diff options
Diffstat (limited to 'compiler/rustc_trait_selection/src/solve/eval_ctxt.rs')
| -rw-r--r-- | compiler/rustc_trait_selection/src/solve/eval_ctxt.rs | 537 |
1 files changed, 508 insertions, 29 deletions
diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs index 95612674e..c29b5b04e 100644 --- a/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs +++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt.rs @@ -2,10 +2,13 @@ use rustc_hir::def_id::DefId; use rustc_infer::infer::at::ToTrace; use rustc_infer::infer::canonical::CanonicalVarValues; use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; -use rustc_infer::infer::{InferCtxt, InferOk, LateBoundRegionConversionTime}; +use rustc_infer::infer::{ + DefineOpaqueTypes, InferCtxt, InferOk, LateBoundRegionConversionTime, TyCtxtInferExt, +}; use rustc_infer::traits::query::NoSolution; use rustc_infer::traits::ObligationCause; use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind}; +use rustc_middle::traits::solve::{CanonicalGoal, Certainty, MaybeCause, QueryResult}; use rustc_middle::ty::{ self, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor, @@ -13,12 +16,32 @@ use rustc_middle::ty::{ use rustc_span::DUMMY_SP; use std::ops::ControlFlow; -use super::search_graph::SearchGraph; -use super::Goal; +use crate::traits::specialization_graph; + +use super::search_graph::{self, OverflowHandler}; +use super::SolverMode; +use super::{search_graph::SearchGraph, Goal}; + +mod canonical; pub struct EvalCtxt<'a, 'tcx> { - // FIXME: should be private. - pub(super) infcx: &'a InferCtxt<'tcx>, + /// The inference context that backs (mostly) inference and placeholder terms + /// instantiated while solving goals. + /// + /// NOTE: The `InferCtxt` that backs the `EvalCtxt` is intentionally private, + /// because the `InferCtxt` is much more general than `EvalCtxt`. Methods such + /// as `take_registered_region_obligations` can mess up query responses, + /// using `At::normalize` is totally wrong, calling `evaluate_root_goal` can + /// cause coinductive unsoundness, etc. + /// + /// Methods that are generally of use for trait solving are *intentionally* + /// re-declared through the `EvalCtxt` below, often with cleaner signatures + /// since we don't care about things like `ObligationCause`s and `Span`s here. + /// If some `InferCtxt` method is missing, please first think defensively about + /// the method's compatibility with this solver, or if an existing one does + /// the job already. + infcx: &'a InferCtxt<'tcx>, + pub(super) var_values: CanonicalVarValues<'tcx>, /// The highest universe index nameable by the caller. /// @@ -33,14 +56,356 @@ pub struct EvalCtxt<'a, 'tcx> { pub(super) search_graph: &'a mut SearchGraph<'tcx>, - /// This field is used by a debug assertion in [`EvalCtxt::evaluate_goal`], - /// see the comment in that method for more details. - pub in_projection_eq_hack: bool, + pub(super) nested_goals: NestedGoals<'tcx>, +} + +#[derive(Debug, Copy, Clone, PartialEq, Eq)] +pub(super) enum IsNormalizesToHack { + Yes, + No, +} + +#[derive(Debug, Clone)] +pub(super) struct NestedGoals<'tcx> { + /// This normalizes-to goal that is treated specially during the evaluation + /// loop. In each iteration we take the RHS of the projection, replace it with + /// a fresh inference variable, and only after evaluating that goal do we + /// equate the fresh inference variable with the actual RHS of the predicate. + /// + /// This is both to improve caching, and to avoid using the RHS of the + /// projection predicate to influence the normalizes-to candidate we select. + /// + /// This is not a 'real' nested goal. We must not forget to