Rollup of 17 pull requests

README.md

@@ -1,6 +1,4 @@
-<a href = "https://www.rust-lang.org/">
-<img width = "90%" height = "auto" src = "https://img.shields.io/badge/Rust-Programming%20Language-black?style=flat&logo=rust" alt = "The Rust Programming Language">
-</a>
+# The Rust Programming Language
 
 This is the main source code repository for [Rust]. It contains the compiler,
 standard library, and documentation.

compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs

@@ -824,7 +824,7 @@ pub(crate) fn codegen_intrinsic_call<'tcx>(
                     }
                     ty => unreachable!("bswap {}", ty),
                 }
-            };
+            }
             let res = CValue::by_val(swap(&mut fx.bcx, arg), fx.layout_of(T));
             ret.write_cvalue(fx, res);
         };

compiler/rustc_error_codes/src/error_codes/E0373.md

@@ -50,3 +50,24 @@ fn foo() -> Box<Fn(u32) -> u32> {
 
 Now that the closure has its own copy of the data, there's no need to worry
 about safety.
+
+This error may also be encountered while using `async` blocks:
+
+```compile_fail,E0373,edition2018
+use std::future::Future;
+
+async fn f() {
+    let v = vec![1, 2, 3i32];
+    spawn(async { //~ ERROR E0373
+        println!("{:?}", v)
+    });
+}
+
+fn spawn<F: Future + Send + 'static>(future: F) {
+    unimplemented!()
+}
+```
+
+Similarly to closures, `async` blocks are not executed immediately and may
+capture closed-over data by reference. For more information, see
+https://rust-lang.github.io/async-book/03_async_await/01_chapter.html.

compiler/rustc_mir/src/borrow_check/diagnostics/conflict_errors.rs

@@ -141,6 +141,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             self.add_moved_or_invoked_closure_note(location, used_place, &mut err);
 
             let mut is_loop_move = false;
+            let mut in_pattern = false;
 
             for move_site in &move_site_vec {
                 let move_out = self.move_data.moves[(*move_site).moi];
@@ -256,6 +257,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         "ref ".to_string(),
                         Applicability::MachineApplicable,
                     );
+                    in_pattern = true;
                 }
 
                 if let Some(DesugaringKind::ForLoop(_)) = move_span.desugaring_kind() {
@@ -302,7 +304,8 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             let place = &self.move_data.move_paths[mpi].place;
             let ty = place.ty(self.body, self.infcx.tcx).ty;
 
-            if is_loop_move {
+            // If we're in pattern, we do nothing in favor of the previous suggestion (#80913).
+            if is_loop_move & !in_pattern {
                 if let ty::Ref(_, _, hir::Mutability::Mut) = ty.kind() {
                     // We have a `&mut` ref, we need to reborrow on each iteration (#62112).
                     err.span_suggestion_verbose(
@@ -1318,21 +1321,30 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             Applicability::MachineApplicable,
         );
 
-        let msg = match category {
+        match category {
             ConstraintCategory::Return(_) | ConstraintCategory::OpaqueType => {
-                format!("{} is returned here", kind)
+                let msg = format!("{} is returned here", kind);
+                err.span_note(constraint_span, &msg);
             }
             ConstraintCategory::CallArgument => {
                 fr_name.highlight_region_name(&mut err);
-                format!("function requires argument type to outlive `{}`", fr_name)
+                if matches!(use_span.generator_kind(), Some(GeneratorKind::Async(_))) {
+                    err.note(
+                        "async blocks are not executed immediately and must either take a \
+                    reference or ownership of outside variables they use",
+                    );
+                } else {
+                    let msg = format!("function requires argument type to outlive `{}`", fr_name);
+                    err.span_note(constraint_span, &msg);
+                }
             }
             _ => bug!(
                 "report_escaping_closure_capture called with unexpected constraint \
                  category: `{:?}`",
                 category
             ),
-        };
-        err.span_note(constraint_span, &msg);
+        }
+
         err
     }
 

library/alloc/src/collections/binary_heap.rs

@@ -161,7 +161,10 @@ use super::SpecExtend;
 /// It is a logic error for an item to be modified in such a way that the
 /// item's ordering relative to any other item, as determined by the `Ord`
 /// trait, changes while it is in the heap. This is normally only possible
-/// through `Cell`, `RefCell`, global state, I/O, or unsafe code.
+/// through `Cell`, `RefCell`, global state, I/O, or unsafe code. The
+/// behavior resulting from such a logic error is not specified, but will
+/// not result in undefined behavior. This could include panics, incorrect
+/// results, aborts, memory leaks, and non-termination.
 ///
 /// # Examples
 ///

