Auto merge of rust-lang#118120 - compiler-errors:closure-kind, r=lcnr

Remove `PredicateKind::ClosureKind`

We don't need the `ClosureKind` predicate kind -- instead, `Fn`-family trait goals are left as ambiguous, and we only need to make progress on `FnOnce` projection goals for inference purposes.

This is similar to how we do confirmation of `Fn`-family trait and projection goals in the new trait solver, which also doesn't use the `ClosureKind` predicate.

Some hacky logic is added in the second commit so that we can keep the error messages the same.

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -662,7 +662,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // this closure yet; this is exactly why the other
                 // code is looking for a self type of an unresolved
                 // inference variable.
-                | ty::PredicateKind::ClosureKind(..)
                 | ty::PredicateKind::Ambiguous
                  => None,
             },

compiler/rustc_infer/src/infer/mod.rs

@@ -906,12 +906,14 @@ impl<'tcx> InferCtxt<'tcx> {
         self.inner.borrow().undo_log.opaque_types_in_snapshot(&snapshot.undo_snapshot)
     }
 
-    pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool
+    pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, expected: T, actual: T) -> bool
     where
         T: at::ToTrace<'tcx>,
     {
         let origin = &ObligationCause::dummy();
-        self.probe(|_| self.at(origin, param_env).sub(DefineOpaqueTypes::No, a, b).is_ok())
+        self.probe(|_| {
+            self.at(origin, param_env).sub(DefineOpaqueTypes::No, expected, actual).is_ok()
+        })
     }
 
     pub fn can_eq<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool

compiler/rustc_infer/src/traits/util.rs

@@ -308,9 +308,6 @@ impl<'tcx, O: Elaboratable<'tcx>> Elaborator<'tcx, O> {
             ty::PredicateKind::Clause(ty::ClauseKind::Projection(..)) => {
                 // Nothing to elaborate in a projection predicate.
             }
-            ty::PredicateKind::ClosureKind(..) => {
-                // Nothing to elaborate when waiting for a closure's kind to be inferred.
-            }
             ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..)) => {
                 // Currently, we do not elaborate const-evaluatable
                 // predicates.

compiler/rustc_middle/src/ty/flags.rs

@@ -263,9 +263,6 @@ impl FlagComputation {
                 self.add_args(slice::from_ref(&arg));
             }
             ty::PredicateKind::ObjectSafe(_def_id) => {}
-            ty::PredicateKind::ClosureKind(_def_id, args, _kind) => {
-                self.add_args(args);
-            }
             ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(uv)) => {
                 self.add_const(uv);
             }

compiler/rustc_middle/src/ty/mod.rs

@@ -548,7 +548,6 @@ impl<'tcx> Predicate<'tcx> {
             | PredicateKind::Clause(ClauseKind::ConstArgHasType(..))
             | PredicateKind::AliasRelate(..)
             | PredicateKind::ObjectSafe(_)
-            | PredicateKind::ClosureKind(_, _, _)
             | PredicateKind::Subtype(_)
             | PredicateKind::Coerce(_)
             | PredicateKind::Clause(ClauseKind::ConstEvaluatable(_))
@@ -1276,7 +1275,6 @@ impl<'tcx> Predicate<'tcx> {
             | PredicateKind::Clause(ClauseKind::RegionOutlives(..))
             | PredicateKind::Clause(ClauseKind::WellFormed(..))
             | PredicateKind::ObjectSafe(..)
-            | PredicateKind::ClosureKind(..)
             | PredicateKind::Clause(ClauseKind::TypeOutlives(..))
             | PredicateKind::Clause(ClauseKind::ConstEvaluatable(..))
             | PredicateKind::ConstEquate(..)
@@ -1296,7 +1294,6 @@ impl<'tcx> Predicate<'tcx> {
             | PredicateKind::Clause(ClauseKind::RegionOutlives(..))
             | PredicateKind::Clause(ClauseKind::WellFormed(..))
             | PredicateKind::ObjectSafe(..)
-            | PredicateKind::ClosureKind(..)
             | PredicateKind::Clause(ClauseKind::TypeOutlives(..))
             | PredicateKind::Clause(ClauseKind::ConstEvaluatable(..))
             | PredicateKind::ConstEquate(..)
@@ -1317,7 +1314,6 @@ impl<'tcx> Predicate<'tcx> {
             | PredicateKind::Clause(ClauseKind::RegionOutlives(..))
             | PredicateKind::Clause(ClauseKind::WellFormed(..))
             | PredicateKind::ObjectSafe(..)
-            | PredicateKind::ClosureKind(..)
             | PredicateKind::Clause(ClauseKind::ConstEvaluatable(..))
             | PredicateKind::ConstEquate(..)
             | PredicateKind::Ambiguous => None,