replace the RHS + /// with a fresh inference variable when we evaluate this goal. That can result + /// in a trait solver cycle. This would currently result in overflow but can be + /// can be unsound with more powerful coinduction in the future. + pub(super) normalizes_to_hack_goal: Option<Goal<'tcx, ty::ProjectionPredicate<'tcx>>>, + /// The rest of the goals which have not yet processed or remain ambiguous. + pub(super) goals: Vec<Goal<'tcx, ty::Predicate<'tcx>>>, +} + +impl NestedGoals<'_> { + pub(super) fn new() -> Self { + Self { normalizes_to_hack_goal: None, goals: Vec::new() } + } + + pub(super) fn is_empty(&self) -> bool { + self.normalizes_to_hack_goal.is_none() && self.goals.is_empty() + } +} + +pub trait InferCtxtEvalExt<'tcx> { + /// Evaluates a goal from **outside** of the trait solver. + /// + /// Using this while inside of the solver is wrong as it uses a new + /// search graph which would break cycle detection. + fn evaluate_root_goal( + &self, + goal: Goal<'tcx, ty::Predicate<'tcx>>, + ) -> Result<(bool, Certainty, Vec<Goal<'tcx, ty::Predicate<'tcx>>>), NoSolution>; +} + +impl<'tcx> InferCtxtEvalExt<'tcx> for InferCtxt<'tcx> { + #[instrument(level = "debug", skip(self), ret)] + fn evaluate_root_goal( + &self, + goal: Goal<'tcx, ty::Predicate<'tcx>>, + ) -> Result<(bool, Certainty, Vec<Goal<'tcx, ty::Predicate<'tcx>>>), NoSolution> { + let mode = if self.intercrate { SolverMode::Coherence } else { SolverMode::Normal }; + let mut search_graph = search_graph::SearchGraph::new(self.tcx, mode); + + let mut ecx = EvalCtxt { + search_graph: &mut search_graph, + infcx: self, + // Only relevant when canonicalizing the response. + max_input_universe: ty::UniverseIndex::ROOT, + var_values: CanonicalVarValues::dummy(), + nested_goals: NestedGoals::new(), + }; + let result = ecx.evaluate_goal(IsNormalizesToHack::No, goal); + + assert!( + ecx.nested_goals.is_empty(), + "root `EvalCtxt` should not have any goals added to it" + ); + + assert!(search_graph.is_empty()); + result + } +} + +impl<'a, 'tcx> EvalCtxt<'a, 'tcx> { + pub(super) fn solver_mode(&self) -> SolverMode { + self.search_graph.solver_mode() + } + + /// The entry point of the solver. + /// + /// This function deals with (coinductive) cycles, overflow, and caching + /// and then calls [`EvalCtxt::compute_goal`] which contains the actual + /// logic of the solver. + /// + /// Instead of calling this function directly, use either [EvalCtxt::evaluate_goal] + /// if you're inside of the solver or [InferCtxtEvalExt::evaluate_root_goal] if you're + /// outside of it. + #[instrument(level = "debug", skip(tcx, search_graph), ret)] + fn evaluate_canonical_goal( + tcx: TyCtxt<'tcx>, + search_graph: &'a mut search_graph::SearchGraph<'tcx>, + canonical_goal: CanonicalGoal<'tcx>, + ) -> QueryResult<'tcx> { + // Deal with overflow, caching, and coinduction. + // + // The actual solver logic happens in `ecx.compute_goal`. + search_graph.with_new_goal(tcx, canonical_goal, |search_graph| { + let intercrate = match search_graph.solver_mode() { + SolverMode::Normal => false, + SolverMode::Coherence => true, + }; + let (ref infcx, goal, var_values) = tcx + .infer_ctxt() + .intercrate(intercrate) + .build_with_canonical(DUMMY_SP, &canonical_goal); + let mut ecx = EvalCtxt { + infcx, + var_values, + max_input_universe: canonical_goal.max_universe, + search_graph, + nested_goals: NestedGoals::new(), + }; + ecx.compute_goal(goal) + }) + } + + /// Recursively evaluates `goal`, returning whether any inference vars have + /// been constrained and the certainty of the result. + fn evaluate_goal( + &mut self, + is_normalizes_to_hack: IsNormalizesToHack, + goal: Goal<'tcx, ty::Predicate<'tcx>>, + ) -> Result<(bool, Certainty, Vec<Goal<'tcx, ty::Predicate<'tcx>>>), NoSolution> { + let (orig_values, canonical_goal) = self.canonicalize_goal(goal); + let canonical_response = + EvalCtxt::evaluate_canonical_goal(self.tcx(), self.search_graph, canonical_goal)?; + + let has_changed = !canonical_response.value.var_values.is_identity(); + let (certainty, nested_goals) = self.instantiate_and_apply_query_response( + goal.param_env, + orig_values, + canonical_response, + )?; + + if !has_changed && !nested_goals.is_empty() { + bug!("an unchanged goal shouldn't have any side-effects on instantiation"); + } + + // Check that rerunning this query with its inference constraints applied + // doesn't result in new inference constraints and has the same result. + // + // If we have projection goals like `<T as Trait>::Assoc == u32` we recursively + // call `exists<U> <T as Trait>::Assoc == U` to enable better caching. This goal + // could constrain `U` to `u32` which would cause this check to result in a + // solver cycle. + if cfg!(debug_assertions) + && has_changed + && is_normalizes_to_hack == IsNormalizesToHack::No + && !self.search_graph.in_cycle() + { + debug!("rerunning goal to check result is stable"); + let (_orig_values, canonical_goal) = self.canonicalize_goal(goal); + let canonical_response = + EvalCtxt::evaluate_canonical_goal(self.tcx(), self.search_graph, canonical_goal)?; + if !canonical_response.value.var_values.is_identity() { + bug!( + "unstable result: re-canonicalized goal={canonical_goal:#?} \ + response={canonical_response:#?}" + ); + } + if certainty != canonical_response.value.certainty { + bug!( + "unstable certainty: {certainty:#?} re-canonicalized goal={canonical_goal:#?} \ + response={canonical_response:#?}" + ); + } + } + + Ok((has_changed, certainty, nested_goals)) + } + + fn compute_goal(&mut self, goal: Goal<'tcx, ty::Predicate<'tcx>>) -> QueryResult<'tcx> { + let Goal { param_env, predicate } = goal; + let kind = predicate.kind(); + if let Some(kind) = kind.no_bound_vars() { + match kind { + ty::PredicateKind::Clause(ty::Clause::Trait(predicate)) => { + self.compute_trait_goal(Goal { param_env, predicate }) + } + ty::PredicateKind::Clause(ty::Clause::Projection(predicate)) => { + self.compute_projection_goal(Goal { param_env, predicate }) + } + ty::PredicateKind::Clause(ty::Clause::TypeOutlives(predicate)) => { + self.compute_type_outlives_goal(Goal { param_env, predicate }) + } + ty::PredicateKind::Clause(ty::Clause::RegionOutlives(predicate)) => { + self.compute_region_outlives_goal(Goal { param_env, predicate }) + } + ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(ct, ty)) => { + self.compute_const_arg_has_type_goal(Goal { param_env, predicate: (ct, ty) }) + } + ty::PredicateKind::Subtype(predicate) => { + self.compute_subtype_goal(Goal { param_env, predicate }) + } + ty::PredicateKind::Coerce(predicate) => { + self.compute_coerce_goal(Goal { param_env, predicate }) + } + ty::PredicateKind::ClosureKind(def_id, substs, kind) => self + .compute_closure_kind_goal(Goal { + param_env, + predicate: (def_id, substs, kind), + }), + ty::PredicateKind::ObjectSafe(trait_def_id) => { + self.compute_object_safe_goal(trait_def_id) + } + ty::PredicateKind::WellFormed(arg) => { + self.compute_well_formed_goal(Goal { param_env, predicate: arg }) + } + ty::PredicateKind::Ambiguous => { + self.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS) + } + // FIXME: implement these predicates :) + ty::PredicateKind::ConstEvaluatable(_) | ty::PredicateKind::ConstEquate(_, _) => { + self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) + } + ty::PredicateKind::TypeWellFormedFromEnv(..) => { + bug!