library/alloc/src/collections/btree/map.rs

@@ -51,6 +51,9 @@ pub(super) const MIN_LEN: usize = node::MIN_LEN_AFTER_SPLIT;
 /// It is a logic error for a key to be modified in such a way that the key's ordering relative to
 /// any other key, as determined by the [`Ord`] trait, changes while it is in the map. This is
 /// normally only possible through [`Cell`], [`RefCell`], global state, I/O, or unsafe code.
+/// The behavior resulting from such a logic error is not specified, but will not result in
+/// undefined behavior. This could include panics, incorrect results, aborts, memory leaks, and
+/// non-termination.
 ///
 /// [`Cell`]: core::cell::Cell
 /// [`RefCell`]: core::cell::RefCell

library/alloc/src/collections/btree/set.rs

@@ -22,6 +22,9 @@ use super::Recover;
 /// It is a logic error for an item to be modified in such a way that the item's ordering relative
 /// to any other item, as determined by the [`Ord`] trait, changes while it is in the set. This is
 /// normally only possible through [`Cell`], [`RefCell`], global state, I/O, or unsafe code.
+/// The behavior resulting from such a logic error is not specified, but will not result in
+/// undefined behavior. This could include panics, incorrect results, aborts, memory leaks, and
+/// non-termination.
 ///
 /// [`Ord`]: core::cmp::Ord
 /// [`Cell`]: core::cell::Cell

library/alloc/src/lib.rs

@@ -120,6 +120,7 @@
 #![feature(receiver_trait)]
 #![cfg_attr(bootstrap, feature(min_const_generics))]
 #![feature(min_specialization)]
+#![feature(set_ptr_value)]
 #![feature(slice_ptr_get)]
 #![feature(slice_ptr_len)]
 #![feature(staged_api)]

library/alloc/src/rc.rs

@@ -353,6 +353,26 @@ impl<T> Rc<T> {
     /// to upgrade the weak reference before this function returns will result
     /// in a `None` value. However, the weak reference may be cloned freely and
     /// stored for use at a later time.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(arc_new_cyclic)]
+    /// #![allow(dead_code)]
+    /// use std::rc::{Rc, Weak};
+    ///
+    /// struct Gadget {
+    ///     self_weak: Weak<Self>,
+    ///     // ... more fields
+    /// }
+    /// impl Gadget {
+    ///     pub fn new() -> Rc<Self> {
+    ///         Rc::new_cyclic(|self_weak| {
+    ///             Gadget { self_weak: self_weak.clone(), /* ... */ }
+    ///         })
+    ///     }
+    /// }
+    /// ```
     #[unstable(feature = "arc_new_cyclic", issue = "75861")]
     pub fn new_cyclic(data_fn: impl FnOnce(&Weak<T>) -> T) -> Rc<T> {
         // Construct the inner in the "uninitialized" state with a single
@@ -829,8 +849,8 @@ impl<T: ?Sized> Rc<T> {
         let offset = unsafe { data_offset(ptr) };
 
         // Reverse the offset to find the original RcBox.
-        let fake_ptr = ptr as *mut RcBox<T>;
-        let rc_ptr = unsafe { set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset)) };
+        let rc_ptr =
+            unsafe { (ptr as *mut RcBox<T>).set_ptr_value((ptr as *mut u8).offset(-offset)) };
 
         unsafe { Self::from_ptr(rc_ptr) }
     }
@@ -850,7 +870,7 @@ impl<T: ?Sized> Rc<T> {
     pub fn downgrade(this: &Self) -> Weak<T> {
         this.inner().inc_weak();
         // Make sure we do not create a dangling Weak
-        debug_assert!(!is_dangling(this.ptr));
+        debug_assert!(!is_dangling(this.ptr.as_ptr()));
         Weak { ptr: this.ptr }
     }
 