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -2781,11 +2781,6 @@ define_print! {
             ty::PredicateKind::ObjectSafe(trait_def_id) => {
                 p!("the trait `", print_def_path(trait_def_id, &[]), "` is object-safe")
             }
-            ty::PredicateKind::ClosureKind(closure_def_id, _closure_args, kind) => p!(
-                "the closure `",
-                print_value_path(closure_def_id, &[]),
-                write("` implements the trait `{}`", kind)
-            ),
             ty::PredicateKind::ConstEquate(c1, c2) => {
                 p!("the constant `", print(c1), "` equals `", print(c2), "`")
             }

compiler/rustc_smir/src/rustc_smir/mod.rs

@@ -1809,13 +1809,6 @@ impl<'tcx> Stable<'tcx> for ty::PredicateKind<'tcx> {
             PredicateKind::ObjectSafe(did) => {
                 stable_mir::ty::PredicateKind::ObjectSafe(tables.trait_def(*did))
             }
-            PredicateKind::ClosureKind(did, generic_args, closure_kind) => {
-                stable_mir::ty::PredicateKind::ClosureKind(
-                    tables.closure_def(*did),
-                    generic_args.stable(tables),
-                    closure_kind.stable(tables),
-                )
-            }
             PredicateKind::Subtype(subtype_predicate) => {
                 stable_mir::ty::PredicateKind::SubType(subtype_predicate.stable(tables))
             }

compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs

@@ -406,8 +406,6 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
                 ty::PredicateKind::Coerce(predicate) => {
                     self.compute_coerce_goal(Goal { param_env, predicate })
                 }
-                ty::PredicateKind::ClosureKind(def_id, args, kind) => self
-                    .compute_closure_kind_goal(Goal { param_env, predicate: (def_id, args, kind) }),
                 ty::PredicateKind::ObjectSafe(trait_def_id) => {
                     self.compute_object_safe_goal(trait_def_id)
                 }

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -135,7 +135,6 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
                                     }
                                     ty::PredicateKind::Clause(_)
                                     | ty::PredicateKind::ObjectSafe(_)
-                                    | ty::PredicateKind::ClosureKind(_, _, _)
                                     | ty::PredicateKind::Ambiguous => {
                                         FulfillmentErrorCode::CodeSelectionError(
                                             SelectionError::Unimplemented,

compiler/rustc_trait_selection/src/traits/auto_trait.rs

@@ -822,7 +822,6 @@ impl<'tcx> AutoTraitFinder<'tcx> {
                 | ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(..))
                 | ty::PredicateKind::AliasRelate(..)
                 | ty::PredicateKind::ObjectSafe(..)
-                | ty::PredicateKind::ClosureKind(..)
                 | ty::PredicateKind::Subtype(..)
                 // FIXME(generic_const_exprs): you can absolutely add this as a where clauses
                 | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))

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

@@ -98,6 +98,12 @@ pub trait TypeErrCtxtExt<'tcx> {
         error: &SelectionError<'tcx>,
     );
 
