Auto merge of #86399 - JohnTitor:rollup-qlm2dvz, r=JohnTitor

Rollup of 7 pull requests

Successful merges:

 - #85663 (Document Arc::from)
 - #85802 (Rename IoSlice(Mut)::advance to advance_slice and add IoSlice(Mut)::advance)
 - #85970 (Remove methods under Implementors on trait pages)
 - #86340 (Use better error message for hard errors in CTFE)
 - #86343 (Do not emit invalid suggestions on multiple mutable borrow errors)
 - #86355 (Remove invalid suggestions for assoc consts on placeholder type error)
 - #86389 (Make `sum()` and `product()` documentation hyperlinks refer to `Iterator` methods.)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -518,4 +518,14 @@ impl InterpError<'_> {
             _ => false,
         }
     }
+
+    /// Should this error be reported as a hard error, preventing compilation, or a soft error,
+    /// causing a deny-by-default lint?
+    pub fn is_hard_err(&self) -> bool {
+        use InterpError::*;
+        match *self {
+            MachineStop(ref err) => err.is_hard_err(),
+            _ => false,
+        }
+    }
 }

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

@@ -453,6 +453,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 &mut err,
                 "",
                 Some(borrow_span),
+                None,
             );
         err.buffer(&mut self.errors_buffer);
     }
@@ -498,6 +499,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 &mut err,
                 "",
                 None,
+                None,
             );
         err
     }
@@ -718,6 +720,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             &mut err,
             first_borrow_desc,
             None,
+            Some((issued_span, span)),
         );
 
         err
@@ -1076,6 +1079,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     &mut err,
                     "",
                     None,
+                    None,
                 );
             }
         } else {
@@ -1093,6 +1097,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 &mut err,
                 "",
                 None,
+                None,
             );
         }
 
@@ -1158,6 +1163,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             &mut err,
             "",
             None,
+            None,
         );
 
         err.buffer(&mut self.errors_buffer);
@@ -1236,6 +1242,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             &mut err,
             "",
             None,
+            None,
         );
 
         let within = if borrow_spans.for_generator() { " by generator" } else { "" };
@@ -1614,6 +1621,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             &mut err,
             "",
             None,
+            None,
         );
 
         self.explain_deref_coercion(loan, &mut err);

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

@@ -66,6 +66,7 @@ impl BorrowExplanation {
         err: &mut DiagnosticBuilder<'_>,
         borrow_desc: &str,
         borrow_span: Option<Span>,
+        multiple_borrow_span: Option<(Span, Span)>,
     ) {
         match *self {
             BorrowExplanation::UsedLater(later_use_kind, var_or_use_span, path_span) => {
@@ -192,14 +193,23 @@ impl BorrowExplanation {
 
                         if let Some(info) = &local_decl.is_block_tail {
                             if info.tail_result_is_ignored {
-                                err.span_suggestion_verbose(
-                                    info.span.shrink_to_hi(),
-                                    "consider adding semicolon after the expression so its \
-                                     temporaries are dropped sooner, before the local variables \
-                                     declared by the block are dropped",
-                                    ";".to_string(),
-                                    Applicability::MaybeIncorrect,
-                                );
+                                // #85581: If the first mutable borrow's scope contains
+                                // the second borrow, this suggestion isn't helpful.
+                                if !multiple_borrow_span
+                                    .map(|(old, new)| {
+                                        old.to(info.span.shrink_to_hi()).contains(new)
+                                    })
+                                    .unwrap_or(false)
+                                {
+                                    err.span_suggestion_verbose(
+                                        info.span.shrink_to_hi(),
+                                        "consider adding semicolon after the expression so its \
+                                        temporaries are dropped sooner, before the local variables \
+                                        declared by the block are dropped",
+                                        ";".to_string(),
+                                        Applicability::MaybeIncorrect,
+                                    );
+                                }
                             } else {
                                 err.note(
                                     "the temporary is part of an expression at the end of a \

compiler/rustc_mir/src/const_eval/error.rs

@@ -157,7 +157,7 @@ impl<'tcx> ConstEvalErr<'tcx> {
         tcx: TyCtxtAt<'tcx>,
         message: &str,
         emit: impl FnOnce(DiagnosticBuilder<'_>),
-        mut lint_root: Option<hir::HirId>,
+        lint_root: Option<hir::HirId>,
     ) -> ErrorHandled {
         let finish = |mut err: DiagnosticBuilder<'_>, span_msg: Option<String>| {
             trace!("reporting const eval failure at {:?}", self.span);
@@ -194,12 +194,6 @@ impl<'tcx> ConstEvalErr<'tcx> {
             _ => {}
         };
 
-        // If we have a 'hard error', then set `lint_root` to `None` so that we don't
-        // emit a lint.
-        if matches!(&self.error, InterpError::MachineStop(err) if err.is_hard_err()) {
-            lint_root = None;
-        }
-
         let err_msg = self.error.to_string();
 
