Compile error messages need to improve when assert_eq!(None, None)

[liigo]

struct A {
    v: int,
}

fn find_a() -> Option<A> {
    None
}

fn main() {
    let a = find_a();
    assert!(a.is_none());
    assert_eq!(a, None); // Got too many irrelevant compile errors!
}

Compile errors:

<std macros>:6:23: 6:50 error: binary operation `==` cannot be applied to type `core::option::Option<A>`
<std macros>:6                 if !((*given_val == *expected_val) &&
                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~
<std macros>:1:1: 14:2 note: in expansion of assert_eq!
assert_eq_none.rs:12:2: 12:22 note: expansion site
<std macros>:9:56: 9:66 error: the trait `core::fmt::Show` is not implemented for the type `A`
<std macros>:9                            (left: `{}`, right: `{}`)", *given_val, *expected_val)
                                                                      ^~~~~~~~~~
note: in expansion of format_args!
<std macros>:32:9: 33:6 note: expansion site
<std macros>:1:1: 34:2 note: in expansion of panic!
<std macros>:8:21: 10:18 note: expansion site
<std macros>:1:1: 14:2 note: in expansion of assert_eq!
assert_eq_none.rs:12:2: 12:22 note: expansion site
<std macros>:9:56: 9:66 note: the trait `core::fmt::Show` must be implemented because it is required by `core::fmt::Show::fmt`
<std macros>:9                            (left: `{}`, right: `{}`)", *given_val, *expected_val)
                                                                      ^~~~~~~~~~
note: in expansion of format_args!
<std macros>:32:9: 33:6 note: expansion site
<std macros>:1:1: 34:2 note: in expansion of panic!
<std macros>:8:21: 10:18 note: expansion site
<std macros>:1:1: 14:2 note: in expansion of assert_eq!
assert_eq_none.rs:12:2: 12:22 note: expansion site
<std macros>:9:68: 9:81 error: the trait `core::fmt::Show` is not implemented for the type `A`
<std macros>:9                            (left: `{}`, right: `{}`)", *given_val, *expected_val)
                                                                                  ^~~~~~~~~~~~~
note: in expansion of format_args!
<std macros>:32:9: 33:6 note: expansion site
<std macros>:1:1: 34:2 note: in expansion of panic!
<std macros>:8:21: 10:18 note: expansion site
<std macros>:1:1: 14:2 note: in expansion of assert_eq!
assert_eq_none.rs:12:2: 12:22 note: expansion site
<std macros>:9:68: 9:81 note: the trait `core::fmt::Show` must be implemented because it is required by `core::fmt::Show::fmt`
<std macros>:9                            (left: `{}`, right: `{}`)", *given_val, *expected_val)
                                                                                  ^~~~~~~~~~~~~
note: in expansion of format_args!
<std macros>:32:9: 33:6 note: expansion site
<std macros>:1:1: 34:2 note: in expansion of panic!
<std macros>:8:21: 10:18 note: expansion site
<std macros>:1:1: 14:2 note: in expansion of assert_eq!
assert_eq_none.rs:12:2: 12:22 note: expansion site
<std macros>:7:23: 7:50 error: the trait `core::cmp::PartialEq` is not implemented for the type `A`
<std macros>:7                      (*expected_val == *given_val)) {
                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~
<std macros>:1:1: 14:2 note: in expansion of assert_eq!
assert_eq_none.rs:12:2: 12:22 note: expansion site
error: aborting due to 4 previous errors

Adding #[deriving(PartialEq,Eq,Show)] to struct A should resolve these compile errors.

[lifthrasiir]

This really is #1679. The type system needs an information about the set of active variants.

[steveklabnik]

Yes, agreed.