Implicit resolution fails for newtypes with shapeless Lazy

[ashleymercer]

Several types in cats such as NonEmptyChain are defined using the newts / newtypes approach: the advantage of this is that there is zero (runtime) overhead to using these types versus the possibly-empty equivalents; however, it leads to several issues, raised here and elsewhere:

• Unexpected behavior of NonEmptyMap #3117
• Obtaining typeTag of NonEmptySet #2928
• Compile error with PlayJson macro and cats.data.Newtype (via NonEmptySet) #2582

To this list I would like to add an issue with implicit resolution when using shapeless Lazy: see milessabin/shapeless#942 for the gory details but, in short, it's impossible to write something like:

def foo(implicit tc: Lazy[Semigroup[NonEmptyChain]]): ...

The non-Lazy version works just fine (as do by-name implicits in scala 2.13+). Interestingly, the Lazy version does work if either (or both) of the following are true:

• the implementation class (NonEmptyChainImpl in this case) is public
• the required implicits are explicitly re-imported at the call site (import NonEmptyChain._)

Clearly the end-user can't control the first, and the second is far from ideal (and took several days to discover as a workaround).

It seems like a lot of these issues boil down to variations on scala/bug#6794 and, given that this is unlikely to be fixed in its entirety any time soon, is there some benefit to considering moving away from newtype altogether?