Handle structural traits more gracefully

Author: compiler-errors

compiler/rustc_trait_selection/src/solve/trait_goals.rs

@@ -6,14 +6,15 @@ use super::assembly::{self, Candidate, CandidateSource};
 use super::infcx_ext::InferCtxtExt;
 use super::{EvalCtxt, Goal, QueryResult};
 use rustc_hir::def_id::DefId;
-use rustc_hir::{Movability, Mutability};
 use rustc_infer::infer::InferCtxt;
 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_span::DUMMY_SP;
 
+mod structural_traits;
+
 impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
     fn self_ty(self) -> Ty<'tcx> {
         self.self_ty()
@@ -85,11 +86,10 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
         ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
     ) -> QueryResult<'tcx> {
-        ecx.infcx.probe(|_| {
-            let constituent_tys =
-                instantiate_constituent_tys_for_auto_trait(ecx.infcx, goal.predicate.self_ty())?;
-            ecx.evaluate_goal_for_constituent_tys_and_make_canonical_response(goal, constituent_tys)
-        })
+        ecx.probe_and_evaluate_goal_for_constituent_tys(
+            goal,
+            structural_traits::instantiate_constituent_tys_for_auto_trait,
+        )
     }
 
     fn consider_trait_alias_candidate(
@@ -112,44 +112,46 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
         ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
     ) -> QueryResult<'tcx> {
-        ecx.infcx.probe(|_| {
-            let constituent_tys =
-                instantiate_constituent_tys_for_sized_trait(ecx.infcx, goal.predicate.self_ty())?;
-            ecx.evaluate_goal_for_constituent_tys_and_make_canonical_response(goal, constituent_tys)
-        })
+        ecx.probe_and_evaluate_goal_for_constituent_tys(
+            goal,
+            structural_traits::instantiate_constituent_tys_for_sized_trait,
+        )
     }
 
     fn consider_builtin_copy_clone_candidate(
         ecx: &mut EvalCtxt<'_, 'tcx>,
         goal: Goal<'tcx, Self>,
     ) -> QueryResult<'tcx> {
-        ecx.infcx.probe(|_| {
-            let constituent_tys = instantiate_constituent_tys_for_copy_clone_trait(
-                ecx.infcx,
-                goal.predicate.self_ty(),
-            )?;
-            ecx.evaluate_goal_for_constituent_tys_and_make_canonical_response(goal, constituent_tys)
-        })
+        ecx.probe_and_evaluate_goal_for_constituent_tys(
+            goal,
+            structural_traits::instantiate_constituent_tys_for_copy_clone_trait,
+        )
     }
 }
 
 impl<'tcx> EvalCtxt<'_, 'tcx> {
-    fn evaluate_goal_for_constituent_tys_and_make_canonical_response(
+    /// Convenience function for traits that are structural, i.e. that only
+    /// have nested subgoals that only change the self type. Unlike other
+    /// evaluate-like helpers, this does a probe, so it doesn't need to be
+    /// wrapped in one.
+    fn probe_and_evaluate_goal_for_constituent_tys(
         &mut self,
         goal: Goal<'tcx, TraitPredicate<'tcx>>,
-        constituent_tys: Vec<Ty<'tcx>>,
+        constituent_tys: impl Fn(&InferCtxt<'tcx>, Ty<'tcx>) -> Result<Vec<Ty<'tcx>>, NoSolution>,
     ) -> QueryResult<'tcx> {
-        self.evaluate_all_and_make_canonical_response(
-            constituent_tys
-                .into_iter()
-                .map(|ty| {
-                    goal.with(
-                        self.tcx(),
-                        ty::Binder::dummy(goal.predicate.with_self_ty(self.tcx(), ty)),
-                    )
-                })
-                .collect(),
-        )
+        self.infcx.probe(|_| {
+            self.evaluate_all_and_make_canonical_response(
+                constituent_tys(self.infcx, goal.predicate.self_ty())?
+                    .into_iter()
+                    .map(|ty| {
+                        goal.with(
+                            self.tcx(),
+                            ty::Binder::dummy(goal.predicate.with_self_ty(self.tcx(), ty)),
+                        )
+                    })
+                    .collect(),
+            )
+        })
     }
 
