error[E0506]: cannot assign to `greeting` because it is borrowed
  --> $DIR/issue-58776-borrowck-scans-children.rs:5:5
   |
LL |     let res = (|| (|| &greeting)())();
   |                --      -------- borrow occurs due to use in closure
   |                |
   |                `greeting` is borrowed here
LL |
LL |     greeting = "DEALLOCATED".to_string();
   |     ^^^^^^^^ `greeting` is assigned to here but it was already borrowed
...
LL |     println!("thread result: {:?}", res);
   |                                     --- borrow later used here

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0506`.