Rollup merge of #107004 - compiler-errors:new-solver-new-candidates-2, r=lcnr

Implement some candidates for the new solver (redux)

Based on #106718, so the diff is hard to read without it. See [here](98700cf...compiler-errors:rust:new-solver-new-candidates-2) for an easier view until that one lands.

Of note:
* 44af916020fb43c12070125c45b6dee4ec303bbc fixes a bug where we need to make the query response *inside* of a probe, or else we make no inference progress (I think)
* 50daad5acd2f163d03e7ffab942534f09bc36e2e implements `consider_assumption` for traits and predicates. I'm not sure if using `sup` here is necessary or if `eq` is fine.
* We decided that all of the `instantiate_constituent_tys_for_*` functions are verbose but ok, since they need to be exhaustive and the logic between each of them is not similar enough, right?

r? ``@lcnr``

Author: compiler-errors

compiler/rustc_middle/src/ty/mod.rs

@@ -2357,6 +2357,11 @@ impl<'tcx> TyCtxt<'tcx> {
         self.trait_def(trait_def_id).has_auto_impl
     }
 
+    /// Returns `true` if this is a trait alias.
+    pub fn trait_is_alias(self, trait_def_id: DefId) -> bool {
+        self.def_kind(trait_def_id) == DefKind::TraitAlias
+    }
+
     pub fn trait_is_coinductive(self, trait_def_id: DefId) -> bool {
         self.trait_is_auto(trait_def_id) || self.lang_items().sized_trait() == Some(trait_def_id)
     }

compiler/rustc_trait_selection/src/solve/assembly.rs

@@ -1,9 +1,10 @@
 //! Code shared by trait and projection goals for candidate assembly.
 
 use super::infcx_ext::InferCtxtExt;
-use super::{CanonicalResponse, Certainty, EvalCtxt, Goal};
+use super::{CanonicalResponse, EvalCtxt, Goal, QueryResult};
 use rustc_hir::def_id::DefId;
 use rustc_infer::traits::query::NoSolution;
+use rustc_infer::traits::util::elaborate_predicates;
 use rustc_middle::ty::TypeFoldable;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use std::fmt::Debug;
@@ -89,19 +90,35 @@ pub(super) trait GoalKind<'tcx>: TypeFoldable<'tcx> + Copy {
         ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
         impl_def_id: DefId,
-    ) -> Result<Certainty, NoSolution>;
+    ) -> QueryResult<'tcx>;
+
+    fn consider_assumption(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+        assumption: ty::Predicate<'tcx>,
+    ) -> QueryResult<'tcx>;
+
+    fn consider_auto_trait_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx>;
+
+    fn consider_trait_alias_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx>;
 
     fn consider_builtin_sized_candidate(
         ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
-    ) -> Result<Certainty, NoSolution>;
+    ) -> QueryResult<'tcx>;
 
-    fn consider_assumption(
+    fn consider_builtin_copy_clone_candidate(
         ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
-        assumption: ty::Predicate<'tcx>,
-    ) -> Result<Certainty, NoSolution>;
+    ) -> QueryResult<'tcx>;
 }
+
 impl<'tcx> EvalCtxt<'_, 'tcx> {
     pub(super) fn assemble_and_evaluate_candidates<G: GoalKind<'tcx>>(
         &mut self,
@@ -119,6 +136,8 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
 
         self.assemble_alias_bound_candidates(goal, &mut candidates);
 
+        self.assemble_object_bound_candidates(goal, &mut candidates);
+
         candidates
     }
 
@@ -180,9 +199,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         tcx.for_each_relevant_impl(
             goal.predicate.trait_def_id(tcx),
             goal.predicate.self_ty(),
-            |impl_def_id| match G::consider_impl_candidate(self, goal, impl_def_id)
-                .and_then(|certainty| self.make_canonical_response(certainty))
-            {
+            |impl_def_id| match G::consider_impl_candidate(self, goal, impl_def_id) {
                 Ok(result) => candidates
                     .push(Candidate { source: CandidateSource::Impl(impl_def_id), result }),
                 Err(NoSolution) => (),
@@ -197,13 +214,21 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
     ) {
         let lang_items = self.tcx().lang_items();
         let trait_def_id = goal.predicate.trait_def_id(self.tcx());
-        let result = if lang_items.sized_trait() == Some(trait_def_id) {
+        let result = if self.tcx().trait_is_auto(trait_def_id) {
+            G::consider_auto_trait_candidate(self, goal)
+        } else if self.tcx().trait_is_alias(trait_def_id) {
+            G::consider_trait_alias_candidate(self, goal)
+        } else if lang_items.sized_trait() == Some(trait_def_id) {
             G::consider_builtin_sized_candidate(self, goal)
+        } else if lang_items.copy_trait() == Some(trait_def_id)
+            || lang_items.clone_trait() == Some(trait_def_id)
+        {
+            G::consider_builtin_copy_clone_candidate(self, goal)
         } else {
             Err(NoSolution)
         };
 
