Crate fix_hidden_lifetime_bug[−][src]

Expand description

`::fix_hidden_lifetime_bug`

Are you getting one of the two following errors (E700)?

error[E0700]: hidden type for `impl Trait` captures lifetime that does not appear in bounds
  --> examples/main.rs:13:40
   |
13 | fn foo<'a, 'b> (it: &'a mut &'b ()) -> impl 'a + Sized {
   |                                        ^^^^^^^^^^^^^^^
   |
note: hidden type `&'a mut &'b ()` captures the lifetime `'b` as defined on the function body at 13:12
  --> examples/main.rs:13:12
   |
13 | fn foo<'a, 'b> (it: &'a mut &'b ()) -> impl 'a + Sized {
   |            ^^

Problematic code

fn foo<'a, 'b> (it: &'a mut &'b ()) -> impl 'a + Sized {
    it
}

error[E0700]: hidden type for `impl Trait` captures lifetime that does not appear in bounds
 --> examples/main.rs:8:45
  |
8 | async fn bar<'a> (_: &(), _: Box<dyn Send>) {
  |                                             ^
  |
note: hidden type `impl Future` captures lifetime smaller than the function body
 --> examples/main.rs:8:45
  |
8 | async fn bar<'a> (_: &(), _: Box<dyn Send>) {
  |                                             ^

Problematic code

async fn bar<'a> (_: &(), _: Box<dyn Send>) {
    /* … */
}

error[E0700]: hidden type for `impl Trait` captures lifetime that does not appear in bounds
 --> examples/main.rs:4:57
  |
4 | async fn baz<'a> (a: &'static (), b: &'_ (), c: &'_ ()) {
  |                                                         ^
  |
note: hidden type `impl Future` captures lifetime smaller than the function body
 --> examples/main.rs:4:57
  |
4 | async fn baz<'a> (a: &'static (), b: &'_ (), c: &'_ ()) {
  |                                                         ^

Problematic code

async fn baz<'a> (a: &'static (), b: &'_ (), c: &'_ ()) {
    /* … */
}

Then you can can the attribute provided by this crate to automagically generate an equivalent signature that soothes this grumpy compiler

See the lifetime bug async issue, as well as this other comment for more info.

The fix is thus to perform the unsugaring from an async fn to an fn yielding a Future, and then just adding the necessary + Captures<'_> bounds.

Usage

cargo add fix_hidden_lifetime_bug, or add the following to your Cargo.toml file:
```
[dependencies]
fix_hidden_lifetime_bug = "x.y.z"
```
- where you can find the version using cargo search fix_hidden_lifetime_bug

Add the following to your lib.rs file:

#[macro_use]
extern crate fix_hidden_lifetime_bug;

Slap a #[fix_hidden_lifetime_bug] on the problematic function:


#[fix_hidden_lifetime_bug] // <-- Add this!
fn foo<'a, 'b>(it: &'a mut &'b ()) -> impl 'a + Sized {
    it
}


#[fix_hidden_lifetime_bug] // <-- Add this!
async fn baz<'a>(fst: &'static str, snd: &str, thrd: &str) {
    /* … */
}

Re-exports

pub use proc_macros::*;

Traits

Captures