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use std::collections::HashSet;
use std::iter;
use std::ops::ControlFlow;
use crate::clauses::ClauseBuilder;
use crate::rust_ir::AdtKind;
use crate::{Interner, RustIrDatabase, TraitRef, WellKnownTrait};
use chalk_ir::{
cast::Cast,
interner::HasInterner,
visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor},
Binders, Const, ConstValue, DebruijnIndex, DomainGoal, DynTy, EqGoal, Goal, LifetimeOutlives,
QuantifiedWhereClauses, Substitution, TraitId, Ty, TyKind, TypeOutlives, WhereClause,
};
struct UnsizeParameterCollector<I: Interner> {
interner: I,
// FIXME should probably use a bitset instead
parameters: HashSet<usize>,
}
impl<I: Interner> TypeVisitor<I> for UnsizeParameterCollector<I> {
type BreakTy = ();
fn as_dyn(&mut self) -> &mut dyn TypeVisitor<I, BreakTy = Self::BreakTy> {
self
}
fn visit_ty(&mut self, ty: &Ty<I>, outer_binder: DebruijnIndex) -> ControlFlow<()> {
let interner = self.interner;
match ty.kind(interner) {
TyKind::BoundVar(bound_var) => {
// check if bound var refers to the outermost binder
if bound_var.debruijn.shifted_in() == outer_binder {
self.parameters.insert(bound_var.index);
}
ControlFlow::Continue(())
}
_ => ty.super_visit_with(self, outer_binder),
}
}
fn visit_const(&mut self, constant: &Const<I>, outer_binder: DebruijnIndex) -> ControlFlow<()> {
let interner = self.interner;
if let ConstValue::BoundVar(bound_var) = constant.data(interner).value {
// check if bound var refers to the outermost binder
if bound_var.debruijn.shifted_in() == outer_binder {
self.parameters.insert(bound_var.index);
}
}
ControlFlow::Continue(())
}
fn interner(&self) -> I {
self.interner
}
}
fn outer_binder_parameters_used<I: Interner>(
interner: I,
v: &Binders<impl TypeVisitable<I> + HasInterner>,
) -> HashSet<usize> {
let mut visitor = UnsizeParameterCollector {
interner,
parameters: HashSet::new(),
};
v.visit_with(&mut visitor, DebruijnIndex::INNERMOST);
visitor.parameters
}
// has nothing to do with occurs check
struct ParameterOccurenceCheck<'p, I: Interner> {
interner: I,
parameters: &'p HashSet<usize>,
}
impl<'p, I: Interner> TypeVisitor<I> for ParameterOccurenceCheck<'p, I> {
type BreakTy = ();
fn as_dyn(&mut self) -> &mut dyn TypeVisitor<I, BreakTy = Self::BreakTy> {
self
}
fn visit_ty(&mut self, ty: &Ty<I>, outer_binder: DebruijnIndex) -> ControlFlow<()> {
let interner = self.interner;
match ty.kind(interner) {
TyKind::BoundVar(bound_var) => {
if bound_var.debruijn.shifted_in() == outer_binder
&& self.parameters.contains(&bound_var.index)
{
ControlFlow::Break(())
} else {
ControlFlow::Continue(())
}
}
_ => ty.super_visit_with(self, outer_binder),
}
}
fn visit_const(&mut self, constant: &Const<I>, outer_binder: DebruijnIndex) -> ControlFlow<()> {
let interner = self.interner;
match constant.data(interner).value {
ConstValue::BoundVar(bound_var) => {
if bound_var.debruijn.shifted_in() == outer_binder
&& self.parameters.contains(&bound_var.index)
{
ControlFlow::Break(())
} else {
ControlFlow::Continue(())
}
}
_ => ControlFlow::Continue(()),
}
}
fn interner(&self) -> I {
self.interner
}
}
fn uses_outer_binder_params<I: Interner>(
interner: I,
v: &Binders<impl TypeVisitable<I> + HasInterner>,
parameters: &HashSet<usize>,
) -> bool {
let mut visitor = ParameterOccurenceCheck {
interner,
parameters,
};
let flow = v.visit_with(&mut visitor, DebruijnIndex::INNERMOST);
matches!(flow, ControlFlow::Break(_))
}
fn principal_id<I: Interner>(
db: &dyn RustIrDatabase<I>,
bounds: &Binders<QuantifiedWhereClauses<I>>,
) -> Option<TraitId<I>> {
let interner = db.interner();
bounds
.skip_binders()
.iter(interner)
.filter_map(|b| b.trait_id())
.find(|&id| !db.trait_datum(id).is_auto_trait())
}
fn auto_trait_ids<'a, I: Interner>(
db: &'a dyn RustIrDatabase<I>,
bounds: &'a Binders<QuantifiedWhereClauses<I>>,
) -> impl Iterator<Item = TraitId<I>> + 'a {
let interner = db.interner();
bounds
.skip_binders()
.iter(interner)
.filter_map(|clause| clause.trait_id())
.filter(move |&id| db.trait_datum(id).is_auto_trait())
}
pub fn add_unsize_program_clauses<I: Interner>(
db: &dyn RustIrDatabase<I>,
builder: &mut ClauseBuilder<'_, I>,
trait_ref: TraitRef<I>,
_ty: TyKind<I>,
) {
let interner = db.interner();
let source_ty = trait_ref.self_type_parameter(interner);
let target_ty = trait_ref
.substitution
.at(interner, 1)
.assert_ty_ref(interner)
.clone();
let unsize_trait_id = trait_ref.trait_id;
// N.B. here rustc asserts that `TraitRef` is not a higher-ranked bound
// i.e. `for<'a> &'a T: Unsize<dyn Trait+'a>` is never provable.
