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Auto merge of rust-lang#105409 - compiler-errors:closure-infer-cycle,…
… r=jackh726
Don't deduce a signature that makes a closure cyclic
Sometimes when elaborating supertrait bounds for closure signature inference, we end up deducing a closure signature that is cyclical because either a parameter or the return type references a projection mentioning `Self` that also has escaping bound vars, which means that it's not eagerly replaced with an inference variable.
Interestingly, this is not *just* related to my PR that elaborates supertrait bounds for closure signature deduction. The committed test `supertrait-hint-cycle-3.rs` shows **stable** code that is fixed by this PR:
```rust
trait Foo<'a> {
type Input;
}
impl<F: Fn(u32)> Foo<'_> for F {
type Input = u32;
}
fn needs_super<F: for<'a> Fn(<F as Foo<'a>>::Input) + for<'a> Foo<'a>>(_: F) {}
fn main() {
needs_super(|_: u32| {});
}
```
Fixes rust-lang#105401
Fixes rust-lang#105396
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,18 @@ | ||
| // check-pass | ||
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| trait Foo<'a> { | ||
| type Input; | ||
| } | ||
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| impl<F: Fn(u32)> Foo<'_> for F { | ||
| type Input = u32; | ||
| } | ||
|
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| trait SuperFn: for<'a> Foo<'a> + for<'a> Fn(<Self as Foo<'a>>::Input) {} | ||
| impl<T> SuperFn for T where T: for<'a> Fn(<Self as Foo<'a>>::Input) + for<'a> Foo<'a> {} | ||
|
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| fn needs_super(_: impl SuperFn) {} | ||
|
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| fn main() { | ||
| needs_super(|_: u32| {}); | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,16 @@ | ||
| // check-pass | ||
|
|
||
|
|
||
| trait Foo<'a> { | ||
| type Input; | ||
| } | ||
|
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| impl<F: Fn(u32)> Foo<'_> for F { | ||
| type Input = u32; | ||
| } | ||
|
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| fn needs_super<F: for<'a> Fn(<F as Foo<'a>>::Input) + for<'a> Foo<'a>>(_: F) {} | ||
|
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| fn main() { | ||
| needs_super(|_: u32| {}); | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,65 @@ | ||
| // edition:2021 | ||
| // check-pass | ||
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| #![feature(type_alias_impl_trait)] | ||
| #![feature(closure_lifetime_binder)] | ||
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| use std::future::Future; | ||
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| trait AsyncFn<I, R>: FnMut(I) -> Self::Fut { | ||
| type Fut: Future<Output = R>; | ||
| } | ||
|
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| impl<F, I, R, Fut> AsyncFn<I, R> for F | ||
| where | ||
| Fut: Future<Output = R>, | ||
| F: FnMut(I) -> Fut, | ||
| { | ||
| type Fut = Fut; | ||
| } | ||
|
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| async fn call<C, R, F>(mut ctx: C, mut f: F) -> Result<R, ()> | ||
| where | ||
| F: for<'a> AsyncFn<&'a mut C, Result<R, ()>>, | ||
| { | ||
| loop { | ||
| match f(&mut ctx).await { | ||
| Ok(val) => return Ok(val), | ||
| Err(_) => continue, | ||
| } | ||
| } | ||
| } | ||
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| trait Cap<'a> {} | ||
| impl<T> Cap<'_> for T {} | ||
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| fn works(ctx: &mut usize) { | ||
| let mut inner = 0; | ||
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| type Ret<'a, 'b: 'a> = impl Future<Output = Result<usize, ()>> + 'a + Cap<'b>; | ||
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| let callback = for<'a, 'b> |c: &'a mut &'b mut usize| -> Ret<'a, 'b> { | ||
| inner += 1; | ||
| async move { | ||
| let _c = c; | ||
| Ok(1usize) | ||
| } | ||
| }; | ||
| call(ctx, callback); | ||
| } | ||
|
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| fn doesnt_work_but_should(ctx: &mut usize) { | ||
| let mut inner = 0; | ||
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| type Ret<'a, 'b: 'a> = impl Future<Output = Result<usize, ()>> + 'a + Cap<'b>; | ||
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| call(ctx, for<'a, 'b> |c: &'a mut &'b mut usize| -> Ret<'a, 'b> { | ||
| inner += 1; | ||
| async move { | ||
| let _c = c; | ||
| Ok(1usize) | ||
| } | ||
| }); | ||
| } | ||
|
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| fn main() {} |
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