Rollup of 6 pull requests

compiler/rustc_ast_lowering/src/lib.rs

@@ -324,16 +324,10 @@ enum FnDeclKind {
 }
 
 impl FnDeclKind {
-    fn impl_trait_return_allowed(&self, tcx: TyCtxt<'_>) -> bool {
+    fn impl_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
         match self {
             FnDeclKind::Fn | FnDeclKind::Inherent => true,
             FnDeclKind::Impl if tcx.features().return_position_impl_trait_in_trait => true,
-            _ => false,
-        }
-    }
-
-    fn impl_trait_in_trait_allowed(&self, tcx: TyCtxt<'_>) -> bool {
-        match self {
             FnDeclKind::Trait if tcx.features().return_position_impl_trait_in_trait => true,
             _ => false,
         }
@@ -1698,9 +1692,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         }));
 
         let output = if let Some((ret_id, span)) = make_ret_async {
-            match kind {
-                FnDeclKind::Trait => {
-                    if !kind.impl_trait_in_trait_allowed(self.tcx) {
+            if !kind.impl_trait_allowed(self.tcx) {
+                match kind {
+                    FnDeclKind::Trait | FnDeclKind::Impl => {
                         self.tcx
                             .sess
                             .create_feature_err(
@@ -1709,51 +1703,27 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             )
                             .emit();
                     }
-                    self.lower_async_fn_ret_ty(
-                        &decl.output,
-                        fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
-                        ret_id,
-                        true,
-                    )
-                }
-                _ => {
-                    if !kind.impl_trait_return_allowed(self.tcx) {
-                        if kind == FnDeclKind::Impl {
-                            self.tcx
-                                .sess
-                                .create_feature_err(
-                                    TraitFnAsync { fn_span, span },
-                                    sym::return_position_impl_trait_in_trait,
-                                )
-                                .emit();
-                        } else {
-                            self.tcx.sess.emit_err(TraitFnAsync { fn_span, span });
-                        }
+                    _ => {
+                        self.tcx.sess.emit_err(TraitFnAsync { fn_span, span });
                     }
-                    self.lower_async_fn_ret_ty(
-                        &decl.output,
-                        fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
-                        ret_id,
-                        false,
-                    )
                 }
             }
+
+            self.lower_async_fn_ret_ty(
+                &decl.output,
+                fn_node_id.expect("`make_ret_async` but no `fn_def_id`"),
+                ret_id,
+                matches!(kind, FnDeclKind::Trait),
+            )
         } else {
             match decl.output {
                 FnRetTy::Ty(ref ty) => {
                     let mut context = match fn_node_id {
-                        Some(fn_node_id) if kind.impl_trait_return_allowed(self.tcx) => {
-                            let fn_def_id = self.local_def_id(fn_node_id);
-                            ImplTraitContext::ReturnPositionOpaqueTy {
-                                origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
-                                in_trait: false,
-                            }
-                        }
-                        Some(fn_node_id) if kind.impl_trait_in_trait_allowed(self.tcx) => {
+                        Some(fn_node_id) if kind.impl_trait_allowed(self.tcx) => {
                             let fn_def_id = self.local_def_id(fn_node_id);
                             ImplTraitContext::ReturnPositionOpaqueTy {
                                 origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
-                                in_trait: true,
+                                in_trait: matches!(kind, FnDeclKind::Trait),
                             }
                         }
                         _ => ImplTraitContext::Disallowed(match kind {

compiler/rustc_builtin_macros/src/cfg_eval.rs

@@ -7,6 +7,7 @@ use rustc_ast::visit::Visitor;
 use rustc_ast::NodeId;
 use rustc_ast::{mut_visit, visit};
 use rustc_ast::{Attribute, HasAttrs, HasTokens};
+use rustc_errors::PResult;
 use rustc_expand::base::{Annotatable, ExtCtxt};
 use rustc_expand::config::StripUnconfigured;
 use rustc_expand::configure;
@@ -144,33 +145,34 @@ impl CfgEval<'_, '_> {
         // the location of `#[cfg]` and `#[cfg_attr]` in the token stream. The tokenization
         // process is lossless, so this process is invisible to proc-macros.
 