+    fn emit_specialized_closure_kind_error(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+        trait_ref: ty::PolyTraitRef<'tcx>,
+    ) -> Option<ErrorGuaranteed>;
+
     fn fn_arg_obligation(&self, obligation: &PredicateObligation<'tcx>) -> bool;
 
     fn report_const_param_not_wf(
@@ -411,6 +417,11 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_predicate)) => {
                         let trait_predicate = bound_predicate.rebind(trait_predicate);
                         let trait_predicate = self.resolve_vars_if_possible(trait_predicate);
+                        let trait_ref = trait_predicate.to_poly_trait_ref();
+
+                        if let Some(_guar) = self.emit_specialized_closure_kind_error(&obligation, trait_ref) {
+                            return;
+                        }
 
                         // FIXME(effects)
                         let predicate_is_const = false;
@@ -425,7 +436,6 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                             // reported on the binding definition (#56607).
                             return;
                         }
-                        let trait_ref = trait_predicate.to_poly_trait_ref();
                         let (post_message, pre_message, type_def, file_note) = self
                             .get_parent_trait_ref(obligation.cause.code())
                             .map(|(t, s)| {
@@ -786,11 +796,6 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                         report_object_safety_error(self.tcx, span, trait_def_id, violations)
                     }
 
-                    ty::PredicateKind::ClosureKind(closure_def_id, closure_args, kind) => {
-                        let found_kind = self.closure_kind(closure_args).unwrap();
-                        self.report_closure_error(&obligation, closure_def_id, found_kind, kind)
-                    }
-
                     ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(ty)) => {
                         let ty = self.resolve_vars_if_possible(ty);
                         match self.tcx.sess.opts.unstable_opts.trait_solver {
@@ -927,6 +932,38 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
         err.emit();
     }
 
+    fn emit_specialized_closure_kind_error(
+        &self,
+        obligation: &PredicateObligation<'tcx>,
+        trait_ref: ty::PolyTraitRef<'tcx>,
+    ) -> Option<ErrorGuaranteed> {
+        if let ty::Closure(closure_def_id, closure_args) = *trait_ref.self_ty().skip_binder().kind()
+            && let Some(expected_kind) = self.tcx.fn_trait_kind_from_def_id(trait_ref.def_id())
+            && let Some(found_kind) = self.closure_kind(closure_args)
+            && !found_kind.extends(expected_kind)
+            && let sig = closure_args.as_closure().sig()
+            && self.can_sub(
+                obligation.param_env,
+                trait_ref,
+                sig.map_bound(|sig| {
+                    ty::TraitRef::new(
+                        self.tcx,
+                        trait_ref.def_id(),
+                        [trait_ref.self_ty().skip_binder(), sig.inputs()[0]],
+                    )
+                }),
+            )
+        {
+            let mut err =
+                self.report_closure_error(&obligation, closure_def_id, found_kind, expected_kind);
+            self.note_obligation_cause(&mut err, &obligation);
+            self.point_at_returns_when_relevant(&mut err, &obligation);
+            Some(err.emit())
+        } else {
+            None
+        }
+    }
+
     fn fn_arg_obligation(&self, obligation: &PredicateObligation<'tcx>) -> bool {
         if let ObligationCauseCode::FunctionArgumentObligation { arg_hir_id, .. } =
             obligation.cause.code()

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -350,7 +350,6 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 | ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(..))
                 | ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(_))
                 | ty::PredicateKind::ObjectSafe(_)
-                | ty::PredicateKind::ClosureKind(..)
                 | ty::PredicateKind::Subtype(_)
                 | ty::PredicateKind::Coerce(_)
                 | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))
@@ -411,19 +410,6 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                     }
                 }
 
-                ty::PredicateKind::ClosureKind(_, closure_args, kind) => {
-                    match self.selcx.infcx.closure_kind(closure_args) {
-                        Some(closure_kind) => {
-                            if closure_kind.extends(kind) {
-                                ProcessResult::Changed(vec![])
-                            } else {
-                                ProcessResult::Error(CodeSelectionError(Unimplemented))
-                            }
-                        }
-                        None => ProcessResult::Unchanged,
-                    }
-                }
-
                 ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => {
                     match wf::obligations(
                         self.selcx.infcx,

compiler/rustc_trait_selection/src/traits/query/type_op/implied_outlives_bounds.rs

