implement consider_assumption

Author: compiler-errors

compiler/rustc_trait_selection/src/solve/infcx_ext.rs

@@ -25,6 +25,13 @@ pub(super) trait InferCtxtExt<'tcx> {
         lhs: T,
         rhs: T,
     ) -> Result<Vec<Goal<'tcx, ty::Predicate<'tcx>>>, NoSolution>;
+
+    fn sup<T: ToTrace<'tcx>>(
+        &self,
+        param_env: ty::ParamEnv<'tcx>,
+        lhs: T,
+        rhs: T,
+    ) -> Result<Vec<Goal<'tcx, ty::Predicate<'tcx>>>, NoSolution>;
 }
 
 impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
@@ -59,4 +66,23 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
                 NoSolution
             })
     }
+
+    #[instrument(level = "debug", skip(self, param_env), ret)]
+    fn sup<T: ToTrace<'tcx>>(
+        &self,
+        param_env: ty::ParamEnv<'tcx>,
+        lhs: T,
+        rhs: T,
+    ) -> Result<Vec<Goal<'tcx, ty::Predicate<'tcx>>>, NoSolution> {
+        self.at(&ObligationCause::dummy(), param_env)
+            .define_opaque_types(false)
+            .sup(lhs, rhs)
+            .map(|InferOk { value: (), obligations }| {
+                obligations.into_iter().map(|o| o.into()).collect()
+            })
+            .map_err(|e| {
+                debug!(?e, "failed to sup");
+                NoSolution
+            })
+    }
 }

compiler/rustc_trait_selection/src/solve/project_goals.rs

@@ -6,7 +6,7 @@ use super::{Certainty, EvalCtxt, Goal, MaybeCause, QueryResult};
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
-use rustc_infer::infer::InferCtxt;
+use rustc_infer::infer::{InferCtxt, LateBoundRegionConversionTime};
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::specialization_graph::LeafDef;
 use rustc_infer::traits::Reveal;
@@ -298,12 +298,37 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
     }
 
     fn consider_assumption(
-        _ecx: &mut EvalCtxt<'_, 'tcx>,
-        _goal: Goal<'tcx, Self>,
+        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() {
-            unimplemented!()
+        if let Some(poly_projection_pred) = assumption.to_opt_poly_projection_pred() {
+            ecx.infcx.probe(|_| {
+                let assumption_projection_pred = ecx.infcx.replace_bound_vars_with_fresh_vars(
+                    DUMMY_SP,
+                    LateBoundRegionConversionTime::HigherRankedType,
+                    poly_projection_pred,
+                );
+                let nested_goals = ecx.infcx.sup(
+                    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)
         }

compiler/rustc_trait_selection/src/solve/trait_goals.rs

@@ -6,10 +6,11 @@ use super::assembly::{self, Candidate, CandidateSource};
 use super::infcx_ext::InferCtxtExt;
 use super::{EvalCtxt, Goal, QueryResult};
 use rustc_hir::def_id::DefId;
+use rustc_infer::infer::LateBoundRegionConversionTime;
 use rustc_infer::traits::query::NoSolution;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
-use rustc_middle::ty::TraitPredicate;
 use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{ToPolyTraitRef, TraitPredicate};
 use rustc_span::DUMMY_SP;
 
 impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
@@ -65,12 +66,20 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
     }
 
     fn consider_assumption(
-        _ecx: &mut EvalCtxt<'_, 'tcx>,
-        _goal: Goal<'tcx, Self>,
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
         assumption: ty::Predicate<'tcx>,
     ) -> QueryResult<'tcx> {
-        if let Some(_poly_trait_pred) = assumption.to_opt_poly_trait_pred() {
-            unimplemented!()
+        if let Some(poly_trait_pred) = assumption.to_opt_poly_trait_pred() {
+            // FIXME: Constness and polarity
+            ecx.infcx.probe(|_| {
+                let nested_goals = ecx.infcx.sup(
+                    goal.param_env,
+                    ty::Binder::dummy(goal.predicate.trait_ref),
+                    poly_trait_pred.to_poly_trait_ref(),
+                )?;
+                ecx.evaluate_all_and_make_canonical_response(nested_goals)
+            })
         } else {
             Err(NoSolution)
         }