trait solver: Implement Fn traits and tuple trait

compiler/rustc_trait_selection/src/solve/assembly.rs

@@ -122,6 +122,17 @@ pub(super) trait GoalKind<'tcx>: TypeFoldable<'tcx> + Copy + Eq {
         ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
     ) -> QueryResult<'tcx>;
+
+    fn consider_builtin_fn_trait_candidates(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+        kind: ty::ClosureKind,
+    ) -> QueryResult<'tcx>;
+
+    fn consider_builtin_tuple_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx>;
 }
 
 impl<'tcx> EvalCtxt<'_, 'tcx> {
@@ -137,7 +148,9 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         if goal.predicate.self_ty().is_ty_var() {
             return vec![Candidate {
                 source: CandidateSource::BuiltinImpl,
-                result: self.make_canonical_response(Certainty::Maybe(MaybeCause::Ambiguity)).unwrap(),
+                result: self
+                    .make_canonical_response(Certainty::Maybe(MaybeCause::Ambiguity))
+                    .unwrap(),
             }];
         }
 
@@ -244,6 +257,10 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
             G::consider_builtin_copy_clone_candidate(self, goal)
         } else if lang_items.pointer_sized() == Some(trait_def_id) {
             G::consider_builtin_pointer_sized_candidate(self, goal)
+        } else if let Some(kind) = self.tcx().fn_trait_kind_from_def_id(trait_def_id) {
+            G::consider_builtin_fn_trait_candidates(self, goal, kind)
+        } else if lang_items.tuple_trait() == Some(trait_def_id) {
+            G::consider_builtin_tuple_candidate(self, goal)
         } else {
             Err(NoSolution)
         };

compiler/rustc_trait_selection/src/solve/project_goals.rs

@@ -2,6 +2,7 @@ use crate::traits::{specialization_graph, translate_substs};
 
 use super::assembly::{self, Candidate, CandidateSource};
 use super::infcx_ext::InferCtxtExt;
+use super::trait_goals::structural_traits;
 use super::{Certainty, EvalCtxt, Goal, MaybeCause, QueryResult};
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::DefKind;
@@ -11,9 +12,9 @@ use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::specialization_graph::LeafDef;
 use rustc_infer::traits::Reveal;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
-use rustc_middle::ty::TypeVisitable;
 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 std::iter;
 use std::ops::ControlFlow;
@@ -353,11 +354,44 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
     }
 
     fn consider_builtin_pointer_sized_candidate(
-        ecx: &mut EvalCtxt<'_, 'tcx>,
+        _ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
     ) -> QueryResult<'tcx> {
         bug!("`PointerSized` does not have an associated type: {:?}", goal);
     }
+
+    fn consider_builtin_fn_trait_candidates(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+        goal_kind: ty::ClosureKind,
+    ) -> QueryResult<'tcx> {
+        if let Some(tupled_inputs_and_output) =
+            structural_traits::extract_tupled_inputs_and_output_from_callable(
+                ecx.tcx(),
+                goal.predicate.self_ty(),
+                goal_kind,
+            )?
+        {
+            let pred = tupled_inputs_and_output
+                .map_bound(|(inputs, output)| ty::ProjectionPredicate {
+                    projection_ty: ecx
+                        .tcx()
+                        .mk_alias_ty(goal.predicate.def_id(), [goal.predicate.self_ty(), inputs]),
+                    term: output.into(),
+                })
+                .to_predicate(ecx.tcx());
+            Self::consider_assumption(ecx, goal, pred)
+        } else {
+            ecx.make_canonical_response(Certainty::Maybe(MaybeCause::Ambiguity))
+        }
+    }
+
+    fn consider_builtin_tuple_candidate(
+        _ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx> {
+        bug!("`Tuple` does not have an associated type: {:?}", goal);
+    }
 }
 
 /// This behavior is also implemented in `rustc_ty_utils` and in the old `project` code.

compiler/rustc_trait_selection/src/solve/trait_goals.rs

@@ -4,16 +4,16 @@ use std::iter;
 
 use super::assembly::{self, Candidate, CandidateSource};
 use super::infcx_ext::InferCtxtExt;
-use super::{Certainty, EvalCtxt, Goal, QueryResult};
+use super::{Certainty, EvalCtxt, Goal, MaybeCause, QueryResult};
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::InferCtxt;
 use rustc_infer::traits::query::NoSolution;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
-use rustc_middle::ty::{self, Ty, TyCtxt};
+use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt};
 use rustc_middle::ty::{TraitPredicate, TypeVisitable};
 use rustc_span::DUMMY_SP;
 
