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 discrimant value is present more than once.

Erroneous code example:

```compile_fail,E0081
enum Enum {
    P = 3,
    X = 3, // error!
    Y = 5,
}
```

Enum discriminants are used to differentiate enum variants stored in memory.
This error indicates that the same value was used for two or more variants,
making it impossible to distinguish them.

```
enum Enum {
    P,
    X = 3, // ok!
    Y = 5,
}
```

Note that variants without a manually specified discriminant are numbered from
top to bottom starting from 0, so clashes can occur with seemingly unrelated
variants.

```compile_fail,E0081
enum Bad {
    X,
    Y = 0, // error!
}
```

Here `X` will have already been specified the discriminant 0 by the time `Y` is
encountered, so a conflict occurs.