("TypeWellFormedFromEnv is only used for Chalk") + } + ty::PredicateKind::AliasRelate(lhs, rhs, direction) => self + .compute_alias_relate_goal(Goal { + param_env, + predicate: (lhs, rhs, direction), + }), + } + } else { + let kind = self.infcx.instantiate_binder_with_placeholders(kind); + let goal = goal.with(self.tcx(), ty::Binder::dummy(kind)); + self.add_goal(goal); + self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes) + } + } + + // Recursively evaluates all the goals added to this `EvalCtxt` to completion, returning + // the certainty of all the goals. + #[instrument(level = "debug", skip(self))] + pub(super) fn try_evaluate_added_goals(&mut self) -> Result<Certainty, NoSolution> { + let mut goals = core::mem::replace(&mut self.nested_goals, NestedGoals::new()); + let mut new_goals = NestedGoals::new(); + + let response = self.repeat_while_none( + |_| Ok(Certainty::Maybe(MaybeCause::Overflow)), + |this| { + let mut has_changed = Err(Certainty::Yes); + + if let Some(goal) = goals.normalizes_to_hack_goal.take() { + // Replace the goal with an unconstrained infer var, so the + // RHS does not affect projection candidate assembly. + let unconstrained_rhs = this.next_term_infer_of_kind(goal.predicate.term); + let unconstrained_goal = goal.with( + this.tcx(), + ty::Binder::dummy(ty::ProjectionPredicate { + projection_ty: goal.predicate.projection_ty, + term: unconstrained_rhs, + }), + ); + + let (_, certainty, instantiate_goals) = + match this.evaluate_goal(IsNormalizesToHack::Yes, unconstrained_goal) { + Ok(r) => r, + Err(NoSolution) => return Some(Err(NoSolution)), + }; + new_goals.goals.extend(instantiate_goals); + + // Finally, equate the goal's RHS with the unconstrained var. + // We put the nested goals from this into goals instead of + // next_goals to avoid needing to process the loop one extra + // time if this goal returns something -- I don't think this + // matters in practice, though. + match this.eq_and_get_goals( + goal.param_env, + goal.predicate.term, + unconstrained_rhs, + ) { + Ok(eq_goals) => { + goals.goals.extend(eq_goals); + } + Err(NoSolution) => return Some(Err(NoSolution)), + }; + + // We only look at the `projection_ty` part here rather than + // looking at the "has changed" return from evaluate_goal, + // because we expect the `unconstrained_rhs` part of the predicate + // to have changed -- that means we actually normalized successfully! + if goal.predicate.projection_ty + != this.resolve_vars_if_possible(goal.predicate.projection_ty) + { + has_changed = Ok(()) + } + + match certainty { + Certainty::Yes => {} + Certainty::Maybe(_) => { + // We need to resolve vars here so that we correctly + // deal with `has_changed` in the next iteration. + new_goals.normalizes_to_hack_goal = + Some(this.resolve_vars_if_possible(goal)); + has_changed = has_changed.map_err(|c| c.unify_with(certainty)); + } + } + } + + for goal in goals.goals.drain(..) { + let (changed, certainty, instantiate_goals) = + match this.evaluate_goal(IsNormalizesToHack::No, goal) { + Ok(result) => result, + Err(NoSolution) => return Some(Err(NoSolution)), + }; + new_goals.goals.extend(instantiate_goals); + + if changed { + has_changed = Ok(()); + } + + match certainty { + Certainty::Yes => {} + Certainty::Maybe(_) => { + new_goals.goals.push(goal); + has_changed = has_changed.map_err(|c| c.unify_with(certainty)); + } + } + } + + core::mem::swap(&mut new_goals, &mut goals); + match has_changed { + Ok(()) => None, + Err(certainty) => Some(Ok(certainty)), + } + }, + ); + + self.nested_goals = goals; + response + } } impl<'tcx> EvalCtxt<'_, 'tcx> { pub(super) fn probe<T>(&mut