diff --git a/src/liballoc/tests/vec.rs b/src/liballoc/tests/vec.rs index 3307bdf94f985..5ddac673c9ff1 100644 --- a/src/liballoc/tests/vec.rs +++ b/src/liballoc/tests/vec.rs @@ -1152,3 +1152,24 @@ fn test_try_reserve_exact() { } } + +#[test] +fn test_stable_push_pop() { + // Test that, if we reserved enough space, adding and removing elements does not + // invalidate references into the vector (such as `v0`). This test also + // runs in Miri, which would detect such problems. + let mut v = Vec::with_capacity(10); + v.push(13); + + // laundering the lifetime -- we take care that `v` does not reallocate, so that's okay. + let v0 = unsafe { &*(&v[0] as *const _) }; + + // Now do a bunch of things and occasionally use `v0` again to assert it is still valid. + v.push(1); + v.push(2); + v.insert(1, 1); + assert_eq!(*v0, 13); + v.remove(1); + v.pop().unwrap(); + assert_eq!(*v0, 13); +} diff --git a/src/liballoc/vec.rs b/src/liballoc/vec.rs index dc661a267e2a6..5cb91395b7bf7 100644 --- a/src/liballoc/vec.rs +++ b/src/liballoc/vec.rs @@ -735,6 +735,75 @@ impl Vec { self } + /// Returns a raw pointer to the vector's buffer. + /// + /// The caller must ensure that the vector outlives the pointer this + /// function returns, or else it will end up pointing to garbage. + /// Modifying the vector may cause its buffer to be reallocated, + /// which would also make any pointers to it invalid. + /// + /// The caller must also ensure that the memory the pointer (non-transitively) points to + /// is never written to (except inside an `UnsafeCell`) using this pointer or any pointer + /// derived from it. If you need to mutate the contents of the slice, use [`as_mut_ptr`]. + /// + /// # Examples + /// + /// ``` + /// let x = vec![1, 2, 4]; + /// let x_ptr = x.as_ptr(); + /// + /// unsafe { + /// for i in 0..x.len() { + /// assert_eq!(*x_ptr.add(i), 1 << i); + /// } + /// } + /// ``` + /// + /// [`as_mut_ptr`]: #method.as_mut_ptr + #[stable(feature = "vec_as_ptr", since = "1.37.0")] + #[inline] + pub fn as_ptr(&self) -> *const T { + // We shadow the slice method of the same name to avoid going through + // `deref`, which creates an intermediate reference. + let ptr = self.buf.ptr(); + unsafe { assume(!ptr.is_null()); } + ptr + } + + /// Returns an unsafe mutable pointer to the vector's buffer. + /// + /// The caller must ensure that the vector outlives the pointer this + /// function returns, or else it will end up pointing to garbage. + /// Modifying the vector may cause its buffer to be reallocated, + /// which would also make any pointers to it invalid. + /// + /// # Examples + /// + /// ``` + /// // Allocate vector big enough for 4 elements. + /// let size = 4; + /// let mut x: Vec = Vec::with_capacity(size); + /// let x_ptr = x.as_mut_ptr(); + /// + /// // Initialize elements via raw pointer writes, then set length. + /// unsafe { + /// for i in 0..size { + /// *x_ptr.add(i) = i as i32; + /// } + /// x.set_len(size); + /// } + /// assert_eq!(&*x, &[0,1,2,3]); + /// ``` + #[stable(feature = "vec_as_ptr", since = "1.37.0")] + #[inline] + pub fn as_mut_ptr(&mut self) -> *mut T { + // We shadow the slice method of the same name to avoid going through + // `deref_mut`, which creates an intermediate reference. + let ptr = self.buf.ptr(); + unsafe { assume(!ptr.is_null()); } + ptr + } + /// Forces the length of the vector to `new_len`. /// /// This is a low-level operation that maintains none of the normal @@ -1706,9 +1775,7 @@ impl ops::Deref for Vec { fn deref(&self) -> &[T] { unsafe { - let p = self.buf.ptr(); - assume(!p.is_null()); - slice::from_raw_parts(p, self.len) + slice::from_raw_parts(self.as_ptr(), self.len) } } } @@ -1717,9 +1784,7 @@ impl ops::Deref for Vec { impl ops::DerefMut for Vec { fn deref_mut(&mut self) -> &mut [T] { unsafe { - let ptr = self.buf.ptr(); - assume(!ptr.is_null()); - slice::from_raw_parts_mut(ptr, self.len) + slice::from_raw_parts_mut(self.as_mut_ptr(), self.len) } } } @@ -1754,7 +1819,6 @@ impl IntoIterator for Vec { fn into_iter(mut self) -> IntoIter { unsafe { let begin = self.as_mut_ptr(); - assume(!begin.is_null()); let end = if mem::size_of::() == 0 { arith_offset(begin as *const i8, self.len() as isize) as *const T } else {