Implement Generator and Future

compiler/rustc_trait_selection/src/solve/assembly.rs

@@ -138,6 +138,16 @@ pub(super) trait GoalKind<'tcx>: TypeFoldable<'tcx> + Copy + Eq {
         ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
     ) -> QueryResult<'tcx>;
+
+    fn consider_builtin_future_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx>;
+
+    fn consider_builtin_generator_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx>;
 }
 
 impl<'tcx> EvalCtxt<'_, 'tcx> {
@@ -266,6 +276,10 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
             G::consider_builtin_tuple_candidate(self, goal)
         } else if lang_items.pointee_trait() == Some(trait_def_id) {
             G::consider_builtin_pointee_candidate(self, goal)
+        } else if lang_items.future_trait() == Some(trait_def_id) {
+            G::consider_builtin_future_candidate(self, goal)
+        } else if lang_items.gen_trait() == Some(trait_def_id) {
+            G::consider_builtin_generator_candidate(self, goal)
         } else {
             Err(NoSolution)
         };

compiler/rustc_trait_selection/src/solve/project_goals.rs

@@ -16,7 +16,7 @@ use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_middle::ty::{ProjectionPredicate, TypeSuperVisitable, TypeVisitor};
 use rustc_middle::ty::{ToPredicate, TypeVisitable};
-use rustc_span::DUMMY_SP;
+use rustc_span::{sym, DUMMY_SP};
 use std::iter;
 use std::ops::ControlFlow;
 
@@ -482,6 +482,73 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
             ecx.evaluate_all_and_make_canonical_response(nested_goals)
         })
     }
+
+    fn consider_builtin_future_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx> {
+        let self_ty = goal.predicate.self_ty();
+        let ty::Generator(def_id, substs, _) = *self_ty.kind() else {
+            return Err(NoSolution);
+        };
+
+        // Generators are not futures unless they come from `async` desugaring
+        let tcx = ecx.tcx();
+        if !tcx.generator_is_async(def_id) {
+            return Err(NoSolution);
+        }
+
+        let term = substs.as_generator().return_ty().into();
+
+        Self::consider_assumption(
+            ecx,
+            goal,
+            ty::Binder::dummy(ty::ProjectionPredicate {
+                projection_ty: ecx.tcx().mk_alias_ty(goal.predicate.def_id(), [self_ty]),
+                term,
+            })
+            .to_predicate(tcx),
+        )
+    }
+
+    fn consider_builtin_generator_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx> {
+        let self_ty = goal.predicate.self_ty();
+        let ty::Generator(def_id, substs, _) = *self_ty.kind() else {
+            return Err(NoSolution);
+        };
+
+        // `async`-desugared generators do not implement the generator trait
+        let tcx = ecx.tcx();
+        if tcx.generator_is_async(def_id) {
+            return Err(NoSolution);
+        }
+
+        let generator = substs.as_generator();
+
+        let name = tcx.associated_item(goal.predicate.def_id()).name;
+        let term = if name == sym::Return {
+            generator.return_ty().into()
+        } else if name == sym::Yield {
+            generator.yield_ty().into()
+        } else {
+            bug!("unexpected associated item `<{self_ty} as Generator>::{name}`")
+        };
+
+        Self::consider_assumption(
+            ecx,
+            goal,
+            ty::Binder::dummy(ty::ProjectionPredicate {
+                projection_ty: ecx
+                    .tcx()
+                    .mk_alias_ty(goal.predicate.def_id(), [self_ty, generator.resume_ty()]),
+                term,
+            })
+            .to_predicate(tcx),
+        )
+    }
 }
 
 /// This behavior is also implemented in `rustc_ty_utils` and in the old `project` code.

compiler/rustc_trait_selection/src/solve/trait_goals.rs

@@ -192,6 +192,50 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
     ) -> QueryResult<'tcx> {
         ecx.make_canonical_response(Certainty::Yes)
     }
+
+    fn consider_builtin_future_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx> {
+        let ty::Generator(def_id, _, _) = *goal.predicate.self_ty().kind() else {
+            return Err(NoSolution);
+        };
+
+        // Generators are not futures unless they come from `async` desugaring
+        let tcx = ecx.tcx();
+        if !tcx.generator_is_async(def_id) {
+            return Err(NoSolution);
+        }
+
+        // Async generator unconditionally implement `Future`
+        ecx.make_canonical_response(Certainty::Yes)
+    }
+
+    fn consider_builtin_generator_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx> {
+        let self_ty = goal.predicate.self_ty();
+        let ty::Generator(def_id, substs, _) = *self_ty.kind() else {
+            return Err(NoSolution);
+        };
+
+        // `async`-desugared generators do not implement the generator trait
+        let tcx = ecx.tcx();
+        if tcx.generator_is_async(def_id) {
+            return Err(NoSolution);
+        }
+
+        let generator = substs.as_generator();
+        Self::consider_assumption(
+            ecx,
+            goal,
+            ty::Binder::dummy(
+                tcx.mk_trait_ref(goal.predicate.def_id(), [self_ty, generator.resume_ty()]),
+            )
+            .to_predicate(tcx),
+        )
+    }
 }
 
 impl<'tcx> EvalCtxt<'_, 'tcx> {

compiler/rustc_trait_selection/src/solve/trait_goals/structural_traits.rs

@@ -173,6 +173,7 @@ pub(super) fn instantiate_constituent_tys_for_copy_clone_trait<'tcx>(
     }
 }
 
+// Returns a binder of the tupled inputs types and output type from a builtin callable type.
 pub(crate) fn extract_tupled_inputs_and_output_from_callable<'tcx>(
     tcx: TyCtxt<'tcx>,
     self_ty: Ty<'tcx>,