[DO NOT MERGE] -Znext-solver=globally experiments

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -1,6 +1,7 @@
 use rustc_ast as ast;
 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
 use rustc_ast::{NodeId, PatKind, attr, token};
+use rustc_errors::E0001;
 use rustc_feature::{AttributeGate, BUILTIN_ATTRIBUTE_MAP, BuiltinAttribute, Features};
 use rustc_session::Session;
 use rustc_session::parse::{feature_err, feature_warn};
@@ -650,10 +651,13 @@ fn check_new_solver_banned_features(sess: &Session, features: &Features) {
         .map(|feat| feat.attr_sp)
     {
         #[allow(rustc::symbol_intern_string_literal)]
-        sess.dcx().emit_err(errors::IncompatibleFeatures {
-            spans: vec![gce_span],
-            f1: Symbol::intern("-Znext-solver=globally"),
-            f2: sym::generic_const_exprs,
-        });
+        sess.dcx()
+            .create_fatal(errors::IncompatibleFeatures {
+                spans: vec![gce_span],
+                f1: Symbol::intern("-Znext-solver=globally"),
+                f2: sym::generic_const_exprs,
+            })
+            .with_code(E0001)
+            .emit();
     }
 }

compiler/rustc_hir_typeck/src/closure.rs

@@ -9,17 +9,18 @@ use rustc_hir as hir;
 use rustc_hir::lang_items::LangItem;
 use rustc_hir_analysis::hir_ty_lowering::HirTyLowerer;
 use rustc_infer::infer::{BoundRegionConversionTime, DefineOpaqueTypes, InferOk, InferResult};
-use rustc_infer::traits::{ObligationCauseCode, PredicateObligations};
+use rustc_infer::traits::{ObligationCause, ObligationCauseCode, PredicateObligations};
 use rustc_macros::{TypeFoldable, TypeVisitable};
 use rustc_middle::span_bug;
+use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::{
-    self, ClosureKind, GenericArgs, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable,
-    TypeVisitableExt, TypeVisitor,
+    self, ClosureKind, GenericArgs, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable,
+    TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor,
 };
 use rustc_span::def_id::LocalDefId;
 use rustc_span::{DUMMY_SP, Span};
 use rustc_trait_selection::error_reporting::traits::ArgKind;
-use rustc_trait_selection::traits;
+use rustc_trait_selection::traits::{self, ObligationCtxt};
 use tracing::{debug, instrument, trace};
 
