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use crate::astconv::{AstConv, OnlySelfBounds, PredicateFilter};
use crate::bounds::Bounds;
use crate::collect::ItemCtxt;
use crate::constrained_generic_params as cgp;
use hir::{HirId, Node};
use rustc_data_structures::fx::FxIndexSet;
use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::intravisit::{self, Visitor};
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_middle::ty::{GenericPredicates, ImplTraitInTraitData, ToPredicate};
use rustc_span::symbol::Ident;
use rustc_span::{Span, DUMMY_SP};
/// Returns a list of all type predicates (explicit and implicit) for the definition with
/// ID `def_id`. This includes all predicates returned by `predicates_defined_on`, plus
/// `Self: Trait` predicates for traits.
pub(super) fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
let mut result = tcx.predicates_defined_on(def_id);
if tcx.is_trait(def_id) {
// For traits, add `Self: Trait` predicate. This is
// not part of the predicates that a user writes, but it
// is something that one must prove in order to invoke a
// method or project an associated type.
//
// In the chalk setup, this predicate is not part of the
// "predicates" for a trait item. But it is useful in
// rustc because if you directly (e.g.) invoke a trait
// method like `Trait::method(...)`, you must naturally
// prove that the trait applies to the types that were
// used, and adding the predicate into this list ensures
// that this is done.
//
// We use a DUMMY_SP here as a way to signal trait bounds that come
// from the trait itself that *shouldn't* be shown as the source of
// an obligation and instead be skipped. Otherwise we'd use
// `tcx.def_span(def_id);`
let span = rustc_span::DUMMY_SP;
result.predicates =
tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(std::iter::once((
ty::TraitRef::identity(tcx, def_id).to_predicate(tcx),
span,
))));
}
debug!("predicates_of(def_id={:?}) = {:?}", def_id, result);
result
}
/// Returns a list of user-specified type predicates for the definition with ID `def_id`.
/// N.B., this does not include any implied/inferred constraints.
#[instrument(level = "trace", skip(tcx), ret)]
fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::GenericPredicates<'_> {
use rustc_hir::*;
match tcx.opt_rpitit_info(def_id.to_def_id()) {
Some(ImplTraitInTraitData::Trait { fn_def_id, .. }) => {
let mut predicates = Vec::new();
// RPITITs should inherit the predicates of their parent. This is
// both to ensure that the RPITITs are only instantiated when the
// parent predicates would hold, and also so that the param-env
// inherits these predicates as assumptions.
let identity_args = ty::GenericArgs::identity_for_item(tcx, def_id);
predicates
.extend(tcx.explicit_predicates_of(fn_def_id).instantiate_own(tcx, identity_args));
// We also install bidirectional outlives predicates for the RPITIT
// to keep the duplicates lifetimes from opaque lowering in sync.
// We only need to compute bidirectional outlives for the duplicated
// opaque lifetimes, which explains the slicing below.
compute_bidirectional_outlives_predicates(
tcx,
&tcx.generics_of(def_id.to_def_id()).params
[tcx.generics_of(fn_def_id).params.len()..],
&mut predicates,
);
return ty::GenericPredicates {
parent: Some(tcx.parent(def_id.to_def_id())),
predicates: tcx.arena.alloc_from_iter(predicates),
};
}
Some(ImplTraitInTraitData::Impl { fn_def_id }) => {
let assoc_item = tcx.associated_item(def_id);
let trait_assoc_predicates =
tcx.explicit_predicates_of(assoc_item.trait_item_def_id.unwrap());
let impl_assoc_identity_args = ty::GenericArgs::identity_for_item(tcx, def_id);
let impl_def_id = tcx.parent(fn_def_id);
let impl_trait_ref_args =
tcx.impl_trait_ref(impl_def_id).unwrap().instantiate_identity().args;
let impl_assoc_args =
impl_assoc_identity_args.rebase_onto(tcx, impl_def_id, impl_trait_ref_args);
let impl_predicates = trait_assoc_predicates.instantiate_own(tcx, impl_assoc_args);
return ty::GenericPredicates {
parent: Some(impl_def_id),
predicates: tcx.arena.alloc_from_iter(impl_predicates),
};
}
None => {}
}
let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
let node = tcx.hir().get(hir_id);
let mut is_trait = None;
let mut is_default_impl_trait = None;
// FIXME: Should ItemCtxt take a LocalDefId?
let icx = ItemCtxt::new(tcx, def_id);
const NO_GENERICS: &hir::Generics<'_> = hir::Generics::empty();
// We use an `IndexSet` to preserve order of insertion.
