debug_assert_with_mut_call: false positive on immutable method call

[taiki-e]

Code:

pub fn f() {
    let v = &mut &mut Vec::<()>::new();
    debug_assert!(v.is_empty()); //~ ERROR do not call a function with mutable arguments inside of `debug_assert!`
}

Error:

error: do not call a function with mutable arguments inside of `debug_assert!`
  --> rust/src/lib.rs:17:19
   |
17 |     debug_assert!(v.is_empty());
   |                   ^^^^^^^^^^^^
   |
   = note: `#[deny(clippy::debug_assert_with_mut_call)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#debug_assert_with_mut_call

[flip1995]

A workaround for this is to deref the vector once:

debug_assert!((*v).is_empty());

[philipc]

Similar issue for code:

use core::cell::{Ref, RefCell};

pub fn f() {
    let mut x = (true,);
    let cell = RefCell::new((&mut x,));
    let r = Ref::map(cell.borrow(), |x| &x.0);
    debug_assert!(r.0);
}

Error:

error: do not call a function with mutable arguments inside of `debug_assert!`
 --> src/lib.rs:7:19
  |
7 |     debug_assert!(r.0);
  |                   ^^^
  |
  = note: `#[deny(clippy::debug_assert_with_mut_call)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#debug_assert_with_mut_call