Rollup of 10 pull requests

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -2077,7 +2077,6 @@ impl<'a> State<'a> {
             ast::ExprKind::Async(capture_clause, _, ref blk) => {
                 self.word_nbsp("async");
                 self.print_capture_clause(capture_clause);
-                self.s.space();
                 // cbox/ibox in analogy to the `ExprKind::Block` arm above
                 self.cbox(INDENT_UNIT);
                 self.ibox(0);

compiler/rustc_infer/src/infer/opaque_types.rs

@@ -461,10 +461,6 @@ impl<'a, 'tcx> Instantiator<'a, 'tcx> {
                     if let Some(def_id) = def_id.as_local() {
                         let opaque_hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
                         let parent_def_id = self.infcx.defining_use_anchor;
-                        let def_scope_default = || {
-                            let opaque_parent_hir_id = tcx.hir().get_parent_item(opaque_hir_id);
-                            parent_def_id == tcx.hir().local_def_id(opaque_parent_hir_id)
-                        };
                         let (in_definition_scope, origin) = match tcx.hir().expect_item(def_id).kind
                         {
                             // Anonymous `impl Trait`
@@ -481,7 +477,14 @@ impl<'a, 'tcx> Instantiator<'a, 'tcx> {
                             }) => {
                                 (may_define_opaque_type(tcx, parent_def_id, opaque_hir_id), origin)
                             }
-                            _ => (def_scope_default(), hir::OpaqueTyOrigin::TyAlias),
+                            ref itemkind => {
+                                span_bug!(
+                                    self.value_span,
+                                    "weird opaque type: {:#?}, {:#?}",
+                                    ty.kind(),
+                                    itemkind
+                                )
+                            }
                         };
                         if in_definition_scope {
                             let opaque_type_key =

compiler/rustc_span/src/symbol.rs

@@ -499,6 +499,7 @@ symbols! {
         core_panic_macro,
         cosf32,
         cosf64,
+        count,
         cr,
         crate_id,
         crate_in_paths,

compiler/rustc_typeck/src/check/method/suggest.rs

@@ -67,6 +67,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
+    fn is_slice_ty(&self, ty: Ty<'tcx>, span: Span) -> bool {
+        self.autoderef(span, ty).any(|(ty, _)| matches!(ty.kind(), ty::Slice(..) | ty::Array(..)))
+    }
+
     pub fn report_method_error(
         &self,
         mut span: Span,
@@ -691,7 +695,23 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
                 let mut restrict_type_params = false;
                 let mut unsatisfied_bounds = false;
-                if !unsatisfied_predicates.is_empty() {
+                if item_name.name == sym::count && self.is_slice_ty(actual, span) {
+                    let msg = "consider using `len` instead";
+                    if let SelfSource::MethodCall(_expr) = source {
+                        err.span_suggestion_short(
+                            span,
+                            msg,
+                            String::from("len"),
+                            Applicability::MachineApplicable,
+                        );
+                    } else {
+                        err.span_label(span, msg);
+                    }
+                    if let Some(iterator_trait) = self.tcx.get_diagnostic_item(sym::Iterator) {
+                        let iterator_trait = self.tcx.def_path_str(iterator_trait);
+                        err.note(&format!("`count` is defined on `{iterator_trait}`, which `{actual}` does not implement"));
+                    }
+                } else if !unsatisfied_predicates.is_empty() {
                     let def_span = |def_id| {
                         self.tcx.sess.source_map().guess_head_span(self.tcx.def_span(def_id))
                     };
@@ -990,9 +1010,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     }
                 }
 
-                let mut fallback_span = true;
-                let msg = "remove this method call";
                 if item_name.name == sym::as_str && actual.peel_refs().is_str() {
+                    let msg = "remove this method call";
+                    let mut fallback_span = true;
                     if let SelfSource::MethodCall(expr) = source {
                         let call_expr =
                             self.tcx.hir().expect_expr(self.tcx.hir().get_parent_node(expr.hir_id));

compiler/rustc_typeck/src/check/op.rs

@@ -492,7 +492,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) -> bool /* did we suggest to call a function because of missing parentheses? */ {
         err.span_label(span, ty.to_string());
         if let FnDef(def_id, _) = *ty.kind() {
-            let source_map = self.tcx.sess.source_map();
             if !self.tcx.has_typeck_results(def_id) {
                 return false;
             }
@@ -517,20 +516,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 .lookup_op_method(fn_sig.output(), &[other_ty], Op::Binary(op, is_assign))
                 .is_ok()
             {
-                if let Ok(snippet) = source_map.span_to_snippet(span) {
-                    let (variable_snippet, applicability) = if !fn_sig.inputs().is_empty() {
-                        (format!("{}( /* arguments */ )", snippet), Applicability::HasPlaceholders)
-                    } else {
-                        (format!("{}()", snippet), Applicability::MaybeIncorrect)
-                    };
+                let (variable_snippet, applicability) = if !fn_sig.inputs().is_empty() {
+                    ("( /* arguments */ )".to_string(), Applicability::HasPlaceholders)
+                } else {
+                    ("()".to_string(), Applicability::MaybeIncorrect)
+                };
 