@@ -1164,7 +1184,7 @@ impl<T: ?Sized> Rc<T> {
             Self::allocate_for_layout(
                 Layout::for_value(&*ptr),
                 |layout| Global.allocate(layout),
-                |mem| set_data_ptr(ptr as *mut T, mem) as *mut RcBox<T>,
+                |mem| (ptr as *mut RcBox<T>).set_ptr_value(mem),
             )
         }
     }
@@ -1203,20 +1223,7 @@ impl<T> Rc<[T]> {
             )
         }
     }
-}
-
-/// Sets the data pointer of a `?Sized` raw pointer.
-///
-/// For a slice/trait object, this sets the `data` field and leaves the rest
-/// unchanged. For a sized raw pointer, this simply sets the pointer.
-unsafe fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T {
-    unsafe {
-        ptr::write(&mut ptr as *mut _ as *mut *mut u8, data as *mut u8);
-    }
-    ptr
-}
 
-impl<T> Rc<[T]> {
     /// Copy elements from slice into newly allocated Rc<\[T\]>
     ///
     /// Unsafe because the caller must either take ownership or bind `T: Copy`
@@ -1860,8 +1867,8 @@ impl<T> Weak<T> {
     }
 }
 
-pub(crate) fn is_dangling<T: ?Sized>(ptr: NonNull<T>) -> bool {
-    let address = ptr.as_ptr() as *mut () as usize;
+pub(crate) fn is_dangling<T: ?Sized>(ptr: *mut T) -> bool {
+    let address = ptr as *mut () as usize;
     address == usize::MAX
 }
 
@@ -1872,7 +1879,7 @@ struct WeakInner<'a> {
     strong: &'a Cell<usize>,
 }
 
-impl<T> Weak<T> {
+impl<T: ?Sized> Weak<T> {
     /// Returns a raw pointer to the object `T` pointed to by this `Weak<T>`.
     ///
     /// The pointer is valid only if there are some strong references. The pointer may be dangling,
@@ -1902,15 +1909,15 @@ impl<T> Weak<T> {
     pub fn as_ptr(&self) -> *const T {
         let ptr: *mut RcBox<T> = NonNull::as_ptr(self.ptr);
 
-        // SAFETY: we must offset the pointer manually, and said pointer may be
-        // a dangling weak (usize::MAX) if T is sized. data_offset is safe to call,
-        // because we know that a pointer to unsized T was derived from a real
-        // unsized T, as dangling weaks are only created for sized T. wrapping_offset
-        // is used so that we can use the same code path for the non-dangling
-        // unsized case and the potentially dangling sized case.
-        unsafe {
-            let offset = data_offset(ptr as *mut T);
-            set_data_ptr(ptr as *mut T, (ptr as *mut u8).wrapping_offset(offset))
+        if is_dangling(ptr) {
+            // If the pointer is dangling, we return the sentinel directly. This cannot be
+            // a valid payload address, as the payload is at least as aligned as RcBox (usize).
+            ptr as *const T
+        } else {
+            // SAFETY: if is_dangling returns false, then the pointer is dereferencable.
+            // The payload may be dropped at this point, and we have to maintain provenance,
+            // so use raw pointer manipulation.
+            unsafe { &raw const (*ptr).value }
         }
     }
 
@@ -1992,22 +1999,24 @@ impl<T> Weak<T> {
     /// [`new`]: Weak::new
     #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub unsafe fn from_raw(ptr: *const T) -> Self {
-        // SAFETY: data_offset is safe to call, because this pointer originates from a Weak.
         // See Weak::as_ptr for context on how the input pointer is derived.
-        let offset = unsafe { data_offset(ptr) };
 
-        // Reverse the offset to find the original RcBox.
-        // SAFETY: we use wrapping_offset here because the pointer may be dangling (but only if T: Sized).
-        let ptr = unsafe {
-            set_data_ptr(ptr as *mut RcBox<T>, (ptr as *mut u8).wrapping_offset(-offset))
+        let ptr = if is_dangling(ptr as *mut T) {
+            // This is a dangling Weak.
+            ptr as *mut RcBox<T>
+        } else {
+            // Otherwise, we're guaranteed the pointer came from a nondangling Weak.
+            // SAFETY: data_offset is safe to call, as ptr references a real (potentially dropped) T.
+            let offset = unsafe { data_offset(ptr) };
+            // Thus, we reverse the offset to get the whole RcBox.
+            // SAFETY: the pointer originated from a Weak, so this offset is safe.
+            unsafe { (ptr as *mut RcBox<T>).set_ptr_value((ptr as *mut u8).offset(-offset)) }
         };
 
