- // We received `&T` arguments. Convert them to `T` by
- // stripping `&` or adding `*`. This isn't necessary for
- // type checking, but it results in much better error
- // messages if something goes wrong.
+ // We received arguments of type `&T`. Convert them to type `T` by stripping
+ // any leading `&` or adding `*`. This isn't necessary for type checking, but
+ // it results in better error messages if something goes wrong.
+ //
+ // Note: for arguments that look like `&{ x }`, which occur with packed
+ // structs, this would cause expressions like `{ self.x } == { other.x }`,
+ // which isn't valid Rust syntax. This wouldn't break compilation because these
+ // AST nodes are constructed within the compiler. But it would mean that code
+ // printed by `-Zunpretty=expanded` (or `cargo expand`) would have invalid
+ // syntax, which would be suboptimal. So we wrap these in parens, giving
+ // `({ self.x }) == ({ other.x })`, which is valid syntax.