Point at fields that make the type recursive
On recursive types of infinite size, point at all the fields that make
the type recursive.
```rust
struct Foo {
bar: Bar,
}
struct Bar {
foo: Foo,
}
```
outputs
```
error[E0072]: recursive type `Foo` has infinite size
--> file.rs:1:1
1 | struct Foo {
| ^^^^^^^^^^ recursive type has infinite size
2 | bar: Bar,
| -------- recursive here
|
= help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `Foo` representable
error[E0072]: recursive type `Bar` has infinite size
--> file.rs:5:1
|
5 | struct Bar {
| ^^^^^^^^^^ recursive type has infinite size
6 | foo: Foo,
| -------- recursive here
|
= help: insert indirection (e.g., a `Box`, `Rc`, or `&`) at some point to make `Bar` representable
```
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