 use super::{CoroutineTypes, Expectation, FnCtxt, check_fn};
@@ -384,56 +385,83 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // Make sure that we didn't infer a signature that mentions itself.
                 // This can happen when we elaborate certain supertrait bounds that
                 // mention projections containing the `Self` type. See #105401.
-                struct MentionsTy<'tcx> {
-                    expected_ty: Ty<'tcx>,
-                }
-                impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for MentionsTy<'tcx> {
-                    type Result = ControlFlow<()>;
-
-                    fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
-                        if t == self.expected_ty {
-                            ControlFlow::Break(())
-                        } else {
-                            t.super_visit_with(self)
-                        }
-                    }
-                }
-
-                // Don't infer a closure signature from a goal that names the closure type as this will
-                // (almost always) lead to occurs check errors later in type checking.
+                //
+                // Doing so will (almost always) lead to occurs check errors later in
+                // type checking.
                 if self.next_trait_solver()
                     && let Some(inferred_sig) = inferred_sig
                 {
-                    // In the new solver it is difficult to explicitly normalize the inferred signature as we
-                    // would have to manually handle universes and rewriting bound vars and placeholders back
-                    // and forth.
-                    //
-                    // Instead we take advantage of the fact that we relating an inference variable with an alias
-                    // will only instantiate the variable if the alias is rigid(*not quite). Concretely we:
-                    // - Create some new variable `?sig`
-                    // - Equate `?sig` with the unnormalized signature, e.g. `fn(<Foo<?x> as Trait>::Assoc)`
-                    // - Depending on whether `<Foo<?x> as Trait>::Assoc` is rigid, ambiguous or normalizeable,
-                    //   we will either wind up with `?sig=<Foo<?x> as Trait>::Assoc/?y/ConcreteTy` respectively.
-                    //
-                    // *: In cases where there are ambiguous aliases in the signature that make use of bound vars
-                    //    they will wind up present in `?sig` even though they are non-rigid.
+                    // If we've got `F: FnOnce(<u32 as Id<F>>::This)` we want to
+                    // use this to infer the signature `FnOnce(u32)` for the closure.
                     //
-                    //    This is a bit weird and means we may wind up discarding the goal due to it naming `expected_ty`
-                    //    even though the normalized form may not name `expected_ty`. However, this matches the existing
-                    //    behaviour of the old solver and would be technically a breaking change to fix.
+                    // We handle self-referential aliases here by relying on generalization
+                    // which replaces such aliases with inference variables. This is currently
+                    // a bit too weak, see trait-system-refactor-initiative#191.
+                    struct ReplaceTy<'tcx> {
+                        tcx: TyCtxt<'tcx>,
+                        expected_ty: Ty<'tcx>,
+                        with_ty: Ty<'tcx>,
+                    }
+                    impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ReplaceTy<'tcx> {
+                        fn cx(&self) -> TyCtxt<'tcx> {
+                            self.tcx
+                        }
+
+                        fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
+                            if t == self.expected_ty {
+                                self.with_ty
+                            } else {
+                                t.super_fold_with(self)
+                            }
+                        }
+                    }
                     let generalized_fnptr_sig = self.next_ty_var(span);
                     let inferred_fnptr_sig = Ty::new_fn_ptr(self.tcx, inferred_sig.sig);
-                    self.demand_eqtype(span, inferred_fnptr_sig, generalized_fnptr_sig);
-
-                    let resolved_sig = self.resolve_vars_if_possible(generalized_fnptr_sig);
-
-                    if resolved_sig.visit_with(&mut MentionsTy { expected_ty }).is_continue() {
-                        expected_sig = Some(ExpectedSig {
-                            cause_span: inferred_sig.cause_span,
-                            sig: resolved_sig.fn_sig(self.tcx),
-                        });
+                    let inferred_fnptr_sig = inferred_fnptr_sig.fold_with(&mut ReplaceTy {
+                        tcx: self.tcx,
+                        expected_ty,
+                        with_ty: generalized_fnptr_sig,
+                    });
+                    let resolved_sig = self.commit_if_ok(|snapshot| {
+                        let outer_universe = self.universe();
+                        let ocx = ObligationCtxt::new(self);
+                        ocx.eq(
+                            &ObligationCause::dummy(),
+                            self.param_env,
+                            generalized_fnptr_sig,
+                            inferred_fnptr_sig,
+                        )?;
+                        if ocx.select_where_possible().is_empty() {
+                            self.leak_check(outer_universe, Some(snapshot))?;
+                            Ok(self.resolve_vars_if_possible(generalized_fnptr_sig))
+                        } else {
+                            Err(TypeError::Mismatch)
+                        }
+                    });
+                    match resolved_sig {
+                        Ok(resolved_sig) => {
+                            expected_sig = Some(ExpectedSig {
+                                cause_span: inferred_sig.cause_span,
+                                sig: resolved_sig.fn_sig(self.tcx),
+                            })
+                        }
+                        Err(_) => {}
                     }
                 } else {
+                    struct MentionsTy<'tcx> {
+                        expected_ty: Ty<'tcx>,
+                    }
+                    impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for MentionsTy<'tcx> {
+                        type Result = ControlFlow<()>;
+
+                        fn visit_ty(&mut self, t: Ty<'tcx>) -> Self::Result {
+                            if t == self.expected_ty {
+                                ControlFlow::Break(())
+                            } else {
+                                t.super_visit_with(self)
+                            }
+                        }
+                    }
                     if inferred_sig.visit_with(&mut MentionsTy { expected_ty }).is_continue() {
                         expected_sig = inferred_sig;
                     }

compiler/rustc_hir_typeck/src/fn_ctxt/inspect_obligations.rs

@@ -1,7 +1,6 @@
 //! A utility module to inspect currently ambiguous obligations in the current context.
 
