Be more informative with object-unsafe supertraits

[emberian]

Currently, we say:

foo.rs:14:22: 14:32 error: cannot convert to a trait object because trait `Foo` is not object-safe [E0038]
foo.rs:14     let test: &Bar = &mut thing;
                               ^~~~~~~~~~
note: cannot call a generic method (`foo`) through a trait object

But we should include the information that it's Bar that is not object-safe, because Foo is not and it inherits from Foo.

[emberian]

@steveklabnik this hasn't been fixed, has it been migrated to RFCs?

[steveklabnik]

Sorry, I saw that #19539 was merged, which says "fixes 19538", and assumed that github incorrectly didn't auto close.

[steveklabnik]

I now see that the number was wrong, and this is a follow-up, not the original issue. My bad.

[nham]

This looks like it might be resolved. Code:

trait Foo {
    fn foo<T>(&self, val: T);
}

trait Bar: Foo { }

pub struct Thing;

impl Foo for Thing {
    fn foo<T>(&self, val: T) { }
}

impl Bar for Thing { }

fn main() {
    let mut thing = Thing;
    let test: &mut Bar = &mut thing;
}

And the current error:

19538.rs:18:26: 18:36 error: cannot convert to a trait object because trait `Bar` is not object-safe [E0038]
19538.rs:18     let test: &mut Bar = &mut thing;
                                     ^~~~~~~~~~
19538.rs:18:26: 18:36 note: method `foo` has generic type parameters
19538.rs:18     let test: &mut Bar = &mut thing;
                                     ^~~~~~~~~~
error: aborting due to previous error