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use std::ops::ControlFlow;
use std::{fmt, iter};
use crate::{
ext::*, goal_builder::GoalBuilder, rust_ir::*, solve::Solver, split::Split, RustIrDatabase,
};
use chalk_ir::{
cast::*,
fold::shift::Shift,
interner::Interner,
visit::{TypeVisitable, TypeVisitor},
*,
};
use tracing::debug;
#[derive(Debug)]
pub enum WfError<I: Interner> {
IllFormedTypeDecl(chalk_ir::AdtId<I>),
IllFormedOpaqueTypeDecl(chalk_ir::OpaqueTyId<I>),
IllFormedTraitImpl(chalk_ir::TraitId<I>),
}
impl<I: Interner> fmt::Display for WfError<I> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
WfError::IllFormedTypeDecl(id) => write!(
f,
"type declaration `{:?}` does not meet well-formedness requirements",
id
),
WfError::IllFormedOpaqueTypeDecl(id) => write!(
f,
"opaque type declaration `{:?}` does not meet well-formedness requirements",
id
),
WfError::IllFormedTraitImpl(id) => write!(
f,
"trait impl for `{:?}` does not meet well-formedness requirements",
id
),
}
}
}
impl<I: Interner> std::error::Error for WfError<I> {}
pub struct WfSolver<'a, I: Interner> {
db: &'a dyn RustIrDatabase<I>,
solver_builder: &'a dyn Fn() -> Box<dyn Solver<I>>,
}
struct InputTypeCollector<I: Interner> {
types: Vec<Ty<I>>,
interner: I,
}
impl<I: Interner> InputTypeCollector<I> {
fn new(interner: I) -> Self {
Self {
types: Vec::new(),
interner,
}
}
fn types_in(interner: I, value: impl TypeVisitable<I>) -> Vec<Ty<I>> {
let mut collector = Self::new(interner);
value.visit_with(&mut collector, DebruijnIndex::INNERMOST);
collector.types
}
}
impl<I: Interner> TypeVisitor<I> for InputTypeCollector<I> {
type BreakTy = ();
fn as_dyn(&mut self) -> &mut dyn TypeVisitor<I, BreakTy = Self::BreakTy> {
self
}
fn interner(&self) -> I {
self.interner
}
fn visit_where_clause(
&mut self,
where_clause: &WhereClause<I>,
outer_binder: DebruijnIndex,
) -> ControlFlow<()> {
match where_clause {
WhereClause::AliasEq(alias_eq) => alias_eq
.alias
.clone()
.intern(self.interner)
.visit_with(self, outer_binder),
WhereClause::Implemented(trait_ref) => trait_ref.visit_with(self, outer_binder),
WhereClause::TypeOutlives(TypeOutlives { ty, .. }) => ty.visit_with(self, outer_binder),
WhereClause::LifetimeOutlives(..) => ControlFlow::Continue(()),
}
}
fn visit_ty(&mut self, ty: &Ty<I>, outer_binder: DebruijnIndex) -> ControlFlow<()> {
let interner = self.interner();
let mut push_ty = || {
self.types
.push(ty.clone().shifted_out_to(interner, outer_binder).unwrap())
};
match ty.kind(interner) {
TyKind::Adt(id, substitution) => {
push_ty();
id.visit_with(self, outer_binder);
substitution.visit_with(self, outer_binder)
}
TyKind::AssociatedType(assoc_ty, substitution) => {
push_ty();
assoc_ty.visit_with(self, outer_binder);
substitution.visit_with(self, outer_binder)
}
TyKind::Scalar(scalar) => {
push_ty();
scalar.visit_with(self, outer_binder)
}
TyKind::Str => {
push_ty();
ControlFlow::Continue(())
}
TyKind::Tuple(arity, substitution) => {
push_ty();
arity.visit_with(self, outer_binder);
substitution.visit_with(self, outer_binder)
}
TyKind::OpaqueType(opaque_ty, substitution) => {
push_ty();
opaque_ty.visit_with(self, outer_binder);
substitution.visit_with(self, outer_binder)
}
TyKind::Slice(substitution) => {
push_ty();
substitution.visit_with(self, outer_binder)
}
TyKind::FnDef(fn_def, substitution) => {
push_ty();
fn_def.visit_with(self, outer_binder);
substitution.visit_with(self, outer_binder)
}
TyKind::Ref(mutability, lifetime, ty) => {
push_ty();
mutability.visit_with(self, outer_binder);
lifetime.visit_with(self, outer_binder);
ty.visit_with(self, outer_binder)
}
TyKind::Raw(mutability, substitution) => {
push_ty();
mutability.visit_with(self, outer_binder);
substitution.visit_with(self, outer_binder)
}
TyKind::Never => {
push_ty();
ControlFlow::Continue(())
}
TyKind::Array(ty, const_) => {
push_ty();
ty.visit_with(self, outer_binder);
const_.visit_with(self, outer_binder)
}
TyKind::Closure(_id, substitution) => {
push_ty();
substitution.visit_with(self, outer_binder)
}
TyKind::Coroutine(_coroutine, substitution) => {
push_ty();
substitution.visit_with(self, outer_binder)
}
TyKind::CoroutineWitness(_witness, substitution) => {
push_ty();
substitution.visit_with(self, outer_binder)
}
TyKind::Foreign(_foreign_ty) => {
push_ty();
ControlFlow::Continue(())
}
TyKind::Error => {
push_ty();
ControlFlow::Continue(())
}
TyKind::Dyn(clauses) => {
push_ty();
clauses.visit_with(self, outer_binder)
}
TyKind::Alias(AliasTy::Projection(proj)) => {
push_ty();
proj.visit_with(self, outer_binder)
}
TyKind::Alias(AliasTy::Opaque(opaque_ty)) => {
push_ty();
opaque_ty.visit_with(self, outer_binder)
}
TyKind::Placeholder(_) => {
push_ty();
ControlFlow::Continue(())
}
// Type parameters do not carry any input types (so we can sort of assume they are
// always WF).
