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Account for missing lifetime in opaque return type
When encountering an opaque closure return type that needs to bound a
lifetime to the function's arguments, including borrows and type params,
provide appropriate suggestions that lead to working code.
Get the user from
```rust
fn foo<G, T>(g: G, dest: &mut T) -> impl FnOnce()
where
G: Get<T>
{
move || {
*dest = g.get();
}
}
```
to
```rust
fn foo<'a, G: 'a, T>(g: G, dest: &'a mut T) -> impl FnOnce() +'a
where
G: Get<T>
{
move || {
*dest = g.get();
}
}
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100 changes: 100 additions & 0 deletions
100
src/test/ui/suggestions/lifetimes/missing-lifetimes-in-signature.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,100 @@ | ||
| pub trait Get<T> { | ||
| fn get(self) -> T; | ||
| } | ||
|
|
||
| struct Foo { | ||
| x: usize, | ||
| } | ||
|
|
||
| impl Get<usize> for Foo { | ||
| fn get(self) -> usize { | ||
| self.x | ||
| } | ||
| } | ||
|
|
||
| fn foo<G, T>(g: G, dest: &mut T) -> impl FnOnce() | ||
| where | ||
| G: Get<T> | ||
| { | ||
| move || { //~ ERROR cannot infer an appropriate lifetime | ||
| *dest = g.get(); | ||
| } | ||
| } | ||
|
|
||
| // After applying suggestion for `foo`: | ||
| fn bar<G, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ | ||
| //~^ ERROR the parameter type `G` may not live long enough | ||
| where | ||
| G: Get<T> | ||
| { | ||
| move || { | ||
| *dest = g.get(); | ||
| } | ||
| } | ||
|
|
||
|
|
||
| // After applying suggestion for `bar`: | ||
| fn baz<G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ //~ ERROR undeclared lifetime | ||
| where | ||
| G: Get<T> | ||
| { | ||
| move || { | ||
| *dest = g.get(); | ||
| } | ||
| } | ||
|
|
||
| // After applying suggestion for `baz`: | ||
| fn qux<'a, G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ | ||
| //~^ ERROR the parameter type `G` may not live long enough | ||
| where | ||
| G: Get<T> | ||
| { | ||
| move || { | ||
| *dest = g.get(); | ||
| } | ||
| } | ||
|
|
||
| // After applying suggestion for `qux`: | ||
| // FIXME: we should suggest be suggesting to change `dest` to `&'a mut T`. | ||
| fn bat<'a, G: 'a, T>(g: G, dest: &mut T) -> impl FnOnce() + '_ + 'a | ||
| where | ||
| G: Get<T> | ||
| { | ||
| move || { //~ ERROR cannot infer an appropriate lifetime | ||
| *dest = g.get(); | ||
| } | ||
| } | ||
|
|
||
| // Potential incorrect attempt: | ||
| fn bak<'a, G, T>(g: G, dest: &'a mut T) -> impl FnOnce() + 'a | ||
| //~^ ERROR the parameter type `G` may not live long enough | ||
| where | ||
| G: Get<T> | ||
| { | ||
| move || { | ||
| *dest = g.get(); | ||
| } | ||
| } | ||
|
|
||
|
|
||
| // We need to tie the lifetime of `G` with the lifetime of `&mut T` and the returned closure: | ||
| fn ok<'a, G: 'a, T>(g: G, dest: &'a mut T) -> impl FnOnce() + 'a | ||
| where | ||
| G: Get<T> | ||
| { | ||
| move || { | ||
| *dest = g.get(); | ||
| } | ||
| } | ||
|
|
||
| // This also works. The `'_` isn't necessary but it's where we arrive to following the suggestions: | ||
| fn ok2<'a, G: 'a, T>(g: G, dest: &'a mut T) -> impl FnOnce() + '_ + 'a | ||
| where | ||
| G: Get<T> | ||
| { | ||
| move || { | ||
| *dest = g.get(); | ||
| } | ||
| } | ||
|
|
||
| fn main() {} |
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