Fix inference for adapt_structure with NamedTuple

src/base.jl

@@ -1,8 +1,10 @@
 # predefined adaptors for working with types from the Julia standard library
 
-# Use recursion on tuples to avoid inference bail-out in `map`
+# Use recursion to avoid inference bail-out in `map`
 #adapt_structure(to, xs::Union{Tuple,NamedTuple}) = map(adapt(to), xs)
-adapt_structure(to, xs::NamedTuple) = map(x->adapt(to,x), xs)
+adapt_structure(to, xs::NamedTuple{names}) where {names} =
+    NamedTuple{names}(adapt_structure(to, Tuple(xs)))
+
 adapt_structure(to, xs::Tuple) = _adapt_tuple_structure(to, xs)
 _adapt_tuple_structure(to, xs::Tuple) =
   (adapt(to, first(xs)), _adapt_tuple_structure(to, Base.tail(xs))...)