TyKind::BoundVar(..) => ControlFlow::Continue(()),
// Higher-kinded types such as `for<'a> fn(&'a u32)` introduce their own implied
// bounds, and these bounds will be enforced upon calling such a function. In some
// sense, well-formedness requirements for the input types of an HKT will be enforced
// lazily, so no need to include them here.
TyKind::Function(..) => ControlFlow::Continue(()),
TyKind::InferenceVar(..) => {
panic!("unexpected inference variable in wf rules: {:?}", ty)
}
}
}
}
impl<'a, I> WfSolver<'a, I>
where
I: Interner,
{
/// Constructs a new `WfSolver`.
pub fn new(
db: &'a dyn RustIrDatabase<I>,
solver_builder: &'a dyn Fn() -> Box<dyn Solver<I>>,
) -> Self {
Self { db, solver_builder }
}
pub fn verify_adt_decl(&self, adt_id: AdtId<I>) -> Result<(), WfError<I>> {
let interner = self.db.interner();
// Given a struct like
//
// ```rust
// struct Foo<T> where T: Eq {
// data: Vec<T>
// }
// ```
let adt_datum = self.db.adt_datum(adt_id);
let is_enum = adt_datum.kind == AdtKind::Enum;
let mut gb = GoalBuilder::new(self.db);
let adt_data = adt_datum
.binders
.map_ref(|b| (&b.variants, &b.where_clauses));
// We make a goal like...
//
// forall<T> { ... }
let wg_goal = gb.forall(
&adt_data,
is_enum,
|gb, _, (variants, where_clauses), is_enum| {
let interner = gb.interner();
// (FromEnv(T: Eq) => ...)
gb.implies(
where_clauses
.iter()
.cloned()
.map(|wc| wc.into_from_env_goal(interner)),
|gb| {
let sub_goals: Vec<_> = variants
.iter()
.flat_map(|variant| {
let fields = &variant.fields;
// When checking if Enum is well-formed, we require that all fields of
// each variant are sized. For `structs`, we relax this requirement to
// all but the last field.
let sized_constraint_goal =
WfWellKnownConstraints::struct_sized_constraint(
gb.db(),
fields,
is_enum,
);
// WellFormed(Vec<T>), for each field type `Vec<T>` or type that appears in the where clauses
let types = InputTypeCollector::types_in(
gb.interner(),
(&fields, &where_clauses),
);
types
.into_iter()
.map(|ty| ty.well_formed().cast(interner))
.chain(sized_constraint_goal.into_iter())
})
.collect();
gb.all(sub_goals)
},
)
},
);
let wg_goal = wg_goal.into_closed_goal(interner);
let mut fresh_solver = (self.solver_builder)();
let is_legal = fresh_solver.has_unique_solution(self.db, &wg_goal);
if !is_legal {
Err(WfError::IllFormedTypeDecl(adt_id))
} else {
Ok(())
}
}
pub fn verify_trait_impl(&self, impl_id: ImplId<I>) -> Result<(), WfError<I>> {
let interner = self.db.interner();
let impl_datum = self.db.impl_datum(impl_id);
let trait_id = impl_datum.trait_id();
let impl_goal = Goal::all(
interner,
impl_header_wf_goal(self.db, impl_id).into_iter().chain(
impl_datum
.associated_ty_value_ids
.iter()
.filter_map(|&id| compute_assoc_ty_goal(self.db, id)),
),
);
if let Some(well_known) = self.db.trait_datum(trait_id).well_known {
self.verify_well_known_impl(impl_id, well_known)?
