empty impl obsolete syntax error is wrong

[metajack]

impl Foo for Bar;
fails with
error: obsolete syntax: empty implementation
and the span points to the next item not the empty impl.

Why not specifically say what the new syntax is?

cc @alexcrichton

[alexcrichton]

The span should actually get fixed by #9525 (sorry about that!), but there should be a NOTE accompanying the error saying why, are you not seeing the note?

[alexcrichton]

This obsolete printing has since been removed.