Auto merge of #85437 - GuillaumeGomez:rollup-3jcirty, r=GuillaumeGomez

Rollup of 7 pull requests

Successful merges:

 - #84587 (rustdoc: Make "rust code block is empty" and "could not parse code block" warnings a lint (`INVALID_RUST_CODEBLOCKS`))
 - #85280 (Toggle-wrap items differently than top-doc.)
 - #85338 (Implement more Iterator methods on core::iter::Repeat)
 - #85339 (Report an error if a lang item has the wrong number of generic arguments)
 - #85369 (Suggest borrowing if a trait implementation is found for &/&mut <type>)
 - #85393 (Suppress spurious errors inside `async fn`)
 - #85415 (Clean up remnants of BorrowOfPackedField)

Failed merges:

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

Author: bors

compiler/rustc_middle/src/mir/query.rs

@@ -32,7 +32,6 @@ pub enum UnsafetyViolationDetails {
     UseOfInlineAssembly,
     InitializingTypeWith,
     CastOfPointerToInt,
-    BorrowOfPackedField,
     UseOfMutableStatic,
     UseOfExternStatic,
     DerefOfRawPointer,
@@ -64,11 +63,6 @@ impl UnsafetyViolationDetails {
             CastOfPointerToInt => {
                 ("cast of pointer to int", "casting pointers to integers in constants")
             }
-            BorrowOfPackedField => (
-                "borrow of packed field",
-                "fields of packed structs might be misaligned: dereferencing a misaligned pointer \
-                 or even just creating a misaligned reference is undefined behavior",
-            ),
             UseOfMutableStatic => (
                 "use of mutable static",
                 "mutable statics can be mutated by multiple threads: aliasing violations or data \

compiler/rustc_mir/src/borrow_check/region_infer/mod.rs

@@ -1241,7 +1241,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
     /// it. However, it works pretty well in practice. In particular,
     /// this is needed to deal with projection outlives bounds like
     ///
-    /// ```ignore (internal compiler representation so lifetime syntax is invalid)
+    /// ```text
     /// <T as Foo<'0>>::Item: '1
     /// ```
     ///

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -64,38 +64,30 @@ impl<'tcx> UnsafetyVisitor<'tcx> {
             SafetyContext::UnsafeFn if unsafe_op_in_unsafe_fn_allowed => {}
             SafetyContext::UnsafeFn => {
                 // unsafe_op_in_unsafe_fn is disallowed
-                if kind == BorrowOfPackedField {
-                    // FIXME handle borrows of packed fields
-                } else {
-                    struct_span_err!(
-                        self.tcx.sess,
-                        span,
-                        E0133,
-                        "{} is unsafe and requires unsafe block",
-                        description,
-                    )
-                    .span_label(span, description)
-                    .note(note)
-                    .emit();
-                }
+                struct_span_err!(
+                    self.tcx.sess,
+                    span,
+                    E0133,
+                    "{} is unsafe and requires unsafe block",
+                    description,
+                )
+                .span_label(span, description)
+                .note(note)
+                .emit();
             }
             SafetyContext::Safe => {
-                if kind == BorrowOfPackedField {
-                    // FIXME handle borrows of packed fields
-                } else {
-                    let fn_sugg = if unsafe_op_in_unsafe_fn_allowed { " function or" } else { "" };
-                    struct_span_err!(
-                        self.tcx.sess,
-                        span,
-                        E0133,
-                        "{} is unsafe and requires unsafe{} block",
-                        description,
-                        fn_sugg,
-                    )
-                    .span_label(span, description)
-                    .note(note)
-                    .emit();
-                }
+                let fn_sugg = if unsafe_op_in_unsafe_fn_allowed { " function or" } else { "" };
+                struct_span_err!(
+                    self.tcx.sess,
+                    span,
+                    E0133,
+                    "{} is unsafe and requires unsafe{} block",
+                    description,
+                    fn_sugg,
+                )
+                .span_label(span, description)
+                .note(note)
+                .emit();
             }
         }
     }
@@ -203,8 +195,6 @@ enum UnsafeOpKind {
     #[allow(dead_code)] // FIXME
     CastOfPointerToInt,
     #[allow(dead_code)] // FIXME
-    BorrowOfPackedField,
-    #[allow(dead_code)] // FIXME
     UseOfMutableStatic,
     #[allow(dead_code)] // FIXME
     UseOfExternStatic,
@@ -244,11 +234,6 @@ impl UnsafeOpKind {
             CastOfPointerToInt => {
                 ("cast of pointer to int", "casting pointers to integers in constants")
             }
-            BorrowOfPackedField => (
-                "borrow of packed field",
-                "fields of packed structs might be misaligned: dereferencing a misaligned pointer \
-                 or even just creating a misaligned reference is undefined behavior",
-            ),
             UseOfMutableStatic => (
                 "use of mutable static",
                 "mutable statics can be mutated by multiple threads: aliasing violations or data \

