error[E0495]: cannot infer an appropriate lifetime for borrow expression due to conflicting requirements
  --> $DIR/regions-return-ref-to-upvar-issue-17403.rs:7:24
   |
LL |         let mut f = || &mut x; //~ ERROR cannot infer
   |                        ^^^^^^
   |
note: first, the lifetime cannot outlive the lifetime  as defined on the body at 7:21...
  --> $DIR/regions-return-ref-to-upvar-issue-17403.rs:7:21
   |
LL |         let mut f = || &mut x; //~ ERROR cannot infer
   |                     ^^^^^^^^^
note: ...so that closure can access `x`
  --> $DIR/regions-return-ref-to-upvar-issue-17403.rs:7:24
   |
LL |         let mut f = || &mut x; //~ ERROR cannot infer
   |                        ^^^^^^
note: but, the lifetime must be valid for the call at 9:17...
  --> $DIR/regions-return-ref-to-upvar-issue-17403.rs:9:17
   |
LL |         let y = f();
   |                 ^^^
note: ...so type `&mut i32` of expression is valid during the expression
  --> $DIR/regions-return-ref-to-upvar-issue-17403.rs:9:17
   |
LL |         let y = f();
   |                 ^^^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0495`.