error[E0501]: cannot borrow `*f` as mutable because previous closure requires unique access
  --> $DIR/borrowck-insert-during-each.rs:26:3
   |
LL |      f.foo(
   |   ___^
   |  |___|
   | ||
LL | ||         |a| { //~ ERROR closure requires unique access to `f`
   | ||         --- closure construction occurs here
LL | ||             f.n.insert(*a);
   | ||             - first borrow occurs due to use of `f` in closure
LL | ||         })
   | ||          ^
   | ||__________|
   | |___________borrow occurs here
   |             borrow later used here

error[E0500]: closure requires unique access to `f` but it is already borrowed
  --> $DIR/borrowck-insert-during-each.rs:27:9
   |
LL |     f.foo(
   |     -
   |     |
   |  ___borrow occurs here
   | |
LL | |         |a| { //~ ERROR closure requires unique access to `f`
   | |         ^^^ closure construction occurs here
LL | |             f.n.insert(*a);
   | |             - second borrow occurs due to use of `f` in closure
LL | |         })
   | |__________- borrow later used here

error: aborting due to 2 previous errors

Some errors occurred: E0500, E0501.
For more information about an error, try `rustc --explain E0500`.