compiler/rustc_passes/src/lang_items.rs

@@ -13,12 +13,13 @@ use crate::weak_lang_items;
 use rustc_middle::middle::cstore::ExternCrate;
 use rustc_middle::ty::TyCtxt;
 
-use rustc_errors::struct_span_err;
+use rustc_errors::{pluralize, struct_span_err};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
 use rustc_hir::lang_items::{extract, ITEM_REFS};
 use rustc_hir::{HirId, LangItem, LanguageItems, Target};
+use rustc_span::Span;
 
 use rustc_middle::ty::query::Providers;
 
@@ -61,8 +62,7 @@ impl LanguageItemCollector<'tcx> {
             match ITEM_REFS.get(&value).cloned() {
                 // Known lang item with attribute on correct target.
                 Some((item_index, expected_target)) if actual_target == expected_target => {
-                    let def_id = self.tcx.hir().local_def_id(hir_id);
-                    self.collect_item(item_index, def_id.to_def_id());
+                    self.collect_item_extended(item_index, hir_id, span);
                 }
                 // Known lang item with attribute on incorrect target.
                 Some((_, expected_target)) => {
@@ -180,6 +180,127 @@ impl LanguageItemCollector<'tcx> {
             self.items.groups[group as usize].push(item_def_id);
         }
     }
+
+    // Like collect_item() above, but also checks whether the lang item is declared
+    // with the right number of generic arguments if it is a trait.
+    fn collect_item_extended(&mut self, item_index: usize, hir_id: HirId, span: Span) {
+        let item_def_id = self.tcx.hir().local_def_id(hir_id).to_def_id();
+        let lang_item = LangItem::from_u32(item_index as u32).unwrap();
+        let name = lang_item.name();
+
+        self.collect_item(item_index, item_def_id);
+
+        // Now check whether the lang_item has the expected number of generic
+        // arguments if it is a trait. Generally speaking, binary and indexing
+        // operations have one (for the RHS/index), unary operations have none,
+        // and the rest also have none except for the closure traits (one for
+        // the argument list), generators (one for the resume argument),
+        // ordering/equality relations (one for the RHS), and various conversion
+        // traits.
+
+        let expected_num = match lang_item {
+            // Binary operations
+            LangItem::Add
+            | LangItem::Sub
+            | LangItem::Mul
+            | LangItem::Div
+            | LangItem::Rem
+            | LangItem::BitXor
+            | LangItem::BitAnd
+            | LangItem::BitOr
+            | LangItem::Shl
+            | LangItem::Shr
+            | LangItem::AddAssign
+            | LangItem::SubAssign
+            | LangItem::MulAssign
+            | LangItem::DivAssign
+            | LangItem::RemAssign
+            | LangItem::BitXorAssign
+            | LangItem::BitAndAssign
+            | LangItem::BitOrAssign
+            | LangItem::ShlAssign
+            | LangItem::ShrAssign
+            | LangItem::Index
+            | LangItem::IndexMut
+
+            // Miscellaneous
+            | LangItem::Unsize
+            | LangItem::CoerceUnsized
+            | LangItem::DispatchFromDyn
+            | LangItem::Fn
+            | LangItem::FnMut
+            | LangItem::FnOnce
+            | LangItem::Generator
+            | LangItem::PartialEq
+            | LangItem::PartialOrd
+                => Some(1),
+
+            // Unary operations
+            LangItem::Neg
+            | LangItem::Not
+
