Suggest defining type parameter when appropriate

[rust.git] / src / liballoc / sync.rs

diff --git a/src/liballoc/sync.rs b/src/liballoc/sync.rs
index dc53ad28407276827775435f9c0c12225b302954..4aa0190b149c108fc35af8f9c897b1908e9b73ac 100644 (file)
--- a/src/liballoc/sync.rs
+++ b/src/liballoc/sync.rs
@@ -545,9 +545,19 @@ impl<T: ?Sized> Arc<T> {
     /// ```
     #[stable(feature = "rc_raw", since = "1.17.0")]
     pub fn into_raw(this: Self) -> *const T {
-        let ptr: *const T = &*this;
+        let ptr: *mut ArcInner<T> = NonNull::as_ptr(this.ptr);
+        let fake_ptr = ptr as *mut T;
         mem::forget(this);
-        ptr
+
+        // SAFETY: This cannot go through Deref::deref.
+        // Instead, we manually offset the pointer rather than manifesting a reference.
+        // This is so that the returned pointer retains the same provenance as our pointer.
+        // This is required so that e.g. `get_mut` can write through the pointer
+        // after the Arc is recovered through `from_raw`.
+        unsafe {
+            let offset = data_offset(&(*ptr).data);
+            set_data_ptr(fake_ptr, (ptr as *mut u8).offset(offset))
+        }
     }
 
     /// Constructs an `Arc` from a raw pointer.