This PR adds the ability to do `deriving ReflBEq, LawfulBEq`. Both
classes have to listed in the `deriving` clause. For `ReflBEq`, a simple
`simp`-based proof is used. For `LawfulBEq`, a dedicated,
syntax-directed tactic is used that should work for derived `BEq`
instances. This is meant to work with `deriving BEq` (but you can try to
use it on hand-rolled `@[methods_specs] instance : BEq…` instances).
Does not support mutual or nested inductives.
This PR fixes an issue that caused some `deriving` handlers to fail when
the name of the type being declared matched that of a declaration in an
open namespace.
Closes#9366