// Preserving the order of insertion is important here so as not to break UI tests.
let mut predicates: FxIndexSet<(ty::Clause<'_>, Span)> = FxIndexSet::default();
let ast_generics = match node {
Node::TraitItem(item) => item.generics,
Node::ImplItem(item) => item.generics,
Node::Item(item) => match item.kind {
ItemKind::Impl(impl_) => {
if impl_.defaultness.is_default() {
is_default_impl_trait = tcx
.impl_trait_ref(def_id)
.map(|t| ty::Binder::dummy(t.instantiate_identity()));
}
impl_.generics
}
ItemKind::Fn(.., generics, _)
| ItemKind::TyAlias(_, generics)
| ItemKind::Const(_, generics, _)
| ItemKind::Enum(_, generics)
| ItemKind::Struct(_, generics)
| ItemKind::Union(_, generics) => generics,
ItemKind::Trait(_, _, generics, self_bounds, ..)
| ItemKind::TraitAlias(generics, self_bounds) => {
is_trait = Some(self_bounds);
generics
}
ItemKind::OpaqueTy(OpaqueTy { generics, .. }) => generics,
_ => NO_GENERICS,
},
Node::ForeignItem(item) => match item.kind {
ForeignItemKind::Static(..) => NO_GENERICS,
ForeignItemKind::Fn(_, _, generics) => generics,
ForeignItemKind::Type => NO_GENERICS,
},
_ => NO_GENERICS,
};
let generics = tcx.generics_of(def_id);
// Below we'll consider the bounds on the type parameters (including `Self`)
// and the explicit where-clauses, but to get the full set of predicates
// on a trait we must also consider the bounds that follow the trait's name,
// like `trait Foo: A + B + C`.
if let Some(self_bounds) = is_trait {
predicates.extend(
icx.astconv()
.compute_bounds(tcx.types.self_param, self_bounds, PredicateFilter::All)
.clauses(),
);
}
// In default impls, we can assume that the self type implements
// the trait. So in:
//
// default impl Foo for Bar { .. }
//
// we add a default where clause `Foo: Bar`. We do a similar thing for traits
// (see below). Recall that a default impl is not itself an impl, but rather a
// set of defaults that can be incorporated into another impl.
if let Some(trait_ref) = is_default_impl_trait {
predicates.insert((trait_ref.to_predicate(tcx), tcx.def_span(def_id)));
}
// Collect the predicates that were written inline by the user on each
// type parameter (e.g., `<T: Foo>`). Also add `ConstArgHasType` predicates
// for each const parameter.
for param in ast_generics.params {
match param.kind {
// We already dealt with early bound lifetimes above.
GenericParamKind::Lifetime { .. } => (),
GenericParamKind::Type { .. } => {
let param_ty = icx.astconv().hir_id_to_bound_ty(param.hir_id);
let mut bounds = Bounds::default();
// Params are implicitly sized unless a `?Sized` bound is found
icx.astconv().add_implicitly_sized(
&mut bounds,
param_ty,
&[],
Some((param.def_id, ast_generics.predicates)),
param.span,
);
trace!(?bounds);
predicates.extend(bounds.clauses());
trace!(?predicates);
}
hir::GenericParamKind::Const { .. } => {
let ct_ty = tcx
.type_of(param.def_id.to_def_id())
.no_bound_vars()
.expect("const parameters cannot be generic");
let ct = icx.astconv().hir_id_to_bound_const(param.hir_id, ct_ty);
predicates.insert((
ty::ClauseKind::ConstArgHasType(ct, ct_ty).to_predicate(tcx),
param.span,
));
}
}
}
trace!(?predicates);
// Add in the bounds that appear in the where-clause.
for predicate in ast_generics.predicates {
match predicate {
hir::WherePredicate::BoundPredicate(bound_pred) => {
let ty = icx.to_ty(bound_pred.bounded_ty);
let bound_vars = tcx.late_bound_vars(bound_pred.hir_id);
// Keep the type around in a dummy predicate, in case of no bounds.