@@ -130,7 +130,6 @@ pub fn compute_implied_outlives_bounds_inner<'tcx>(
                 | ty::PredicateKind::Subtype(..)
                 | ty::PredicateKind::Coerce(..)
                 | ty::PredicateKind::Clause(ty::ClauseKind::Projection(..))
-                | ty::PredicateKind::ClosureKind(..)
                 | ty::PredicateKind::ObjectSafe(..)
                 | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))
                 | ty::PredicateKind::ConstEquate(..)

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

@@ -288,8 +288,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         }
                     }
                     None => {
-                        debug!("assemble_unboxed_candidates: closure_kind not yet known");
-                        candidates.vec.push(ClosureCandidate { is_const });
+                        if kind == ty::ClosureKind::FnOnce {
+                            candidates.vec.push(ClosureCandidate { is_const });
+                        } else {
+                            candidates.ambiguous = true;
+                        }
                     }
                 }
             }

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

@@ -821,11 +821,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         obligation: &PolyTraitObligation<'tcx>,
     ) -> Result<Vec<PredicateObligation<'tcx>>, SelectionError<'tcx>> {
-        let kind = self
-            .tcx()
-            .fn_trait_kind_from_def_id(obligation.predicate.def_id())
-            .unwrap_or_else(|| bug!("closure candidate for non-fn trait {:?}", obligation));
-
         // Okay to skip binder because the args on closure types never
         // touch bound regions, they just capture the in-scope
         // type/region parameters.
@@ -835,15 +830,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         };
 
         let trait_ref = self.closure_trait_ref_unnormalized(obligation, args);
-        let mut nested = self.confirm_poly_trait_refs(obligation, trait_ref)?;
+        let nested = self.confirm_poly_trait_refs(obligation, trait_ref)?;
 
         debug!(?closure_def_id, ?trait_ref, ?nested, "confirm closure candidate obligations");
 
-        nested.push(obligation.with(
-            self.tcx(),
-            ty::Binder::dummy(ty::PredicateKind::ClosureKind(closure_def_id, args, kind)),
-        ));
-
         Ok(nested)
     }
 

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

@@ -885,19 +885,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                     }
                 }
 
-                ty::PredicateKind::ClosureKind(_, closure_args, kind) => {
-                    match self.infcx.closure_kind(closure_args) {
-                        Some(closure_kind) => {
-                            if closure_kind.extends(kind) {
-                                Ok(EvaluatedToOk)
-                            } else {
-                                Ok(EvaluatedToErr)
-                            }
-                        }
-                        None => Ok(EvaluatedToAmbig),
-                    }
-                }
-
                 ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(uv)) => {
                     match const_evaluatable::is_const_evaluatable(
                         self.infcx,

compiler/rustc_traits/src/normalize_erasing_regions.rs

@@ -58,7 +58,6 @@ fn not_outlives_predicate(p: ty::Predicate<'_>) -> bool {
         | ty::PredicateKind::AliasRelate(..)
         | ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(..))
         | ty::PredicateKind::ObjectSafe(..)
-        | ty::PredicateKind::ClosureKind(..)
         | ty::PredicateKind::Subtype(..)
         | ty::PredicateKind::Coerce(..)
         | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))

compiler/rustc_type_ir/src/predicate_kind.rs

@@ -129,11 +129,6 @@ pub enum PredicateKind<I: Interner> {
     /// Trait must be object-safe.
     ObjectSafe(I::DefId),
 