}
debug!("WF trait goal: {:?}", impl_goal);
let mut fresh_solver = (self.solver_builder)();
let is_legal =
fresh_solver.has_unique_solution(self.db, &impl_goal.into_closed_goal(interner));
if is_legal {
Ok(())
} else {
Err(WfError::IllFormedTraitImpl(trait_id))
}
}
pub fn verify_opaque_ty_decl(&self, opaque_ty_id: OpaqueTyId<I>) -> Result<(), WfError<I>> {
// Given an opaque type like
// ```notrust
// opaque type Foo<T>: Clone where T: Bar = Baz;
// ```
let interner = self.db.interner();
let mut gb = GoalBuilder::new(self.db);
let datum = self.db.opaque_ty_data(opaque_ty_id);
let bound = &datum.bound;
// We make a goal like
//
// forall<T>
let goal = gb.forall(bound, opaque_ty_id, |gb, _, bound, opaque_ty_id| {
let interner = gb.interner();
let subst = Substitution::from1(interner, gb.db().hidden_opaque_type(opaque_ty_id));
let bounds = bound.bounds.clone().substitute(interner, &subst);
let where_clauses = bound.where_clauses.clone().substitute(interner, &subst);
let clauses = where_clauses
.iter()
.cloned()
.map(|wc| wc.into_from_env_goal(interner));
// if (WellFormed(T: Bar))
gb.implies(clauses, |gb| {
let interner = gb.interner();
// all(WellFormed(Baz: Clone))
gb.all(
bounds
.iter()
.cloned()
.map(|b| b.into_well_formed_goal(interner)),
)
})
});
debug!("WF opaque type goal: {:#?}", goal);
let mut new_solver = (self.solver_builder)();
let is_legal = new_solver.has_unique_solution(self.db, &goal.into_closed_goal(interner));
if is_legal {
Ok(())
} else {
Err(WfError::IllFormedOpaqueTypeDecl(opaque_ty_id))
}
}
/// Verify builtin rules for well-known traits
pub fn verify_well_known_impl(
&self,
impl_id: ImplId<I>,
well_known: WellKnownTrait,
) -> Result<(), WfError<I>> {
let mut solver = (self.solver_builder)();
let impl_datum = self.db.impl_datum(impl_id);
let is_legal = match well_known {
WellKnownTrait::Copy => {
WfWellKnownConstraints::copy_impl_constraint(&mut *solver, self.db, &impl_datum)
}
WellKnownTrait::Drop => {
WfWellKnownConstraints::drop_impl_constraint(&mut *solver, self.db, &impl_datum)
}
WellKnownTrait::CoerceUnsized => {
WfWellKnownConstraints::coerce_unsized_impl_constraint(
&mut *solver,
self.db,
&impl_datum,
)
}
WellKnownTrait::DispatchFromDyn => {
WfWellKnownConstraints::dispatch_from_dyn_constraint(
&mut *solver,
self.db,
&impl_datum,
)
}
WellKnownTrait::Clone | WellKnownTrait::Unpin => true,
// You can't add a manual implementation for the following traits:
WellKnownTrait::Fn
| WellKnownTrait::FnOnce
| WellKnownTrait::FnMut
| WellKnownTrait::Unsize
| WellKnownTrait::Sized
| WellKnownTrait::DiscriminantKind
| WellKnownTrait::Coroutine
| WellKnownTrait::Pointee
| WellKnownTrait::Tuple
| WellKnownTrait::FnPtr => false,
};
if is_legal {
Ok(())
} else {
Err(WfError::IllFormedTraitImpl(impl_datum.trait_id()))
}
}
}
fn impl_header_wf_goal<I: Interner>(
db: &dyn RustIrDatabase<I>,
impl_id: ImplId<I>,
) -> Option<Goal<I>> {
let impl_datum = db.impl_datum(impl_id);
if !impl_datum.is_positive() {
return None;
}
let impl_fields = impl_datum
.binders
.map_ref(|v| (&v.trait_ref, &v.where_clauses));
let mut gb = GoalBuilder::new(db);
// forall<P0...Pn> {...}
let well_formed_goal = gb.forall(&impl_fields, (), |gb, _, (trait_ref, where_clauses), ()| {
let interner = gb.interner();
// if (WC && input types are well formed) { ... }
gb.implies(
impl_wf_environment(interner, where_clauses, trait_ref),
|gb| {
// We retrieve all the input types of the where clauses appearing on the trait impl,
// e.g. in:
// ```
// impl<T, K> Foo for (T, K) where T: Iterator<Item = (HashSet<K>, Vec<Box<T>>)> { ... }
// ```
// we would retrieve `HashSet<K>`, `Box<T>`, `Vec<Box<T>>`, `(HashSet<K>, Vec<Box<T>>)`.