-mod structural_traits;
+pub mod structural_traits;
 
 impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
     fn self_ty(self) -> Ty<'tcx> {
@@ -150,6 +150,41 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
             Err(NoSolution)
         }
     }
+
+    fn consider_builtin_fn_trait_candidates(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+        goal_kind: ty::ClosureKind,
+    ) -> QueryResult<'tcx> {
+        if let Some(tupled_inputs_and_output) =
+            structural_traits::extract_tupled_inputs_and_output_from_callable(
+                ecx.tcx(),
+                goal.predicate.self_ty(),
+                goal_kind,
+            )?
+        {
+            let pred = tupled_inputs_and_output
+                .map_bound(|(inputs, _)| {
+                    ecx.tcx()
+                        .mk_trait_ref(goal.predicate.def_id(), [goal.predicate.self_ty(), inputs])
+                })
+                .to_predicate(ecx.tcx());
+            Self::consider_assumption(ecx, goal, pred)
+        } else {
+            ecx.make_canonical_response(Certainty::Maybe(MaybeCause::Ambiguity))
+        }
+    }
+
+    fn consider_builtin_tuple_candidate(
+        ecx: &mut EvalCtxt<'_, 'tcx>,
+        goal: Goal<'tcx, Self>,
+    ) -> QueryResult<'tcx> {
+        if let ty::Tuple(..) = goal.predicate.self_ty().kind() {
+            ecx.make_canonical_response(Certainty::Yes)
+        } else {
+            Err(NoSolution)
+        }
+    }
 }
 
 impl<'tcx> EvalCtxt<'_, 'tcx> {

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

@@ -1,6 +1,6 @@
 use rustc_hir::{Movability, Mutability};
 use rustc_infer::{infer::InferCtxt, traits::query::NoSolution};
-use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty::{self, Ty, TyCtxt};
 
 // Calculates the constituent types of a type for `auto trait` purposes.
 //
@@ -172,3 +172,52 @@ pub(super) fn instantiate_constituent_tys_for_copy_clone_trait<'tcx>(
         }
     }
 }
+
+pub(crate) fn extract_tupled_inputs_and_output_from_callable<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    self_ty: Ty<'tcx>,
+    goal_kind: ty::ClosureKind,
+) -> Result<Option<ty::Binder<'tcx, (Ty<'tcx>, Ty<'tcx>)>>, NoSolution> {
+    match *self_ty.kind() {
+        ty::FnDef(def_id, substs) => Ok(Some(
+            tcx.bound_fn_sig(def_id)
+                .subst(tcx, substs)
+                .map_bound(|sig| (tcx.mk_tup(sig.inputs().iter()), sig.output())),
+        )),
+        ty::FnPtr(sig) => {
+            Ok(Some(sig.map_bound(|sig| (tcx.mk_tup(sig.inputs().iter()), sig.output()))))
+        }
+        ty::Closure(_, substs) => {
+            let closure_substs = substs.as_closure();
+            match closure_substs.kind_ty().to_opt_closure_kind() {
+                Some(closure_kind) if closure_kind.extends(goal_kind) => {}
+                None => return Ok(None),
+                _ => return Err(NoSolution),
+            }
+            Ok(Some(closure_substs.sig().map_bound(|sig| (sig.inputs()[0], sig.output()))))
+        }
+        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::Dynamic(_, _, _)
+        | ty::Generator(_, _, _)
+        | ty::GeneratorWitness(_)
+        | ty::Never
+        | ty::Tuple(_)
+        | ty::Alias(_, _)
+        | ty::Param(_)
+        | ty::Placeholder(_)
+        | ty::Bound(_, _)
+        | ty::Infer(_)
+        | ty::Error(_) => Err(NoSolution),
+    }
+}

tests/ui/traits/new-solver/fn-trait-closure.rs

@@ -0,0 +1,15 @@
+// compile-flags: -Ztrait-solver=next
+// known-bug: unknown
+// failure-status: 101
+// dont-check-compiler-stderr
+
+// This test will fail until we fix `FulfillmentCtxt::relationships`. That's
+// because we create a type variable for closure upvar types, which is not
+// constrained until after we try to do fallback on diverging type variables.
+// Thus, we will call that function, which is unimplemented.
+
+fn require_fn(_: impl Fn() -> i32) {}
+
+fn main() {
+    require_fn(|| -> i32 { 1i32 });
+}

tests/ui/traits/new-solver/fn-trait.rs

@@ -0,0 +1,13 @@
+// compile-flags: -Ztrait-solver=next
+// check-pass
+
+fn require_fn(_: impl Fn() -> i32) {}
+
+fn f() -> i32 {
+    1i32
+}
+
+fn main() {
+    require_fn(f);
+    require_fn(f as fn() -> i32);
+}