error[E0616]: field `len` of struct `sub::S` is private
  --> $DIR/issue-26472.rs:21:13
   |
LL |     let v = s.len;
   |             ^^^^^
   |
   = note: a method `len` also exists, perhaps you wish to call it

error: aborting due to previous error

If you want more information on this error, try using "rustc --explain E0616"