error[E0106]: missing lifetime specifier
  --> $DIR/issue-30255.rs:9:24
   |
LL | fn f(a: &S, b: i32) -> &i32 {
   |         --             ^ expected named lifetime parameter
   |
   = help: this function's return type contains a borrowed value, but the signature does not say which one of `a`'s 2 lifetimes it is borrowed from
help: consider introducing a named lifetime parameter
   |
LL | fn f<'a>(a: &'a S, b: i32) -> &'a i32 {
   |     ++++     ++                ++

error[E0106]: missing lifetime specifier
  --> $DIR/issue-30255.rs:14:34
   |
LL | fn g(a: &S, b: bool, c: &i32) -> &i32 {
   |         --              ----     ^ expected named lifetime parameter
   |
   = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from one of `a`'s 2 lifetimes or `c`
help: consider introducing a named lifetime parameter
   |
LL | fn g<'a>(a: &'a S, b: bool, c: &'a i32) -> &'a i32 {
   |     ++++     ++                 ++          ++

error[E0106]: missing lifetime specifier
  --> $DIR/issue-30255.rs:19:44
   |
LL | fn h(a: &bool, b: bool, c: &S, d: &i32) -> &i32 {
   |         -----              --     ----     ^ expected named lifetime parameter
   |
   = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from `a`, one of `c`'s 2 lifetimes, or `d`
help: consider introducing a named lifetime parameter
   |
LL | fn h<'a>(a: &'a bool, b: bool, c: &'a S, d: &'a i32) -> &'a i32 {
   |     ++++     ++                    ++        ++          ++

error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0106`.
