Auto merge of rust-lang#85720 - Dylan-DPC:rollup-in5917x, r=Dylan-DPC

Rollup of 8 pull requests

Successful merges:

 - rust-lang#85478 (Disallow shadowing const parameters)
 - rust-lang#85625 (Prevent double drop in `Vec::dedup_by` if a destructor panics)
 - rust-lang#85627 (Fix a few details in THIR unsafeck)
 - rust-lang#85633 (Post-monomorphization errors traces MVP)
 - rust-lang#85670 (Remove arrays/IntoIterator message from Iterator trait.)
 - rust-lang#85678 (fix `matches!` and `assert_matches!` on edition 2021)
 - rust-lang#85679 (Remove num_as_ne_bytes feature)
 - rust-lang#85712 (Fix typo in core::array::IntoIter comment)

Failed merges:

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

Author: bors

compiler/rustc_middle/src/mir/mono.rs

@@ -186,6 +186,15 @@ impl<'tcx> MonoItem<'tcx> {
     pub fn codegen_dep_node(&self, tcx: TyCtxt<'tcx>) -> DepNode {
         crate::dep_graph::make_compile_mono_item(tcx, self)
     }
+
+    /// Returns the item's `CrateNum`
+    pub fn krate(&self) -> CrateNum {
+        match self {
+            MonoItem::Fn(ref instance) => instance.def_id().krate,
+            MonoItem::Static(def_id) => def_id.krate,
+            MonoItem::GlobalAsm(..) => LOCAL_CRATE,
+        }
+    }
 }
 
 impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for MonoItem<'tcx> {

compiler/rustc_mir/src/monomorphize/collector.rs

@@ -184,7 +184,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::sync::{par_iter, MTLock, MTRef, ParallelIterator};
 use rustc_errors::{ErrorReported, FatalError};
 use rustc_hir as hir;
-use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId};
+use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
 use rustc_hir::lang_items::LangItem;
 use rustc_index::bit_set::GrowableBitSet;
@@ -342,7 +342,8 @@ fn collect_roots(tcx: TyCtxt<'_>, mode: MonoItemCollectionMode) -> Vec<MonoItem<
         .collect()
 }
 
-// Collect all monomorphized items reachable from `starting_point`
+/// Collect all monomorphized items reachable from `starting_point`, and emit a note diagnostic if a
+/// post-monorphization error is encountered during a collection step.
 fn collect_items_rec<'tcx>(
     tcx: TyCtxt<'tcx>,
     starting_point: Spanned<MonoItem<'tcx>>,
@@ -359,6 +360,31 @@ fn collect_items_rec<'tcx>(
     let mut neighbors = Vec::new();
     let recursion_depth_reset;
 
+    //
+    // Post-monomorphization errors MVP
+    //
+    // We can encounter errors while monomorphizing an item, but we don't have a good way of
+    // showing a complete stack of spans ultimately leading to collecting the erroneous one yet.
+    // (It's also currently unclear exactly which diagnostics and information would be interesting
+    // to report in such cases)
+    //
+    // This leads to suboptimal error reporting: a post-monomorphization error (PME) will be
+    // shown with just a spanned piece of code causing the error, without information on where
+    // it was called from. This is especially obscure if the erroneous mono item is in a
+    // dependency. See for example issue #85155, where, before minimization, a PME happened two
+    // crates downstream from libcore's stdarch, without a way to know which dependency was the
+    // cause.
+    //
+    // If such an error occurs in the current crate, its span will be enough to locate the
+    // source. If the cause is in another crate, the goal here is to quickly locate which mono
+    // item in the current crate is ultimately responsible for causing the error.
+    //
+    // To give at least _some_ context to the user: while collecting mono items, we check the
+    // error count. If it has changed, a PME occurred, and we trigger some diagnostics about the
+    // current step of mono items collection.
+    //
+    let error_count = tcx.sess.diagnostic().err_count();
+
     match starting_point.node {
         MonoItem::Static(def_id) => {
             let instance = Instance::mono(tcx, def_id);
@@ -411,6 +437,22 @@ fn collect_items_rec<'tcx>(
         }
     }
 