// That way, `where Ty:` is not a complete noop (see #53696) and `Ty`
// is still checked for WF.
if bound_pred.bounds.is_empty() {
if let ty::Param(_) = ty.kind() {
// This is a `where T:`, which can be in the HIR from the
// transformation that moves `?Sized` to `T`'s declaration.
// We can skip the predicate because type parameters are
// trivially WF, but also we *should*, to avoid exposing
// users who never wrote `where Type:,` themselves, to
// compiler/tooling bugs from not handling WF predicates.
} else {
let span = bound_pred.bounded_ty.span;
let predicate = ty::Binder::bind_with_vars(
ty::ClauseKind::WellFormed(ty.into()),
bound_vars,
);
predicates.insert((predicate.to_predicate(tcx), span));
}
}
let mut bounds = Bounds::default();
icx.astconv().add_bounds(
ty,
bound_pred.bounds.iter(),
&mut bounds,
bound_vars,
OnlySelfBounds(false),
);
predicates.extend(bounds.clauses());
}
hir::WherePredicate::RegionPredicate(region_pred) => {
let r1 = icx.astconv().ast_region_to_region(®ion_pred.lifetime, None);
predicates.extend(region_pred.bounds.iter().map(|bound| {
let (r2, span) = match bound {
hir::GenericBound::Outlives(lt) => {
(icx.astconv().ast_region_to_region(lt, None), lt.ident.span)
}
_ => bug!(),
};
let pred = ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(r1, r2))
.to_predicate(tcx);
(pred, span)
}))
}
hir::WherePredicate::EqPredicate(..) => {
// FIXME(#20041)
}
}
}
if tcx.features().generic_const_exprs {
predicates.extend(const_evaluatable_predicates_of(tcx, def_id));
}
let mut predicates: Vec<_> = predicates.into_iter().collect();
// Subtle: before we store the predicates into the tcx, we
// sort them so that predicates like `T: Foo<Item=U>` come
// before uses of `U`. This avoids false ambiguity errors
// in trait checking. See `setup_constraining_predicates`
// for details.
if let Node::Item(&Item { kind: ItemKind::Impl { .. }, .. }) = node {
let self_ty = tcx.type_of(def_id).instantiate_identity();
let trait_ref = tcx.impl_trait_ref(def_id).map(ty::EarlyBinder::instantiate_identity);
cgp::setup_constraining_predicates(
tcx,
&mut predicates,
trait_ref,
&mut cgp::parameters_for_impl(self_ty, trait_ref),
);
}
// Opaque types duplicate some of their generic parameters.
// We create bi-directional Outlives predicates between the original
// and the duplicated parameter, to ensure that they do not get out of sync.
if let Node::Item(&Item { kind: ItemKind::OpaqueTy(..), .. }) = node {
let opaque_ty_id = tcx.hir().parent_id(hir_id);
let opaque_ty_node = tcx.hir().get(opaque_ty_id);
let Node::Ty(&Ty { kind: TyKind::OpaqueDef(_, lifetimes, _), .. }) = opaque_ty_node else {
bug!("unexpected {opaque_ty_node:?}")
};
debug!(?lifetimes);
compute_bidirectional_outlives_predicates(tcx, &generics.params, &mut predicates);
debug!(?predicates);
}
ty::GenericPredicates {
parent: generics.parent,
predicates: tcx.arena.alloc_from_iter(predicates),
}
}
/// Opaques have duplicated lifetimes and we need to compute bidirectional outlives predicates to
/// enforce that these lifetimes stay in sync.
fn compute_bidirectional_outlives_predicates<'tcx>(
tcx: TyCtxt<'tcx>,
opaque_own_params: &[ty::GenericParamDef],
predicates: &mut Vec<(ty::Clause<'tcx>, Span)>,
) {
for param in opaque_own_params {
let orig_lifetime = tcx.map_rpit_lifetime_to_fn_lifetime(param.def_id.expect_local());
if let ty::ReEarlyBound(..) = *orig_lifetime {
let dup_lifetime = ty::Region::new_early_bound(
tcx,
ty::EarlyBoundRegion { def_id: param.def_id, index: param.index, name: param.name },
);
let span = tcx.def_span(param.def_id);
predicates.push((
ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(orig_lifetime, dup_lifetime))
.to_predicate(tcx),
span,
));
predicates.push((
ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(dup_lifetime, orig_lifetime))
.to_predicate(tcx),
span,
));
}
}
}
fn const_evaluatable_predicates_of(
tcx: TyCtxt<'_>,
def_id: LocalDefId,
) -> FxIndexSet<(ty::Clause<'_>, Span)> {
struct ConstCollector<'tcx> {
tcx: TyCtxt<'tcx>,
preds: FxIndexSet<(ty::Clause<'tcx>, Span)>,
}
impl<'tcx> intravisit::Visitor<'tcx> for ConstCollector<'tcx> {
fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) {
let ct = ty::Const::from_anon_const(self.tcx, c.def_id);
if let ty::ConstKind::Unevaluated(_) = ct.kind() {
let span = self.tcx.def_span(c.def_id);
self.preds
.insert((ty::ClauseKind::ConstEvaluatable(ct).to_predicate(self.tcx), span));
}
}
fn visit_const_param_default(&mut self, _param: HirId, _ct: &'tcx hir::AnonConst) {
// Do not look into const param defaults,
// these get checked when they are actually instantiated.