// We will have to prove that these types are well-formed (e.g. an additional `K: Hash`
// bound would be needed here).
let types = InputTypeCollector::types_in(gb.interner(), &where_clauses);
// Things to prove well-formed: input types of the where-clauses, projection types
// appearing in the header, associated type values, and of course the trait ref.
debug!(input_types=?types);
let goals = types
.into_iter()
.map(|ty| ty.well_formed().cast(interner))
.chain(Some((*trait_ref).clone().well_formed().cast(interner)));
gb.all::<_, Goal<I>>(goals)
},
)
});
Some(well_formed_goal)
}
/// Creates the conditions that an impl (and its contents of an impl)
/// can assume to be true when proving that it is well-formed.
fn impl_wf_environment<'i, I: Interner>(
interner: I,
where_clauses: &'i [QuantifiedWhereClause<I>],
trait_ref: &'i TraitRef<I>,
) -> impl Iterator<Item = ProgramClause<I>> + 'i {
// if (WC) { ... }
let wc = where_clauses
.iter()
.cloned()
.map(move |qwc| qwc.into_from_env_goal(interner).cast(interner));
// We retrieve all the input types of the type on which we implement the trait: we will
// *assume* that these types are well-formed, e.g. we will be able to derive that
// `K: Hash` holds without writing any where clause.
//
// Example:
// ```
// struct HashSet<K> where K: Hash { ... }
//
// impl<K> Foo for HashSet<K> {
// // Inside here, we can rely on the fact that `K: Hash` holds
// }
// ```
let types = InputTypeCollector::types_in(interner, trait_ref);
let types_wf = types
.into_iter()
.map(move |ty| ty.into_from_env_goal(interner).cast(interner));
wc.chain(types_wf)
}
/// Associated type values are special because they can be parametric (independently of
/// the impl), so we issue a special goal which is quantified using the binders of the
/// associated type value, for example in:
///
/// ```ignore
/// trait Foo {
/// type Item<'a>: Clone where Self: 'a
/// }
///
/// impl<T> Foo for Box<T> {
/// type Item<'a> = Box<&'a T>;
/// }
/// ```
///
/// we would issue the following subgoal: `forall<'a> { WellFormed(Box<&'a T>) }`.
///
/// Note that there is no binder for `T` in the above: the goal we
/// generate is expected to be exected in the context of the
/// larger WF goal for the impl, which already has such a
/// binder. So the entire goal for the impl might be:
///
/// ```ignore
/// forall<T> {
/// WellFormed(Box<T>) /* this comes from the impl, not this routine */,
/// forall<'a> { WellFormed(Box<&'a T>) },
/// }
/// ```
fn compute_assoc_ty_goal<I: Interner>(
db: &dyn RustIrDatabase<I>,
assoc_ty_id: AssociatedTyValueId<I>,
) -> Option<Goal<I>> {
let mut gb = GoalBuilder::new(db);
let assoc_ty = &db.associated_ty_value(assoc_ty_id);
// Create `forall<T, 'a> { .. }`
Some(gb.forall(
&assoc_ty.value.map_ref(|v| &v.ty),
assoc_ty_id,
|gb, assoc_ty_substitution, value_ty, assoc_ty_id| {
let interner = gb.interner();
let db = gb.db();
// Hmm, because `Arc<AssociatedTyValue>` does not implement `TypeFoldable`, we can't pass this value through,
// just the id, so we have to fetch `assoc_ty` from the database again.
// Implementing `TypeFoldable` for `AssociatedTyValue` doesn't *quite* seem right though, as that
// would result in a deep clone, and the value is inert. We could do some more refatoring
// (move the `Arc` behind a newtype, for example) to fix this, but for now doesn't
// seem worth it.
let assoc_ty = &db.associated_ty_value(assoc_ty_id);
let (impl_parameters, projection) = db
.impl_parameters_and_projection_from_associated_ty_value(
assoc_ty_substitution.as_slice(interner),
assoc_ty,
);
// If (/* impl WF environment */) { ... }
let impl_id = assoc_ty.impl_id;
let impl_datum = &db.impl_datum(impl_id);
let ImplDatumBound {
trait_ref: impl_trait_ref,
where_clauses: impl_where_clauses,
} = impl_datum
.binders
.clone()
.substitute(interner, impl_parameters);
let impl_wf_clauses =
impl_wf_environment(interner, &impl_where_clauses, &impl_trait_ref);
gb.implies(impl_wf_clauses, |gb| {
// Get the bounds and where clauses from the trait
// declaration, substituted appropriately.
