trait_goals: param-env candidates

Author: compiler-errors

compiler/rustc_trait_selection/src/solve/assembly.rs

@@ -56,6 +56,11 @@ pub(super) trait GoalKind<'tcx>: TypeFoldable<'tcx> + Copy {
         goal: Goal<'tcx, Self>,
         object_bounds: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
     );
+
+    fn consider_param_env_candidates(
+        acx: &mut AssemblyCtxt<'_, 'tcx, Self>,
+        goal: Goal<'tcx, Self>,
+    );
 }
 
 /// An abstraction which correctly deals with the canonical results for candidates.
@@ -83,6 +88,8 @@ impl<'a, 'tcx, G: GoalKind<'tcx>> AssemblyCtxt<'a, 'tcx, G> {
 
         acx.assemble_bound_candidates(goal);
 
+        acx.assemble_param_env_candidates(goal);
+
         acx.candidates
     }
 
@@ -171,4 +178,8 @@ impl<'a, 'tcx, G: GoalKind<'tcx>> AssemblyCtxt<'a, 'tcx, G> {
             _ => {}
         }
     }
+
+    fn assemble_param_env_candidates(&mut self, goal: Goal<'tcx, G>) {
+        G::consider_param_env_candidates(self, goal);
+    }
 }

compiler/rustc_trait_selection/src/solve/project_goals.rs

@@ -227,6 +227,13 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
     ) {
         todo!()
     }
+
+    fn consider_param_env_candidates(
+        _acx: &mut AssemblyCtxt<'_, 'tcx, Self>,
+        _goal: Goal<'tcx, Self>,
+    ) {
+        todo!()
+    }
 }
 
 /// This behavior is also implemented in `rustc_ty_utils` and in the old `project` code.

compiler/rustc_trait_selection/src/solve/trait_goals.rs

@@ -169,6 +169,28 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
             acx.try_insert_candidate(CandidateSource::ObjectAutoBound, Certainty::Yes);
         }
     }
+
+    fn consider_param_env_candidates(
+        acx: &mut AssemblyCtxt<'_, 'tcx, Self>,
+        goal: Goal<'tcx, Self>,
+    ) {
+        for (idx, predicate) in goal.param_env.caller_bounds().iter().enumerate() {
+            let Some(poly_trait_pred) = predicate.to_opt_poly_trait_pred() else { continue };
+            if poly_trait_pred.skip_binder().def_id() != goal.predicate.def_id() {
+                continue;
+            };
+            // FIXME: constness? polarity?
+            let poly_trait_ref = poly_trait_pred.map_bound(|trait_pred| trait_pred.trait_ref);
+            // FIXME: Faster to do a filter first with a rejection context?
+
+            match_poly_trait_ref_against_goal(
+                acx,
+                goal,
+                poly_trait_ref,
+                CandidateSource::ParamEnv(idx),
+            );
+        }
+    }
 }
 
 fn match_poly_trait_ref_against_goal<'tcx>(