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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A non-ident or non-wildcard pattern has been used as a parameter of a function
pointer type.

Erroneous code example:

```compile_fail,E0561
type A1 = fn(mut param: u8); // error!
type A2 = fn(&param: u32); // error!
```

When using an alias over a function type, you cannot e.g. denote a parameter as
being mutable.

To fix the issue, remove patterns (`_` is allowed though). Example:

```
type A1 = fn(param: u8); // ok!
type A2 = fn(_: u32); // ok!
```

You can also omit the parameter name:

```
type A3 = fn(i16); // ok!
```