Rollup of 6 pull requests

compiler/rustc_hir/src/hir.rs

@@ -1395,7 +1395,7 @@ pub struct LetExpr<'hir> {
     pub pat: &'hir Pat<'hir>,
     pub ty: Option<&'hir Ty<'hir>>,
     pub init: &'hir Expr<'hir>,
-    /// `Recovered::Yes` when this let expressions is not in a syntanctically valid location.
+    /// `Recovered::Yes` when this let expressions is not in a syntactically valid location.
     /// Used to prevent building MIR in such situations.
     pub recovered: ast::Recovered,
 }

compiler/rustc_hir_typeck/src/coercion.rs

@@ -1859,7 +1859,7 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
         };
 
         // If this is due to an explicit `return`, suggest adding a return type.
-        if let Some((fn_id, fn_decl, can_suggest)) = fcx.get_fn_decl(parent_id)
+        if let Some((fn_id, fn_decl, can_suggest)) = fcx.get_fn_decl(block_or_return_id)
             && !due_to_block
         {
             fcx.suggest_missing_return_type(&mut err, fn_decl, expected, found, can_suggest, fn_id);

compiler/rustc_passes/messages.ftl

@@ -444,6 +444,9 @@ passes_macro_export_on_decl_macro =
 passes_macro_use =
     `#[{$name}]` only has an effect on `extern crate` and modules
 
+passes_may_dangle =
+    `#[may_dangle]` must be applied to a lifetime or type generic parameter in `Drop` impl
+
 passes_maybe_string_interpolation = you might have meant to use string interpolation in this string literal
 passes_missing_const_err =
     attributes `#[rustc_const_unstable]` and `#[rustc_const_stable]` require the function or method to be `const`
@@ -475,8 +478,8 @@ passes_multiple_start_functions =
     .previous = previous `#[start]` function here
 
 passes_must_not_suspend =
-    `must_not_suspend` attribute should be applied to a struct, enum, or trait
-    .label = is not a struct, enum, or trait
+    `must_not_suspend` attribute should be applied to a struct, enum, union, or trait
+    .label = is not a struct, enum, union, or trait
 
 passes_must_use_async =
     `must_use` attribute on `async` functions applies to the anonymous `Future` returned by the function, not the value within

compiler/rustc_passes/src/check_attr.rs

@@ -189,6 +189,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                 [sym::collapse_debuginfo, ..] => self.check_collapse_debuginfo(attr, span, target),
                 [sym::must_not_suspend, ..] => self.check_must_not_suspend(attr, span, target),
                 [sym::must_use, ..] => self.check_must_use(hir_id, attr, target),
+                [sym::may_dangle, ..] => self.check_may_dangle(hir_id, attr),
                 [sym::rustc_pass_by_value, ..] => self.check_pass_by_value(attr, span, target),
                 [sym::rustc_allow_incoherent_impl, ..] => {
                     self.check_allow_incoherent_impl(attr, span, target)
@@ -255,7 +256,6 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     | sym::cfg_attr
                     // need to be fixed
                     | sym::cfi_encoding // FIXME(cfi_encoding)
-                    | sym::may_dangle // FIXME(dropck_eyepatch)
                     | sym::pointee // FIXME(derive_smart_pointer)
                     | sym::omit_gdb_pretty_printer_section // FIXME(omit_gdb_pretty_printer_section)
                     | sym::used // handled elsewhere to restrict to static items
@@ -1363,7 +1363,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    /// Checks if `#[must_not_suspend]` is applied to a function.
+    /// Checks if `#[must_not_suspend]` is applied to a struct, enum, union, or trait.
     fn check_must_not_suspend(&self, attr: &Attribute, span: Span, target: Target) {
         match target {
             Target::Struct | Target::Enum | Target::Union | Target::Trait => {}
@@ -1373,6 +1373,27 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
+    /// Checks if `#[may_dangle]` is applied to a lifetime or type generic parameter in `Drop` impl.
+    fn check_may_dangle(&self, hir_id: HirId, attr: &Attribute) {
+        if let hir::Node::GenericParam(param) = self.tcx.hir_node(hir_id)
+            && matches!(
+                param.kind,
+                hir::GenericParamKind::Lifetime { .. } | hir::GenericParamKind::Type { .. }
+            )
+            && matches!(param.source, hir::GenericParamSource::Generics)
+            && let parent_hir_id = self.tcx.parent_hir_id(hir_id)
+            && let hir::Node::Item(item) = self.tcx.hir_node(parent_hir_id)
+            && let hir::ItemKind::Impl(impl_) = item.kind
+            && let Some(trait_) = impl_.of_trait
+            && let Some(def_id) = trait_.trait_def_id()
+            && self.tcx.is_lang_item(def_id, hir::LangItem::Drop)
+        {
+            return;
+        }
+
+        self.dcx().emit_err(errors::InvalidMayDangle { attr_span: attr.span });
+    }
+
     /// Checks if `#[cold]` is applied to a non-function.
     fn check_cold(&self, hir_id: HirId, attr: &Attribute, span: Span, target: Target) {
         match target {

