::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 {
     |            ^^
  

  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>) {
    |                                             ^
  

  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: &'_ ()) {
    |                                                         ^
  

  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

Usage

1. 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

2. Add the following to your lib.rs file:

   #[macro_use]
   extern crate fix_hidden_lifetime_bug;
   

3. Slap a #[fix_hidden_lifetime_bug] on the problematic function:

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

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