//
// We do not want the following to error:
//
// struct Foo<const N: usize, const M: usize = { N + 1 }>;
// struct Bar<const N: usize>(Foo<N, 3>);
}
}
let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
let node = tcx.hir().get(hir_id);
let mut collector = ConstCollector { tcx, preds: FxIndexSet::default() };
if let hir::Node::Item(item) = node && let hir::ItemKind::Impl(impl_) = item.kind {
if let Some(of_trait) = &impl_.of_trait {
debug!("const_evaluatable_predicates_of({:?}): visit impl trait_ref", def_id);
collector.visit_trait_ref(of_trait);
}
debug!("const_evaluatable_predicates_of({:?}): visit_self_ty", def_id);
collector.visit_ty(impl_.self_ty);
}
if let Some(generics) = node.generics() {
debug!("const_evaluatable_predicates_of({:?}): visit_generics", def_id);
collector.visit_generics(generics);
}
if let Some(fn_sig) = tcx.hir().fn_sig_by_hir_id(hir_id) {
debug!("const_evaluatable_predicates_of({:?}): visit_fn_decl", def_id);
collector.visit_fn_decl(fn_sig.decl);
}
debug!("const_evaluatable_predicates_of({:?}) = {:?}", def_id, collector.preds);
collector.preds
}
pub(super) fn trait_explicit_predicates_and_bounds(
tcx: TyCtxt<'_>,
def_id: LocalDefId,
) -> ty::GenericPredicates<'_> {
assert_eq!(tcx.def_kind(def_id), DefKind::Trait);
gather_explicit_predicates_of(tcx, def_id)
}
pub(super) fn explicit_predicates_of<'tcx>(
tcx: TyCtxt<'tcx>,
def_id: LocalDefId,
) -> ty::GenericPredicates<'tcx> {
let def_kind = tcx.def_kind(def_id);
if let DefKind::Trait = def_kind {
// Remove bounds on associated types from the predicates, they will be
// returned by `explicit_item_bounds`.
let predicates_and_bounds = tcx.trait_explicit_predicates_and_bounds(def_id);
let trait_identity_args = ty::GenericArgs::identity_for_item(tcx, def_id);
let is_assoc_item_ty = |ty: Ty<'tcx>| {
// For a predicate from a where clause to become a bound on an
// associated type:
// * It must use the identity args of the item.
// * We're in the scope of the trait, so we can't name any
// parameters of the GAT. That means that all we need to
// check are that the args of the projection are the
// identity args of the trait.
// * It must be an associated type for this trait (*not* a
// supertrait).
if let ty::Alias(ty::Projection, projection) = ty.kind() {
projection.args == trait_identity_args
// FIXME(return_type_notation): This check should be more robust
&& !tcx.is_impl_trait_in_trait(projection.def_id)
&& tcx.associated_item(projection.def_id).container_id(tcx)
== def_id.to_def_id()
} else {
false
}
};
let predicates: Vec<_> = predicates_and_bounds
.predicates
.iter()
.copied()
.filter(|(pred, _)| match pred.kind().skip_binder() {
ty::ClauseKind::Trait(tr) => !is_assoc_item_ty(tr.self_ty()),
ty::ClauseKind::Projection(proj) => !is_assoc_item_ty(proj.projection_ty.self_ty()),
ty::ClauseKind::TypeOutlives(outlives) => !is_assoc_item_ty(outlives.0),
_ => true,
})
.collect();
if predicates.len() == predicates_and_bounds.predicates.len() {
predicates_and_bounds
} else {
ty::GenericPredicates {
parent: predicates_and_bounds.parent,
predicates: tcx.arena.alloc_slice(&predicates),
}
}
} else {
if matches!(def_kind, DefKind::AnonConst) && tcx.features().generic_const_exprs {
let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
let parent_def_id = tcx.hir().get_parent_item(hir_id);
if let Some(defaulted_param_def_id) =
tcx.hir().opt_const_param_default_param_def_id(hir_id)
{
// In `generics_of` we set the generics' parent to be our parent's parent which means that
// we lose out on the predicates of our actual parent if we dont return those predicates here.
