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Add E0316.md

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This commit is contained in:
Fabian Wolff 2021-06-07 13:05:17 +02:00
parent a20870bdb9
commit c01d63ab76
2 changed files with 33 additions and 1 deletions
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2
compiler/rustc_error_codes/src/error_codes.rs
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@ -157,6 +157,7 @@ E0308: include_str!("./error_codes/E0308.md"),
E0309: include_str!("./error_codes/E0309.md"),
E0310: include_str!("./error_codes/E0310.md"),
E0312: include_str!("./error_codes/E0312.md"),
E0316: include_str!("./error_codes/E0316.md"),
E0317: include_str!("./error_codes/E0317.md"),
E0321: include_str!("./error_codes/E0321.md"),
E0322: include_str!("./error_codes/E0322.md"),
@ -555,7 +556,6 @@ E0783: include_str!("./error_codes/E0783.md"),
// variable
// E0314, // closure outlives stack frame
// E0315, // cannot invoke closure outside of its lifetime
E0316, // nested quantification of lifetimes
// E0319, // trait impls for defaulted traits allowed just for structs/enums
E0320, // recursive overflow during dropck
// E0372, // coherence not object safe

32
compiler/rustc_error_codes/src/error_codes/E0316.md Normal file
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@ -0,0 +1,32 @@
A `where` clause contains a nested quantification over lifetimes.
Erroneous code example:
```compile_fail,E0316
trait Tr<'a, 'b> {}
fn foo<T>(t: T)
where
for<'a> &'a T: for<'b> Tr<'a, 'b>, // error: nested quantification
{
}
```
Rust syntax allows lifetime quantifications in two places within
`where` clauses: Quantifying over the trait bound only (as in
`Ty: for<'l> Trait<'l>`) and quantifying over the whole clause
(as in `for<'l> &'l Ty: Trait<'l>`). Using both in the same clause
leads to a nested lifetime quantification, which is not supported.
The following example compiles, because the clause with the nested
quantification has been rewritten to use only one `for<>`:
```
trait Tr<'a, 'b> {}
fn foo<T>(t: T)
where
for<'a, 'b> &'a T: Tr<'a, 'b>, // ok
{
}
```