type "(option[int])[]" does not round-trip

Reduced from src/test/run-pass/alloca-from-derived-tydesc.rs

```
type r = (option[int])[];
```

rustc --pretty normal ~/Desktop/a.rs > ~/Desktop/ap.rs

```
type r = option[int][];
```

rustc ~/Desktop/ap.rs

```
ap.rs:1:21:1:22: error: expecting ;, found [
```

Which is wrong, the pretty-printer (omitting the parens) or the parser (requiring the parens)?