+            // Miscellaneous
+            | LangItem::Deref
+            | LangItem::DerefMut
+            | LangItem::Sized
+            | LangItem::StructuralPeq
+            | LangItem::StructuralTeq
+            | LangItem::Copy
+            | LangItem::Clone
+            | LangItem::Sync
+            | LangItem::DiscriminantKind
+            | LangItem::PointeeTrait
+            | LangItem::Freeze
+            | LangItem::Drop
+            | LangItem::Receiver
+            | LangItem::Future
+            | LangItem::Unpin
+            | LangItem::Termination
+            | LangItem::Try
+            | LangItem::Send
+            | LangItem::UnwindSafe
+            | LangItem::RefUnwindSafe
+                => Some(0),
+
+            // Not a trait
+            _ => None,
+        };
+
+        if let Some(expected_num) = expected_num {
+            let (actual_num, generics_span) = match self.tcx.hir().get(hir_id) {
+                hir::Node::Item(hir::Item {
+                    kind: hir::ItemKind::Trait(_, _, generics, ..),
+                    ..
+                }) => (generics.params.len(), generics.span),
+                _ => bug!("op/index/deref lang item target is not a trait: {:?}", lang_item),
+            };
+
+            if expected_num != actual_num {
+                // We are issuing E0718 "incorrect target" here, because while the
+                // item kind of the target is correct, the target is still wrong
+                // because of the wrong number of generic arguments.
+                struct_span_err!(
+                    self.tcx.sess,
+                    span,
+                    E0718,
+                    "`{}` language item must be applied to a trait with {} generic argument{}",
+                    name,
+                    expected_num,
+                    pluralize!(expected_num)
+                )
+                .span_label(
+                    generics_span,
+                    format!(
+                        "this trait has {} generic argument{}, not {}",
+                        actual_num,
+                        pluralize!(actual_num),
+                        expected_num
+                    ),
+                )
+                .emit();
+            }
+        }
+    }
 }
 
 /// Traverses and collects all the lang items in all crates.

compiler/rustc_trait_selection/src/opaque_types.rs

@@ -46,6 +46,7 @@ pub struct OpaqueTypeDecl<'tcx> {
     /// type Foo = impl Baz;
     /// fn bar() -> Foo {
     /// //          ^^^ This is the span we are looking for!
+    /// }
     /// ```
     ///
     /// In cases where the fn returns `(impl Trait, impl Trait)` or

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -686,17 +686,36 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             return false;
         }
 
+        // Blacklist traits for which it would be nonsensical to suggest borrowing.
+        // For instance, immutable references are always Copy, so suggesting to
+        // borrow would always succeed, but it's probably not what the user wanted.
+        let blacklist: Vec<_> =
+            [LangItem::Copy, LangItem::Clone, LangItem::Unpin, LangItem::Sized, LangItem::Send]
+                .iter()
+                .filter_map(|lang_item| self.tcx.lang_items().require(*lang_item).ok())
+                .collect();
+
         let span = obligation.cause.span;
         let param_env = obligation.param_env;
         let trait_ref = trait_ref.skip_binder();
 
