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use rustc_data_structures::fx::FxIndexMap;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::DefId;
use rustc_middle::ty::{self, GenericArg, GenericArgKind, Ty, TyCtxt};
use rustc_span::Span;
use tracing::debug;
use super::explicit::ExplicitPredicatesMap;
use super::utils::*;
/// Infer predicates for the items in the crate.
///
/// `global_inferred_outlives`: this is initially the empty map that
/// was generated by walking the items in the crate. This will
/// now be filled with inferred predicates.
pub(super) fn infer_predicates(
tcx: TyCtxt<'_>,
) -> FxIndexMap<DefId, ty::EarlyBinder<'_, RequiredPredicates<'_>>> {
debug!("infer_predicates");
let mut explicit_map = ExplicitPredicatesMap::new();
let mut global_inferred_outlives = FxIndexMap::default();
// If new predicates were added then we need to re-calculate
// all crates since there could be new implied predicates.
'outer: loop {
let mut predicates_added = false;
// Visit all the crates and infer predicates
for id in tcx.hir().items() {
let item_did = id.owner_id;
debug!("InferVisitor::visit_item(item={:?})", item_did);
let mut item_required_predicates = RequiredPredicates::default();
match tcx.def_kind(item_did) {
DefKind::Union | DefKind::Enum | DefKind::Struct => {
let adt_def = tcx.adt_def(item_did.to_def_id());
// Iterate over all fields in item_did
for field_def in adt_def.all_fields() {
// Calculating the predicate requirements necessary
// for item_did.
//
// For field of type &'a T (reference) or Adt
// (struct/enum/union) there will be outlive
// requirements for adt_def.
let field_ty = tcx.type_of(field_def.did).instantiate_identity();
let field_span = tcx.def_span(field_def.did);
insert_required_predicates_to_be_wf(
tcx,
field_ty,
field_span,
&global_inferred_outlives,
&mut item_required_predicates,
&mut explicit_map,
);
}
}
DefKind::TyAlias if tcx.type_alias_is_lazy(item_did) => {
insert_required_predicates_to_be_wf(
tcx,
tcx.type_of(item_did).instantiate_identity(),
tcx.def_span(item_did),
&global_inferred_outlives,
&mut item_required_predicates,
&mut explicit_map,
);
}
_ => {}
};
// If new predicates were added (`local_predicate_map` has more
// predicates than the `global_inferred_outlives`), the new predicates
// might result in implied predicates for their parent types.
// Therefore mark `predicates_added` as true and which will ensure
// we walk the crates again and re-calculate predicates for all
// items.
let item_predicates_len: usize = global_inferred_outlives
.get(&item_did.to_def_id())
.map_or(0, |p| p.as_ref().skip_binder().len());
if item_required_predicates.len() > item_predicates_len {
predicates_added = true;
global_inferred_outlives
.insert(item_did.to_def_id(), ty::EarlyBinder::bind(item_required_predicates));
}
}
if !predicates_added {
break 'outer;
}
}
global_inferred_outlives
}
fn insert_required_predicates_to_be_wf<'tcx>(
tcx: TyCtxt<'tcx>,
ty: Ty<'tcx>,
span: Span,
global_inferred_outlives: &FxIndexMap<DefId, ty::EarlyBinder<'tcx, RequiredPredicates<'tcx>>>,
required_predicates: &mut RequiredPredicates<'tcx>,
explicit_map: &mut ExplicitPredicatesMap<'tcx>,
) {
for arg in ty.walk() {
let leaf_ty = match arg.unpack() {
GenericArgKind::Type(ty) => ty,
// No predicates from lifetimes or constants, except potentially
// constants' types, but `walk` will get to them as well.
GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => continue,
};
match *leaf_ty.kind() {
ty::Ref(region, rty, _) => {
// The type is `&'a T` which means that we will have
// a predicate requirement of `T: 'a` (`T` outlives `'a`).
//
// We also want to calculate potential predicates for the `T`.
debug!("Ref");
insert_outlives_predicate(tcx, rty.into(), region, span, required_predicates);
}
ty::Adt(def, args) => {
// For ADTs (structs/enums/unions), we check inferred and explicit predicates.
debug!("Adt");
check_inferred_predicates(
tcx,
def.did(),
args,
global_inferred_outlives,
required_predicates,
);
check_explicit_predicates(
tcx,
def.did(),
args,
required_predicates,
explicit_map,
None,
);
}
ty::Alias(ty::Weak, alias) => {
// This corresponds to a type like `Type<'a, T>`.
// We check inferred and explicit predicates.
debug!("Weak");
check_inferred_predicates(
tcx,
alias.def_id,
alias.args,
global_inferred_outlives,
required_predicates,
);
check_explicit_predicates(
tcx,
alias.def_id,
alias.args,
required_predicates,
explicit_map,
None,
);
}
ty::Dynamic(obj, ..) => {
// This corresponds to `dyn Trait<..>`. In this case, we should
// use the explicit predicates as well.
debug!("Dynamic");
if let Some(ex_trait_ref) = obj.principal() {
// Here, we are passing the type `usize` as a
// placeholder value with the function
// `with_self_ty`, since there is no concrete type
// `Self` for a `dyn Trait` at this
// stage. Therefore when checking explicit
// predicates in `check_explicit_predicates` we
// need to ignore checking the explicit_map for
// Self type.
let args = ex_trait_ref.with_self_ty(tcx, tcx.types.usize).skip_binder().args;
check_explicit_predicates(
tcx,
ex_trait_ref.skip_binder().def_id,
args,
required_predicates,
explicit_map,
Some(tcx.types.self_param),
);
}
}
ty::Alias(ty::Projection, alias) => {
// This corresponds to a type like `<() as Trait<'a, T>>::Type`.