+    // Check for PMEs and emit a diagnostic if one happened. To try to show relevant edges of the
+    // mono item graph where the PME diagnostics are currently the most problematic (e.g. ones
+    // involving a dependency, and the lack of context is confusing) in this MVP, we focus on
+    // diagnostics on edges crossing a crate boundary: the collected mono items which are not
+    // defined in the local crate.
+    if tcx.sess.diagnostic().err_count() > error_count && starting_point.node.krate() != LOCAL_CRATE
+    {
+        tcx.sess.span_note_without_error(
+            starting_point.span,
+            &format!(
+                "the above error was encountered while instantiating `{}`",
+                starting_point.node
+            ),
+        );
+    }
+
     record_accesses(tcx, starting_point.node, neighbors.iter().map(|i| &i.node), inlining_map);
 
     for neighbour in neighbors {

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -42,7 +42,7 @@ impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
             self.warn_unused_unsafe(
                 hir_id,
                 block_span,
-                Some(self.tcx.sess.source_map().guess_head_span(enclosing_span)),
+                Some((self.tcx.sess.source_map().guess_head_span(enclosing_span), "block")),
             );
             f(self);
         } else {
@@ -52,7 +52,15 @@ impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
             f(self);
 
             if let SafetyContext::UnsafeBlock { used: false, span, hir_id } = self.safety_context {
-                self.warn_unused_unsafe(hir_id, span, self.body_unsafety.unsafe_fn_sig_span());
+                self.warn_unused_unsafe(
+                    hir_id,
+                    span,
+                    if self.unsafe_op_in_unsafe_fn_allowed() {
+                        self.body_unsafety.unsafe_fn_sig_span().map(|span| (span, "fn"))
+                    } else {
+                        None
+                    },
+                );
             }
             self.safety_context = prev_context;
             return;
@@ -72,16 +80,20 @@ impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
             SafetyContext::UnsafeFn if unsafe_op_in_unsafe_fn_allowed => {}
             SafetyContext::UnsafeFn => {
                 // unsafe_op_in_unsafe_fn is disallowed
-                struct_span_err!(
-                    self.tcx.sess,
+                self.tcx.struct_span_lint_hir(
+                    UNSAFE_OP_IN_UNSAFE_FN,
+                    self.hir_context,
                     span,
-                    E0133,
-                    "{} is unsafe and requires unsafe block",
-                    description,
+                    |lint| {
+                        lint.build(&format!(
+                            "{} is unsafe and requires unsafe block (error E0133)",
+                            description,
+                        ))
+                        .span_label(span, description)
+                        .note(note)
+                        .emit();
+                    },
                 )
-                .span_label(span, description)
-                .note(note)
-                .emit();
             }
             SafetyContext::Safe => {
                 let fn_sugg = if unsafe_op_in_unsafe_fn_allowed { " function or" } else { "" };
@@ -104,18 +116,15 @@ impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
         &self,
         hir_id: hir::HirId,
         block_span: Span,
-        enclosing_span: Option<Span>,
+        enclosing_unsafe: Option<(Span, &'static str)>,
     ) {
         let block_span = self.tcx.sess.source_map().guess_head_span(block_span);
         self.tcx.struct_span_lint_hir(UNUSED_UNSAFE, hir_id, block_span, |lint| {
             let msg = "unnecessary `unsafe` block";
             let mut db = lint.build(msg);
             db.span_label(block_span, msg);
-            if let Some(enclosing_span) = enclosing_span {
-                db.span_label(
-                    enclosing_span,
-                    format!("because it's nested under this `unsafe` block"),
-                );
+            if let Some((span, kind)) = enclosing_unsafe {
+                db.span_label(span, format!("because it's nested under this `unsafe` {}", kind));
             }
             db.emit();
         });

