rustc-ap-rustc_error_codes 638.0.0

Automatically published version of the package `rustc_error_codes` in the rust-lang/rust repository from commit 30ca215b4e38b32aa7abdd635c5e2d56f5724494 The publishing script for this crate lives at: https://github.com/alexcrichton/rustc-auto-publish
Documentation 
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The `+` type operator was used in an ambiguous context.

Erroneous code example:

```compile_fail,E0178
trait Foo {}

struct Bar<'a> {
    x: &'a Foo + 'a,     // error!
    y: &'a mut Foo + 'a, // error!
    z: fn() -> Foo + 'a, // error!
}
```

In types, the `+` type operator has low precedence, so it is often necessary
to use parentheses:

```
trait Foo {}

struct Bar<'a> {
    x: &'a (Foo + 'a),     // ok!
    y: &'a mut (Foo + 'a), // ok!
    z: fn() -> (Foo + 'a), // ok!
}
```

More details can be found in [RFC 438].

[RFC 438]: https://github.com/rust-lang/rfcs/pull/438