-        match result.and_then(|certainty| self.make_canonical_response(certainty)) {
+        match result {
             Ok(result) => {
                 candidates.push(Candidate { source: CandidateSource::BuiltinImpl, result })
             }
@@ -217,9 +242,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         candidates: &mut Vec<Candidate<'tcx>>,
     ) {
         for (i, assumption) in goal.param_env.caller_bounds().iter().enumerate() {
-            match G::consider_assumption(self, goal, assumption)
-                .and_then(|certainty| self.make_canonical_response(certainty))
-            {
+            match G::consider_assumption(self, goal, assumption) {
                 Ok(result) => {
                     candidates.push(Candidate { source: CandidateSource::ParamEnv(i), result })
                 }
@@ -268,14 +291,60 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
             .subst_iter_copied(self.tcx(), alias_ty.substs)
             .enumerate()
         {
-            match G::consider_assumption(self, goal, assumption)
-                .and_then(|certainty| self.make_canonical_response(certainty))
-            {
+            match G::consider_assumption(self, goal, assumption) {
                 Ok(result) => {
                     candidates.push(Candidate { source: CandidateSource::AliasBound(i), result })
                 }
                 Err(NoSolution) => (),
             }
         }
     }
+
+    fn assemble_object_bound_candidates<G: GoalKind<'tcx>>(
+        &mut self,
+        goal: Goal<'tcx, G>,
+        candidates: &mut Vec<Candidate<'tcx>>,
+    ) {
+        let self_ty = goal.predicate.self_ty();
+        let bounds = match *self_ty.kind() {
+            ty::Bool
+            | ty::Char
+            | ty::Int(_)
+            | ty::Uint(_)
+            | ty::Float(_)
+            | ty::Adt(_, _)
+            | ty::Foreign(_)
+            | ty::Str
+            | ty::Array(_, _)
+            | ty::Slice(_)
+            | ty::RawPtr(_)
+            | ty::Ref(_, _, _)
+            | ty::FnDef(_, _)
+            | ty::FnPtr(_)
+            | ty::Alias(..)
+            | ty::Closure(..)
+            | ty::Generator(..)
+            | ty::GeneratorWitness(_)
+            | ty::Never
+            | ty::Tuple(_)
+            | ty::Param(_)
+            | ty::Placeholder(..)
+            | ty::Infer(_)
+            | ty::Error(_) => return,
+            ty::Bound(..) => bug!("unexpected bound type: {goal:?}"),
+            ty::Dynamic(bounds, ..) => bounds,
+        };
+
+        let tcx = self.tcx();
+        for assumption in
+            elaborate_predicates(tcx, bounds.iter().map(|bound| bound.with_self_ty(tcx, self_ty)))
+        {
+            match G::consider_assumption(self, goal, assumption.predicate) {
+                Ok(result) => {
+                    candidates.push(Candidate { source: CandidateSource::BuiltinImpl, result })
+                }
+                Err(NoSolution) => (),
+            }
+        }
+    }
 }

compiler/rustc_trait_selection/src/solve/infcx_ext.rs

@@ -1,10 +1,10 @@
 use rustc_infer::infer::at::ToTrace;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
-use rustc_infer::infer::{InferCtxt, InferOk};
+use rustc_infer::infer::{InferCtxt, InferOk, LateBoundRegionConversionTime};
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::ObligationCause;
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
-use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty::{self, Ty, TypeFoldable};
 use rustc_span::DUMMY_SP;
 
 use super::Goal;
@@ -25,6 +25,11 @@ pub(super) trait InferCtxtExt<'tcx> {
         lhs: T,
         rhs: T,
     ) -> Result<Vec<Goal<'tcx, ty::Predicate<'tcx>>>, NoSolution>;
+
+    fn instantiate_bound_vars_with_infer<T: TypeFoldable<'tcx> + Copy>(
+        &self,
+        value: ty::Binder<'tcx, T>,
+    ) -> T;
 }
 
 impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
@@ -59,4 +64,15 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
                 NoSolution
             })
     }
+
+    fn instantiate_bound_vars_with_infer<T: TypeFoldable<'tcx> + Copy>(
+        &self,
+        value: ty::Binder<'tcx, T>,
+    ) -> T {
+        self.replace_bound_vars_with_fresh_vars(
+            DUMMY_SP,
+            LateBoundRegionConversionTime::HigherRankedType,
+            value,
+        )
+    }
 }

compiler/rustc_trait_selection/src/solve/mod.rs

@@ -313,6 +313,13 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
             }
         })
     }
+
+    fn evaluate_all_and_make_canonical_response(
+        &mut self,
+        goals: Vec<Goal<'tcx, ty::Predicate<'tcx>>>,
+    ) -> QueryResult<'tcx> {
+        self.evaluate_all(goals).and_then(|certainty| self.make_canonical_response(certainty))
+    }
 }
 
 #[instrument(level = "debug", skip(infcx), ret)]

compiler/rustc_trait_selection/src/solve/project_goals.rs

@@ -191,7 +191,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
         ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, ProjectionPredicate<'tcx>>,
         impl_def_id: DefId,
-    ) -> Result<Certainty, NoSolution> {
+    ) -> QueryResult<'tcx> {
         let tcx = ecx.tcx();
 
         let goal_trait_ref = goal.predicate.projection_ty.trait_ref(tcx);
@@ -229,7 +229,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
                 impl_def_id
             )? else {
                 let certainty = Certainty::Maybe(MaybeCause::Ambiguity);
-                return Ok(trait_ref_certainty.unify_and(certainty));
+                return ecx.make_canonical_response(trait_ref_certainty.unify_and(certainty));
             };
 
             if !assoc_def.item.defaultness(tcx).has_value() {
@@ -286,27 +286,70 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
             let rhs_certainty =
                 ecx.evaluate_all(nested_goals).expect("failed to unify with unconstrained term");
 
-            Ok(trait_ref_certainty.unify_and(rhs_certainty))
+            ecx.make_canonical_response(trait_ref_certainty.unify_and(rhs_certainty))
         })
     }
 
+    fn consider_assumption(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+        assumption: ty::Predicate<'tcx>,
+    ) -> QueryResult<'tcx> {
+        if let Some(poly_projection_pred) = assumption.to_opt_poly_projection_pred() {
+            ecx.infcx.probe(|_| {
+                let assumption_projection_pred =
+                    ecx.infcx.instantiate_bound_vars_with_infer(poly_projection_pred);
+                let nested_goals = ecx.infcx.eq(
+                    goal.param_env,
+                    goal.predicate.projection_ty,
+                    assumption_projection_pred.projection_ty,
+                )?;
+                let subst_certainty = ecx.evaluate_all(nested_goals)?;
+
+                // The term of our goal should be fully unconstrained, so this should never fail.
+                //
+                // It can however be ambiguous when the resolved type is a projection.
+                let nested_goals = ecx
+                    .infcx
+                    .eq(goal.param_env, goal.predicate.term, assumption_projection_pred.term)
+                    .expect("failed to unify with unconstrained term");
+                let rhs_certainty = ecx
+                    .evaluate_all(nested_goals)
+                    .expect("failed to unify with unconstrained term");
+
+                ecx.make_canonical_response(subst_certainty.unify_and(rhs_certainty))
+            })
+        } else {
+            Err(NoSolution)
+        }
+    }
+
+    fn consider_auto_trait_candidate(
+        _ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx> {
+        bug!("auto traits do not have associated types: {:?}", goal);
+    }
+
+    fn consider_trait_alias_candidate(
+        _ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx> {
+        bug!("trait aliases do not have associated types: {:?}", goal);
+    }
+
     fn consider_builtin_sized_candidate(
         _ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
-    ) -> Result<Certainty, NoSolution> {
+    ) -> QueryResult<'tcx> {
         bug!("`Sized` does not have an associated type: {:?}", goal);
     }
 
-    fn consider_assumption(
+    fn consider_builtin_copy_clone_candidate(
         _ecx: &mut EvalCtxt<'_, 'tcx>,
-        _goal: Goal<'tcx, Self>,
-        assumption: ty::Predicate<'tcx>,
-    ) -> Result<Certainty, NoSolution> {
-        if let Some(_poly_projection_pred) = assumption.to_opt_poly_projection_pred() {
-            unimplemented!()
-        } else {
-            Err(NoSolution)
-        }
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx> {
+        bug!("`Copy`/`Clone` does not have an associated type: {:?}", goal);
     }
 }