error: captured variable cannot escape `FnMut` closure body
  --> $DIR/issue-95079-missing-move-in-nested-closure.rs:3:29
   |
LL | fn foo1(s: &str) -> impl Iterator<Item = String> + '_ {
   |         - variable defined here
LL |     None.into_iter()
LL |         .flat_map(move |()| s.chars().map(|c| format!("{}{}", c, s)))
   |                           - -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |                           | |
   |                           | returns a reference to a captured variable which escapes the closure body
   |                           | variable captured here
   |                           inferred to be a `FnMut` closure
   |
   = note: `FnMut` closures only have access to their captured variables while they are executing...
   = note: ...therefore, they cannot allow references to captured variables to escape
help: consider adding 'move' keyword before the nested closure
   |
LL |         .flat_map(move |()| s.chars().map(move |c| format!("{}{}", c, s)))
   |                                           ++++

error: lifetime may not live long enough
  --> $DIR/issue-95079-missing-move-in-nested-closure.rs:9:15
   |
LL |     move |()| s.chars().map(|c| format!("{}{}", c, s))
   |     --------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'1` must outlive `'2`
   |     |       |
   |     |       return type of closure `Map<Chars<'_>, [closure@$DIR/issue-95079-missing-move-in-nested-closure.rs:9:29: 9:32]>` contains a lifetime `'2`
   |     lifetime `'1` represents this closure's body
   |
   = note: closure implements `Fn`, so references to captured variables can't escape the closure
help: consider adding 'move' keyword before the nested closure
   |
LL |     move |()| s.chars().map(move |c| format!("{}{}", c, s))
   |                             ++++

error: aborting due to 2 previous errors