Auto merge of rust-lang#69590 - Dylan-DPC:rollup-i3z0sic, r=Dylan-DPC

Rollup of 7 pull requests

Successful merges:

 - rust-lang#69504 (Use assert_ne in hash tests)
 - rust-lang#69571 (remove unneeded .as_ref() calls.)
 - rust-lang#69572 (use .iter() instead of .into_iter() on references)
 - rust-lang#69581 (fix aliasing violation in align_to_mut)
 - rust-lang#69582 (improve transmute and Vec::from_raw_parts docs)
 - rust-lang#69584 (Correct comment to match behavior)
 - rust-lang#69587 (rustc_parse: Tweak the function parameter name check)

Failed merges:

r? @ghost

Author: bors

src/liballoc/vec.rs

@@ -404,7 +404,10 @@ impl<T> Vec<T> {
     ///
     /// * `ptr` needs to have been previously allocated via [`String`]/`Vec<T>`
     ///   (at least, it's highly likely to be incorrect if it wasn't).
-    /// * `ptr`'s `T` needs to have the same size and alignment as it was allocated with.
+    /// * `T` needs to have the same size and alignment as what `ptr` was allocated with.
+    ///   (`T` having a less strict alignment is not sufficient, the alignment really
+    ///   needs to be equal to satsify the [`dealloc`] requirement that memory must be
+    ///   allocated and deallocated with the same layout.)
     /// * `length` needs to be less than or equal to `capacity`.
     /// * `capacity` needs to be the capacity that the pointer was allocated with.
     ///
@@ -423,6 +426,7 @@ impl<T> Vec<T> {
     /// function.
     ///
     /// [`String`]: ../../std/string/struct.String.html
+    /// [`dealloc`]: ../../alloc/alloc/trait.GlobalAlloc.html#tymethod.dealloc
     ///
     /// # Examples
     ///

src/libcore/intrinsics.rs

@@ -881,7 +881,8 @@ extern "rust-intrinsic" {
     /// // clone the vector as we will reuse them later
     /// let v_clone = v_orig.clone();
     ///
-    /// // Using transmute: this is Undefined Behavior, and a bad idea.
+    /// // Using transmute: this relies on the unspecified data layout of `Vec`, which is a
+    /// // bad idea and could cause Undefined Behavior.
     /// // However, it is no-copy.
     /// let v_transmuted = unsafe {
     ///     std::mem::transmute::<Vec<&i32>, Vec<Option<&i32>>>(v_clone)
@@ -897,13 +898,14 @@ extern "rust-intrinsic" {
     ///
     /// let v_clone = v_orig.clone();
     ///
-    /// // The no-copy, unsafe way, still using transmute, but not UB.
-    /// // This is equivalent to the original, but safer, and reuses the
-    /// // same `Vec` internals. Therefore, the new inner type must have the
-    /// // exact same size, and the same alignment, as the old type.
+    /// // The no-copy, unsafe way, still using transmute, but not relying on the data layout.
+    /// // Like the first approach, this reuses the `Vec` internals.
+    /// // Therefore, the new inner type must have the
+    /// // exact same size, *and the same alignment*, as the old type.
     /// // The same caveats exist for this method as transmute, for
     /// // the original inner type (`&i32`) to the converted inner type
-    /// // (`Option<&i32>`), so read the nomicon pages linked above.
+    /// // (`Option<&i32>`), so read the nomicon pages linked above and also
+    /// // consult the [`from_raw_parts`] documentation.
     /// let v_from_raw = unsafe {
     // FIXME Update this when vec_into_raw_parts is stabilized
     ///     // Ensure the original vector is not dropped.
@@ -914,6 +916,8 @@ extern "rust-intrinsic" {
     /// };
     /// ```
     ///
+    /// [`from_raw_parts`]: ../../std/vec/struct.Vec.html#method.from_raw_parts
+    ///
     /// Implementing `split_at_mut`:
     ///
     /// ```

src/libcore/slice/mod.rs

@@ -2571,11 +2571,13 @@ impl<T> [T] {
             let (left, rest) = self.split_at_mut(offset);
             // now `rest` is definitely aligned, so `from_raw_parts_mut` below is okay
             let (us_len, ts_len) = rest.align_to_offsets::<U>();
+            let rest_len = rest.len();
             let mut_ptr = rest.as_mut_ptr();
+            // We can't use `rest` again after this, that would invalidate its alias `mut_ptr`!
             (
                 left,
                 from_raw_parts_mut(mut_ptr as *mut U, us_len),
-                from_raw_parts_mut(mut_ptr.add(rest.len() - ts_len), ts_len),
+                from_raw_parts_mut(mut_ptr.add(rest_len - ts_len), ts_len),
             )
         }
     }

