Bad error with deriving(Eq)

[comex]

This code is erroneous because A does not implement Eq:

struct A;
#[deriving(Eq)]
struct B(A);

However, trying to compile it produces two errors, one of which is nonsensical:

/tmp/z.rs:3:10: 3:12 error: mismatched types: expected `&&A` but found `&A` (expected &-ptr but found struct A)
/tmp/z.rs:3 struct B(A);
                     ^~
/tmp/z.rs:2:12: 2:14 note: in expansion of #[deriving(Eq)]
/tmp/z.rs:3:10: 3:12 note: expansion site
/tmp/z.rs:3:10: 3:12 error: failed to find an implementation of trait std::cmp::Eq for A
/tmp/z.rs:3 struct B(A);
                     ^~
/tmp/z.rs:2:12: 2:14 note: in expansion of #[deriving(Eq)]
/tmp/z.rs:3:10: 3:12 note: expansion site
task 'rustc' failed at 'explicit failure', /usr/src/rust/src/libsyntax/diagnostic.rs:41
task '<main>' failed at 'explicit failure', /usr/src/rust/src/librustc/lib.rs:440

[huonw]

Closing as a dupe of #7621. This is an unfortunate implementation detail that is required to get #[deriving] to work with types that move; I know approximately how to fix it and have attempted it, but I couldn't get the fix to actually work completely.