5702cfa255
Re-stabilize Weak::as_ptr and friends for unsized T As per [T-lang consensus](https://hackmd.io/7r3_is6uTz-163fsOV8Vfg), this uses a branch to handle the dangling case. The discussed optimization of only doing the branch in the T: ?Sized case is left for a followup patch, as doing so is not trivial (as it requires specialization) and not _obviously_ better (as it requires using `wrapping_offset` rather than `offset` more). <details><summary>Basically said optimization</summary> Specialize on `T: Sized`: ```rust fn as_ptr(&self) -> *const T { if [ T is Sized ] || !is_dangling(ptr) { (ptr as *mut T).set_ptr_value( (ptr as *mut u8).wrapping_offset(data_offset) ) } else { ptr::null() } } fn from_raw(*const T) -> Self { if [ T is Sized ] || !ptr.is_null() { let ptr = (ptr as *mut RcBox).set_ptr_value( (ptr as *mut u8).wrapping_offset(-data_offset) ); Weak { ptr } } else { Weak::new() } } ``` (but with more `set_ptr_value` to avoid `Sized` restrictions and maintain metadata.) Written in this fashion, this is not a correctness-critical specialization (i.e. so long as `[ T is Sized ]` is false for unsized `T`, it can be `rand()` for sized `T` without breaking correctness), but it's still touchy, so I'd rather do it in another PR with separate review. --- </details> This effectively reverts #80422 and re-establishes #74160. T-libs [previously signed off](https://github.com/rust-lang/rust/pull/74160#issuecomment-660539373) on this stable API change in #74160. |
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