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

Rollup of 7 pull requests

Successful merges:

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

Failed merges:

r? @ghost

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;

src/librustc_mir/borrow_check/diagnostics/move_errors.rs

@@ -519,7 +519,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
     }
 
     fn add_move_error_details(&self, err: &mut DiagnosticBuilder<'a>, binds_to: &[Local]) {
-        for (j, local) in binds_to.into_iter().enumerate() {
+        for (j, local) in binds_to.iter().enumerate() {
             let bind_to = &self.body.local_decls[*local];
             let binding_span = bind_to.source_info.span;
 

src/librustc_mir/dataflow/generic/engine.rs

@@ -419,7 +419,7 @@ impl RustcMirAttrs {
         let mut ret = RustcMirAttrs::default();
 
         let rustc_mir_attrs = attrs
-            .into_iter()
+            .iter()
             .filter(|attr| attr.check_name(sym::rustc_mir))
             .flat_map(|attr| attr.meta_item_list().into_iter().flat_map(|v| v.into_iter()));
 

src/librustc_mir/dataflow/impls/borrows.rs

@@ -195,7 +195,7 @@ impl<'a, 'tcx> Borrows<'a, 'tcx> {
             .local_map
             .get(&place.local)
             .into_iter()
-            .flat_map(|bs| bs.into_iter())
+            .flat_map(|bs| bs.iter())
             .copied();
 
         // If the borrowed place is a local with no projections, all other borrows of this

src/librustc_mir/interpret/operand.rs

@@ -509,7 +509,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         &self,
         ops: &[mir::Operand<'tcx>],
     ) -> InterpResult<'tcx, Vec<OpTy<'tcx, M::PointerTag>>> {
-        ops.into_iter().map(|op| self.eval_operand(op, None)).collect()
+        ops.iter().map(|op| self.eval_operand(op, None)).collect()
     }
 
     // Used when the miri-engine runs into a constant and for extracting information from constants

src/librustc_mir/monomorphize/collector.rs

@@ -401,10 +401,8 @@ fn record_accesses<'tcx>(
     // We collect this into a `SmallVec` to avoid calling `is_inlining_candidate` in the lock.
     // FIXME: Call `is_inlining_candidate` when pushing to `neighbors` in `collect_items_rec`
     // instead to avoid creating this `SmallVec`.
-    let accesses: SmallVec<[_; 128]> = callees
-        .into_iter()
-        .map(|mono_item| (*mono_item, is_inlining_candidate(mono_item)))
-        .collect();
+    let accesses: SmallVec<[_; 128]> =
+        callees.iter().map(|mono_item| (*mono_item, is_inlining_candidate(mono_item))).collect();
 
     inlining_map.lock_mut().record_accesses(caller, &accesses);
 }

src/librustc_mir/transform/check_unsafety.rs

@@ -644,7 +644,7 @@ pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: DefId) {
         }
     }
 
-    let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
+    let mut unsafe_blocks: Vec<_> = unsafe_blocks.iter().collect();
     unsafe_blocks.sort_by_cached_key(|(hir_id, _)| tcx.hir().hir_to_node_id(*hir_id));
     let used_unsafe: FxHashSet<_> =
         unsafe_blocks.iter().flat_map(|&&(id, used)| used.then_some(id)).collect();

src/librustc_mir/transform/uninhabited_enum_branching.rs

@@ -100,7 +100,7 @@ impl<'tcx> MirPass<'tcx> for UninhabitedEnumBranching {
                 &mut body.basic_blocks_mut()[bb].terminator_mut().kind
             {
                 let vals = &*values;
-                let zipped = vals.iter().zip(targets.into_iter());
+                let zipped = vals.iter().zip(targets.iter());
 
                 let mut matched_values = Vec::with_capacity(allowed_variants.len());
                 let mut matched_targets = Vec::with_capacity(allowed_variants.len() + 1);

src/librustc_parse/parser/item.rs

@@ -6,6 +6,7 @@ use crate::maybe_whole;
 
