bjoernager/rust
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merge builtin unsize candidates again

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This commit is contained in:
lcnr 2024-01-08 15:38:01 +01:00
parent 0d71860368
commit ea4e5b8458
3 changed files with 41 additions and 87 deletions
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90
compiler/rustc_trait_selection/src/solve/trait_goals.rs
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@ -490,53 +490,6 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
ecx.evaluate_added_goals_and_make_canonical_response(certainty)
}
fn consider_unsize_to_dyn_candidate(
ecx: &mut EvalCtxt<'_, 'tcx>,
goal: Goal<'tcx, Self>,
) -> QueryResult<'tcx> {
ecx.probe(|_| ProbeKind::UnsizeAssembly).enter(|ecx| {
let a_ty = goal.predicate.self_ty();
// We need to normalize the b_ty since it's destructured as a `dyn Trait`.
let Some(b_ty) =
ecx.try_normalize_ty(goal.param_env, goal.predicate.trait_ref.args.type_at(1))
else {
return ecx.evaluate_added_goals_and_make_canonical_response(Certainty::OVERFLOW);
};
let ty::Dynamic(b_data, b_region, ty::Dyn) = *b_ty.kind() else {
return Err(NoSolution);
};
let tcx = ecx.tcx();
// Can only unsize to an object-safe trait.
if b_data.principal_def_id().is_some_and(|def_id| !tcx.check_is_object_safe(def_id)) {
return Err(NoSolution);
}
// Check that the type implements all of the predicates of the trait object.
// (i.e. the principal, all of the associated types match, and any auto traits)
ecx.add_goals(
GoalSource::ImplWhereBound,
b_data.iter().map(|pred| goal.with(tcx, pred.with_self_ty(tcx, a_ty))),
);
// The type must be `Sized` to be unsized.
if let Some(sized_def_id) = tcx.lang_items().sized_trait() {
ecx.add_goal(
GoalSource::ImplWhereBound,
goal.with(tcx, ty::TraitRef::new(tcx, sized_def_id, [a_ty])),
);
} else {
return Err(NoSolution);
}
// The type must outlive the lifetime of the `dyn` we're unsizing into.
ecx.add_goal(GoalSource::Misc, goal.with(tcx, ty::OutlivesPredicate(a_ty, b_region)));
ecx.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
})
}
/// ```ignore (builtin impl example)
/// trait Trait {
/// fn foo(&self);
@ -588,8 +541,11 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
goal, a_data, a_region, b_data, b_region,
),
// `T` -> `dyn Trait` unsizing is handled separately in `consider_unsize_to_dyn_candidate`
(_, &ty::Dynamic(..)) => vec![],
// `T` -> `dyn Trait` unsizing.
(_, &ty::Dynamic(b_region, b_data, ty::Dyn)) => result_to_single(
ecx.consider_builtin_unsize_to_dyn_candidate(goal, b_region, b_data),
BuiltinImplSource::Misc,
),
// `[T; N]` -> `[T]` unsizing
(&ty::Array(a_elem_ty, ..), &ty::Slice(b_elem_ty)) => result_to_single(
@ -691,6 +647,42 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
responses
}
fn consider_builtin_unsize_to_dyn_candidate(
&mut self,
goal: Goal<'tcx, (Ty<'tcx>, Ty<'tcx>)>,
b_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
b_region: ty::Region<'tcx>,
) -> QueryResult<'tcx> {
let tcx = self.tcx();
let Goal { predicate: (a_ty, _), .. } = goal;
// Can only unsize to an object-safe trait.
if b_data.principal_def_id().is_some_and(|def_id| !tcx.check_is_object_safe(def_id)) {
return Err(NoSolution);
}
// Check that the type implements all of the predicates of the trait object.
// (i.e. the principal, all of the associated types match, and any auto traits)
self.add_goals(
GoalSource::ImplWhereBound,
b_data.iter().map(|pred| goal.with(tcx, pred.with_self_ty(tcx, a_ty))),
);
// The type must be `Sized` to be unsized.
if let Some(sized_def_id) = tcx.lang_items().sized_trait() {
self.add_goal(
GoalSource::ImplWhereBound,
goal.with(tcx, ty::TraitRef::new(tcx, sized_def_id, [a_ty])),
);
} else {
return Err(NoSolution);
}
// The type must outlive the lifetime of the `dyn` we're unsizing into.
self.add_goal(GoalSource::Misc, goal.with(tcx, ty::OutlivesPredicate(a_ty, b_region)));
self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
}
fn consider_builtin_upcast_to_principal(
&mut self,
goal: Goal<'tcx, (Ty<'tcx>, Ty<'tcx>)>,