-        let parse_annotatable_with: fn(&mut Parser<'_>) -> _ = match annotatable {
-            Annotatable::Item(_) => {
-                |parser| Annotatable::Item(parser.parse_item(ForceCollect::Yes).unwrap().unwrap())
-            }
-            Annotatable::TraitItem(_) => |parser| {
-                Annotatable::TraitItem(
-                    parser.parse_trait_item(ForceCollect::Yes).unwrap().unwrap().unwrap(),
-                )
-            },
-            Annotatable::ImplItem(_) => |parser| {
-                Annotatable::ImplItem(
-                    parser.parse_impl_item(ForceCollect::Yes).unwrap().unwrap().unwrap(),
-                )
-            },
-            Annotatable::ForeignItem(_) => |parser| {
-                Annotatable::ForeignItem(
-                    parser.parse_foreign_item(ForceCollect::Yes).unwrap().unwrap().unwrap(),
-                )
-            },
-            Annotatable::Stmt(_) => |parser| {
-                Annotatable::Stmt(P(parser.parse_stmt(ForceCollect::Yes).unwrap().unwrap()))
-            },
-            Annotatable::Expr(_) => {
-                |parser| Annotatable::Expr(parser.parse_expr_force_collect().unwrap())
-            }
-            _ => unreachable!(),
-        };
+        let parse_annotatable_with: for<'a> fn(&mut Parser<'a>) -> PResult<'a, _> =
+            match annotatable {
+                Annotatable::Item(_) => {
+                    |parser| Ok(Annotatable::Item(parser.parse_item(ForceCollect::Yes)?.unwrap()))
+                }
+                Annotatable::TraitItem(_) => |parser| {
+                    Ok(Annotatable::TraitItem(
+                        parser.parse_trait_item(ForceCollect::Yes)?.unwrap().unwrap(),
+                    ))
+                },
+                Annotatable::ImplItem(_) => |parser| {
+                    Ok(Annotatable::ImplItem(
+                        parser.parse_impl_item(ForceCollect::Yes)?.unwrap().unwrap(),
+                    ))
+                },
+                Annotatable::ForeignItem(_) => |parser| {
+                    Ok(Annotatable::ForeignItem(
+                        parser.parse_foreign_item(ForceCollect::Yes)?.unwrap().unwrap(),
+                    ))
+                },
+                Annotatable::Stmt(_) => |parser| {
+                    Ok(Annotatable::Stmt(P(parser.parse_stmt(ForceCollect::Yes)?.unwrap())))
+                },
+                Annotatable::Expr(_) => {
+                    |parser| Ok(Annotatable::Expr(parser.parse_expr_force_collect()?))
+                }
+                _ => unreachable!(),
+            };
 
         // 'Flatten' all nonterminals (i.e. `TokenKind::Interpolated`)
         // to `None`-delimited groups containing the corresponding tokens. This
@@ -193,7 +195,13 @@ impl CfgEval<'_, '_> {
         let mut parser =
             rustc_parse::stream_to_parser(&self.cfg.sess.parse_sess, orig_tokens, None);
         parser.capture_cfg = true;
-        annotatable = parse_annotatable_with(&mut parser);
+        match parse_annotatable_with(&mut parser) {
+            Ok(a) => annotatable = a,
+            Err(mut err) => {
+                err.emit();
+                return Some(annotatable);
+            }
+        }
 
         // Now that we have our re-parsed `AttrTokenStream`, recursively configuring
         // our attribute target will correctly the tokens as well.

compiler/rustc_data_structures/src/obligation_forest/mod.rs

@@ -95,6 +95,10 @@ pub trait ForestObligation: Clone + Debug {
 pub trait ObligationProcessor {
     type Obligation: ForestObligation;
     type Error: Debug;
+    type OUT: OutcomeTrait<
+        Obligation = Self::Obligation,
+        Error = Error<Self::Obligation, Self::Error>,
+    >;
 
     fn needs_process_obligation(&self, obligation: &Self::Obligation) -> bool;
 
