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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Type parameter defaults cannot use `Self` on structs, enums, or unions.

Erroneous code example:

```compile_fail,E0735
struct Foo<X = Box<Self>> {
    field1: Option<X>,
    field2: Option<X>,
}
// error: type parameters cannot use `Self` in their defaults.
```