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//! Code for projecting associated types out of trait references.
use super::check_args_compatible;
use super::specialization_graph;
use super::translate_args;
use super::util;
use super::MismatchedProjectionTypes;
use super::Obligation;
use super::ObligationCause;
use super::PredicateObligation;
use super::Selection;
use super::SelectionContext;
use super::SelectionError;
use super::{Normalized, NormalizedTy, ProjectionCacheEntry, ProjectionCacheKey};
use rustc_middle::traits::BuiltinImplSource;
use rustc_middle::traits::ImplSource;
use rustc_middle::traits::ImplSourceUserDefinedData;
use crate::errors::InherentProjectionNormalizationOverflow;
use crate::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use crate::infer::{InferCtxt, InferOk, LateBoundRegionConversionTime};
use crate::traits::error_reporting::TypeErrCtxtExt as _;
use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
use crate::traits::select::ProjectionMatchesProjection;
use rustc_data_structures::sso::SsoHashSet;
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_errors::ErrorGuaranteed;
use rustc_hir::def::DefKind;
use rustc_hir::lang_items::LangItem;
use rustc_infer::infer::at::At;
use rustc_infer::infer::resolve::OpportunisticRegionResolver;
use rustc_infer::infer::DefineOpaqueTypes;
use rustc_infer::traits::FulfillmentError;
use rustc_infer::traits::ObligationCauseCode;
use rustc_infer::traits::TraitEngine;
use rustc_middle::traits::select::OverflowError;
use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
use rustc_middle::ty::visit::{MaxUniverse, TypeVisitable, TypeVisitableExt};
use rustc_middle::ty::{self, Term, ToPredicate, Ty, TyCtxt};
use rustc_span::symbol::sym;
use std::collections::BTreeMap;
pub use rustc_middle::traits::Reveal;
pub type PolyProjectionObligation<'tcx> = Obligation<'tcx, ty::PolyProjectionPredicate<'tcx>>;
pub type ProjectionObligation<'tcx> = Obligation<'tcx, ty::ProjectionPredicate<'tcx>>;
pub type ProjectionTyObligation<'tcx> = Obligation<'tcx, ty::AliasTy<'tcx>>;
pub(super) struct InProgress;
pub trait NormalizeExt<'tcx> {
/// Normalize a value using the `AssocTypeNormalizer`.
///
/// This normalization should be used when the type contains inference variables or the
/// projection may be fallible.
fn normalize<T: TypeFoldable<TyCtxt<'tcx>>>(&self, t: T) -> InferOk<'tcx, T>;
/// Deeply normalizes `value`, replacing all aliases which can by normalized in
/// the current environment. In the new solver this errors in case normalization
/// fails or is ambiguous. This only normalizes opaque types with `Reveal::All`.
///
/// In the old solver this simply uses `normalizes` and adds the nested obligations
/// to the `fulfill_cx`. This is necessary as we otherwise end up recomputing the
/// same goals in both a temporary and the shared context which negatively impacts
/// performance as these don't share caching.
///
/// FIXME(-Ztrait-solver=next): This has the same behavior as `traits::fully_normalize`
/// in the new solver, but because of performance reasons, we currently reuse an
/// existing fulfillment context in the old solver. Once we also eagerly prove goals with
/// the old solver or have removed the old solver, remove `traits::fully_normalize` and
/// rename this function to `At::fully_normalize`.
fn deeply_normalize<T: TypeFoldable<TyCtxt<'tcx>>>(
self,
value: T,
fulfill_cx: &mut dyn TraitEngine<'tcx>,
) -> Result<T, Vec<FulfillmentError<'tcx>>>;
}
impl<'tcx> NormalizeExt<'tcx> for At<'_, 'tcx> {
fn normalize<T: TypeFoldable<TyCtxt<'tcx>>>(&self, value: T) -> InferOk<'tcx, T> {
if self.infcx.next_trait_solver() {
InferOk { value, obligations: Vec::new() }
} else {
let mut selcx = SelectionContext::new(self.infcx);
let Normalized { value, obligations } =
normalize_with_depth(&mut selcx, self.param_env, self.cause.clone(), 0, value);
InferOk { value, obligations }
}
}
fn deeply_normalize<T: TypeFoldable<TyCtxt<'tcx>>>(
self,
value: T,
fulfill_cx: &mut dyn TraitEngine<'tcx>,
) -> Result<T, Vec<FulfillmentError<'tcx>>> {
if self.infcx.next_trait_solver() {
crate::solve::deeply_normalize(self, value)
} else {
let value = self
.normalize(value)
.into_value_registering_obligations(self.infcx, &mut *fulfill_cx);
let errors = fulfill_cx.select_where_possible(self.infcx);
let value = self.infcx.resolve_vars_if_possible(value);
if errors.is_empty() { Ok(value) } else { Err(errors) }
}
}
}
/// When attempting to resolve `<T as TraitRef>::Name` ...