@@ -111,7 +115,11 @@ pub trait ObligationProcessor {
     /// In other words, if we had O1 which required O2 which required
     /// O3 which required O1, we would give an iterator yielding O1,
     /// O2, O3 (O1 is not yielded twice).
-    fn process_backedge<'c, I>(&mut self, cycle: I, _marker: PhantomData<&'c Self::Obligation>)
+    fn process_backedge<'c, I>(
+        &mut self,
+        cycle: I,
+        _marker: PhantomData<&'c Self::Obligation>,
+    ) -> Result<(), Self::Error>
     where
         I: Clone + Iterator<Item = &'c Self::Obligation>;
 }
@@ -402,12 +410,11 @@ impl<O: ForestObligation> ObligationForest<O> {
 
     /// Performs a fixpoint computation over the obligation list.
     #[inline(never)]
-    pub fn process_obligations<P, OUT>(&mut self, processor: &mut P) -> OUT
+    pub fn process_obligations<P>(&mut self, processor: &mut P) -> P::OUT
     where
         P: ObligationProcessor<Obligation = O>,
-        OUT: OutcomeTrait<Obligation = O, Error = Error<O, P::Error>>,
     {
-        let mut outcome = OUT::new();
+        let mut outcome = P::OUT::new();
 
         // Fixpoint computation: we repeat until the inner loop stalls.
         loop {
@@ -473,7 +480,7 @@ impl<O: ForestObligation> ObligationForest<O> {
             }
 
             self.mark_successes();
-            self.process_cycles(processor);
+            self.process_cycles(processor, &mut outcome);
             self.compress(|obl| outcome.record_completed(obl));
         }
 
@@ -558,7 +565,7 @@ impl<O: ForestObligation> ObligationForest<O> {
 
     /// Report cycles between all `Success` nodes, and convert all `Success`
     /// nodes to `Done`. This must be called after `mark_successes`.
-    fn process_cycles<P>(&mut self, processor: &mut P)
+    fn process_cycles<P>(&mut self, processor: &mut P, outcome: &mut P::OUT)
     where
         P: ObligationProcessor<Obligation = O>,
     {
@@ -568,16 +575,21 @@ impl<O: ForestObligation> ObligationForest<O> {
             // to handle the no-op cases immediately to avoid the cost of the
             // function call.
             if node.state.get() == NodeState::Success {
-                self.find_cycles_from_node(&mut stack, processor, index);
+                self.find_cycles_from_node(&mut stack, processor, index, outcome);
             }
         }
 
         debug_assert!(stack.is_empty());
         self.reused_node_vec = stack;
     }
 
-    fn find_cycles_from_node<P>(&self, stack: &mut Vec<usize>, processor: &mut P, index: usize)
-    where
+    fn find_cycles_from_node<P>(
+        &self,
+        stack: &mut Vec<usize>,
+        processor: &mut P,
+        index: usize,
+        outcome: &mut P::OUT,
+    ) where
         P: ObligationProcessor<Obligation = O>,
     {
         let node = &self.nodes[index];
@@ -586,17 +598,20 @@ impl<O: ForestObligation> ObligationForest<O> {
                 None => {
                     stack.push(index);
                     for &dep_index in node.dependents.iter() {
-                        self.find_cycles_from_node(stack, processor, dep_index);
+                        self.find_cycles_from_node(stack, processor, dep_index, outcome);
                     }
                     stack.pop();
                     node.state.set(NodeState::Done);
                 }
                 Some(rpos) => {
                     // Cycle detected.
-                    processor.process_backedge(
+                    let result = processor.process_backedge(
                         stack[rpos..].iter().map(|&i| &self.nodes[i].obligation),
                         PhantomData,
                     );
+                    if let Err(err) = result {
+                        outcome.record_error(Error { error: err, backtrace: self.error_at(index) });
+                    }
                 }
             }
         }

compiler/rustc_data_structures/src/obligation_forest/tests.rs

@@ -64,6 +64,7 @@ where
 {
     type Obligation = O;
     type Error = E;
+    type OUT = TestOutcome<O, E>;
 
     fn needs_process_obligation(&self, _obligation: &Self::Obligation) -> bool {
         true
@@ -76,10 +77,15 @@ where
         (self.process_obligation)(obligation)
     }
 
