Proposal: GHC.Generics marked UNSAFE for SafeHaskell

[Ryan Newton]

> Here?s a thought: doesn?t Generic already have an unused phantom type
> that's only there ?just in case we need to add something in the future??
> How about using that to track whether an instance was derived or not, and
> enforce *that* with SafeHaskell? Your SafeEq can then use a Generic
> Derived constraint or whatever.
>
Ah this sounds promising.  You mean that 'x' param in from/to?  So to use
that, whereever I call to/from I would have to constrain that x to be
"Derived".

But do I understand correctly that GHC would have to modified so that its
derived instances of Generic force that x param to be Derived?
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