error[E0621]: explicit lifetime required in the type of `y`
  --> $DIR/mismatched.rs:4:42
   |
LL | fn foo(x: &'a u32, y: &u32) -> &'a u32 { y }
   |                       ----               ^ lifetime `'a` required
   |                       |
   |                       help: add explicit lifetime `'a` to the type of `y`: `&'a u32`

error[E0623]: lifetime mismatch
  --> $DIR/mismatched.rs:6:46
   |
LL | fn foo2(x: &'a u32, y: &'b u32) -> &'a u32 { y }
   |                        -------     -------   ^ ...but data from `y` is returned here
   |                        |
   |                        this parameter and the return type are declared with different lifetimes...

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0621, E0623.
For more information about an error, try `rustc --explain E0621`.