 use rustc_infer::traits::{self, ObligationCause, PredicateObligations};
-use rustc_middle::traits::solve::GoalSource;
 use rustc_middle::ty::{self, Ty, TypeVisitableExt};
 use rustc_span::Span;
 use rustc_trait_selection::solve::Certainty;
@@ -37,10 +36,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) -> bool {
         match predicate.kind().skip_binder() {
             ty::PredicateKind::Clause(ty::ClauseKind::Trait(data)) => {
-                self.type_matches_expected_vid(expected_vid, data.self_ty())
+                self.type_matches_expected_vid(data.self_ty(), expected_vid)
             }
             ty::PredicateKind::Clause(ty::ClauseKind::Projection(data)) => {
-                self.type_matches_expected_vid(expected_vid, data.projection_term.self_ty())
+                self.type_matches_expected_vid(data.projection_term.self_ty(), expected_vid)
             }
             ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(..))
             | ty::PredicateKind::Subtype(..)
@@ -60,7 +59,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     }
 
     #[instrument(level = "debug", skip(self), ret)]
-    fn type_matches_expected_vid(&self, expected_vid: ty::TyVid, ty: Ty<'tcx>) -> bool {
+    fn type_matches_expected_vid(&self, ty: Ty<'tcx>, expected_vid: ty::TyVid) -> bool {
         let ty = self.shallow_resolve(ty);
         debug!(?ty);
 
@@ -76,7 +75,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         &self,
         self_ty: ty::TyVid,
     ) -> PredicateObligations<'tcx> {
-        let obligations = self.fulfillment_cx.borrow().pending_obligations();
+        let sub_root_var = self.sub_unification_table_root_var(self_ty);
+        let obligations = self
+            .fulfillment_cx
+            .borrow()
+            .pending_obligations_potentially_referencing_sub_root(sub_root_var);
         debug!(?obligations);
         let mut obligations_for_self_ty = PredicateObligations::new();
         for obligation in obligations {
@@ -125,23 +128,21 @@ impl<'a, 'tcx> ProofTreeVisitor<'tcx> for NestedObligationsForSelfTy<'a, 'tcx> {
             return;
         }
 
+        // We don't care about any pending goals which don't actually
+        // use the self type.
+        if !inspect_goal
+            .orig_values()
+            .iter()
+            .filter_map(|arg| arg.as_type())
+            .any(|ty| self.fcx.type_matches_expected_vid(ty, self.self_ty))
+        {
+            debug!(goal = ?inspect_goal.goal(), "goal does not mention self type");
+            return;
+        }
+
         let tcx = self.fcx.tcx;
         let goal = inspect_goal.goal();
-        if self.fcx.predicate_has_self_ty(goal.predicate, self.self_ty)
-            // We do not push the instantiated forms of goals as it would cause any
-            // aliases referencing bound vars to go from having escaping bound vars to
-            // being able to be normalized to an inference variable.
-            //
-            // This is mostly just a hack as arbitrary nested goals could still contain
-            // such aliases while having a different `GoalSource`. Closure signature inference
-            // however can't really handle *every* higher ranked `Fn` goal also being present
-            // in the form of `?c: Fn<(<?x as Trait<'!a>>::Assoc)`.
-            //
-            // This also just better matches the behaviour of the old solver where we do not
-            // encounter instantiated forms of goals, only nested goals that referred to bound
-            // vars from instantiated goals.
-            && !matches!(inspect_goal.source(), GoalSource::InstantiateHigherRanked)
-        {
+        if self.fcx.predicate_has_self_ty(goal.predicate, self.self_ty) {
             self.obligations_for_self_ty.push(traits::Obligation::new(
                 tcx,
                 self.root_cause.clone(),

compiler/rustc_hir_typeck/src/lib.rs

@@ -219,6 +219,12 @@ fn typeck_with_inspect<'tcx>(
     // the future.
     fcx.check_repeat_exprs();
 
+    // We need to handle opaque types before emitting ambiguity errors as applying
+    // defining uses may guide type inference.
+    if fcx.next_trait_solver() {
+        fcx.try_handle_opaque_type_uses_next();
+    }
+
     fcx.type_inference_fallback();
 