#[derive(Debug)]
pub enum ProjectionError<'tcx> {
/// ...we found multiple sources of information and couldn't resolve the ambiguity.
TooManyCandidates,
/// ...an error occurred matching `T : TraitRef`
TraitSelectionError(SelectionError<'tcx>),
}
#[derive(PartialEq, Eq, Debug)]
enum ProjectionCandidate<'tcx> {
/// From a where-clause in the env or object type
ParamEnv(ty::PolyProjectionPredicate<'tcx>),
/// From the definition of `Trait` when you have something like
/// `<<A as Trait>::B as Trait2>::C`.
TraitDef(ty::PolyProjectionPredicate<'tcx>),
/// Bounds specified on an object type
Object(ty::PolyProjectionPredicate<'tcx>),
/// From an "impl" (or a "pseudo-impl" returned by select)
Select(Selection<'tcx>),
}
enum ProjectionCandidateSet<'tcx> {
None,
Single(ProjectionCandidate<'tcx>),
Ambiguous,
Error(SelectionError<'tcx>),
}
impl<'tcx> ProjectionCandidateSet<'tcx> {
fn mark_ambiguous(&mut self) {
*self = ProjectionCandidateSet::Ambiguous;
}
fn mark_error(&mut self, err: SelectionError<'tcx>) {
*self = ProjectionCandidateSet::Error(err);
}
// Returns true if the push was successful, or false if the candidate
// was discarded -- this could be because of ambiguity, or because
// a higher-priority candidate is already there.
fn push_candidate(&mut self, candidate: ProjectionCandidate<'tcx>) -> bool {
use self::ProjectionCandidate::*;
use self::ProjectionCandidateSet::*;
// This wacky variable is just used to try and
// make code readable and avoid confusing paths.
// It is assigned a "value" of `()` only on those
// paths in which we wish to convert `*self` to
// ambiguous (and return false, because the candidate
// was not used). On other paths, it is not assigned,
// and hence if those paths *could* reach the code that
// comes after the match, this fn would not compile.
let convert_to_ambiguous;
match self {
None => {
*self = Single(candidate);
return true;
}
Single(current) => {
// Duplicates can happen inside ParamEnv. In the case, we
// perform a lazy deduplication.
if current == &candidate {
return false;
}
// Prefer where-clauses. As in select, if there are multiple
// candidates, we prefer where-clause candidates over impls. This
// may seem a bit surprising, since impls are the source of
// "truth" in some sense, but in fact some of the impls that SEEM
// applicable are not, because of nested obligations. Where
// clauses are the safer choice. See the comment on
// `select::SelectionCandidate` and #21974 for more details.
match (current, candidate) {
(ParamEnv(..), ParamEnv(..)) => convert_to_ambiguous = (),
(ParamEnv(..), _) => return false,
(_, ParamEnv(..)) => unreachable!(),
(_, _) => convert_to_ambiguous = (),
}
}
Ambiguous | Error(..) => {
return false;
}
}
// We only ever get here when we moved from a single candidate
// to ambiguous.
let () = convert_to_ambiguous;
*self = Ambiguous;
false
}
}
/// States returned from `poly_project_and_unify_type`. Takes the place
/// of the old return type, which was:
/// ```ignore (not-rust)
/// Result<
/// Result<Option<Vec<PredicateObligation<'tcx>>>, InProgress>,
/// MismatchedProjectionTypes<'tcx>,
/// >
/// ```
pub(super) enum ProjectAndUnifyResult<'tcx> {
/// The projection bound holds subject to the given obligations. If the
/// projection cannot be normalized because the required trait bound does
/// not hold, this is returned, with `obligations` being a predicate that
/// cannot be proven.
