pub fn replace_range(&mut self, range: impl RangeBounds<usize>, replace_with: &str) {
        let (start, end) = self.ensure_range(range);
        let dest_len = end - start;
        match dest_len.cmp(&replace_with.len()) {
            Ordering::Equal => unsafe { self.replace_range_same_size(start, end, replace_with) },
            Ordering::Greater => unsafe { self.replace_range_shrink(start, end, replace_with) },
            Ordering::Less => unsafe { self.replace_range_grow(start, end, replace_with) },
        }
    }

    /// Replace into the same size.
    unsafe fn replace_range_same_size(&mut self, start: usize, end: usize, replace_with: &str) {
        core::ptr::copy_nonoverlapping(
            replace_with.as_ptr(),
            self.as_mut_ptr().add(start),
            end - start,
        );
    }

    /// Replace, so self.len() gets smaller.
    unsafe fn replace_range_shrink(&mut self, start: usize, end: usize, replace_with: &str) {
        let total_len = self.len();
        let dest_len = end - start;
        let new_len = total_len - (dest_len - replace_with.len());
        let amount = total_len - end;
        let data = self.as_mut_ptr();
        // first insert the replacement string, overwriting the current content
        core::ptr::copy_nonoverlapping(replace_with.as_ptr(), data.add(start), replace_with.len());
        // then move the tail of the CompactString forward to its new place, filling the gap
        core::ptr::copy(
            data.add(total_len - amount),
            data.add(new_len - amount),
            amount,
        );
        // and lastly we set the new length
        self.set_len(new_len);
    }

    /// Replace, so self.len() gets bigger.
    unsafe fn replace_range_grow(&mut self, start: usize, end: usize, replace_with: &str) {
        let dest_len = end - start;
        self.reserve(replace_with.len() - dest_len);
        let total_len = self.len();
        let new_len = total_len + (replace_with.len() - dest_len);
        let amount = total_len - end;
        // first grow the string, so MIRI knows that the full range is usable
        self.set_len(new_len);
        let data = self.as_mut_ptr();
        // then move the tail of the CompactString back to its new place
        core::ptr::copy(
            data.add(total_len - amount),
            data.add(new_len - amount),
            amount,
        );
        // and lastly insert the replacement string
        core::ptr::copy_nonoverlapping(replace_with.as_ptr(), data.add(start), replace_with.len());
    }

    pub fn insert_str(&mut self, idx: usize, string: &str) {
        assert!(self.is_char_boundary(idx), "idx must lie on char boundary");

        let new_len = self.len() + string.len();
        self.reserve(string.len());

        // SAFETY: We just checked that we may split self at idx.
        //         We set the length only after reserving the memory.
        //         We fill the gap with valid UTF-8 data.
        unsafe {
            // first move the tail to the new back
            let data = self.as_mut_ptr();
            core::ptr::copy(
                data.add(idx),
                data.add(idx + string.len()),
                new_len - idx - string.len(),
            );

            // then insert the new bytes
            core::ptr::copy_nonoverlapping(string.as_ptr(), data.add(idx), string.len());

            // and lastly resize the string
            self.set_len(new_len);
        }
    }

/// An iterator over the exacted data by [`CompactString::drain()`].
#[must_use = "iterators are lazy and do nothing unless consumed"]
pub struct Drain<'a> {
    compact_string: *mut CompactString,
    start: usize,
    end: usize,
    chars: core::str::Chars<'a>,
}

// SAFETY: Drain keeps the lifetime of the CompactString it belongs to.
unsafe impl Send for Drain<'_> {}
unsafe impl Sync for Drain<'_> {}

impl fmt::Debug for Drain<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_tuple("Drain").field(&self.as_str()).finish()
    }
}

impl fmt::Display for Drain<'_> {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(self.as_str())
    }
}

impl Drop for Drain<'_> {
    #[inline]
    fn drop(&mut self) {
        // SAFETY: Drain keeps a mutable reference to compact_string, so one one else can access
        //         the CompactString, but this function right now. CompactString::drain() ensured
        //         that the new extracted range does not split a UTF-8 character.
        unsafe { (*self.compact_string).replace_range_shrink(self.start, self.end, "") };
    }
}

    pub(crate) unsafe fn new(text: &str) -> Self {
        debug_assert!(text.len() <= MAX_SIZE);

        let len = text.len();
        let mut buffer = InlineBuffer([0u8; MAX_SIZE]);

        // set the length in the last byte
        buffer.0[MAX_SIZE - 1] = len as u8 | LENGTH_MASK;

        // copy the string into our buffer
        //
        // note: in the case where len == MAX_SIZE, we'll overwrite the len, but that's okay because
        // when reading the length we can detect that the last byte is part of UTF-8 and return a
        // length of MAX_SIZE
        //
        // SAFETY:
        // * src (`text`) is valid for `len` bytes because `len` comes from `text`
        // * dst (`buffer`) is valid for `len` bytes because we assert src is less than MAX_SIZE
        // * src and dst don't overlap because we created dst
        //
        ptr::copy_nonoverlapping(text.as_ptr(), buffer.0.as_mut_ptr(), len);

        buffer
    }

#[repr(C)]
pub(crate) struct Repr(
    /// We have a pointer in the representation to properly carry provenance.
    *const (),
    /// Then we need two `usize`s (aka WORDs) of data, for the first we just define a `usize`...
    usize,
    /// ...but the second we breakup into multiple pieces...
    #[cfg(target_pointer_width = "64")]
    u32,
    u16,
    u8,
    /// ...so that the last byte can be a [`LastByte`], which allows the compiler to see a niche
    /// value.
    LastByte,
);
static_assertions::assert_eq_size!([u8; MAX_SIZE], Repr);

unsafe impl Send for Repr {}
unsafe impl Sync for Repr {}