-        if let ObligationCauseCode::ImplDerivedObligation(obligation) = &obligation.cause.code {
-            // Try to apply the original trait binding obligation by borrowing.
-            let self_ty = trait_ref.self_ty();
-            let found = self_ty.to_string();
-            let new_self_ty = self.tcx.mk_imm_ref(self.tcx.lifetimes.re_static, self_ty);
-            let substs = self.tcx.mk_substs_trait(new_self_ty, &[]);
-            let new_trait_ref = ty::TraitRef::new(obligation.parent_trait_ref.def_id(), substs);
+        let found_ty = trait_ref.self_ty();
+        let found_ty_str = found_ty.to_string();
+        let imm_borrowed_found_ty = self.tcx.mk_imm_ref(self.tcx.lifetimes.re_static, found_ty);
+        let imm_substs = self.tcx.mk_substs_trait(imm_borrowed_found_ty, &[]);
+        let mut_borrowed_found_ty = self.tcx.mk_mut_ref(self.tcx.lifetimes.re_static, found_ty);
+        let mut_substs = self.tcx.mk_substs_trait(mut_borrowed_found_ty, &[]);
+
+        // Try to apply the original trait binding obligation by borrowing.
+        let mut try_borrowing = |new_trait_ref: ty::TraitRef<'tcx>,
+                                 expected_trait_ref: ty::TraitRef<'tcx>,
+                                 mtbl: bool,
+                                 blacklist: &[DefId]|
+         -> bool {
+            if blacklist.contains(&expected_trait_ref.def_id) {
+                return false;
+            }
+
             let new_obligation = Obligation::new(
                 ObligationCause::dummy(),
                 param_env,
@@ -713,8 +732,8 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
 
                     let msg = format!(
                         "the trait bound `{}: {}` is not satisfied",
-                        found,
-                        obligation.parent_trait_ref.skip_binder().print_only_trait_path(),
+                        found_ty_str,
+                        expected_trait_ref.print_only_trait_path(),
                     );
                     if has_custom_message {
                         err.note(&msg);
@@ -730,7 +749,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                         span,
                         &format!(
                             "expected an implementor of trait `{}`",
-                            obligation.parent_trait_ref.skip_binder().print_only_trait_path(),
+                            expected_trait_ref.print_only_trait_path(),
                         ),
                     );
 
@@ -745,16 +764,52 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
 
                         err.span_suggestion(
                             span,
-                            "consider borrowing here",
-                            format!("&{}", snippet),
+                            &format!(
+                                "consider{} borrowing here",
+                                if mtbl { " mutably" } else { "" }
+                            ),
+                            format!("&{}{}", if mtbl { "mut " } else { "" }, snippet),
                             Applicability::MaybeIncorrect,
                         );
                     }
                     return true;
                 }
             }
+            return false;
+        };
+
+        if let ObligationCauseCode::ImplDerivedObligation(obligation) = &obligation.cause.code {
+            let expected_trait_ref = obligation.parent_trait_ref.skip_binder();
+            let new_imm_trait_ref =
+                ty::TraitRef::new(obligation.parent_trait_ref.def_id(), imm_substs);
+            let new_mut_trait_ref =
+                ty::TraitRef::new(obligation.parent_trait_ref.def_id(), mut_substs);
+            if try_borrowing(new_imm_trait_ref, expected_trait_ref, false, &[]) {
+                return true;
+            } else {
+                return try_borrowing(new_mut_trait_ref, expected_trait_ref, true, &[]);
+            }
+        } else if let ObligationCauseCode::BindingObligation(_, _)
+        | ObligationCauseCode::ItemObligation(_) = &obligation.cause.code
+        {
+            if try_borrowing(
+                ty::TraitRef::new(trait_ref.def_id, imm_substs),
+                trait_ref,
+                false,
+                &blacklist[..],
+            ) {
+                return true;
+            } else {
+                return try_borrowing(
+                    ty::TraitRef::new(trait_ref.def_id, mut_substs),
+                    trait_ref,
+                    true,
+                    &blacklist[..],
+                );
+            }
+        } else {
+            false
         }
-        false
     }
 
     /// Whenever references are used by mistake, like `for (i, e) in &vec.iter().enumerate()`,