src/libcore/tests/slice.rs

@@ -1570,6 +1570,18 @@ fn test_align_to_empty_mid() {
     }
 }
 
+#[test]
+fn test_align_to_mut_aliasing() {
+    let mut val = [1u8, 2, 3, 4, 5];
+    // `align_to_mut` used to create `mid` in a way that there was some intermediate
+    // incorrect aliasing, invalidating the resulting `mid` slice.
+    let (begin, mid, end) = unsafe { val.align_to_mut::<[u8; 2]>() };
+    assert!(begin.len() == 0);
+    assert!(end.len() == 1);
+    mid[0] = mid[1];
+    assert_eq!(val, [3, 4, 3, 4, 5])
+}
+
 #[test]
 fn test_slice_partition_dedup_by() {
     let mut slice: [i32; 9] = [1, -1, 2, 3, 1, -5, 5, -2, 2];

src/librustc/ty/context.rs

@@ -2291,13 +2291,13 @@ impl<'tcx> TyCtxt<'tcx> {
 
     #[inline]
     pub fn intern_tup(self, ts: &[Ty<'tcx>]) -> Ty<'tcx> {
-        let kinds: Vec<_> = ts.into_iter().map(|&t| GenericArg::from(t)).collect();
+        let kinds: Vec<_> = ts.iter().map(|&t| GenericArg::from(t)).collect();
         self.mk_ty(Tuple(self.intern_substs(&kinds)))
     }
 
     pub fn mk_tup<I: InternAs<[Ty<'tcx>], Ty<'tcx>>>(self, iter: I) -> I::Output {
         iter.intern_with(|ts| {
-            let kinds: Vec<_> = ts.into_iter().map(|&t| GenericArg::from(t)).collect();
+            let kinds: Vec<_> = ts.iter().map(|&t| GenericArg::from(t)).collect();
             self.mk_ty(Tuple(self.intern_substs(&kinds)))
         })
     }

src/librustc_builtin_macros/proc_macro_harness.rs

@@ -149,7 +149,7 @@ impl<'a> CollectProcMacros<'a> {
                         .span_err(attr.span(), "attribute must be of form: `attributes(foo, bar)`");
                     &[]
                 })
-                .into_iter()
+                .iter()
                 .filter_map(|attr| {
                     let attr = match attr.meta_item() {
                         Some(meta_item) => meta_item,

src/librustc_infer/infer/canonical/query_response.rs

@@ -630,7 +630,7 @@ pub fn make_query_region_constraints<'tcx>(
     assert!(givens.is_empty());
 
     let outlives: Vec<_> = constraints
-        .into_iter()
+        .iter()
         .map(|(k, _)| match *k {
             // Swap regions because we are going from sub (<=) to outlives
             // (>=).

src/librustc_infer/traits/on_unimplemented.rs

@@ -237,10 +237,8 @@ impl<'tcx> OnUnimplementedDirective {
             }
         }
 
-        let options: FxHashMap<Symbol, String> = options
-            .into_iter()
-            .filter_map(|(k, v)| v.as_ref().map(|v| (*k, v.to_owned())))
-            .collect();
+        let options: FxHashMap<Symbol, String> =
+            options.iter().filter_map(|(k, v)| v.as_ref().map(|v| (*k, v.to_owned()))).collect();
         OnUnimplementedNote {
             label: label.map(|l| l.format(tcx, trait_ref, &options)),
             message: message.map(|m| m.format(tcx, trait_ref, &options)),

src/librustc_infer/traits/select.rs

@@ -2411,7 +2411,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         types
             .skip_binder()
-            .into_iter()
+            .iter()
             .flat_map(|ty| {
                 // binder moved -\
                 let ty: ty::Binder<Ty<'tcx>> = ty::Binder::bind(ty); // <----/

src/librustc_lint/builtin.rs

@@ -739,7 +739,7 @@ impl EarlyLintPass for DeprecatedAttr {
 }
 
 fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &[ast::Attribute]) {
-    let mut attrs = attrs.into_iter().peekable();
+    let mut attrs = attrs.iter().peekable();
 
     // Accumulate a single span for sugared doc comments.
     let mut sugared_span: Option<Span> = None;