+Note [View pattern usage]
+~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+ let (r, (r -> x)) = x in ...
+Here the pattern binds 'r', and then uses it *only* in the view pattern.
+We want to "see" this use, and in let-bindings we collect all uses and
+report unused variables at the binding level. So we must use bindLocalName
+here, *not* bindLocalNameFV. Trac #3943.