compiler/rustc_resolve/src/diagnostics.rs

@@ -425,24 +425,29 @@ impl<'a> Resolver<'a> {
                 }
                 err
             }
-            ResolutionError::BindingShadowsSomethingUnacceptable(what_binding, name, binding) => {
-                let res = binding.res();
-                let shadows_what = res.descr();
+            ResolutionError::BindingShadowsSomethingUnacceptable {
+                shadowing_binding_descr,
+                name,
+                participle,
+                article,
+                shadowed_binding_descr,
+                shadowed_binding_span,
+            } => {
                 let mut err = struct_span_err!(
                     self.session,
                     span,
                     E0530,
                     "{}s cannot shadow {}s",
-                    what_binding,
-                    shadows_what
+                    shadowing_binding_descr,
+                    shadowed_binding_descr,
                 );
                 err.span_label(
                     span,
-                    format!("cannot be named the same as {} {}", res.article(), shadows_what),
+                    format!("cannot be named the same as {} {}", article, shadowed_binding_descr),
                 );
-                let participle = if binding.is_import() { "imported" } else { "defined" };
-                let msg = format!("the {} `{}` is {} here", shadows_what, name, participle);
-                err.span_label(binding.span, msg);
+                let msg =
+                    format!("the {} `{}` is {} here", shadowed_binding_descr, name, participle);
+                err.span_label(shadowed_binding_span, msg);
                 err
             }
             ResolutionError::ForwardDeclaredTyParam => {

compiler/rustc_resolve/src/late.rs

@@ -1763,13 +1763,33 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                 // to something unusable as a pattern (e.g., constructor function),
                 // but we still conservatively report an error, see
                 // issues/33118#issuecomment-233962221 for one reason why.
+                let binding = binding.expect("no binding for a ctor or static");
                 self.report_error(
                     ident.span,
-                    ResolutionError::BindingShadowsSomethingUnacceptable(
-                        pat_src.descr(),
-                        ident.name,
-                        binding.expect("no binding for a ctor or static"),
-                    ),
+                    ResolutionError::BindingShadowsSomethingUnacceptable {
+                        shadowing_binding_descr: pat_src.descr(),
+                        name: ident.name,
+                        participle: if binding.is_import() { "imported" } else { "defined" },
+                        article: binding.res().article(),
+                        shadowed_binding_descr: binding.res().descr(),
+                        shadowed_binding_span: binding.span,
+                    },
+                );
+                None
+            }
+            Res::Def(DefKind::ConstParam, def_id) => {
+                // Same as for DefKind::Const above, but here, `binding` is `None`, so we
+                // have to construct the error differently
+                self.report_error(
+                    ident.span,
+                    ResolutionError::BindingShadowsSomethingUnacceptable {
+                        shadowing_binding_descr: pat_src.descr(),
+                        name: ident.name,
+                        participle: "defined",
+                        article: res.article(),
+                        shadowed_binding_descr: res.descr(),
+                        shadowed_binding_span: self.r.opt_span(def_id).expect("const parameter defined outside of local crate"),
+                    }
                 );
                 None
             }

compiler/rustc_resolve/src/lib.rs

@@ -233,7 +233,14 @@ enum ResolutionError<'a> {
         /* current */ &'static str,
     ),
     /// Error E0530: `X` bindings cannot shadow `Y`s.
-    BindingShadowsSomethingUnacceptable(&'static str, Symbol, &'a NameBinding<'a>),
+    BindingShadowsSomethingUnacceptable {
+        shadowing_binding_descr: &'static str,
+        name: Symbol,
+        participle: &'static str,
+        article: &'static str,
+        shadowed_binding_descr: &'static str,
+        shadowed_binding_span: Span,
+    },
     /// Error E0128: generic parameters with a default cannot use forward-declared identifiers.
     ForwardDeclaredTyParam, // FIXME(const_generics_defaults)
     /// ERROR E0770: the type of const parameters must not depend on other generic parameters.

library/alloc/src/vec/mod.rs

@@ -1619,6 +1619,8 @@ impl<T, A: Allocator> Vec<T, A> {
                 let prev_ptr = ptr.add(gap.write.wrapping_sub(1));
 
                 if same_bucket(&mut *read_ptr, &mut *prev_ptr) {
+                    // Increase `gap.read` now since the drop may panic.
+                    gap.read += 1;
                     /* We have found duplicate, drop it in-place */
                     ptr::drop_in_place(read_ptr);
                 } else {
@@ -1631,9 +1633,8 @@ impl<T, A: Allocator> Vec<T, A> {
 
                     /* We have filled that place, so go further */
                     gap.write += 1;
+                    gap.read += 1;
                 }
-
-                gap.read += 1;
             }
 