         // Regular case - emit a lint.

compiler/rustc_mir/src/const_eval/eval_queries.rs

@@ -312,22 +312,17 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
             let err = ConstEvalErr::new(&ecx, error, None);
             // Some CTFE errors raise just a lint, not a hard error; see
             // <https://github.com/rust-lang/rust/issues/71800>.
-            let emit_as_lint = if let Some(def) = def.as_local() {
+            let is_hard_err = if let Some(def) = def.as_local() {
                 // (Associated) consts only emit a lint, since they might be unused.
-                matches!(tcx.def_kind(def.did.to_def_id()), DefKind::Const | DefKind::AssocConst)
+                !matches!(tcx.def_kind(def.did.to_def_id()), DefKind::Const | DefKind::AssocConst)
+                    // check if the inner InterpError is hard
+                    || err.error.is_hard_err()
             } else {
                 // use of broken constant from other crate: always an error
-                false
+                true
             };
-            if emit_as_lint {
-                let hir_id = tcx.hir().local_def_id_to_hir_id(def.as_local().unwrap().did);
-                Err(err.report_as_lint(
-                    tcx.at(tcx.def_span(def.did)),
-                    "any use of this value will cause an error",
-                    hir_id,
-                    Some(err.span),
-                ))
-            } else {
+
+            if is_hard_err {
                 let msg = if is_static {
                     Cow::from("could not evaluate static initializer")
                 } else {
@@ -345,6 +340,14 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
                 };
 
                 Err(err.report_as_error(ecx.tcx.at(ecx.cur_span()), &msg))
+            } else {
+                let hir_id = tcx.hir().local_def_id_to_hir_id(def.as_local().unwrap().did);
+                Err(err.report_as_lint(
+                    tcx.at(tcx.def_span(def.did)),
+                    "any use of this value will cause an error",
+                    hir_id,
+                    Some(err.span),
+                ))
             }
         }
         Ok(mplace) => {

compiler/rustc_typeck/src/collect.rs

@@ -179,8 +179,7 @@ crate fn placeholder_type_error(
     // Suggest, but only if it is not a function in const or static
     if suggest {
         let mut is_fn = false;
-        let mut is_const = false;
-        let mut is_static = false;
+        let mut is_const_or_static = false;
 
         if let Some(hir_ty) = hir_ty {
             if let hir::TyKind::BareFn(_) = hir_ty.kind {
@@ -190,19 +189,26 @@ crate fn placeholder_type_error(
                 let parent_id = tcx.hir().get_parent_node(hir_ty.hir_id);
                 let parent_node = tcx.hir().get(parent_id);
 
-                if let hir::Node::Item(item) = parent_node {
-                    if let hir::ItemKind::Const(_, _) = item.kind {
-                        is_const = true;
-                    } else if let hir::ItemKind::Static(_, _, _) = item.kind {
-                        is_static = true;
-                    }
-                }
+                is_const_or_static = match parent_node {
+                    Node::Item(&hir::Item {
+                        kind: hir::ItemKind::Const(..) | hir::ItemKind::Static(..),
+                        ..
+                    })
+                    | Node::TraitItem(&hir::TraitItem {
+                        kind: hir::TraitItemKind::Const(..),
+                        ..
+                    })
+                    | Node::ImplItem(&hir::ImplItem {
+                        kind: hir::ImplItemKind::Const(..), ..
+                    }) => true,
+                    _ => false,
+                };
             }
         }
 
         // if function is wrapped around a const or static,
         // then don't show the suggestion
-        if !(is_fn && (is_const || is_static)) {
+        if !(is_fn && is_const_or_static) {
             err.multipart_suggestion(
                 "use type parameters instead",
                 sugg,

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

@@ -38,6 +38,7 @@ impl<T> Iterator for IntoIter<T> {
     }
 
     #[inline]
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item
     where
         Self: TrustedRandomAccess,

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

@@ -103,6 +103,7 @@ impl<'a, T> Iterator for Iter<'a, T> {
     }
 
     #[inline]
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item
     where
         Self: TrustedRandomAccess,

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

@@ -89,6 +89,7 @@ impl<'a, T> Iterator for IterMut<'a, T> {
     }
 
     #[inline]
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item
     where
         Self: TrustedRandomAccess,

library/alloc/src/sync.rs

@@ -2300,6 +2300,20 @@ impl<T: ?Sized + Hash> Hash for Arc<T> {
 
 #[stable(feature = "from_for_ptrs", since = "1.6.0")]
 impl<T> From<T> for Arc<T> {
+    /// Converts a `T` into an `Arc<T>`
+    ///
+    /// The conversion moves the value into a
+    /// newly allocated `Arc`. It is equivalent to
+    /// calling `Arc::new(t)`.
+    ///
+    /// # Example
+    /// ```rust
+    /// # use std::sync::Arc;
+    /// let x = 5;
+    /// let arc = Arc::new(5);
+    ///
+    /// assert_eq!(Arc::from(x), arc);
+    /// ```
     fn from(t: T) -> Self {
         Arc::new(t)
     }

library/alloc/src/vec/into_iter.rs

@@ -163,6 +163,7 @@ impl<T, A: Allocator> Iterator for IntoIter<T, A> {
         self.len()
     }
 
