error[E0284]: type annotations needed
  --> $DIR/question-mark-type-infer.rs:12:21
   |
LL |     l.iter().map(f).collect()?
   |                     ^^^^^^^
   |                     |
   |                     cannot infer type
   |                     help: consider specifying the type argument in the method call: `collect::<B>`
   |
   = note: cannot resolve `<_ as std::ops::Try>::Ok == _`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0284`.