// (See comment in `generics_of` for more information on why the parent shenanigans is necessary)
//
// struct Foo<T, const N: usize = { <T as Trait>::ASSOC }>(T) where T: Trait;
// ^^^ ^^^^^^^^^^^^^^^^^^^^^^^ the def id we are calling
// ^^^ explicit_predicates_of on
// parent item we dont have set as the
// parent of generics returned by `generics_of`
//
// In the above code we want the anon const to have predicates in its param env for `T: Trait`
// and we would be calling `explicit_predicates_of(Foo)` here
let parent_preds = tcx.explicit_predicates_of(parent_def_id);
// If we dont filter out `ConstArgHasType` predicates then every single defaulted const parameter
// will ICE because of #106994. FIXME(generic_const_exprs): remove this when a more general solution
// to #106994 is implemented.
let filtered_predicates = parent_preds
.predicates
.into_iter()
.filter(|(pred, _)| {
if let ty::ClauseKind::ConstArgHasType(ct, _) = pred.kind().skip_binder() {
match ct.kind() {
ty::ConstKind::Param(param_const) => {
let defaulted_param_idx = tcx
.generics_of(parent_def_id)
.param_def_id_to_index[&defaulted_param_def_id.to_def_id()];
param_const.index < defaulted_param_idx
}
_ => bug!(
"`ConstArgHasType` in `predicates_of`\
that isn't a `Param` const"
),
}
} else {
true
}
})
.cloned();
return GenericPredicates {
parent: parent_preds.parent,
predicates: { tcx.arena.alloc_from_iter(filtered_predicates) },
};
}
let parent_def_kind = tcx.def_kind(parent_def_id);
if matches!(parent_def_kind, DefKind::OpaqueTy) {
// In `instantiate_identity` we inherit the predicates of our parent.
// However, opaque types do not have a parent (see `gather_explicit_predicates_of`), which means
// that we lose out on the predicates of our actual parent if we dont return those predicates here.
//
//
// fn foo<T: Trait>() -> impl Iterator<Output = Another<{ <T as Trait>::ASSOC }> > { todo!() }
// ^^^^^^^^^^^^^^^^^^^ the def id we are calling
// explicit_predicates_of on
//
// In the above code we want the anon const to have predicates in its param env for `T: Trait`.
// However, the anon const cannot inherit predicates from its parent since it's opaque.
//
// To fix this, we call `explicit_predicates_of` directly on `foo`, the parent's parent.
// In the above example this is `foo::{opaque#0}` or `impl Iterator`
let parent_hir_id = tcx.hir().local_def_id_to_hir_id(parent_def_id.def_id);
// In the above example this is the function `foo`
let item_def_id = tcx.hir().get_parent_item(parent_hir_id);
// In the above code example we would be calling `explicit_predicates_of(foo)` here
return tcx.explicit_predicates_of(item_def_id);
}
}
gather_explicit_predicates_of(tcx, def_id)
}
}
/// Ensures that the super-predicates of the trait with a `DefId`
/// of `trait_def_id` are converted and stored. This also ensures that
/// the transitive super-predicates are converted.