// We only use the explicit predicates of the trait but
// not the ones of the associated type itself.
debug!("Projection");
check_explicit_predicates(
tcx,
tcx.parent(alias.def_id),
alias.args,
required_predicates,
explicit_map,
None,
);
}
// FIXME(inherent_associated_types): Use the explicit predicates from the parent impl.
ty::Alias(ty::Inherent, _) => {}
_ => {}
}
}
}
/// Check the explicit predicates declared on the type.
///
/// ### Example
///
/// ```ignore (illustrative)
/// struct Outer<'a, T> {
/// field: Inner<T>,
/// }
///
/// struct Inner<U> where U: 'static, U: Outer {
/// // ...
/// }
/// ```
/// Here, we should fetch the explicit predicates, which
/// will give us `U: 'static` and `U: Outer`. The latter we
/// can ignore, but we will want to process `U: 'static`,
/// applying the instantiation as above.
fn check_explicit_predicates<'tcx>(
tcx: TyCtxt<'tcx>,
def_id: DefId,
args: &[GenericArg<'tcx>],
required_predicates: &mut RequiredPredicates<'tcx>,
explicit_map: &mut ExplicitPredicatesMap<'tcx>,
ignored_self_ty: Option<Ty<'tcx>>,
) {
debug!(
"check_explicit_predicates(def_id={:?}, \
args={:?}, \
explicit_map={:?}, \
required_predicates={:?}, \
ignored_self_ty={:?})",
def_id, args, explicit_map, required_predicates, ignored_self_ty,
);
let explicit_predicates = explicit_map.explicit_predicates_of(tcx, def_id);
for (outlives_predicate, &span) in explicit_predicates.as_ref().skip_binder() {
debug!("outlives_predicate = {outlives_predicate:?}");
// Careful: If we are inferring the effects of a `dyn Trait<..>`
// type, then when we look up the predicates for `Trait`,
// we may find some that reference `Self`. e.g., perhaps the
// definition of `Trait` was:
//
// ```
// trait Trait<'a, T> where Self: 'a { .. }
// ```
//
// we want to ignore such predicates here, because
// there is no type parameter for them to affect. Consider
// a struct containing `dyn Trait`:
//
// ```
// struct MyStruct<'x, X> { field: Box<dyn Trait<'x, X>> }
// ```
//
// The `where Self: 'a` predicate refers to the *existential, hidden type*
// that is represented by the `dyn Trait`, not to the `X` type parameter
// (or any other generic parameter) declared on `MyStruct`.
//
// Note that we do this check for self **before** applying `args`. In the
// case that `args` come from a `dyn Trait` type, our caller will have
// included `Self = usize` as the value for `Self`. If we were
// to apply the args, and not filter this predicate, we might then falsely
// conclude that e.g., `X: 'x` was a reasonable inferred requirement.
//
// Another similar case is where we have an inferred
// requirement like `<Self as Trait>::Foo: 'b`. We presently
// ignore such requirements as well (cc #54467)-- though
// conceivably it might be better if we could extract the `Foo
// = X` binding from the object type (there must be such a
// binding) and thus infer an outlives requirement that `X:
// 'b`.
if let Some(self_ty) = ignored_self_ty
&& let GenericArgKind::Type(ty) = outlives_predicate.0.unpack()
&& ty.walk().any(|arg| arg == self_ty.into())
{
debug!("skipping self ty = {ty:?}");
continue;
}
let predicate = explicit_predicates.rebind(*outlives_predicate).instantiate(tcx, args);
debug!("predicate = {predicate:?}");
insert_outlives_predicate(tcx, predicate.0, predicate.1, span, required_predicates);
}
}
/// Check the inferred predicates declared on the type.
///
/// ### Example
///
/// ```ignore (illustrative)
/// struct Outer<'a, T> {
/// outer: Inner<'a, T>,
/// }
///
/// struct Inner<'b, U> {
/// inner: &'b U,
/// }
/// ```
///
/// Here, when processing the type of field `outer`, we would request the
/// set of implicit predicates computed for `Inner` thus far. This will
/// initially come back empty, but in next round we will get `U: 'b`.
/// We then apply the instantiation `['b => 'a, U => T]` and thus get the
/// requirement that `T: 'a` holds for `Outer`.
fn check_inferred_predicates<'tcx>(
tcx: TyCtxt<'tcx>,
def_id: DefId,
args: ty::GenericArgsRef<'tcx>,
global_inferred_outlives: &FxIndexMap<DefId, ty::EarlyBinder<'tcx, RequiredPredicates<'tcx>>>,
required_predicates: &mut RequiredPredicates<'tcx>,
) {
// Load the current set of inferred and explicit predicates from `global_inferred_outlives`
// and filter the ones that are `TypeOutlives`.
let Some(predicates) = global_inferred_outlives.get(&def_id) else {
return;
};
for (&predicate, &span) in predicates.as_ref().skip_binder() {
// `predicate` is `U: 'b` in the example above.
// So apply the instantiation to get `T: 'a`.
let ty::OutlivesPredicate(arg, region) =
predicates.rebind(predicate).instantiate(tcx, args);
insert_outlives_predicate(tcx, arg, region, span, required_predicates);
}
}