-    /// No direct syntax. May be thought of as `where T: FnFoo<...>`
-    /// for some generic args `...` and `T` being a closure type.
-    /// Satisfied (or refuted) once we know the closure's kind.
-    ClosureKind(I::DefId, I::GenericArgs, I::ClosureKind),
-
     /// `T1 <: T2`
     ///
     /// This obligation is created most often when we have two
@@ -173,7 +168,6 @@ where
     I::Term: Copy,
     I::CoercePredicate: Copy,
     I::SubtypePredicate: Copy,
-    I::ClosureKind: Copy,
     ClauseKind<I>: Copy,
 {
 }
@@ -183,9 +177,6 @@ impl<I: Interner> PartialEq for PredicateKind<I> {
         match (self, other) {
             (Self::Clause(l0), Self::Clause(r0)) => l0 == r0,
             (Self::ObjectSafe(l0), Self::ObjectSafe(r0)) => l0 == r0,
-            (Self::ClosureKind(l0, l1, l2), Self::ClosureKind(r0, r1, r2)) => {
-                l0 == r0 && l1 == r1 && l2 == r2
-            }
             (Self::Subtype(l0), Self::Subtype(r0)) => l0 == r0,
             (Self::Coerce(l0), Self::Coerce(r0)) => l0 == r0,
             (Self::ConstEquate(l0, l1), Self::ConstEquate(r0, r1)) => l0 == r0 && l1 == r1,
@@ -207,18 +198,12 @@ where
     I::Term: TypeFoldable<I>,
     I::CoercePredicate: TypeFoldable<I>,
     I::SubtypePredicate: TypeFoldable<I>,
-    I::ClosureKind: TypeFoldable<I>,
     ClauseKind<I>: TypeFoldable<I>,
 {
     fn try_fold_with<F: FallibleTypeFolder<I>>(self, folder: &mut F) -> Result<Self, F::Error> {
         Ok(match self {
             PredicateKind::Clause(c) => PredicateKind::Clause(c.try_fold_with(folder)?),
             PredicateKind::ObjectSafe(d) => PredicateKind::ObjectSafe(d.try_fold_with(folder)?),
-            PredicateKind::ClosureKind(d, g, k) => PredicateKind::ClosureKind(
-                d.try_fold_with(folder)?,
-                g.try_fold_with(folder)?,
-                k.try_fold_with(folder)?,
-            ),
             PredicateKind::Subtype(s) => PredicateKind::Subtype(s.try_fold_with(folder)?),
             PredicateKind::Coerce(s) => PredicateKind::Coerce(s.try_fold_with(folder)?),
             PredicateKind::ConstEquate(a, b) => {
@@ -242,18 +227,12 @@ where
     I::Term: TypeVisitable<I>,
     I::CoercePredicate: TypeVisitable<I>,
     I::SubtypePredicate: TypeVisitable<I>,
-    I::ClosureKind: TypeVisitable<I>,
     ClauseKind<I>: TypeVisitable<I>,
 {
     fn visit_with<V: TypeVisitor<I>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
         match self {
             PredicateKind::Clause(p) => p.visit_with(visitor),
             PredicateKind::ObjectSafe(d) => d.visit_with(visitor),
-            PredicateKind::ClosureKind(d, g, k) => {
-                d.visit_with(visitor)?;
-                g.visit_with(visitor)?;
-                k.visit_with(visitor)
-            }
             PredicateKind::Subtype(s) => s.visit_with(visitor),
             PredicateKind::Coerce(s) => s.visit_with(visitor),
             PredicateKind::ConstEquate(a, b) => {
@@ -313,9 +292,6 @@ impl<I: Interner> fmt::Debug for PredicateKind<I> {
             PredicateKind::ObjectSafe(trait_def_id) => {
                 write!(f, "ObjectSafe({trait_def_id:?})")
             }
-            PredicateKind::ClosureKind(closure_def_id, closure_args, kind) => {
-                write!(f, "ClosureKind({closure_def_id:?}, {closure_args:?}, {kind:?})")
-            }
             PredicateKind::ConstEquate(c1, c2) => write!(f, "ConstEquate({c1:?}, {c2:?})"),
             PredicateKind::Ambiguous => write!(f, "Ambiguous"),
             PredicateKind::AliasRelate(t1, t2, dir) => {