self, f: impl FnOnce(&mut EvalCtxt<'_, 'tcx>) -> T) -> T { - self.infcx.probe(|_| f(self)) + let mut ecx = EvalCtxt { + infcx: self.infcx, + var_values: self.var_values, + max_input_universe: self.max_input_universe, + search_graph: self.search_graph, + nested_goals: self.nested_goals.clone(), + }; + self.infcx.probe(|_| f(&mut ecx)) } pub(super) fn tcx(&self) -> TyCtxt<'tcx> { @@ -61,6 +426,15 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { ) } + /// Returns a ty infer or a const infer depending on whether `kind` is a `Ty` or `Const`. + /// If `kind` is an integer inference variable this will still return a ty infer var. + pub(super) fn next_term_infer_of_kind(&self, kind: ty::Term<'tcx>) -> ty::Term<'tcx> { + match kind.unpack() { + ty::TermKind::Ty(_) => self.next_ty_infer().into(), + ty::TermKind::Const(ct) => self.next_const_infer(ct.ty()).into(), + } + } + /// Is the projection predicate is of the form `exists<T> <Ty as Trait>::Assoc = T`. /// /// This is the case if the `term` is an inference variable in the innermost universe @@ -74,7 +448,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { if let &ty::Infer(ty::TyVar(vid)) = ty.kind() { match self.infcx.probe_ty_var(vid) { Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"), - Err(universe) => universe == self.universe(), + Err(universe) => universe == self.infcx.universe(), } } else { false @@ -84,7 +458,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { if let ty::ConstKind::Infer(ty::InferConst::Var(vid)) = ct.kind() { match self.infcx.probe_const_var(vid) { Ok(value) => bug!("resolved var in query: {goal:?} {value:?}"), - Err(universe) => universe == self.universe(), + Err(universe) => universe == self.infcx.universe(), } } else { false @@ -93,37 +467,42 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { }; // Guard against `<T as Trait<?0>>::Assoc = ?0>`. - struct ContainsTerm<'tcx> { + struct ContainsTerm<'a, 'tcx> { term: ty::Term<'tcx>, + infcx: &'a InferCtxt<'tcx>, } - impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ContainsTerm<'tcx> { + impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ContainsTerm<'_, 'tcx> { type BreakTy = (); fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> { - if t.needs_infer() { - if ty::Term::from(t) == self.term { - ControlFlow::Break(()) - } else { - t.super_visit_with(self) - } + if let Some(vid) = t.ty_vid() + && let ty::TermKind::Ty(term) = self.term.unpack() + && let Some(term_vid) = term.ty_vid() + && self.infcx.root_var(vid) == self.infcx.root_var(term_vid) + { + ControlFlow::Break(()) + } else if t.has_non_region_infer() { + t.super_visit_with(self) } else { ControlFlow::Continue(()) } } fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> { - if c.needs_infer() { - if ty::Term::from(c) == self.term { - ControlFlow::Break(()) - } else { - c.super_visit_with(self) - } + if let ty::ConstKind::Infer(ty::InferConst::Var(vid)) = c.kind() + && let ty::TermKind::Const(term) = self.term.unpack() + && let ty::ConstKind::Infer(ty::InferConst::Var(term_vid)) = term.kind() + && self.infcx.root_const_var(vid) == self.infcx.root_const_var(term_vid) + { + ControlFlow::Break(()) + } else if c.has_non_region_infer() { + c.super_visit_with(self) } else { ControlFlow::Continue(()) } } } - let mut visitor = ContainsTerm { term: goal.predicate.term }; + let mut visitor = ContainsTerm { infcx: self.infcx, term: goal.predicate.term }; term_is_infer && goal.predicate.projection_ty.visit_with(&mut visitor).is_continue() @@ -132,6 +511,49 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { #[instrument(level = "debug", skip(self, param_env), ret)] pub(super) fn eq<T: ToTrace<'tcx>>( + &mut self, + param_env: ty::ParamEnv<'tcx>, + lhs: T, + rhs: T, + ) -> Result<(), NoSolution> { + self.infcx + .at(&ObligationCause::dummy(), param_env) + .eq(DefineOpaqueTypes::No, lhs, rhs) + .map(|InferOk { value: (), obligations }| { + self.add_goals(obligations.into_iter().map(|o| o.into())); + }) + .map_err(|e| { + debug!