Make boxed 1-tuples have known keys
Unlike other tuples, which use special syntax and are "known" by way
of a special isBuiltInOcc_maybe
code path, boxed 1-tuples do not
use special syntax. Therefore, in order to make sure that the
internals of GHC are aware of the data Unit a = Unit a
definition
in GHC.Tuple
, we give Unit
known keys. For the full details, see
Note [One-tuples] (Wrinkle: Make boxed one-tuple names have known keys)
in GHC.Builtin.Types
.
Fixes #18097 (closed).