error: captured variable cannot escape `FnMut` closure body --> $DIR/issue-53040.rs:5:8 | LL | || &mut v; | - ^^^^^^ returns a reference to a captured variable which escapes the closure body | | | 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 error: aborting due to previous error