-                    err.span_suggestion(
-                        span,
-                        "you might have forgotten to call this function",
-                        variable_snippet,
-                        applicability,
-                    );
-                }
+                err.span_suggestion_verbose(
+                    span.shrink_to_hi(),
+                    "you might have forgotten to call this function",
+                    variable_snippet,
+                    applicability,
+                );
                 return true;
             }
         }

compiler/rustc_typeck/src/collect/type_of.rs

@@ -172,7 +172,7 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<
                 // We've encountered an `AnonConst` in some path, so we need to
                 // figure out which generic parameter it corresponds to and return
                 // the relevant type.
-                let (arg_index, segment) = path
+                let filtered = path
                     .segments
                     .iter()
                     .filter_map(|seg| seg.args.map(|args| (args.args, seg)))
@@ -181,10 +181,17 @@ pub(super) fn opt_const_param_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<
                             .filter(|arg| arg.is_const())
                             .position(|arg| arg.id() == hir_id)
                             .map(|index| (index, seg))
-                    })
-                    .unwrap_or_else(|| {
-                        bug!("no arg matching AnonConst in path");
                     });
+                let (arg_index, segment) = match filtered {
+                    None => {
+                        tcx.sess.delay_span_bug(
+                            tcx.def_span(def_id),
+                            "no arg matching AnonConst in path",
+                        );
+                        return None;
+                    }
+                    Some(inner) => inner,
+                };
 
                 // Try to use the segment resolution if it is valid, otherwise we
                 // default to the path resolution.

library/alloc/src/collections/vec_deque/mod.rs

@@ -720,9 +720,9 @@ impl<T, A: Allocator> VecDeque<T, A> {
     ///
     /// Note that the allocator may give the collection more space than it
     /// requests. Therefore, capacity can not be relied upon to be precisely
-    /// minimal. Prefer [`reserve`] if future insertions are expected.
+    /// minimal. Prefer [`try_reserve`] if future insertions are expected.
     ///
-    /// [`reserve`]: VecDeque::reserve
+    /// [`try_reserve`]: VecDeque::try_reserve
     ///
     /// # Errors
     ///

library/alloc/src/string.rs

@@ -1044,9 +1044,9 @@ impl String {
     ///
     /// Note that the allocator may give the collection more space than it
     /// requests. Therefore, capacity can not be relied upon to be precisely
-    /// minimal. Prefer [`reserve`] if future insertions are expected.
+    /// minimal. Prefer [`try_reserve`] if future insertions are expected.
     ///
-    /// [`reserve`]: String::reserve
+    /// [`try_reserve`]: String::try_reserve
     ///
     /// # Errors
     ///

library/alloc/src/vec/mod.rs

@@ -881,9 +881,9 @@ impl<T, A: Allocator> Vec<T, A> {
     ///
     /// Note that the allocator may give the collection more space than it
     /// requests. Therefore, capacity can not be relied upon to be precisely
-    /// minimal. Prefer [`reserve`] if future insertions are expected.
+    /// minimal. Prefer [`try_reserve`] if future insertions are expected.
     ///
-    /// [`reserve`]: Vec::reserve
+    /// [`try_reserve`]: Vec::try_reserve
     ///
     /// # Errors
     ///

library/core/src/array/iter.rs

@@ -84,6 +84,135 @@ impl<T, const N: usize> IntoIter<T, N> {
         IntoIterator::into_iter(array)
     }
 
