An unknown tuple struct/variant has been used.
Erroneous code example:
```compile_fail,E0531
let Type(x) = Type(12); // error!
match Bar(12) {
Bar(x) => {} // error!
_ => {}
}
```
In most cases, it's either a forgotten import or a typo. However, let's look at
how you can have such a type:
```edition2018
struct Type(u32); // this is a tuple struct
enum Foo {
Bar(u32), // this is a tuple variant
}
use Foo::*; // To use Foo's variant directly, we need to import them in
// the scope.
```
Either way, it should work fine with our previous code:
```edition2018
struct Type(u32);
enum Foo {
Bar(u32),
}
use Foo::*;
let Type(x) = Type(12); // ok!
match Type(12) {
Type(x) => {} // ok!
_ => {}
}
```