compiler/rustc_passes/src/errors.rs

@@ -737,6 +737,13 @@ pub struct NonExportedMacroInvalidAttrs {
     pub attr_span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(passes_may_dangle)]
+pub struct InvalidMayDangle {
+    #[primary_span]
+    pub attr_span: Span,
+}
+
 #[derive(LintDiagnostic)]
 #[diag(passes_unused_duplicate)]
 pub struct UnusedDuplicate {

compiler/rustc_query_impl/src/plumbing.rs

@@ -702,11 +702,17 @@ macro_rules! define_queries {
                     let name = stringify!($name);
                     $crate::plumbing::create_query_frame(tcx, rustc_middle::query::descs::$name, key, kind, name)
                 };
-                tcx.query_system.states.$name.try_collect_active_jobs(
+                let res = tcx.query_system.states.$name.try_collect_active_jobs(
                     tcx,
                     make_query,
                     qmap,
-                ).unwrap();
+                );
+                // this can be called during unwinding, and the function has a `try_`-prefix, so
+                // don't `unwrap()` here, just manually check for `None` and do best-effort error
+                // reporting.
+                if res.is_none() {
+                    tracing::warn!("Failed to collect active jobs for query with name `{}`!", stringify!($name));
+                }
             }
 
             pub fn alloc_self_profile_query_strings<'tcx>(tcx: TyCtxt<'tcx>, string_cache: &mut QueryKeyStringCache) {

compiler/rustc_query_system/src/query/plumbing.rs

@@ -181,8 +181,15 @@ where
         cache.complete(key, result, dep_node_index);
 
         let job = {
-            let mut lock = state.active.lock_shard_by_value(&key);
-            lock.remove(&key).unwrap().expect_job()
+            let val = {
+                // don't keep the lock during the `unwrap()` of the retrieved value, or we taint the
+                // underlying shard.
+                // since unwinding also wants to look at this map, this can also prevent a double
+                // panic.
+                let mut lock = state.active.lock_shard_by_value(&key);
+                lock.remove(&key)
+            };
+            val.unwrap().expect_job()
         };
 
         job.signal_complete();

