Rollup of 10 pull requests

compiler/rustc_mir/src/transform/check_consts/ops.rs

@@ -72,7 +72,7 @@ impl NonConstOp for FnCallIndirect {
 
 /// A function call where the callee is not marked as `const`.
 #[derive(Debug)]
-pub struct FnCallNonConst(pub DefId);
+pub struct FnCallNonConst;
 impl NonConstOp for FnCallNonConst {
     fn build_error(&self, ccx: &ConstCx<'_, 'tcx>, span: Span) -> DiagnosticBuilder<'tcx> {
         struct_span_err!(

compiler/rustc_mir/src/transform/check_consts/validation.rs

@@ -789,10 +789,10 @@ impl Visitor<'tcx> for Validator<'mir, 'tcx> {
         }
     }
 
+    #[instrument(skip(self))]
     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
         use rustc_target::spec::abi::Abi::RustIntrinsic;
 
-        trace!("visit_terminator: terminator={:?} location={:?}", terminator, location);
         self.super_terminator(terminator, location);
 
         match &terminator.kind {
@@ -816,8 +816,9 @@ impl Visitor<'tcx> for Validator<'mir, 'tcx> {
 
                 // Attempting to call a trait method?
                 if let Some(trait_id) = tcx.trait_of_item(callee) {
+                    trace!("attempting to call a trait method");
                     if !self.tcx.features().const_trait_impl {
-                        self.check_op(ops::FnCallNonConst(callee));
+                        self.check_op(ops::FnCallNonConst);
                         return;
                     }
 
@@ -871,25 +872,26 @@ impl Visitor<'tcx> for Validator<'mir, 'tcx> {
                     return;
                 }
 
+                let is_intrinsic = tcx.fn_sig(callee).abi() == RustIntrinsic;
+
                 // HACK: This is to "unstabilize" the `transmute` intrinsic
                 // within const fns. `transmute` is allowed in all other const contexts.
                 // This won't really scale to more intrinsics or functions. Let's allow const
                 // transmutes in const fn before we add more hacks to this.
-                if tcx.fn_sig(callee).abi() == RustIntrinsic
-                    && tcx.item_name(callee) == sym::transmute
-                {
+                if is_intrinsic && tcx.item_name(callee) == sym::transmute {
                     self.check_op(ops::Transmute);
                     return;
                 }
 
                 if !tcx.is_const_fn_raw(callee) {
-                    self.check_op(ops::FnCallNonConst(callee));
+                    self.check_op(ops::FnCallNonConst);
                     return;
                 }
 
                 // If the `const fn` we are trying to call is not const-stable, ensure that we have
                 // the proper feature gate enabled.
                 if let Some(gate) = is_unstable_const_fn(tcx, callee) {
+                    trace!(?gate, "calling unstable const fn");
                     if self.span.allows_unstable(gate) {
                         return;
                     }
@@ -904,12 +906,14 @@ impl Visitor<'tcx> for Validator<'mir, 'tcx> {
                     // If this crate is not using stability attributes, or the caller is not claiming to be a
                     // stable `const fn`, that is all that is required.
                     if !self.ccx.is_const_stable_const_fn() {
+                        trace!("crate not using stability attributes or caller not stably const");
                         return;
                     }
 
                     // Otherwise, we are something const-stable calling a const-unstable fn.
 
                     if super::rustc_allow_const_fn_unstable(tcx, caller, gate) {
+                        trace!("rustc_allow_const_fn_unstable gate active");
                         return;
                     }
 
@@ -923,10 +927,16 @@ impl Visitor<'tcx> for Validator<'mir, 'tcx> {
                 let callee_is_unstable_unmarked = tcx.lookup_const_stability(callee).is_none()
                     && tcx.lookup_stability(callee).map_or(false, |s| s.level.is_unstable());
                 if callee_is_unstable_unmarked {
-                    if self.ccx.is_const_stable_const_fn() {
+                    trace!("callee_is_unstable_unmarked");
+                    // We do not use `const` modifiers for intrinsic "functions", as intrinsics are
+                    // `extern` funtions, and these have no way to get marked `const`. So instead we
+                    // use `rustc_const_(un)stable` attributes to mean that the intrinsic is `const`
+                    if self.ccx.is_const_stable_const_fn() || is_intrinsic {
                         self.check_op(ops::FnCallUnstable(callee, None));
+                        return;
                     }
                 }
+                trace!("permitting call");
             }
 