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, i: usize) -> Self::Item
     where
         Self: TrustedRandomAccess,

library/core/src/array/iter.rs

@@ -132,6 +132,7 @@ impl<T, const N: usize> Iterator for IntoIter<T, N> {
     }
 
     #[inline]
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item
     where
         Self: TrustedRandomAccess,

library/core/src/iter/adapters/cloned.rs

@@ -58,6 +58,7 @@ where
         self.it.map(T::clone).fold(init, f)
     }
 
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> T
     where
         Self: TrustedRandomAccess,

library/core/src/iter/adapters/copied.rs

@@ -74,6 +74,7 @@ where
         self.it.count()
     }
 
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> T
     where
         Self: TrustedRandomAccess,

library/core/src/iter/adapters/enumerate.rs

@@ -111,6 +111,7 @@ where
     }
 
     #[rustc_inherit_overflow_checks]
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> <Self as Iterator>::Item
     where
         Self: TrustedRandomAccess,

library/core/src/iter/adapters/fuse.rs

@@ -114,6 +114,7 @@ where
     }
 
     #[inline]
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item
     where
         Self: TrustedRandomAccess,

library/core/src/iter/adapters/map.rs

@@ -122,6 +122,7 @@ where
         self.iter.fold(init, map_fold(self.f, g))
     }
 
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> B
     where
         Self: TrustedRandomAccess,

library/core/src/iter/adapters/zip.rs

@@ -88,6 +88,7 @@ where
     }
 
     #[inline]
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item
     where
         Self: TrustedRandomAccess,

library/core/src/iter/range.rs

@@ -667,6 +667,7 @@ impl<A: Step> Iterator for ops::Range<A> {
     }
 
     #[inline]
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, idx: usize) -> Self::Item
     where
         Self: TrustedRandomAccess,

library/core/src/iter/traits/accum.rs

@@ -3,12 +3,11 @@ use crate::num::Wrapping;
 
 /// Trait to represent types that can be created by summing up an iterator.
 ///
-/// This trait is used to implement the [`sum()`] method on iterators. Types which
-/// implement the trait can be generated by the [`sum()`] method. Like
-/// [`FromIterator`] this trait should rarely be called directly and instead
-/// interacted with through [`Iterator::sum()`].
+/// This trait is used to implement [`Iterator::sum()`]. Types which implement
+/// this trait can be generated by using the [`sum()`] method on an iterator.
+/// Like [`FromIterator`], this trait should rarely be called directly.
 ///
-/// [`sum()`]: Sum::sum
+/// [`sum()`]: Iterator::sum
 /// [`FromIterator`]: iter::FromIterator
 #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 pub trait Sum<A = Self>: Sized {
@@ -21,12 +20,11 @@ pub trait Sum<A = Self>: Sized {
 /// Trait to represent types that can be created by multiplying elements of an
 /// iterator.
 ///
-/// This trait is used to implement the [`product()`] method on iterators. Types
-/// which implement the trait can be generated by the [`product()`] method. Like
-/// [`FromIterator`] this trait should rarely be called directly and instead
-/// interacted with through [`Iterator::product()`].
+/// This trait is used to implement [`Iterator::product()`]. Types which implement
+/// this trait can be generated by using the [`product()`] method on an iterator.
+/// Like [`FromIterator`], this trait should rarely be called directly.
 ///
-/// [`product()`]: Product::product
+/// [`product()`]: Iterator::product
 /// [`FromIterator`]: iter::FromIterator
 #[stable(feature = "iter_arith_traits", since = "1.12.0")]
 pub trait Product<A = Self>: Sized {

library/core/src/slice/iter.rs

@@ -2148,6 +2148,7 @@ impl<'a, T, const N: usize> Iterator for ArrayChunks<'a, T, N> {
         self.iter.last()
     }
 
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, i: usize) -> &'a [T; N] {
         // SAFETY: The safety guarantees of `__iterator_get_unchecked` are
         // transferred to the caller.
@@ -2260,6 +2261,7 @@ impl<'a, T, const N: usize> Iterator for ArrayChunksMut<'a, T, N> {
         self.iter.last()
     }
 
+    #[doc(hidden)]
     unsafe fn __iterator_get_unchecked(&mut self, i: usize) -> &'a mut [T; N] {
         // SAFETY: The safety guarantees of `__iterator_get_unchecked` are transferred to
         // the caller.