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -17,8 +17,7 @@ use rustc_infer::infer::{DefineOpaqueTypes, HigherRankedType, InferOk};
 use rustc_infer::traits::ObligationCauseCode;
 use rustc_middle::traits::{BuiltinImplSource, SignatureMismatchData};
 use rustc_middle::ty::{
-    self, GenericArgs, GenericArgsRef, GenericParamDefKind, ToPolyTraitRef, TraitPredicate, Ty,
-    TyCtxt, Upcast,
+    self, GenericArgs, GenericArgsRef, GenericParamDefKind, ToPolyTraitRef, Ty, TyCtxt, Upcast,
 };
 use rustc_middle::{bug, span_bug};
 use rustc_span::def_id::DefId;
@@ -292,90 +291,120 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         obligation: &PolyTraitObligation<'tcx>,
     ) -> Result<Vec<PredicateObligation<'tcx>>, SelectionError<'tcx>> {
-        use rustc_transmute::{Answer, Condition};
-        #[instrument(level = "debug", skip(tcx, obligation, predicate))]
+        use rustc_transmute::{Answer, Assume, Condition};
+
+        /// Generate sub-obligations for reference-to-reference transmutations.
+        fn reference_obligations<'tcx>(
+            tcx: TyCtxt<'tcx>,
+            obligation: &PolyTraitObligation<'tcx>,
+            (src_lifetime, src_ty, src_mut): (ty::Region<'tcx>, Ty<'tcx>, Mutability),
+            (dst_lifetime, dst_ty, dst_mut): (ty::Region<'tcx>, Ty<'tcx>, Mutability),
+            assume: Assume,
+        ) -> Vec<PredicateObligation<'tcx>> {
+            let make_transmute_obl = |src, dst| {
+                let transmute_trait = obligation.predicate.def_id();
+                let assume = obligation.predicate.skip_binder().trait_ref.args.const_at(2);
+                let trait_ref = ty::TraitRef::new(
+                    tcx,
+                    transmute_trait,
+                    [
+                        ty::GenericArg::from(dst),
+                        ty::GenericArg::from(src),
+                        ty::GenericArg::from(assume),
+                    ],
+                );
+                Obligation::with_depth(
+                    tcx,
+                    obligation.cause.clone(),
+                    obligation.recursion_depth + 1,
+                    obligation.param_env,
+                    obligation.predicate.rebind(trait_ref),
+                )
+            };
+
+            let make_freeze_obl = |ty| {
+                let trait_ref = ty::TraitRef::new(
+                    tcx,
+                    tcx.require_lang_item(LangItem::Freeze, None),
+                    [ty::GenericArg::from(ty)],
+                );
+                Obligation::with_depth(
+                    tcx,
+                    obligation.cause.clone(),
+                    obligation.recursion_depth + 1,
+                    obligation.param_env,
+                    trait_ref,
+                )
+            };
+
+            let make_outlives_obl = |target, region| {
+                let outlives = ty::OutlivesPredicate(target, region);
+                Obligation::with_depth(
+                    tcx,
+                    obligation.cause.clone(),
+                    obligation.recursion_depth + 1,
+                    obligation.param_env,
+                    obligation.predicate.rebind(outlives),
+                )
+            };
+
+            // Given a transmutation from `&'a (mut) Src` and `&'dst (mut) Dst`,
+            // it is always the case that `Src` must be transmutable into `Dst`,
+            // and that that `'src` must outlive `'dst`.
+            let mut obls = vec![make_transmute_obl(src_ty, dst_ty)];
+            if !assume.lifetimes {
+                obls.push(make_outlives_obl(src_lifetime, dst_lifetime));
+            }
+
+            // Given a transmutation from `&Src`, both `Src` and `Dst` must be
+            // `Freeze`, otherwise, using the transmuted value could lead to
+            // data races.
+            if src_mut == Mutability::Not {
+                obls.extend([make_freeze_obl(src_ty), make_freeze_obl(dst_ty)])
+            }
+
+            // Given a transmutation into `&'dst mut Dst`, it also must be the
+            // case that `Dst` is transmutable into `Src`. For example,
+            // transmuting bool -> u8 is OK as long as you can't update that u8
+            // to be > 1, because you could later transmute the u8 back to a
+            // bool and get undefined behavior. It also must be the case that
+            // `'dst` lives exactly as long as `'src`.
+            if dst_mut == Mutability::Mut {
+                obls.push(make_transmute_obl(dst_ty, src_ty));
+                if !assume.lifetimes {
+                    obls.push(make_outlives_obl(dst_lifetime, src_lifetime));
+                }
+            }
+
+            obls
+        }
+
+        /// Flatten the `Condition` tree into a conjunction of obligations.
+        #[instrument(level = "debug", skip(tcx, obligation))]
         fn flatten_answer_tree<'tcx>(
             tcx: TyCtxt<'tcx>,
             obligation: &PolyTraitObligation<'tcx>,
-            predicate: TraitPredicate<'tcx>,
             cond: Condition<rustc_transmute::layout::rustc::Ref<'tcx>>,
+            assume: Assume,
         ) -> Vec<PredicateObligation<'tcx>> {
             match cond {
                 // FIXME(bryangarza): Add separate `IfAny` case, instead of treating as `IfAll`
                 // Not possible until the trait solver supports disjunctions of obligations
                 Condition::IfAll(conds) | Condition::IfAny(conds) => conds
                     .into_iter()
-                    .flat_map(|cond| flatten_answer_tree(tcx, obligation, predicate, cond))
+                    .flat_map(|cond| flatten_answer_tree(tcx, obligation, cond, assume))
                     .collect(),
-                Condition::IfTransmutable { src, dst } => {
-                    let transmute_trait = obligation.predicate.def_id();
-                    let assume_const = predicate.trait_ref.args.const_at(2);
-                    let make_transmute_obl = |from_ty, to_ty| {
-                        let trait_ref = ty::TraitRef::new(
-                            tcx,
-                            transmute_trait,
-                            [
-                                ty::GenericArg::from(to_ty),
-                                ty::GenericArg::from(from_ty),
-                                ty::GenericArg::from(assume_const),
-                            ],
-                        );
-                        Obligation::with_depth(
-                            tcx,
-                            obligation.cause.clone(),
-                            obligation.recursion_depth + 1,
-                            obligation.param_env,
-                            trait_ref,
-                        )
-                    };
-
-                    let make_freeze_obl = |ty| {
-                        let trait_ref = ty::TraitRef::new(
-                            tcx,
-                            tcx.require_lang_item(LangItem::Freeze, None),
-                            [ty::GenericArg::from(ty)],
-                        );
-                        Obligation::with_depth(
-                            tcx,
-                            obligation.cause.clone(),
-                            obligation.recursion_depth + 1,
-                            obligation.param_env,
-                            trait_ref,
-                        )
-                    };
-
-                    let mut obls = vec![];
-
-                    // If the source is a shared reference, it must be `Freeze`;
-                    // otherwise, transmuting could lead to data races.
-                    if src.mutability == Mutability::Not {
-                        obls.extend([make_freeze_obl(src.ty), make_freeze_obl(dst.ty)])
-                    }
-
-                    // If Dst is mutable, check bidirectionally.
-                    // For example, transmuting bool -> u8 is OK as long as you can't update that u8
-                    // to be > 1, because you could later transmute the u8 back to a bool and get UB.
-                    match dst.mutability {
-                        Mutability::Not => obls.push(make_transmute_obl(src.ty, dst.ty)),
-                        Mutability::Mut => obls.extend([
-                            make_transmute_obl(src.ty, dst.ty),
-                            make_transmute_obl(dst.ty, src.ty),
-                        ]),
-                    }
-
-                    obls
-                }
+                Condition::IfTransmutable { src, dst } => reference_obligations(
+                    tcx,
+                    obligation,
+                    (src.lifetime, src.ty, src.mutability),
+                    (dst.lifetime, dst.ty, dst.mutability),
+                    assume,
+                ),
             }
         }
 