     // Even though coercion casts provide type hints, we check casts after fallback for

compiler/rustc_hir_typeck/src/opaque_types.rs

@@ -22,6 +22,29 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
     /// inference variables.
     ///
     /// It then uses these defining uses to guide inference for all other uses.
+    ///
+    /// Unlike `handle_opaque_type_uses_next`, this does not report errors.
+    pub(super) fn try_handle_opaque_type_uses_next(&mut self) {
+        // We clone the opaques instead of stealing them here as they are still used for
+        // normalization in the next generation trait solver.
+        let mut opaque_types: Vec<_> = self.infcx.clone_opaque_types();
+        for entry in &mut opaque_types {
+            *entry = self.resolve_vars_if_possible(*entry);
+        }
+        debug!(?opaque_types);
+
+        self.compute_definition_site_hidden_types(&opaque_types, true);
+        self.apply_definition_site_hidden_types(&opaque_types);
+    }
+
+    /// This takes all the opaque type uses during HIR typeck. It first computes
+    /// the concrete hidden type by iterating over all defining uses.
+    ///
+    /// A use during HIR typeck is defining if all non-lifetime arguments are
+    /// unique generic parameters and the hidden type does not reference any
+    /// inference variables.
+    ///
+    /// It then uses these defining uses to guide inference for all other uses.
     #[instrument(level = "debug", skip(self))]
     pub(super) fn handle_opaque_type_uses_next(&mut self) {
         // We clone the opaques instead of stealing them here as they are still used for
@@ -35,7 +58,7 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
         }
         debug!(?opaque_types);
 
-        self.compute_definition_site_hidden_types(&opaque_types);
+        self.compute_definition_site_hidden_types(&opaque_types, false);
         self.apply_definition_site_hidden_types(&opaque_types);
     }
 }
@@ -74,6 +97,7 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
     fn compute_definition_site_hidden_types(
         &mut self,
         opaque_types: &[(OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>)],
+        first_pass: bool,
     ) {
         let tcx = self.tcx;
         let TypingMode::Analysis { defining_opaque_types_and_generators } = self.typing_mode()
@@ -94,12 +118,22 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
                     continue;
                 }
 
-                usage_kind.merge(self.consider_opaque_type_use(opaque_type_key, hidden_type));
+                usage_kind.merge(self.consider_opaque_type_use(
+                    opaque_type_key,
+                    hidden_type,
+                    first_pass,
+                ));
                 if let UsageKind::HasDefiningUse = usage_kind {
                     break;
                 }
             }
 
+            // If this the first pass (`try_handle_opaque_type_uses_next`),
+            // then do not report any errors.
+            if first_pass {
+                continue;
+            }
+
             let guar = match usage_kind {
                 UsageKind::None => {
                     if let Some(guar) = self.tainted_by_errors() {
@@ -152,6 +186,7 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
         &mut self,
         opaque_type_key: OpaqueTypeKey<'tcx>,
         hidden_type: OpaqueHiddenType<'tcx>,
+        first_pass: bool,
     ) -> UsageKind<'tcx> {
         if let Err(err) = opaque_type_has_defining_use_args(
             &self,
@@ -199,7 +234,13 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
             .borrow_mut()
             .hidden_types
             .insert(opaque_type_key.def_id, hidden_type);
-        assert!(prev.is_none());
+
+        // We do want to insert opaque types the first pass, because we want to
+        // equate them. So, the second pass (where we report errors) will have
+        // a hidden type inserted.
+        if first_pass {
+            assert!(prev.is_none());
+        }
         UsageKind::HasDefiningUse
     }
 
@@ -209,10 +250,12 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
     ) {
         let tcx = self.tcx;
         for &(key, hidden_type) in opaque_types {
-            let expected = *self.typeck_results.borrow_mut().hidden_types.get(&key.def_id).unwrap();
-
-            let expected = EarlyBinder::bind(expected.ty).instantiate(tcx, key.args);
-            self.demand_eqtype(hidden_type.span, expected, hidden_type.ty);
+            // On the first pass to this function, some opaque types may not
+            // have a hidden type assigned.
+            if let Some(expected) = self.typeck_results.borrow_mut().hidden_types.get(&key.def_id) {
+                let expected = EarlyBinder::bind(expected.ty).instantiate(tcx, key.args);
+                self.demand_eqtype(hidden_type.span, expected, hidden_type.ty);
+            }
         }
     }