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Rollup merge of #69188 - GuillaumeGomez:clean-up-e0309, r=Dylan-DPC

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Clean up E0309 explanation

r? @Dylan-DPC
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Yuki Okushi 2020-02-17 13:46:59 +09:00 • committed by GitHub
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22
src/librustc_error_codes/error_codes/E0309.md
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@ -1,9 +1,7 @@
The type definition contains some field whose type
requires an outlives annotation. Outlives annotations
(e.g., `T: 'a`) are used to guarantee that all the data in T is valid
for at least the lifetime `'a`. This scenario most commonly
arises when the type contains an associated type reference
like `<T as SomeTrait<'a>>::Output`, as shown in this example:
A parameter type is missing an explicit lifetime bound and may not live long
enough.
Erroneous code example:
```compile_fail,E0309
// This won't compile because the applicable impl of
@ -25,9 +23,15 @@ where
}
```
Here, the where clause `T: 'a` that appears on the impl is not known to be
satisfied on the struct. To make this example compile, you have to add
a where-clause like `T: 'a` to the struct definition:
The type definition contains some field whose type requires an outlives
annotation. Outlives annotations (e.g., `T: 'a`) are used to guarantee that all
the data in T is valid for at least the lifetime `'a`. This scenario most
commonly arises when the type contains an associated type reference like
`<T as SomeTrait<'a>>::Output`, as shown in the previous code.
There, the where clause `T: 'a` that appears on the impl is not known to be
satisfied on the struct. To make this example compile, you have to add a
where-clause like `T: 'a` to the struct definition:
```
struct Foo<'a, T>