//
// From our example:
//
// * bounds
// * original in trait, `Clone`
// * after substituting impl parameters, `Clone`
// * note that the self-type is not yet supplied for bounds,
// we will do that later
// * where clauses
// * original in trait, `Self: 'a`
// * after substituting impl parameters, `Box<!T>: '!a`
let assoc_ty_datum = db.associated_ty_data(projection.associated_ty_id);
let AssociatedTyDatumBound {
bounds: defn_bounds,
where_clauses: defn_where_clauses,
} = assoc_ty_datum
.binders
.clone()
.substitute(interner, &projection.substitution);
// Create `if (/* where clauses on associated type value */) { .. }`
gb.implies(
defn_where_clauses
.iter()
.cloned()
.map(|qwc| qwc.into_from_env_goal(interner)),
|gb| {
let types = InputTypeCollector::types_in(gb.interner(), value_ty);
// We require that `WellFormed(T)` for each type that appears in the value
let wf_goals = types
.into_iter()
.map(|ty| ty.well_formed())
.casted(interner);
// Check that the `value_ty` meets the bounds from the trait.
// Here we take the substituted bounds (`defn_bounds`) and we
// supply the self-type `value_ty` to yield the final result.
//
// In our example, the bound was `Clone`, so the combined
// result is `Box<!T>: Clone`. This is then converted to a
// well-formed goal like `WellFormed(Box<!T>: Clone)`.
let bound_goals = defn_bounds
.iter()
.cloned()
.flat_map(|qb| qb.into_where_clauses(interner, (*value_ty).clone()))
.map(|qwc| qwc.into_well_formed_goal(interner))
.casted(interner);
// Concatenate the WF goals of inner types + the requirements from trait
gb.all::<_, Goal<I>>(wf_goals.chain(bound_goals))
},
)
})
},
))
}
/// Defines methods to compute well-formedness goals for well-known
/// traits (e.g. a goal for all fields of struct in a Copy impl to be Copy)
struct WfWellKnownConstraints;
impl WfWellKnownConstraints {
/// Computes a goal to prove Sized constraints on a struct definition.
/// Struct is considered well-formed (in terms of Sized) when it either
/// has no fields or all of it's fields except the last are proven to be Sized.
pub fn struct_sized_constraint<I: Interner>(
db: &dyn RustIrDatabase<I>,
fields: &[Ty<I>],
size_all: bool,
) -> Option<Goal<I>> {
let excluded = if size_all { 0 } else { 1 };
if fields.len() <= excluded {
return None;
}
let interner = db.interner();
let sized_trait = db.well_known_trait_id(WellKnownTrait::Sized)?;
Some(Goal::all(
interner,
fields[..fields.len() - excluded].iter().map(|ty| {
TraitRef {
trait_id: sized_trait,
substitution: Substitution::from1(interner, ty.clone()),
}
.cast(interner)
}),
))
}
/// Verify constraints on a Copy implementation.
/// Copy impl is considered well-formed for
/// a) certain builtin types (scalar values, shared ref, etc..)
/// b) adts which
/// 1) have all Copy fields
/// 2) don't have a Drop impl
fn copy_impl_constraint<I: Interner>(
solver: &mut dyn Solver<I>,
db: &dyn RustIrDatabase<I>,
impl_datum: &ImplDatum<I>,
) -> bool {
let interner = db.interner();
let mut gb = GoalBuilder::new(db);
let impl_fields = impl_datum
.binders
.map_ref(|v| (&v.trait_ref, &v.where_clauses));
// Implementations for scalars, pointer types and never type are provided by libcore.
// User implementations on types other than ADTs are forbidden.
match impl_datum
.binders
.skip_binders()
.trait_ref
.self_type_parameter(interner)
.kind(interner)
{
TyKind::Scalar(_)
| TyKind::Raw(_, _)
| TyKind::Ref(Mutability::Not, _, _)
| TyKind::Never => return true,
TyKind::Adt(_, _) => (),
_ => return false,
};
// Well fomedness goal for ADTs
let well_formed_goal =
gb.forall(&impl_fields, (), |gb, _, (trait_ref, where_clauses), ()| {
let interner = gb.interner();
let ty = trait_ref.self_type_parameter(interner);
let (adt_id, substitution) = match ty.kind(interner) {
TyKind::Adt(adt_id, substitution) => (*adt_id, substitution),
_ => unreachable!(),
};
// if (WC) { ... }
gb.implies(
impl_wf_environment(interner, where_clauses, trait_ref),
|gb| -> Goal<I> {
let db = gb.db();
// not { Implemented(ImplSelfTy: Drop) }
let neg_drop_goal =
db.well_known_trait_id(WellKnownTrait::Drop)
.map(|drop_trait_id| {
TraitRef {
trait_id: drop_trait_id,
substitution: Substitution::from1(interner, ty.clone()),
}
.cast::<Goal<I>>(interner)
.negate(interner)
});
let adt_datum = db.adt_datum(adt_id);
let goals = adt_datum
.binders
.map_ref(|b| &b.variants)
.cloned()
.substitute(interner, substitution)
.into_iter()
.flat_map(|v| {
v.fields.into_iter().map(|f| {
// Implemented(FieldTy: Copy)
TraitRef {
trait_id: trait_ref.trait_id,
substitution: Substitution::from1(interner, f),
}
.cast(interner)
})
})
.chain(neg_drop_goal.into_iter());
gb.all(goals)
},
)
});
solver.has_unique_solution(db, &well_formed_goal.into_closed_goal(interner))
}
/// Verifies constraints on a Drop implementation
/// Drop implementation is considered well-formed if:
/// a) it's implemented on an ADT
/// b) The generic parameters of the impl's type must all be parameters
/// of the Drop impl itself (i.e., no specialization like
/// `impl Drop for S<Foo> {...}` is allowed).