-    fn process_backedge<'c, I>(&mut self, _cycle: I, _marker: PhantomData<&'c Self::Obligation>)
+    fn process_backedge<'c, I>(
+        &mut self,
+        _cycle: I,
+        _marker: PhantomData<&'c Self::Obligation>,
+    ) -> Result<(), Self::Error>
     where
         I: Clone + Iterator<Item = &'c Self::Obligation>,
     {
+        Ok(())
     }
 }
 

compiler/rustc_infer/src/traits/mod.rs

@@ -105,6 +105,8 @@ pub struct FulfillmentError<'tcx> {
 
 #[derive(Clone)]
 pub enum FulfillmentErrorCode<'tcx> {
+    /// Inherently impossible to fulfill; this trait is implemented if and only if it is already implemented.
+    CodeCycle(Vec<Obligation<'tcx, ty::Predicate<'tcx>>>),
     CodeSelectionError(SelectionError<'tcx>),
     CodeProjectionError(MismatchedProjectionTypes<'tcx>),
     CodeSubtypeError(ExpectedFound<Ty<'tcx>>, TypeError<'tcx>), // always comes from a SubtypePredicate

compiler/rustc_infer/src/traits/structural_impls.rs

@@ -47,6 +47,7 @@ impl<'tcx> fmt::Debug for traits::FulfillmentErrorCode<'tcx> {
                 write!(f, "CodeConstEquateError({:?}, {:?})", a, b)
             }
             super::CodeAmbiguity => write!(f, "Ambiguity"),
+            super::CodeCycle(ref cycle) => write!(f, "Cycle({:?})", cycle),
         }
     }
 }

compiler/rustc_middle/src/ty/query.rs

@@ -277,8 +277,9 @@ macro_rules! define_callbacks {
             fn default() -> Self {
                 Providers {
                     $($name: |_, key| bug!(
-                        "`tcx.{}({:?})` unsupported by its crate; \
-                         perhaps the `{}` query was never assigned a provider function",
+                        "`tcx.{}({:?})` is not supported for external or local crate;\n
+                        hint: Queries can be either made to the local crate, or the external crate. This error means you tried to use it for one that's not supported (likely the local crate).\n
+                        If that's not the case, {} was likely never assigned to a provider function.\n",
                         stringify!($name),
                         key,
                         stringify!($name),

compiler/rustc_parse/src/parser/attr_wrapper.rs

@@ -459,6 +459,5 @@ fn make_token_stream(
             panic!("Unexpected last token {:?}", last_token)
         }
     }
-    assert!(stack.is_empty(), "Stack should be empty: final_buf={:?} stack={:?}", final_buf, stack);
     AttrTokenStream::new(final_buf.inner)
 }

compiler/rustc_trait_selection/src/traits/codegen.rs

@@ -4,10 +4,12 @@
 // general routines.
 
 use crate::infer::{DefiningAnchor, TyCtxtInferExt};
+use crate::traits::error_reporting::InferCtxtExt;
 use crate::traits::{
     ImplSource, Obligation, ObligationCause, SelectionContext, TraitEngine, TraitEngineExt,
     Unimplemented,
 };
+use rustc_infer::traits::FulfillmentErrorCode;
 use rustc_middle::traits::CodegenObligationError;
 use rustc_middle::ty::{self, TyCtxt};
 
@@ -62,6 +64,14 @@ pub fn codegen_select_candidate<'tcx>(
         // optimization to stop iterating early.
         let errors = fulfill_cx.select_all_or_error(&infcx);
         if !errors.is_empty() {
+            // `rustc_monomorphize::collector` assumes there are no type errors.
+            // Cycle errors are the only post-monomorphization errors possible; emit them now so
+            // `rustc_ty_utils::resolve_associated_item` doesn't return `None` post-monomorphization.
+            for err in errors {
+                if let FulfillmentErrorCode::CodeCycle(cycle) = err.code {
+                    infcx.report_overflow_error_cycle(&cycle);
+                }
+            }
             return Err(CodegenObligationError::FulfillmentError);
         }
 

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

@@ -1540,6 +1540,9 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
                 }
                 diag.emit();
             }
+            FulfillmentErrorCode::CodeCycle(ref cycle) => {
+                self.report_overflow_error_cycle(cycle);
+            }
         }
     }