 use rustc_ast_pretty::pprust;
 use rustc_errors::{struct_span_err, Applicability, PResult, StashKey};
+use rustc_span::edition::Edition;
 use rustc_span::source_map::{self, Span};
 use rustc_span::symbol::{kw, sym, Symbol};
 use syntax::ast::{self, AttrStyle, AttrVec, Attribute, Ident, DUMMY_NODE_ID};
@@ -636,7 +637,7 @@ impl<'a> Parser<'a> {
     }
 
     pub fn parse_trait_item(&mut self) -> PResult<'a, Option<Option<P<AssocItem>>>> {
-        self.parse_assoc_item(|t| t.span.rust_2018())
+        self.parse_assoc_item(|edition| edition >= Edition::Edition2018)
     }
 
     /// Parses associated items.
@@ -1380,7 +1381,7 @@ impl<'a> Parser<'a> {
 /// The parsing configuration used to parse a parameter list (see `parse_fn_params`).
 ///
 /// The function decides if, per-parameter `p`, `p` must have a pattern or just a type.
-type ReqName = fn(&token::Token) -> bool;
+type ReqName = fn(Edition) -> bool;
 
 /// Parsing of functions and methods.
 impl<'a> Parser<'a> {
@@ -1536,7 +1537,7 @@ impl<'a> Parser<'a> {
 
         let is_name_required = match self.token.kind {
             token::DotDotDot => false,
-            _ => req_name(&self.normalized_token),
+            _ => req_name(self.normalized_token.span.edition()),
         };
         let (pat, ty) = if is_name_required || self.is_named_param() {
             debug!("parse_param_general parse_pat (is_name_required:{})", is_name_required);

src/librustc_privacy/lib.rs

@@ -657,7 +657,7 @@ impl EmbargoVisitor<'tcx> {
                 .map(|module_hir_id| self.tcx.hir().expect_item(module_hir_id))
             {
                 if let hir::ItemKind::Mod(m) = &item.kind {
-                    for item_id in m.item_ids.as_ref() {
+                    for item_id in m.item_ids {
                         let item = self.tcx.hir().expect_item(item_id.id);
                         let def_id = self.tcx.hir().local_def_id(item_id.id);
                         if !self.tcx.hygienic_eq(segment.ident, item.ident, def_id) {

src/librustc_resolve/diagnostics.rs

@@ -1426,7 +1426,7 @@ crate fn show_candidates(
     // we want consistent results across executions, but candidates are produced
     // by iterating through a hash map, so make sure they are ordered:
     let mut path_strings: Vec<_> =
-        candidates.into_iter().map(|c| path_names_to_string(&c.path)).collect();
+        candidates.iter().map(|c| path_names_to_string(&c.path)).collect();
     path_strings.sort();
     path_strings.dedup();
 

src/librustc_save_analysis/sig.rs

@@ -430,7 +430,7 @@ impl Sig for ast::Item {
                 sig.text.push_str(" = ");
                 let ty = match ty {
                     Some(ty) => ty.make(offset + sig.text.len(), id, scx)?,
-                    None => Err("Ty")?,
+                    None => return Err("Ty"),
                 };
                 sig.text.push_str(&ty.text);
                 sig.text.push(';');

src/librustc_span/source_map.rs

@@ -395,7 +395,7 @@ impl SourceMap {
                         .unwrap_or_else(|x| x);
                     let special_chars = end_width_idx - start_width_idx;
                     let non_narrow: usize = f.non_narrow_chars[start_width_idx..end_width_idx]
-                        .into_iter()
+                        .iter()
                         .map(|x| x.width())
                         .sum();
                     col.0 - special_chars + non_narrow
@@ -413,7 +413,7 @@ impl SourceMap {
                         .binary_search_by_key(&pos, |x| x.pos())
                         .unwrap_or_else(|x| x);
                     let non_narrow: usize =
-                        f.non_narrow_chars[0..end_width_idx].into_iter().map(|x| x.width()).sum();
+                        f.non_narrow_chars[0..end_width_idx].iter().map(|x| x.width()).sum();
                     chpos.0 - end_width_idx + non_narrow
                 };
                 Loc { file: f, line: 0, col: chpos, col_display }

src/librustc_traits/lowering/mod.rs

@@ -256,7 +256,7 @@ fn program_clauses_for_trait(tcx: TyCtxt<'_>, def_id: DefId) -> Clauses<'_> {
 