/// c) Any bounds on the genereic parameters of the impl must be
/// deductible from the bounds imposed by the struct definition
/// (i.e. the implementation must be exactly as generic as the ADT definition).
///
/// ```rust,ignore
/// struct S<T1, T2> { }
/// struct Foo<T> { }
///
/// impl<U1: Copy, U2: Sized> Drop for S<U2, Foo<U1>> { }
/// ```
///
/// generates the following:
/// goal derived from c):
///
/// ```notrust
/// forall<U1, U2> {
/// Implemented(U1: Copy), Implemented(U2: Sized) :- FromEnv(S<U2, Foo<U1>>)
/// }
/// ```
///
/// goal derived from b):
/// ```notrust
/// forall <T1, T2> {
/// exists<U1, U2> {
/// S<T1, T2> = S<U2, Foo<U1>>
/// }
/// }
/// ```
fn drop_impl_constraint<I: Interner>(
solver: &mut dyn Solver<I>,
db: &dyn RustIrDatabase<I>,
impl_datum: &ImplDatum<I>,
) -> bool {
let interner = db.interner();
let adt_id = match impl_datum.self_type_adt_id(interner) {
Some(id) => id,
// Drop can only be implemented on a nominal type
None => return false,
};
let mut gb = GoalBuilder::new(db);
let adt_datum = db.adt_datum(adt_id);
let impl_fields = impl_datum
.binders
.map_ref(|v| (&v.trait_ref, &v.where_clauses));
// forall<ImplP1...ImplPn> { .. }
let implied_by_adt_def_goal =
gb.forall(&impl_fields, (), |gb, _, (trait_ref, where_clauses), ()| {
let interner = gb.interner();
// FromEnv(ImplSelfType) => ...
gb.implies(
iter::once(
FromEnv::Ty(trait_ref.self_type_parameter(interner))
.cast::<DomainGoal<I>>(interner),
),
|gb| {
// All(ImplWhereClauses)
gb.all(
where_clauses
.iter()
.map(|wc| wc.clone().into_well_formed_goal(interner)),
)
},
)
});
let impl_self_ty = impl_datum
.binders
.map_ref(|b| b.trait_ref.self_type_parameter(interner));
// forall<StructP1..StructPN> {...}
let eq_goal = gb.forall(
&adt_datum.binders,
(adt_id, impl_self_ty),
|gb, substitution, _, (adt_id, impl_self_ty)| {
let interner = gb.interner();
let def_adt = TyKind::Adt(adt_id, substitution).intern(interner);
// exists<ImplP1...ImplPn> { .. }
gb.exists(&impl_self_ty, def_adt, |gb, _, impl_adt, def_adt| {
let interner = gb.interner();
// StructName<StructP1..StructPn> = ImplSelfType
GoalData::EqGoal(EqGoal {
a: GenericArgData::Ty(def_adt).intern(interner),
b: GenericArgData::Ty(impl_adt.clone()).intern(interner),
})
.intern(interner)
})
},
);
let well_formed_goal = gb.all([implied_by_adt_def_goal, eq_goal].iter());
solver.has_unique_solution(db, &well_formed_goal.into_closed_goal(interner))
}
/// Verify constraints a CoerceUnsized impl.
/// Rules for CoerceUnsized impl to be considered well-formed:
/// 1) pointer conversions: `&[mut] T -> &[mut] U`, `&[mut] T -> *[mut] U`,
/// `*[mut] T -> *[mut] U` are considered valid if
/// 1) `T: Unsize<U>`
/// 2) mutability is respected, i.e. immutable -> immutable, mutable -> immutable,
/// mutable -> mutable conversions are allowed, immutable -> mutable is not.