             // Forbid all `Drop` terminators unless the place being dropped is a local with no

compiler/rustc_mir/src/transform/check_unsafety.rs

@@ -568,24 +568,23 @@ fn is_enclosed(
     tcx: TyCtxt<'_>,
     used_unsafe: &FxHashSet<hir::HirId>,
     id: hir::HirId,
-) -> Option<(String, hir::HirId)> {
+    unsafe_op_in_unsafe_fn_allowed: bool,
+) -> Option<(&'static str, hir::HirId)> {
     let parent_id = tcx.hir().get_parent_node(id);
     if parent_id != id {
         if used_unsafe.contains(&parent_id) {
-            Some(("block".to_string(), parent_id))
+            Some(("block", parent_id))
         } else if let Some(Node::Item(&hir::Item {
             kind: hir::ItemKind::Fn(ref sig, _, _), ..
         })) = tcx.hir().find(parent_id)
         {
-            if sig.header.unsafety == hir::Unsafety::Unsafe
-                && !tcx.features().unsafe_block_in_unsafe_fn
-            {
-                Some(("fn".to_string(), parent_id))
+            if sig.header.unsafety == hir::Unsafety::Unsafe && unsafe_op_in_unsafe_fn_allowed {
+                Some(("fn", parent_id))
             } else {
                 None
             }
         } else {
-            is_enclosed(tcx, used_unsafe, parent_id)
+            is_enclosed(tcx, used_unsafe, parent_id, unsafe_op_in_unsafe_fn_allowed)
         }
     } else {
         None
@@ -598,7 +597,9 @@ fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id
         let msg = "unnecessary `unsafe` block";
         let mut db = lint.build(msg);
         db.span_label(span, msg);
-        if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
+        if let Some((kind, id)) =
+            is_enclosed(tcx, used_unsafe, id, unsafe_op_in_unsafe_fn_allowed(tcx, id))
+        {
             db.span_label(
                 tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
                 format!("because it's nested under this `unsafe` {}", kind),

compiler/rustc_mir_build/src/build/matches/simplify.rs

@@ -55,7 +55,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         // * the bindings from the previous iteration of the loop is prepended to the bindings from
         // the current iteration (in the implementation this is done by mem::swap and extend)
         // * after all iterations, these new bindings are then appended to the bindings that were
-        // prexisting (i.e. `candidate.binding` when the function was called).
+        // preexisting (i.e. `candidate.binding` when the function was called).
         //
         // example:
         // candidate.bindings = [1, 2, 3]

compiler/rustc_passes/src/stability.rs

@@ -55,6 +55,21 @@ impl InheritDeprecation {
     }
 }
 
+/// Whether to inherit const stability flags for nested items. In most cases, we do not want to
+/// inherit const stability: just because an enclosing `fn` is const-stable does not mean
+/// all `extern` imports declared in it should be const-stable! However, trait methods
+/// inherit const stability attributes from their parent and do not have their own.
+enum InheritConstStability {
+    Yes,
+    No,
+}
+
+impl InheritConstStability {
+    fn yes(&self) -> bool {
+        matches!(self, InheritConstStability::Yes)
+    }
+}
+
 // A private tree-walker for producing an Index.
 struct Annotator<'a, 'tcx> {
     tcx: TyCtxt<'tcx>,
@@ -75,6 +90,7 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
         item_sp: Span,
         kind: AnnotationKind,
         inherit_deprecation: InheritDeprecation,
+        inherit_const_stability: InheritConstStability,
         visit_children: F,
     ) where
         F: FnOnce(&mut Self),
@@ -140,6 +156,8 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
             const_stab
         });
 
+        // `impl const Trait for Type` items forward their const stability to their
+        // immediate children.
         if const_stab.is_none() {
             debug!("annotate: const_stab not found, parent = {:?}", self.parent_const_stab);
             if let Some(parent) = self.parent_const_stab {
@@ -228,7 +246,7 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
         self.recurse_with_stability_attrs(
             depr.map(|(d, _)| DeprecationEntry::local(d, hir_id)),
             stab,
-            const_stab,
+            if inherit_const_stability.yes() { const_stab } else { None },
             visit_children,
         );
     }
@@ -325,6 +343,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
     fn visit_item(&mut self, i: &'tcx Item<'tcx>) {
         let orig_in_trait_impl = self.in_trait_impl;
         let mut kind = AnnotationKind::Required;
+        let mut const_stab_inherit = InheritConstStability::No;
         match i.kind {
             // Inherent impls and foreign modules serve only as containers for other items,
             // they don't have their own stability. They still can be annotated as unstable
@@ -338,6 +357,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
             hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) => {
                 self.in_trait_impl = true;
                 kind = AnnotationKind::DeprecationProhibited;
+                const_stab_inherit = InheritConstStability::Yes;
             }
             hir::ItemKind::Struct(ref sd, _) => {
                 if let Some(ctor_hir_id) = sd.ctor_hir_id() {
@@ -347,16 +367,23 @@ impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
                         i.span,
                         AnnotationKind::Required,
                         InheritDeprecation::Yes,
+                        InheritConstStability::No,
                         |_| {},
                     )
                 }
             }
             _ => {}
         }
 
-        self.annotate(i.hir_id, &i.attrs, i.span, kind, InheritDeprecation::Yes, |v| {
-            intravisit::walk_item(v, i)
-        });
+        self.annotate(
+            i.hir_id,
+            &i.attrs,
+            i.span,
+            kind,
+            InheritDeprecation::Yes,
+            const_stab_inherit,
+            |v| intravisit::walk_item(v, i),
+        );
         self.in_trait_impl = orig_in_trait_impl;
     }
 