pub(super) fn super_predicates_of(
tcx: TyCtxt<'_>,
trait_def_id: LocalDefId,
) -> ty::GenericPredicates<'_> {
implied_predicates_with_filter(tcx, trait_def_id.to_def_id(), PredicateFilter::SelfOnly)
}
pub(super) fn super_predicates_that_define_assoc_item(
tcx: TyCtxt<'_>,
(trait_def_id, assoc_name): (DefId, Ident),
) -> ty::GenericPredicates<'_> {
implied_predicates_with_filter(tcx, trait_def_id, PredicateFilter::SelfThatDefines(assoc_name))
}
pub(super) fn implied_predicates_of(
tcx: TyCtxt<'_>,
trait_def_id: LocalDefId,
) -> ty::GenericPredicates<'_> {
implied_predicates_with_filter(
tcx,
trait_def_id.to_def_id(),
if tcx.is_trait_alias(trait_def_id.to_def_id()) {
PredicateFilter::All
} else {
PredicateFilter::SelfAndAssociatedTypeBounds
},
)
}
/// Ensures that the super-predicates of the trait with a `DefId`
/// of `trait_def_id` are converted and stored. This also ensures that
/// the transitive super-predicates are converted.
pub(super) fn implied_predicates_with_filter(
tcx: TyCtxt<'_>,
trait_def_id: DefId,
filter: PredicateFilter,
) -> ty::GenericPredicates<'_> {
let Some(trait_def_id) = trait_def_id.as_local() else {
// if `assoc_name` is None, then the query should've been redirected to an
// external provider
assert!(matches!(filter, PredicateFilter::SelfThatDefines(_)));
return tcx.super_predicates_of(trait_def_id);
};
let trait_hir_id = tcx.hir().local_def_id_to_hir_id(trait_def_id);
let Node::Item(item) = tcx.hir().get(trait_hir_id) else {
bug!("trait_node_id {} is not an item", trait_hir_id);
};
let (generics, bounds) = match item.kind {
hir::ItemKind::Trait(.., generics, supertraits, _) => (generics, supertraits),
hir::ItemKind::TraitAlias(generics, supertraits) => (generics, supertraits),
_ => span_bug!(item.span, "super_predicates invoked on non-trait"),
};
let icx = ItemCtxt::new(tcx, trait_def_id);
let self_param_ty = tcx.types.self_param;
let superbounds = icx.astconv().compute_bounds(self_param_ty, bounds, filter);
let where_bounds_that_match = icx.type_parameter_bounds_in_generics(
generics,
item.owner_id.def_id,
self_param_ty,
filter,
);
// Combine the two lists to form the complete set of superbounds:
let implied_bounds =
&*tcx.arena.alloc_from_iter(superbounds.clauses().chain(where_bounds_that_match));
debug!(?implied_bounds);
// Now require that immediate supertraits are converted, which will, in
// turn, reach indirect supertraits, so we detect cycles now instead of
// overflowing during elaboration.
if matches!(filter, PredicateFilter::SelfOnly) {
for &(pred, span) in implied_bounds {
debug!("superbound: {:?}", pred);
if let ty::ClauseKind::Trait(bound) = pred.kind().skip_binder()
&& bound.polarity == ty::ImplPolarity::Positive
{
tcx.at(span).super_predicates_of(bound.def_id());
}
}
}
ty::GenericPredicates { parent: None, predicates: implied_bounds }
}
/// Returns the predicates defined on `item_def_id` of the form
/// `X: Foo` where `X` is the type parameter `def_id`.
#[instrument(level = "trace", skip(tcx))]
pub(super) fn type_param_predicates(
tcx: TyCtxt<'_>,
(item_def_id, def_id, assoc_name): (LocalDefId, LocalDefId, Ident),
) -> ty::GenericPredicates<'_> {
use rustc_hir::*;
use rustc_middle::ty::Ty;
// In the AST, bounds can derive from two places. Either
// written inline like `<T: Foo>` or in a where-clause like
// `where T: Foo`.
let param_id = tcx.hir().local_def_id_to_hir_id(def_id);
let param_owner = tcx.hir().ty_param_owner(def_id);
let generics = tcx.generics_of(param_owner);
let index = generics.param_def_id_to_index[&def_id.to_def_id()];
let ty = Ty::new_param(tcx, index, tcx.hir().ty_param_name(def_id));
// Don't look for bounds where the type parameter isn't in scope.
let parent = if item_def_id == param_owner {
None
} else {
tcx.generics_of(item_def_id).parent.map(|def_id| def_id.expect_local())
};
let mut result = parent
.map(|parent| {
let icx = ItemCtxt::new(tcx, parent);
icx.get_type_parameter_bounds(DUMMY_SP, def_id, assoc_name)
})
.unwrap_or_default();
let mut extend = None;
let item_hir_id = tcx.hir().local_def_id_to_hir_id(item_def_id);
let ast_generics = match tcx.hir().get(item_hir_id) {
Node::TraitItem(item) => &item.generics,
Node::ImplItem(item) => &item.generics,
Node::Item(item) => {
match item.kind {
ItemKind::Fn(.., generics, _)
| ItemKind::Impl(&hir::Impl { generics, .. })
| ItemKind::TyAlias(_, generics)
| ItemKind::Const(_, generics, _)
| ItemKind::OpaqueTy(&OpaqueTy {
generics,
origin: hir::OpaqueTyOrigin::TyAlias { .. },
..