(?e, "failed to equate"); + NoSolution + }) + } + + #[instrument(level = "debug", skip(self, param_env), ret)] + pub(super) fn sub<T: ToTrace<'tcx>>( + &mut self, + param_env: ty::ParamEnv<'tcx>, + sub: T, + sup: T, + ) -> Result<(), NoSolution> { + self.infcx + .at(&ObligationCause::dummy(), param_env) + .sub(DefineOpaqueTypes::No, sub, sup) + .map(|InferOk { value: (), obligations }| { + self.add_goals(obligations.into_iter().map(|o| o.into())); + }) + .map_err(|e| { + debug!(?e, "failed to subtype"); + NoSolution + }) + } + + /// Equates two values returning the nested goals without adding them + /// to the nested goals of the `EvalCtxt`. + /// + /// If possible, try using `eq` instead which automatically handles nested + /// goals correctly. + #[instrument(level = "trace", skip(self, param_env), ret)] + pub(super) fn eq_and_get_goals<T: ToTrace<'tcx>>( &self, param_env: ty::ParamEnv<'tcx>, lhs: T, @@ -139,7 +561,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { ) -> Result<Vec<Goal<'tcx, ty::Predicate<'tcx>>>, NoSolution> { self.infcx .at(&ObligationCause::dummy(), param_env) - .eq(lhs, rhs) + .eq(DefineOpaqueTypes::No, lhs, rhs) .map(|InferOk { value: (), obligations }| { obligations.into_iter().map(|o| o.into()).collect() }) @@ -178,7 +600,64 @@ impl<'tcx> EvalCtxt<'_, 'tcx> { self.infcx.fresh_substs_for_item(DUMMY_SP, def_id) } - pub(super) fn universe(&self) -> ty::UniverseIndex { - self.infcx.universe() + pub(super) fn translate_substs( + &self, + param_env: ty::ParamEnv<'tcx>, + source_impl: DefId, + source_substs: ty::SubstsRef<'tcx>, + target_node: specialization_graph::Node, + ) -> ty::SubstsRef<'tcx> { + crate::traits::translate_substs( + self.infcx, + param_env, + source_impl, + source_substs, + target_node, + ) + } + + pub(super) fn register_ty_outlives(&self, ty: Ty<'tcx>, lt: ty::Region<'tcx>) { + self.infcx.register_region_obligation_with_cause(ty, lt, &ObligationCause::dummy()); + } + + pub(super) fn register_region_outlives(&self, a: ty::Region<'tcx>, b: ty::Region<'tcx>) { + // `b : a` ==> `a <= b` + // (inlined from `InferCtxt::region_outlives_predicate`) + self.infcx.sub_regions( + rustc_infer::infer::SubregionOrigin::RelateRegionParamBound(DUMMY_SP), + b, + a, + ); + } + + /// Computes the list of goals required for `arg` to be well-formed + pub(super) fn well_formed_goals( + &self, + param_env: ty::ParamEnv<'tcx>, + arg: ty::GenericArg<'tcx>, + ) -> Option<impl Iterator<Item = Goal<'tcx, ty::Predicate<'tcx>>>> { + crate::traits::wf::unnormalized_obligations(self.infcx, param_env, arg) + .map(|obligations| obligations.into_iter().map(|obligation| obligation.into())) + } + + pub(super) fn is_transmutable( + &self, + src_and_dst: rustc_transmute::Types<'tcx>, + scope: Ty<'tcx>, + assume: rustc_transmute::Assume, + ) -> Result<Certainty, NoSolution> { + // FIXME(transmutability): This really should be returning nested goals for `Answer::If*` + match rustc_transmute::TransmuteTypeEnv::new(self.infcx).is_transmutable( + ObligationCause::dummy(), + ty::Binder::dummy(src_and_dst), + scope, + assume, + ) { + rustc_transmute::Answer::Yes => Ok(Certainty::Yes), + rustc_transmute::Answer::No(_) + | rustc_transmute::Answer::IfTransmutable { .. } + | rustc_transmute::Answer::IfAll(_) + | rustc_transmute::Answer::IfAny(_) => Err(NoSolution), + } } } |