/// 2) struct conversions of structures with the same definition, `S<P0...Pn>` -> `S<Q0...Qn>`.
/// To check if this impl is legal, we would walk down the fields of `S`
/// and consider their types with both substitutes. We are looking to find
/// exactly one (non-phantom) field that has changed its type (from `T` to `U`), and
/// expect `T` to be unsizeable to `U`, i.e. `T: CoerceUnsized<U>`.
///
/// As an example, consider a struct
/// ```rust
/// struct Foo<T, U> {
/// extra: T,
/// ptr: *mut U,
/// }
/// ```
///
/// We might have an impl that allows (e.g.) `Foo<T, [i32; 3]>` to be unsized
/// to `Foo<T, [i32]>`. That impl would look like:
/// ```rust,ignore
/// impl<T, U: Unsize<V>, V> CoerceUnsized<Foo<T, V>> for Foo<T, U> {}
/// ```
/// In this case:
///
/// - `extra` has type `T` before and type `T` after
/// - `ptr` has type `*mut U` before and type `*mut V` after
///
/// Since just one field changed, we would then check that `*mut U: CoerceUnsized<*mut V>`
/// is implemented. This will work out because `U: Unsize<V>`, and we have a libcore rule
/// that `*mut U` can be coerced to `*mut V` if `U: Unsize<V>`.
fn coerce_unsized_impl_constraint<I: Interner>(
solver: &mut dyn Solver<I>,
db: &dyn RustIrDatabase<I>,
impl_datum: &ImplDatum<I>,
) -> bool {
let interner = db.interner();
let mut gb = GoalBuilder::new(db);
let (binders, impl_datum) = impl_datum.binders.as_ref().into();
let trait_ref: &TraitRef<I> = &impl_datum.trait_ref;
let source = trait_ref.self_type_parameter(interner);
let target = trait_ref
.substitution
.at(interner, 1)
.assert_ty_ref(interner)
.clone();
let mut place_in_environment = |goal| -> Goal<I> {
gb.forall(
&Binders::new(
binders.clone(),
(goal, trait_ref, &impl_datum.where_clauses),
),
(),
|gb, _, (goal, trait_ref, where_clauses), ()| {
let interner = gb.interner();
gb.implies(
impl_wf_environment(interner, where_clauses, trait_ref),
|_| goal,
)
},
)
};
match (source.kind(interner), target.kind(interner)) {
(TyKind::Ref(s_m, _, source), TyKind::Ref(t_m, _, target))
| (TyKind::Ref(s_m, _, source), TyKind::Raw(t_m, target))
| (TyKind::Raw(s_m, source), TyKind::Raw(t_m, target)) => {
if (*s_m, *t_m) == (Mutability::Not, Mutability::Mut) {
return false;
}
let unsize_trait_id =
if let Some(id) = db.well_known_trait_id(WellKnownTrait::Unsize) {
id
} else {
return false;
};
// Source: Unsize<Target>
let unsize_goal: Goal<I> = TraitRef {
trait_id: unsize_trait_id,
substitution: Substitution::from_iter(
interner,
[source.clone(), target.clone()].iter().cloned(),
),
}
.cast(interner);
// ImplEnv -> Source: Unsize<Target>
let unsize_goal = place_in_environment(unsize_goal);
solver.has_unique_solution(db, &unsize_goal.into_closed_goal(interner))
}
(TyKind::Adt(source_id, subst_a), TyKind::Adt(target_id, subst_b)) => {
let adt_datum = db.adt_datum(*source_id);
if source_id != target_id || adt_datum.kind != AdtKind::Struct {
return false;
}
let fields = adt_datum
.binders
.map_ref(|bound| &bound.variants.last().unwrap().fields)
.cloned();
let (source_fields, target_fields) = (
fields.clone().substitute(interner, subst_a),
fields.substitute(interner, subst_b),
);
// collect fields with unequal ids
let uneq_field_ids: Vec<usize> = (0..source_fields.len())
.filter(|&i| {
// ignore phantom data fields
if let Some(adt_id) = source_fields[i].adt_id(interner) {
if db.adt_datum(adt_id).flags.phantom_data {
return false;
}
}
let eq_goal: Goal<I> = EqGoal {
a: source_fields[i].clone().cast(interner),
b: target_fields[i].clone().cast(interner),
}
.cast(interner);
// ImplEnv -> Source.fields[i] = Target.fields[i]
let eq_goal = place_in_environment(eq_goal);
// We are interested in !UNEQUAL! fields
!solver.has_unique_solution(db, &eq_goal.into_closed_goal(interner))
})
.collect();
if uneq_field_ids.len() != 1 {
return false;
}
let field_id = uneq_field_ids[0];
// Source.fields[i]: CoerceUnsized<TargetFields[i]>
let coerce_unsized_goal: Goal<I> = TraitRef {
trait_id: trait_ref.trait_id,
substitution: Substitution::from_iter(
interner,
[
source_fields[field_id].clone(),
target_fields[field_id].clone(),
]
.iter()
.cloned(),
),
}
.cast(interner);
// ImplEnv -> Source.fields[i]: CoerceUnsized<TargetFields[i]>
let coerce_unsized_goal = place_in_environment(coerce_unsized_goal);
solver.has_unique_solution(db, &coerce_unsized_goal.into_closed_goal(interner))
}
_ => false,
}
}
/// Verify constraints of a DispatchFromDyn impl.