})
| ItemKind::Enum(_, generics)
| ItemKind::Struct(_, generics)
| ItemKind::Union(_, generics) => generics,
ItemKind::Trait(_, _, generics, ..) => {
// Implied `Self: Trait` and supertrait bounds.
if param_id == item_hir_id {
let identity_trait_ref =
ty::TraitRef::identity(tcx, item_def_id.to_def_id());
extend = Some((identity_trait_ref.to_predicate(tcx), item.span));
}
generics
}
_ => return result,
}
}
Node::ForeignItem(item) => match item.kind {
ForeignItemKind::Fn(_, _, generics) => generics,
_ => return result,
},
_ => return result,
};
let icx = ItemCtxt::new(tcx, item_def_id);
let extra_predicates = extend.into_iter().chain(
icx.type_parameter_bounds_in_generics(
ast_generics,
def_id,
ty,
PredicateFilter::SelfThatDefines(assoc_name),
)
.into_iter()
.filter(|(predicate, _)| match predicate.kind().skip_binder() {
ty::ClauseKind::Trait(data) => data.self_ty().is_param(index),
_ => false,
}),
);
result.predicates =
tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(extra_predicates));
result
}
impl<'tcx> ItemCtxt<'tcx> {
/// Finds bounds from `hir::Generics`. This requires scanning through the
/// AST. We do this to avoid having to convert *all* the bounds, which
/// would create artificial cycles. Instead, we can only convert the
/// bounds for a type parameter `X` if `X::Foo` is used.
#[instrument(level = "trace", skip(self, ast_generics))]
fn type_parameter_bounds_in_generics(
&self,
ast_generics: &'tcx hir::Generics<'tcx>,
param_def_id: LocalDefId,
ty: Ty<'tcx>,
filter: PredicateFilter,
) -> Vec<(ty::Clause<'tcx>, Span)> {
let mut bounds = Bounds::default();
for predicate in ast_generics.predicates {
let hir::WherePredicate::BoundPredicate(predicate) = predicate else {
continue;
};
let (only_self_bounds, assoc_name) = match filter {
PredicateFilter::All | PredicateFilter::SelfAndAssociatedTypeBounds => {
(OnlySelfBounds(false), None)
}
PredicateFilter::SelfOnly => (OnlySelfBounds(true), None),
PredicateFilter::SelfThatDefines(assoc_name) => {
(OnlySelfBounds(true), Some(assoc_name))
}
};
// Subtle: If we're collecting `SelfAndAssociatedTypeBounds`, then we
// want to only consider predicates with `Self: ...`, but we don't want
// `OnlySelfBounds(true)` since we want to collect the nested associated
// type bound as well.
let bound_ty = if predicate.is_param_bound(param_def_id.to_def_id()) {
ty
} else if matches!(filter, PredicateFilter::All) {
self.to_ty(predicate.bounded_ty)
} else {
continue;
};
let bound_vars = self.tcx.late_bound_vars(predicate.hir_id);
self.astconv().add_bounds(
bound_ty,
predicate.bounds.iter().filter(|bound| {
assoc_name
.map_or(true, |assoc_name| self.bound_defines_assoc_item(bound, assoc_name))
}),
&mut bounds,
bound_vars,
only_self_bounds,
);
}
bounds.clauses().collect()
}
#[instrument(level = "trace", skip(self))]
fn bound_defines_assoc_item(&self, b: &hir::GenericBound<'_>, assoc_name: Ident) -> bool {
match b {
hir::GenericBound::Trait(poly_trait_ref, _) => {
let trait_ref = &poly_trait_ref.trait_ref;
if let Some(trait_did) = trait_ref.trait_def_id() {
self.tcx.trait_may_define_assoc_item(trait_did, assoc_name)
} else {
false
}
}
_ => false,
}
}
}