Lambdas in unsafe are inlined at every call site

[lucic71]

The corresponding Rust closure is not saved in a let binding, instead, on every closure call, the body is fully inlined.

template <typename F> int apply(F fn, int x) { return fn(x); }

int main() {
  int base = 10;
  auto add_base = [&base](int x) { return x + base; };
  return apply(add_base, 5);
}

becomes

pub unsafe fn apply_0(mut fn_: impl Fn(i32) -> i32, mut x: i32) -> i32 {
    return fn_(x);
}
unsafe fn main_0() -> i32 {
    let mut base: i32 = 10;
    return apply_0(
        (|x: i32| {
            return x + base;
        })
        .clone(),
        5,
    );
}

A stored closure that captures locals by reference keeps the local borrowed for as long as the closure lives. So let foo = || { a += 1; a }; return foo() + a; does not compile