     // `WellFormed(WC)`
     let wf_conditions = where_clauses
-        .into_iter()
+        .iter()
         .map(|wc| wc.subst(tcx, bound_vars))
         .map(|wc| wc.map_bound(|goal| goal.into_well_formed_goal()));
 

src/librustc_typeck/collect/type_of.rs

@@ -239,7 +239,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                             .segments
                             .iter()
                             .filter_map(|seg| seg.args.as_ref())
-                            .map(|generic_args| generic_args.args.as_ref())
+                            .map(|generic_args| generic_args.args)
                             .find_map(|args| {
                                 args.iter()
                                     .filter(|arg| arg.is_const())

src/librustdoc/clean/mod.rs

@@ -2388,9 +2388,9 @@ impl Clean<TypeBindingKind> for hir::TypeBindingKind<'_> {
             hir::TypeBindingKind::Equality { ref ty } => {
                 TypeBindingKind::Equality { ty: ty.clean(cx) }
             }
-            hir::TypeBindingKind::Constraint { ref bounds } => TypeBindingKind::Constraint {
-                bounds: bounds.into_iter().map(|b| b.clean(cx)).collect(),
-            },
+            hir::TypeBindingKind::Constraint { ref bounds } => {
+                TypeBindingKind::Constraint { bounds: bounds.iter().map(|b| b.clean(cx)).collect() }
+            }
         }
     }
 }

src/librustdoc/html/markdown.rs

@@ -738,7 +738,7 @@ impl Markdown<'_> {
             return String::new();
         }
         let replacer = |_: &str, s: &str| {
-            if let Some(&(_, ref replace)) = links.into_iter().find(|link| &*link.0 == s) {
+            if let Some(&(_, ref replace)) = links.iter().find(|link| &*link.0 == s) {
                 Some((replace.clone(), s.to_owned()))
             } else {
                 None
@@ -816,7 +816,7 @@ impl MarkdownSummaryLine<'_> {
         }
 
         let replacer = |_: &str, s: &str| {
-            if let Some(&(_, ref replace)) = links.into_iter().find(|link| &*link.0 == s) {
+            if let Some(&(_, ref replace)) = links.iter().find(|link| &*link.0 == s) {
                 Some((replace.clone(), s.to_owned()))
             } else {
                 None

src/librustdoc/html/render/cache.rs

@@ -670,7 +670,7 @@ fn get_index_type_name(clean_type: &clean::Type, accept_generic: bool) -> Option
     match *clean_type {
         clean::ResolvedPath { ref path, .. } => {
             let segments = &path.segments;
-            let path_segment = segments.into_iter().last().unwrap_or_else(|| panic!(
+            let path_segment = segments.iter().last().unwrap_or_else(|| panic!(
                 "get_index_type_name(clean_type: {:?}, accept_generic: {:?}) had length zero path",
                 clean_type, accept_generic
             ));

src/libstd/path.rs

@@ -2011,7 +2011,7 @@ impl Path {
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn file_name(&self) -> Option<&OsStr> {
         self.components().next_back().and_then(|p| match p {
-            Component::Normal(p) => Some(p.as_ref()),
+            Component::Normal(p) => Some(p),
             _ => None,
         })
     }

src/libstd/time.rs

@@ -284,7 +284,7 @@ impl Instant {
     }
 
     /// Returns the amount of time elapsed from another instant to this one,
-    /// or zero duration if that instant is earlier than this one.
+    /// or zero duration if that instant is later than this one.
     ///
     /// # Examples
     ///