             /* Technically we could let `gap` clean up with its Drop, but

library/alloc/tests/vec.rs

@@ -2234,48 +2234,50 @@ fn test_vec_dedup() {
 #[test]
 fn test_vec_dedup_panicking() {
     #[derive(Debug)]
-    struct Panic {
-        drop_counter: &'static AtomicU32,
+    struct Panic<'a> {
+        drop_counter: &'a Cell<u32>,
         value: bool,
         index: usize,
     }
 
-    impl PartialEq for Panic {
+    impl<'a> PartialEq for Panic<'a> {
         fn eq(&self, other: &Self) -> bool {
             self.value == other.value
         }
     }
 
-    impl Drop for Panic {
+    impl<'a> Drop for Panic<'a> {
         fn drop(&mut self) {
-            let x = self.drop_counter.fetch_add(1, Ordering::SeqCst);
-            assert!(x != 4);
+            self.drop_counter.set(self.drop_counter.get() + 1);
+            if !std::thread::panicking() {
+                assert!(self.index != 4);
+            }
         }
     }
 
-    static DROP_COUNTER: AtomicU32 = AtomicU32::new(0);
+    let drop_counter = &Cell::new(0);
     let expected = [
-        Panic { drop_counter: &DROP_COUNTER, value: false, index: 0 },
-        Panic { drop_counter: &DROP_COUNTER, value: false, index: 5 },
-        Panic { drop_counter: &DROP_COUNTER, value: true, index: 6 },
-        Panic { drop_counter: &DROP_COUNTER, value: true, index: 7 },
+        Panic { drop_counter, value: false, index: 0 },
+        Panic { drop_counter, value: false, index: 5 },
+        Panic { drop_counter, value: true, index: 6 },
+        Panic { drop_counter, value: true, index: 7 },
     ];
     let mut vec = vec![
-        Panic { drop_counter: &DROP_COUNTER, value: false, index: 0 },
+        Panic { drop_counter, value: false, index: 0 },
         // these elements get deduplicated
-        Panic { drop_counter: &DROP_COUNTER, value: false, index: 1 },
-        Panic { drop_counter: &DROP_COUNTER, value: false, index: 2 },
-        Panic { drop_counter: &DROP_COUNTER, value: false, index: 3 },
-        Panic { drop_counter: &DROP_COUNTER, value: false, index: 4 },
-        // here it panics
-        Panic { drop_counter: &DROP_COUNTER, value: false, index: 5 },
-        Panic { drop_counter: &DROP_COUNTER, value: true, index: 6 },
-        Panic { drop_counter: &DROP_COUNTER, value: true, index: 7 },
+        Panic { drop_counter, value: false, index: 1 },
+        Panic { drop_counter, value: false, index: 2 },
+        Panic { drop_counter, value: false, index: 3 },
+        Panic { drop_counter, value: false, index: 4 },
+        // here it panics while dropping the item with index==4
+        Panic { drop_counter, value: false, index: 5 },
+        Panic { drop_counter, value: true, index: 6 },
+        Panic { drop_counter, value: true, index: 7 },
     ];
 
-    let _ = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| {
-        vec.dedup();
-    }));
+    let _ = catch_unwind(AssertUnwindSafe(|| vec.dedup())).unwrap_err();
+
+    assert_eq!(drop_counter.get(), 4);
 
     let ok = vec.iter().zip(expected.iter()).all(|(x, y)| x.index == y.index);
 

library/core/src/array/iter.rs

@@ -139,7 +139,7 @@ impl<T, const N: usize> Iterator for IntoIter<T, N> {
         // SAFETY: Callers are only allowed to pass an index that is in bounds
         // Additionally Self: TrustedRandomAccess is only implemented for T: Copy which means even
         // multiple repeated reads of the same index would be safe and the
-        // values aree !Drop, thus won't suffer from double drops.
+        // values are !Drop, thus won't suffer from double drops.
         unsafe { self.data.get_unchecked(self.alive.start + idx).assume_init_read() }
     }
 }

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

@@ -79,11 +79,6 @@ fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {}
         _Self = "std::string::String",
         label = "`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`"
     ),
-    on(
-        _Self = "[]",
-        label = "arrays do not yet implement `IntoIterator`; try using `std::array::IntoIter::new(arr)`",
-        note = "see <https://github.com/rust-lang/rust/pull/65819> for more details"
-    ),
     on(
         _Self = "{integral}",
         note = "if you want to iterate between `start` until a value `end`, use the exclusive range \