Keep unsafe reference helpers internal

core/src/util/trust.rs

@@ -1,15 +1,26 @@
-#[allow(clippy::missing_safety_doc)]
+/// Extends a shared reference's lifetime.
-pub unsafe fn forget_ref<'a, T>(x: &T) -> &'a T {
+///
+/// # Safety
+/// The pointee must remain alive and shared-borrowed for all of `'a`.
+pub(crate) unsafe fn forget_ref<'a, T>(x: &T) -> &'a T {
     unsafe { std::mem::transmute::<&T, &T>(x) }
 }
 
-#[allow(clippy::missing_safety_doc)]
+/// Extends an exclusive reference's lifetime.
-pub unsafe fn forget_mut<'a, T>(x: &mut T) -> &'a mut T {
+///
+/// # Safety
+/// The pointee must remain alive and exclusively borrowed for all of `'a`.
+pub(crate) unsafe fn forget_mut<'a, T>(x: &mut T) -> &'a mut T {
     unsafe { std::mem::transmute::<&mut T, &mut T>(x) }
 }
 
-#[allow(clippy::mut_from_ref, clippy::missing_safety_doc)]
+/// Converts a shared reference into an exclusive reference.
-pub unsafe fn to_mut<T>(x: &T) -> &mut T {
+///
+/// # Safety
+/// The caller must have exclusive access to the pointee for the returned
+/// reference's lifetime.
+#[allow(clippy::mut_from_ref)]
+pub(crate) unsafe fn to_mut<T>(x: &T) -> &mut T {
     #[allow(mutable_transmutes)]
     unsafe {
         std::mem::transmute::<&T, &mut T>(x)