error[E0261]: use of undeclared lifetime name `'f`
  --> $DIR/span-bug-issue-121414.rs:5:22
   |
LL | impl<'a> Bar for Foo<'f> {
   |      -               ^^ undeclared lifetime
   |      |
   |      help: consider introducing lifetime `'f` here: `'f,`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0261`.