compiler/rustc_error_codes/src/error_codes/E0297.md

#### Note: this error code is no longer emitted by the compiler.

Patterns used to bind names must be irrefutable. That is, they must guarantee
that a name will be extracted in all cases. Instead of pattern matching the
loop variable, consider using a `match` or `if let` inside the loop body. For
instance:

```compile_fail,E0005
let xs : Vec<Option<i32>> = vec![Some(1), None];

// This fails because `None` is not covered.
for Some(x) in xs {
    // ...
}
```

Match inside the loop instead:

```
let xs : Vec<Option<i32>> = vec![Some(1), None];

for item in xs {
    match item {
        Some(x) => {},
        None => {},
    }
}
```

Or use `if let`:

```
let xs : Vec<Option<i32>> = vec![Some(1), None];

for item in xs {
    if let Some(x) = item {
        // ...
    }
}
```