         // SAFETY: we now have recovered the original Weak pointer, so can create the Weak.
         Weak { ptr: unsafe { NonNull::new_unchecked(ptr) } }
     }
-}
 
-impl<T: ?Sized> Weak<T> {
     /// Attempts to upgrade the `Weak` pointer to an [`Rc`], delaying
     /// dropping of the inner value if successful.
     ///
@@ -2070,7 +2079,7 @@ impl<T: ?Sized> Weak<T> {
     /// (i.e., when this `Weak` was created by `Weak::new`).
     #[inline]
     fn inner(&self) -> Option<WeakInner<'_>> {
-        if is_dangling(self.ptr) {
+        if is_dangling(self.ptr.as_ptr()) {
             None
         } else {
             // We are careful to *not* create a reference covering the "data" field, as
@@ -2325,21 +2334,19 @@ impl<T: ?Sized> AsRef<T> for Rc<T> {
 #[stable(feature = "pin", since = "1.33.0")]
 impl<T: ?Sized> Unpin for Rc<T> {}
 
-/// Get the offset within an `RcBox` for
-/// a payload of type described by a pointer.
+/// Get the offset within an `RcBox` for the payload behind a pointer.
 ///
 /// # Safety
 ///
-/// This has the same safety requirements as `align_of_val_raw`. In effect:
-///
-/// - This function is safe for any argument if `T` is sized, and
-/// - if `T` is unsized, the pointer must have appropriate pointer metadata
-///   acquired from the real instance that you are getting this offset for.
+/// The pointer must point to (and have valid metadata for) a previously
+/// valid instance of T, but the T is allowed to be dropped.
 unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
-    // Align the unsized value to the end of the `RcBox`.
-    // Because it is ?Sized, it will always be the last field in memory.
-    // Note: This is a detail of the current implementation of the compiler,
-    // and is not a guaranteed language detail. Do not rely on it outside of std.
+    // Align the unsized value to the end of the RcBox.
+    // Because RcBox is repr(C), it will always be the last field in memory.
+    // SAFETY: since the only unsized types possible are slices, trait objects,
+    // and extern types, the input safety requirement is currently enough to
+    // satisfy the requirements of align_of_val_raw; this is an implementation
+    // detail of the language that may not be relied upon outside of std.
     unsafe { data_offset_align(align_of_val_raw(ptr)) }
 }
 

library/alloc/src/rc/tests.rs

@@ -208,6 +208,30 @@ fn into_from_weak_raw() {
     }
 }
 
+#[test]
+fn test_into_from_weak_raw_unsized() {
+    use std::fmt::Display;
+    use std::string::ToString;
+
+    let arc: Rc<str> = Rc::from("foo");
+    let weak: Weak<str> = Rc::downgrade(&arc);
+
+    let ptr = Weak::into_raw(weak.clone());
+    let weak2 = unsafe { Weak::from_raw(ptr) };
+
+    assert_eq!(unsafe { &*ptr }, "foo");
+    assert!(weak.ptr_eq(&weak2));
+
+    let arc: Rc<dyn Display> = Rc::new(123);
+    let weak: Weak<dyn Display> = Rc::downgrade(&arc);
+
+    let ptr = Weak::into_raw(weak.clone());
+    let weak2 = unsafe { Weak::from_raw(ptr) };
+
+    assert_eq!(unsafe { &*ptr }.to_string(), "123");
+    assert!(weak.ptr_eq(&weak2));
+}
+
 #[test]
 fn get_mut() {
     let mut x = Rc::new(3);
@@ -294,6 +318,23 @@ fn test_unsized() {
     assert_eq!(foo, foo.clone());
 }
 
+#[test]
+fn test_maybe_thin_unsized() {
+    // If/when custom thin DSTs exist, this test should be updated to use one
+    use std::ffi::{CStr, CString};
+
+    let x: Rc<CStr> = Rc::from(CString::new("swordfish").unwrap().into_boxed_c_str());
+    assert_eq!(format!("{:?}", x), "\"swordfish\"");
+    let y: Weak<CStr> = Rc::downgrade(&x);
+    drop(x);
+
+    // At this point, the weak points to a dropped DST
+    assert!(y.upgrade().is_none());
+    // But we still need to be able to get the alloc layout to drop.
+    // CStr has no drop glue, but custom DSTs might, and need to work.
+    drop(y);
+}
+
 #[test]
 fn test_from_owned() {
     let foo = 123;