     pub(super) fn compute_trait_goal(
@@ -227,187 +229,3 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
         candidate
     }
 }
-
-// Calculates the constituent types of a type for `auto trait` purposes.
-//
-// For types with an "existential" binder, i.e. generator witnesses, we also
-// instantiate the binder with placeholders eagerly.
-fn instantiate_constituent_tys_for_auto_trait<'tcx>(
-    infcx: &InferCtxt<'tcx>,
-    ty: Ty<'tcx>,
-) -> Result<Vec<Ty<'tcx>>, NoSolution> {
-    let tcx = infcx.tcx;
-    match *ty.kind() {
-        ty::Uint(_)
-        | ty::Int(_)
-        | ty::Bool
-        | ty::Float(_)
-        | ty::FnDef(..)
-        | ty::FnPtr(_)
-        | ty::Str
-        | ty::Error(_)
-        | ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
-        | ty::Never
-        | ty::Char => Ok(vec![]),
-
-        ty::Placeholder(..)
-        | ty::Dynamic(..)
-        | ty::Param(..)
-        | ty::Foreign(..)
-        | ty::Alias(ty::Projection, ..)
-        | ty::Bound(..)
-        | ty::Infer(ty::TyVar(_)) => {
-            // FIXME: Do we need to mark anything as ambiguous here? Yeah?
-            Err(NoSolution)
-        }
-
-        ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => bug!(),
-
-        ty::RawPtr(ty::TypeAndMut { ty: element_ty, .. }) | ty::Ref(_, element_ty, _) => {
-            Ok(vec![element_ty])
-        }
-
-        ty::Array(element_ty, _) | ty::Slice(element_ty) => Ok(vec![element_ty]),
-
-        ty::Tuple(ref tys) => {
-            // (T1, ..., Tn) -- meets any bound that all of T1...Tn meet
-            Ok(tys.iter().collect())
-        }
-
-        ty::Closure(_, ref substs) => Ok(vec![substs.as_closure().tupled_upvars_ty()]),
-
-        ty::Generator(_, ref substs, _) => {
-            let generator_substs = substs.as_generator();
-            Ok(vec![generator_substs.tupled_upvars_ty(), generator_substs.witness()])
-        }
-
-        ty::GeneratorWitness(types) => {
-            Ok(infcx.replace_bound_vars_with_placeholders(types).to_vec())
-        }
-
-        // For `PhantomData<T>`, we pass `T`.
-        ty::Adt(def, substs) if def.is_phantom_data() => Ok(vec![substs.type_at(0)]),
-
-        ty::Adt(def, substs) => Ok(def.all_fields().map(|f| f.ty(tcx, substs)).collect()),
-
-        ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => {
-            // We can resolve the `impl Trait` to its concrete type,
-            // which enforces a DAG between the functions requiring
-            // the auto trait bounds in question.
-            Ok(vec![tcx.bound_type_of(def_id).subst(tcx, substs)])
-        }
-    }
-}
-
-fn instantiate_constituent_tys_for_sized_trait<'tcx>(
-    infcx: &InferCtxt<'tcx>,
-    ty: Ty<'tcx>,
-) -> Result<Vec<Ty<'tcx>>, NoSolution> {
-    match *ty.kind() {
-        ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
-        | ty::Uint(_)
-        | ty::Int(_)
-        | ty::Bool
-        | ty::Float(_)
-        | ty::FnDef(..)
-        | ty::FnPtr(_)
-        | ty::RawPtr(..)
-        | ty::Char
-        | ty::Ref(..)
-        | ty::Generator(..)
-        | ty::GeneratorWitness(..)
-        | ty::Array(..)
-        | ty::Closure(..)
-        | ty::Never
-        | ty::Dynamic(_, _, ty::DynStar)
-        | ty::Error(_) => Ok(vec![]),
-
-        ty::Str
-        | ty::Slice(_)
-        | ty::Dynamic(..)
-        | ty::Foreign(..)
-        | ty::Alias(..)
-        | ty::Param(_) => Err(NoSolution),
-
-        ty::Infer(ty::TyVar(_)) => bug!("FIXME: ambiguous"),
-
-        ty::Placeholder(..)
-        | ty::Bound(..)
-        | ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => bug!(),
-
-        ty::Tuple(tys) => Ok(tys.to_vec()),
-
-        ty::Adt(def, substs) => {
-            let sized_crit = def.sized_constraint(infcx.tcx);
-            Ok(sized_crit
-                .0
-                .iter()
-                .map(|ty| sized_crit.rebind(*ty).subst(infcx.tcx, substs))
-                .collect())
-        }
-    }
-}
-
-fn instantiate_constituent_tys_for_copy_clone_trait<'tcx>(
-    infcx: &InferCtxt<'tcx>,
-    ty: Ty<'tcx>,
-) -> Result<Vec<Ty<'tcx>>, NoSolution> {
-    match *ty.kind() {
-        ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
-        | ty::FnDef(..)
-        | ty::FnPtr(_)
-        | ty::Error(_) => Ok(vec![]),
-
-        // Implementations are provided in core
-        ty::Uint(_)
-        | ty::Int(_)
-        | ty::Bool
-        | ty::Float(_)
-        | ty::Char
-        | ty::RawPtr(..)
-        | ty::Never
-        | ty::Ref(_, _, Mutability::Not)
-        | ty::Array(..) => Err(NoSolution),
-
-        ty::Dynamic(..)
-        | ty::Str
-        | ty::Slice(_)
-        | ty::Generator(_, _, Movability::Static)
-        | ty::Foreign(..)
-        | ty::Ref(_, _, Mutability::Mut)
-        | ty::Adt(_, _)
-        | ty::Alias(_, _)
-        | ty::Param(_) => Err(NoSolution),
-
-        ty::Infer(ty::TyVar(_)) => bug!("FIXME: ambiguous"),
-
-        ty::Placeholder(..)
-        | ty::Bound(..)
-        | ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => bug!(),
-
-        ty::Tuple(tys) => Ok(tys.to_vec()),
-
-        ty::Closure(_, substs) => match *substs.as_closure().tupled_upvars_ty().kind() {
-            ty::Tuple(tys) => Ok(tys.to_vec()),
-            ty::Infer(ty::TyVar(_)) => bug!("FIXME: ambiguous"),
-            _ => bug!(),
-        },
-
-        ty::Generator(_, substs, Movability::Movable) => {
-            if infcx.tcx.features().generator_clone {
-                let generator = substs.as_generator();
-                match *generator.tupled_upvars_ty().kind() {
-                    ty::Tuple(tys) => Ok(tys.iter().chain([generator.witness()]).collect()),
-                    ty::Infer(ty::TyVar(_)) => bug!("FIXME: ambiguous"),
-                    _ => bug!(),
-                }
-            } else {
-                Err(NoSolution)
-            }
-        }
-
-        ty::GeneratorWitness(types) => {
-            Ok(infcx.replace_bound_vars_with_placeholders(types).to_vec())
-        }
-    }
-}