@@ -367,6 +394,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
             ti.span,
             AnnotationKind::Required,
             InheritDeprecation::Yes,
+            InheritConstStability::No,
             |v| {
                 intravisit::walk_trait_item(v, ti);
             },
@@ -376,9 +404,17 @@ impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
     fn visit_impl_item(&mut self, ii: &'tcx hir::ImplItem<'tcx>) {
         let kind =
             if self.in_trait_impl { AnnotationKind::Prohibited } else { AnnotationKind::Required };
-        self.annotate(ii.hir_id, &ii.attrs, ii.span, kind, InheritDeprecation::Yes, |v| {
-            intravisit::walk_impl_item(v, ii);
-        });
+        self.annotate(
+            ii.hir_id,
+            &ii.attrs,
+            ii.span,
+            kind,
+            InheritDeprecation::Yes,
+            InheritConstStability::No,
+            |v| {
+                intravisit::walk_impl_item(v, ii);
+            },
+        );
     }
 
     fn visit_variant(&mut self, var: &'tcx Variant<'tcx>, g: &'tcx Generics<'tcx>, item_id: HirId) {
@@ -388,6 +424,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
             var.span,
             AnnotationKind::Required,
             InheritDeprecation::Yes,
+            InheritConstStability::No,
             |v| {
                 if let Some(ctor_hir_id) = var.data.ctor_hir_id() {
                     v.annotate(
@@ -396,6 +433,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
                         var.span,
                         AnnotationKind::Required,
                         InheritDeprecation::Yes,
+                        InheritConstStability::No,
                         |_| {},
                     );
                 }
@@ -412,6 +450,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
             s.span,
             AnnotationKind::Required,
             InheritDeprecation::Yes,
+            InheritConstStability::No,
             |v| {
                 intravisit::walk_struct_field(v, s);
             },
@@ -425,6 +464,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
             i.span,
             AnnotationKind::Required,
             InheritDeprecation::Yes,
+            InheritConstStability::No,
             |v| {
                 intravisit::walk_foreign_item(v, i);
             },
@@ -438,6 +478,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
             md.span,
             AnnotationKind::Required,
             InheritDeprecation::Yes,
+            InheritConstStability::No,
             |_| {},
         );
     }
@@ -451,9 +492,17 @@ impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
             _ => AnnotationKind::Prohibited,
         };
 
-        self.annotate(p.hir_id, &p.attrs, p.span, kind, InheritDeprecation::No, |v| {
-            intravisit::walk_generic_param(v, p);
-        });
+        self.annotate(
+            p.hir_id,
+            &p.attrs,
+            p.span,
+            kind,
+            InheritDeprecation::No,
+            InheritConstStability::No,
+            |v| {
+                intravisit::walk_generic_param(v, p);
+            },
+        );
     }
 }
 
@@ -618,6 +667,7 @@ fn new_index(tcx: TyCtxt<'tcx>) -> Index<'tcx> {
             krate.item.span,
             AnnotationKind::Required,
             InheritDeprecation::Yes,
+            InheritConstStability::No,
             |v| intravisit::walk_crate(v, krate),
         );
     }

compiler/rustc_typeck/src/check/callee.rs

@@ -25,24 +25,24 @@ pub fn check_legal_trait_for_method_call(
     tcx: TyCtxt<'_>,
     span: Span,
     receiver: Option<Span>,
+    expr_span: Span,
     trait_id: DefId,
 ) {
     if tcx.lang_items().drop_trait() == Some(trait_id) {
         let mut err = struct_span_err!(tcx.sess, span, E0040, "explicit use of destructor method");
         err.span_label(span, "explicit destructor calls not allowed");
 
-        let snippet = receiver
+        let (sp, suggestion) = receiver
             .and_then(|s| tcx.sess.source_map().span_to_snippet(s).ok())
-            .unwrap_or_default();
-
-        let suggestion =
-            if snippet.is_empty() { "drop".to_string() } else { format!("drop({})", snippet) };
+            .filter(|snippet| !snippet.is_empty())
+            .map(|snippet| (expr_span, format!("drop({})", snippet)))
+            .unwrap_or_else(|| (span, "drop".to_string()));
 
         err.span_suggestion(
-            span,
-            &format!("consider using `drop` function: `{}`", suggestion),
-            String::new(),
-            Applicability::Unspecified,
+            sp,
+            "consider using `drop` function",
+            suggestion,
+            Applicability::MaybeIncorrect,
         );
 
         err.emit();

compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs

@@ -1163,7 +1163,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 debug!("instantiate_value_path: def_id={:?} container={:?}", def_id, container);
                 match container {
                     ty::TraitContainer(trait_did) => {
-                        callee::check_legal_trait_for_method_call(tcx, span, None, trait_did)
+                        callee::check_legal_trait_for_method_call(tcx, span, None, span, trait_did)
                     }
                     ty::ImplContainer(impl_def_id) => {
                         if segments.len() == 1 {

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

@@ -508,6 +508,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                 self.tcx,
                 self.span,
                 Some(self.self_expr.span),
+                self.call_expr.span,
                 trait_def_id,
             ),
             ty::ImplContainer(..) => {}