///
/// Rules for DispatchFromDyn impl to be considered well-formed:
///
/// * Self and the type parameter must both be references or raw pointers with the same mutabilty
/// * OR all the following hold:
/// - Self and the type parameter must be structs
/// - Self and the type parameter must have the same definitions
/// - Self must not be `#[repr(packed)]` or `#[repr(C)]`
/// - Self must have exactly one field which is not a 1-ZST (there may be any number of 1-ZST
/// fields), and that field must have a different type in the type parameter (i.e., it is
/// the field being coerced)
/// - `DispatchFromDyn` is implemented for the type of the field being coerced.
fn dispatch_from_dyn_constraint<I: Interner>(
solver: &mut dyn Solver<I>,
db: &dyn RustIrDatabase<I>,
impl_datum: &ImplDatum<I>,
) -> bool {
let interner = db.interner();
let mut gb = GoalBuilder::new(db);
let (binders, impl_datum) = impl_datum.binders.as_ref().into();
let trait_ref: &TraitRef<I> = &impl_datum.trait_ref;
// DispatchFromDyn specifies that Self (source) can be coerced to T (target; its single type parameter).
let source = trait_ref.self_type_parameter(interner);
let target = trait_ref
.substitution
.at(interner, 1)
.assert_ty_ref(interner)
.clone();
let mut place_in_environment = |goal| -> Goal<I> {
gb.forall(
&Binders::new(
binders.clone(),
(goal, trait_ref, &impl_datum.where_clauses),
),
(),
|gb, _, (goal, trait_ref, where_clauses), ()| {
let interner = gb.interner();
gb.implies(
impl_wf_environment(interner, &where_clauses, &trait_ref),
|_| goal,
)
},
)
};
match (source.kind(interner), target.kind(interner)) {
(TyKind::Ref(s_m, _, _), TyKind::Ref(t_m, _, _))
| (TyKind::Raw(s_m, _), TyKind::Raw(t_m, _))
if s_m == t_m =>
{
true
}
(TyKind::Adt(source_id, subst_a), TyKind::Adt(target_id, subst_b)) => {
let adt_datum = db.adt_datum(*source_id);
// Definitions are equal and are structs.
if source_id != target_id || adt_datum.kind != AdtKind::Struct {
return false;
}
// Not repr(C) or repr(packed).
let repr = db.adt_repr(*source_id);
if repr.c || repr.packed {
return false;
}
// Collect non 1-ZST fields; there must be exactly one.
let fields = adt_datum
.binders
.map_ref(|bound| &bound.variants.last().unwrap().fields)
.cloned();
let (source_fields, target_fields) = (
fields.clone().substitute(interner, subst_a),
fields.substitute(interner, subst_b),
);
let mut non_zst_fields: Vec<_> = source_fields
.iter()
.zip(target_fields.iter())
.filter(|(sf, _)| match sf.adt_id(interner) {
Some(adt) => !db.adt_size_align(adt).one_zst(),
None => true,
})
.collect();
if non_zst_fields.len() != 1 {
return false;
}
// The field being coerced (the interesting field).
let (field_src, field_tgt) = non_zst_fields.pop().unwrap();
// The interesting field is different in the source and target types.
let eq_goal: Goal<I> = EqGoal {
a: field_src.clone().cast(interner),
b: field_tgt.clone().cast(interner),
}
.cast(interner);
let eq_goal = place_in_environment(eq_goal);
if solver.has_unique_solution(db, &eq_goal.into_closed_goal(interner)) {
return false;
}
// Type(field_src): DispatchFromDyn<Type(field_tgt)>
let field_dispatch_goal: Goal<I> = TraitRef {
trait_id: trait_ref.trait_id,
substitution: Substitution::from_iter(
interner,
[field_src.clone(), field_tgt.clone()].iter().cloned(),
),
}
.cast(interner);
let field_dispatch_goal = place_in_environment(field_dispatch_goal);
if !solver.has_unique_solution(db, &field_dispatch_goal.into_closed_goal(interner))
{
return false;
}
true
}
_ => false,
}
}
}