+    /// Creates an iterator over the elements in a partially-initialized buffer.
+    ///
+    /// If you have a fully-initialized array, then use [`IntoIterator`].
+    /// But this is useful for returning partial results from unsafe code.
+    ///
+    /// # Safety
+    ///
+    /// - The `buffer[initialized]` elements must all be initialized.
+    /// - The range must be canonical, with `initialized.start <= initialized.end`.
+    /// - The range must in in-bounds for the buffer, with `initialized.end <= N`.
+    ///   (Like how indexing `[0][100..100]` fails despite the range being empty.)
+    ///
+    /// It's sound to have more elements initialized than mentioned, though that
+    /// will most likely result in them being leaked.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(array_into_iter_constructors)]
+    ///
+    /// #![feature(maybe_uninit_array_assume_init)]
+    /// #![feature(maybe_uninit_uninit_array)]
+    /// use std::array::IntoIter;
+    /// use std::mem::MaybeUninit;
+    ///
+    /// # // Hi!  Thanks for reading the code.  This is restricted to `Copy` because
+    /// # // otherwise it could leak.  A fully-general version this would need a drop
+    /// # // guard to handle panics from the iterator, but this works for an example.
+    /// fn next_chunk<T: Copy, const N: usize>(
+    ///     it: &mut impl Iterator<Item = T>,
+    /// ) -> Result<[T; N], IntoIter<T, N>> {
+    ///     let mut buffer = MaybeUninit::uninit_array();
+    ///     let mut i = 0;
+    ///     while i < N {
+    ///         match it.next() {
+    ///             Some(x) => {
+    ///                 buffer[i].write(x);
+    ///                 i += 1;
+    ///             }
+    ///             None => {
+    ///                 // SAFETY: We've initialized the first `i` items
+    ///                 unsafe {
+    ///                     return Err(IntoIter::new_unchecked(buffer, 0..i));
+    ///                 }
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     // SAFETY: We've initialized all N items
+    ///     unsafe { Ok(MaybeUninit::array_assume_init(buffer)) }
+    /// }
+    ///
+    /// let r: [_; 4] = next_chunk(&mut (10..16)).unwrap();
+    /// assert_eq!(r, [10, 11, 12, 13]);
+    /// let r: IntoIter<_, 40> = next_chunk(&mut (10..16)).unwrap_err();
+    /// assert_eq!(r.collect::<Vec<_>>(), vec![10, 11, 12, 13, 14, 15]);
+    /// ```
+    #[unstable(feature = "array_into_iter_constructors", issue = "91583")]
+    #[rustc_const_unstable(feature = "const_array_into_iter_constructors", issue = "91583")]
+    pub const unsafe fn new_unchecked(
+        buffer: [MaybeUninit<T>; N],
+        initialized: Range<usize>,
+    ) -> Self {
+        Self { data: buffer, alive: initialized }
+    }
+
+    /// Creates an iterator over `T` which returns no elements.
+    ///
+    /// If you just need an empty iterator, then use
+    /// [`iter::empty()`](crate::iter::empty) instead.
+    /// And if you need an empty array, use `[]`.
+    ///
+    /// But this is useful when you need an `array::IntoIter<T, N>` *specifically*.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(array_into_iter_constructors)]
+    /// use std::array::IntoIter;
+    ///
+    /// let empty = IntoIter::<i32, 3>::empty();
+    /// assert_eq!(empty.len(), 0);
+    /// assert_eq!(empty.as_slice(), &[]);
+    ///
+    /// let empty = IntoIter::<std::convert::Infallible, 200>::empty();
+    /// assert_eq!(empty.len(), 0);
+    /// ```
+    ///
+    /// `[1, 2].into_iter()` and `[].into_iter()` have different types
+    /// ```should_fail,edition2021
+    /// #![feature(array_into_iter_constructors)]
+    /// use std::array::IntoIter;
+    ///
+    /// pub fn get_bytes(b: bool) -> IntoIter<i8, 4> {
+    ///     if b {
+    ///         [1, 2, 3, 4].into_iter()
+    ///     } else {
+    ///         [].into_iter() // error[E0308]: mismatched types
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// But using this method you can get an empty iterator of appropriate size:
+    /// ```edition2021
+    /// #![feature(array_into_iter_constructors)]
+    /// use std::array::IntoIter;
+    ///
+    /// pub fn get_bytes(b: bool) -> IntoIter<i8, 4> {
+    ///     if b {
+    ///         [1, 2, 3, 4].into_iter()
+    ///     } else {
+    ///         IntoIter::empty()
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(get_bytes(true).collect::<Vec<_>>(), vec![1, 2, 3, 4]);
+    /// assert_eq!(get_bytes(false).collect::<Vec<_>>(), vec![]);
+    /// ```
+    #[unstable(feature = "array_into_iter_constructors", issue = "91583")]
+    #[rustc_const_unstable(feature = "const_array_into_iter_constructors", issue = "91583")]
+    pub const fn empty() -> Self {
+        let buffer = MaybeUninit::uninit_array();
+        let initialized = 0..0;
+
+        // SAFETY: We're telling it that none of the elements are initialized,
+        // which is trivially true.  And ∀N: usize, 0 <= N.
+        unsafe { Self::new_unchecked(buffer, initialized) }
+    }
+
     /// Returns an immutable slice of all elements that have not been yielded
     /// yet.
     #[stable(feature = "array_value_iter", since = "1.51.0")]

library/core/src/lib.rs

@@ -101,6 +101,7 @@
 #![feature(const_align_of_val)]
 #![feature(const_alloc_layout)]
 #![feature(const_arguments_as_str)]
+#![feature(const_array_into_iter_constructors)]
 #![feature(const_bigint_helper_methods)]
 #![feature(const_caller_location)]
 #![feature(const_cell_into_inner)]
@@ -138,6 +139,7 @@
 #![feature(const_type_name)]
 #![feature(const_default_impls)]
 #![feature(duration_consts_float)]
+#![feature(maybe_uninit_uninit_array)]
 #![feature(ptr_metadata)]
 #![feature(slice_ptr_get)]
 #![feature(str_internals)]