notes, I would say 'no more undesirable than any other named lifetime'. We should implement that lint.

I retitled the issue to be less dramatic =)

Triage: Marking as E-help-wanted to implement a lint that warns when an elided lifetime ends up being a named lifetime. There seems to be a broad consensus that this would be good to lint for.

@rustbot

@rustbot claim

Rollup merge of rust-lang#129207 - GrigorenkoPV:elided-is-named, r=cj…

Unrolled build for rust-lang#129207

Rollup merge of #129207 - GrigorenkoPV:elided-is-named, r=cjgillot

Auto merge of #138677 - shepmaster:consistent-elided-lifetime-syntax,…

Navigation Menu

Repository navigation

Elision in method can take `'static` from `self`, perhaps surprising #48686

1 remaining item

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Elision in method can take 'static from self, perhaps surprising #48686

Description

Activity

leoyvens commented on Mar 2, 2018

nikomatsakis commented on Mar 6, 2018

nikomatsakis commented on Mar 6, 2018

Enselic commented on Nov 18, 2023

GrigorenkoPV commented on Aug 15, 2024

1 remaining item

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

Elision in method can take `'static` from `self`, perhaps surprising #48686