Unsoundness in UtilMSBIntroSorter::reader

[lwz23]

Hello, thank you for your contribution in this project, I am scanning the unsoundness problem in rust project.
I notice the following code:

impl<P: MutablePointsReader> UtilMSBIntroSorter<P> {
    pub fn new(k: i32, packed_bytes_length: i32, reader: *mut P, bits_per_doc_id: i32) -> Self {
        UtilMSBIntroSorter {
            k,
            packed_bytes_length,
            pivot_doc: 0,
            pivot: vec![0u8; packed_bytes_length as usize + 1],
            scratch: vec![0u8; packed_bytes_length as usize + 1],
            reader,
            bits_per_doc_id,
        }
    }

    #[inline]
    #[allow(clippy::mut_from_ref)]
    fn reader(&self) -> &mut P {
        unsafe { &mut *self.reader }
    }
}

Considering that pub mod core, and new is also a pub function. I assume that users can directly call this function. This potential situation could result in *self.reader being dereference a null pointer, and directly dereferencing it might trigger undefined behavior (UB). For safety reasons, I felt it necessary to report this issue. If you have performed checks elsewhere that ensure this is safe, please don’t take offense at my raising this issue.
I suggest Several possible fixes:

1. If there is no external usage for UtilMSBIntroSorter or new, they should not marked as pub, at least its new should not marked as pub
2. new method should add additional check for null pointer.
3. mark new method as unsafe and proper doc to let users know that they should provide valid Pointers.

[lwz23]

ping