-        // We erase regions here because transmutability calls layout queries,
-        // which does not handle inference regions and doesn't particularly
-        // care about other regions. Erasing late-bound regions is equivalent
-        // to instantiating the binder with placeholders then erasing those
-        // placeholder regions.
-        let predicate = self
-            .tcx()
-            .erase_regions(self.tcx().instantiate_bound_regions_with_erased(obligation.predicate));
+        let predicate = obligation.predicate.skip_binder();
 
         let Some(assume) = rustc_transmute::Assume::from_const(
             self.infcx.tcx,
@@ -387,6 +416,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         let dst = predicate.trait_ref.args.type_at(0);
         let src = predicate.trait_ref.args.type_at(1);
+
         debug!(?src, ?dst);
         let mut transmute_env = rustc_transmute::TransmuteTypeEnv::new(self.infcx);
         let maybe_transmutable = transmute_env.is_transmutable(
@@ -397,7 +427,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         let fully_flattened = match maybe_transmutable {
             Answer::No(_) => Err(Unimplemented)?,
-            Answer::If(cond) => flatten_answer_tree(self.tcx(), obligation, predicate, cond),
+            Answer::If(cond) => flatten_answer_tree(self.tcx(), obligation, cond, assume),
             Answer::Yes => vec![],
         };
 

compiler/rustc_transmute/src/layout/mod.rs

@@ -63,7 +63,9 @@ pub mod rustc {
     use std::fmt::{self, Write};
 
     use rustc_middle::mir::Mutability;
-    use rustc_middle::ty::{self, Ty};
+    use rustc_middle::ty::layout::{LayoutCx, LayoutError};
+    use rustc_middle::ty::{self, Ty, TyCtxt};
+    use rustc_target::abi::Layout;
 
     /// A reference in the layout.
     #[derive(Debug, Hash, Eq, PartialEq, Clone, Copy)]
@@ -120,4 +122,13 @@ pub mod rustc {
             self != &Self::Primitive
         }
     }
+
+    pub(crate) fn layout_of<'tcx>(
+        cx: LayoutCx<'tcx, TyCtxt<'tcx>>,
+        ty: Ty<'tcx>,
+    ) -> Result<Layout<'tcx>, &'tcx LayoutError<'tcx>> {
+        use rustc_middle::ty::layout::LayoutOf;
+        let ty = cx.tcx.erase_regions(ty);
+        cx.layout_of(ty).map(|tl| tl.layout)
+    }
 }