//
// In chalk it would be awkward to implement and I am not sure
// there is a need for it, the original comment states that this restriction
// could be lifted.
//
// for more info visit `fn assemble_candidates_for_unsizing` and
// `fn confirm_builtin_unisize_candidate` in rustc.
match (source_ty.kind(interner), target_ty.kind(interner)) {
// dyn Trait + AutoX + 'a -> dyn Trait + AutoY + 'b
(
TyKind::Dyn(DynTy {
bounds: bounds_a,
lifetime: lifetime_a,
}),
TyKind::Dyn(DynTy {
bounds: bounds_b,
lifetime: lifetime_b,
}),
) => {
let principal_a = principal_id(db, bounds_a);
let principal_b = principal_id(db, bounds_b);
let auto_trait_ids_a: Vec<_> = auto_trait_ids(db, bounds_a).collect();
let auto_trait_ids_b: Vec<_> = auto_trait_ids(db, bounds_b).collect();
let may_apply = principal_a == principal_b
&& auto_trait_ids_b
.iter()
.all(|id_b| auto_trait_ids_a.iter().any(|id_a| id_a == id_b));
if !may_apply {
return;
}
// COMMENT FROM RUSTC:
// ------------------
// Require that the traits involved in this upcast are **equal**;
// only the **lifetime bound** is changed.
//
// This condition is arguably too strong -- it would
// suffice for the source trait to be a *subtype* of the target
// trait. In particular, changing from something like
// `for<'a, 'b> Foo<'a, 'b>` to `for<'a> Foo<'a, 'a>` should be
// permitted.
// <...>
// I've modified this to `.eq` because I want to continue rejecting
// that [`old-lub-glb-object.rs`] test (as we have
// done for quite some time) before we are firmly comfortable
// with what our behavior should be there. -nikomatsakis
// ------------------
// Construct a new trait object type by taking the source ty,
// filtering out auto traits of source that are not present in target
// and changing source lifetime to target lifetime.
//
// In order for the coercion to be valid, this new type
// should be equal to target type.
let new_source_ty = TyKind::Dyn(DynTy {
bounds: bounds_a.map_ref(|bounds| {
QuantifiedWhereClauses::from_iter(
interner,
bounds.iter(interner).filter(|bound| {
let trait_id = match bound.trait_id() {
Some(id) => id,
None => return true,
};
if auto_trait_ids_a.iter().all(|&id_a| id_a != trait_id) {
return true;
}
auto_trait_ids_b.iter().any(|&id_b| id_b == trait_id)
}),
)
}),
lifetime: lifetime_b.clone(),
})
.intern(interner);
// Check that new source is equal to target
let eq_goal = EqGoal {
a: new_source_ty.cast(interner),
b: target_ty.clone().cast(interner),
}
.cast(interner);
// Check that source lifetime outlives target lifetime
let lifetime_outlives_goal: Goal<I> = WhereClause::LifetimeOutlives(LifetimeOutlives {
a: lifetime_a.clone(),
b: lifetime_b.clone(),
})
.cast(interner);
builder.push_clause(trait_ref, [eq_goal, lifetime_outlives_goal].iter());
}
// T -> dyn Trait + 'a
(_, TyKind::Dyn(DynTy { bounds, lifetime })) => {
// Check if all traits in trait object are object safe
let object_safe_goals = bounds
.skip_binders()
.iter(interner)
.filter_map(|bound| bound.trait_id())
.map(|id| DomainGoal::ObjectSafe(id).cast(interner));
// Check that T implements all traits of the trait object
let source_ty_bounds = bounds
.clone()
.substitute(interner, &Substitution::from1(interner, source_ty.clone()));
// Check that T is sized because we can only make
// a trait object from a sized type
let self_sized_goal: WhereClause<_> = TraitRef {
trait_id: db
.well_known_trait_id(WellKnownTrait::Sized)
.expect("Expected Sized to be defined when proving Unsize"),
substitution: Substitution::from1(interner, source_ty.clone()),
}
.cast(interner);
// Check that `source_ty` outlives `'a`
let source_ty_outlives: Goal<_> = WhereClause::TypeOutlives(TypeOutlives {
ty: source_ty,
lifetime: lifetime.clone(),
})
.cast(interner);
builder.push_clause(
trait_ref,
source_ty_bounds
.iter(interner)
.map(|bound| bound.clone().cast::<Goal<I>>(interner))
.chain(object_safe_goals)
.chain(iter::once(self_sized_goal.cast(interner)))
.chain(iter::once(source_ty_outlives)),
);
}
(TyKind::Array(array_ty, _array_const), TyKind::Slice(slice_ty)) => {
let eq_goal = EqGoal {
a: array_ty.clone().cast(interner),
b: slice_ty.clone().cast(interner),
};
builder.push_clause(trait_ref, iter::once(eq_goal));
}
// Adt<T> -> Adt<U>
(TyKind::Adt(adt_id_a, substitution_a), TyKind::Adt(adt_id_b, substitution_b)) => {
if adt_id_a != adt_id_b {
return;
}
let adt_id = *adt_id_a;
let adt_datum = db.adt_datum(adt_id);
// Unsizing of enums is not allowed
if adt_datum.kind == AdtKind::Enum {
return;
}
// We have a `struct` so we're guaranteed a single variant
let fields_len = adt_datum
.binders
.skip_binders()
.variants
.last()
.unwrap()
.fields
.len();
if fields_len == 0 {
return;
}
let adt_tail_field = adt_datum
.binders
.map_ref(|bound| bound.variants.last().unwrap().fields.last().unwrap())
.cloned();
// Collect unsize parameters that last field contains and
// ensure there at least one of them.
let unsize_parameter_candidates =
outer_binder_parameters_used(interner, &adt_tail_field);
if unsize_parameter_candidates.is_empty() {
return;
}
// Ensure none of the other fields mention the parameters used
// in unsizing.
// We specifically want variables specified by the outermost binder
// i.e. the struct generic arguments binder.
if uses_outer_binder_params(
interner,
&adt_datum
.binders
.map_ref(|bound| &bound.variants.last().unwrap().fields[..fields_len - 1]),
&unsize_parameter_candidates,
) {
return;
}
let parameters_a = substitution_a.as_slice(interner);
let parameters_b = substitution_b.as_slice(interner);
// Check that the source adt with the target's
// unsizing parameters is equal to the target.
// We construct a new substitution where if a parameter is used in the
// coercion (i.e. it's a non-lifetime struct parameter used by it's last field),
// then we take that parameter from target substitution, otherwise we take
// it from the source substitution.
//
// In order for the coercion to be valid, target struct and
// struct with this newly constructed substitution applied to it should be equal.
let substitution = Substitution::from_iter(
interner,
parameters_a.iter().enumerate().map(|(i, p)| {
if unsize_parameter_candidates.contains(&i) {
¶meters_b[i]
} else {
p
}
}),
);
let eq_goal = EqGoal {
a: TyKind::Adt(adt_id, substitution)
.intern(interner)
.cast(interner),
b: target_ty.clone().cast(interner),
}
.cast(interner);
// Extract `TailField<T>` and `TailField<U>` from `Struct<T>` and `Struct<U>`.
let source_tail_field = adt_tail_field.clone().substitute(interner, substitution_a);
let target_tail_field = adt_tail_field.substitute(interner, substitution_b);
// Check that `TailField<T>: Unsize<TailField<U>>`
let last_field_unsizing_goal: Goal<I> = TraitRef {
trait_id: unsize_trait_id,
substitution: Substitution::from_iter(
interner,
[source_tail_field, target_tail_field].iter().cloned(),
),
}
.cast(interner);
builder.push_clause(trait_ref, [eq_goal, last_field_unsizing_goal].iter());
}
// (.., T) -> (.., U)
(TyKind::Tuple(arity_a, substitution_a), TyKind::Tuple(arity_b, substitution_b)) => {
if arity_a != arity_b || *arity_a == 0 {
return;
}
let arity = arity_a;
let tail_ty_a = substitution_a.iter(interner).last().unwrap();
let tail_ty_b = substitution_b.iter(interner).last().unwrap();
// Check that the source tuple with the target's
// last element is equal to the target.
let new_tuple = TyKind::Tuple(
*arity,
Substitution::from_iter(
interner,
substitution_a
.iter(interner)
.take(arity - 1)
.chain(iter::once(tail_ty_b)),
),
)
.cast(interner)
.intern(interner);
let eq_goal: Goal<I> = EqGoal {
a: new_tuple.cast(interner),
b: target_ty.clone().cast(interner),
}
.cast(interner);
// Check that `T: Unsize<U>`
let last_field_unsizing_goal: Goal<I> = TraitRef {
trait_id: unsize_trait_id,
substitution: Substitution::from_iter(
interner,
[tail_ty_a, tail_ty_b].iter().cloned(),
),
}
.cast(interner);
builder.push_clause(trait_ref, [eq_goal, last_field_unsizing_goal].iter());
}
_ => (),
}
}