Holds(Vec<PredicateObligation<'tcx>>),
/// The projection cannot be normalized due to ambiguity. Resolving some
/// inference variables in the projection may fix this.
FailedNormalization,
/// The project cannot be normalized because `poly_project_and_unify_type`
/// is called recursively while normalizing the same projection.
Recursive,
// the projection can be normalized, but is not equal to the expected type.
// Returns the type error that arose from the mismatch.
MismatchedProjectionTypes(MismatchedProjectionTypes<'tcx>),
}
/// Evaluates constraints of the form:
/// ```ignore (not-rust)
/// for<...> <T as Trait>::U == V
/// ```
/// If successful, this may result in additional obligations. Also returns
/// the projection cache key used to track these additional obligations.
#[instrument(level = "debug", skip(selcx))]
pub(super) fn poly_project_and_unify_type<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &PolyProjectionObligation<'tcx>,
) -> ProjectAndUnifyResult<'tcx> {
let infcx = selcx.infcx;
let r = infcx.commit_if_ok(|_snapshot| {
let old_universe = infcx.universe();
let placeholder_predicate =
infcx.instantiate_binder_with_placeholders(obligation.predicate);
let new_universe = infcx.universe();
let placeholder_obligation = obligation.with(infcx.tcx, placeholder_predicate);
match project_and_unify_type(selcx, &placeholder_obligation) {
ProjectAndUnifyResult::MismatchedProjectionTypes(e) => Err(e),
ProjectAndUnifyResult::Holds(obligations)
if old_universe != new_universe
&& selcx.tcx().features().generic_associated_types_extended =>
{
// If the `generic_associated_types_extended` feature is active, then we ignore any
// obligations references lifetimes from any universe greater than or equal to the
// universe just created. Otherwise, we can end up with something like `for<'a> I: 'a`,
// which isn't quite what we want. Ideally, we want either an implied
// `for<'a where I: 'a> I: 'a` or we want to "lazily" check these hold when we
// substitute concrete regions. There is design work to be done here; until then,
// however, this allows experimenting potential GAT features without running into
// well-formedness issues.
let new_obligations = obligations
.into_iter()
.filter(|obligation| {
let mut visitor = MaxUniverse::new();
obligation.predicate.visit_with(&mut visitor);
visitor.max_universe() < new_universe
})
.collect();
Ok(ProjectAndUnifyResult::Holds(new_obligations))
}
other => Ok(other),
}
});
match r {
Ok(inner) => inner,
Err(err) => ProjectAndUnifyResult::MismatchedProjectionTypes(err),
}
}
/// Evaluates constraints of the form:
/// ```ignore (not-rust)
/// <T as Trait>::U == V
/// ```
/// If successful, this may result in additional obligations.
///
/// See [poly_project_and_unify_type] for an explanation of the return value.
#[instrument(level = "debug", skip(selcx))]
fn project_and_unify_type<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionObligation<'tcx>,
) -> ProjectAndUnifyResult<'tcx> {
let mut obligations = vec![];
let infcx = selcx.infcx;
let normalized = match opt_normalize_projection_type(
selcx,
obligation.param_env,
obligation.predicate.projection_ty,
obligation.cause.clone(),
obligation.recursion_depth,
&mut obligations,
) {
Ok(Some(n)) => n,
Ok(None) => return ProjectAndUnifyResult::FailedNormalization,
Err(InProgress) => return ProjectAndUnifyResult::Recursive,
};
debug!(?normalized, ?obligations, "project_and_unify_type result");
let actual = obligation.predicate.term;
// For an example where this is necessary see tests/ui/impl-trait/nested-return-type2.rs
// This allows users to omit re-mentioning all bounds on an associated type and just use an
// `impl Trait` for the assoc type to add more bounds.
let InferOk { value: actual, obligations: new } =
selcx.infcx.replace_opaque_types_with_inference_vars(
actual,
obligation.cause.body_id,
obligation.cause.span,
obligation.param_env,
);
obligations.extend(new);
// Need to define opaque types to support nested opaque types like `impl Fn() -> impl Trait`
match infcx.at(&obligation.cause, obligation.param_env).eq(
DefineOpaqueTypes::Yes,
normalized,
actual,
) {
Ok(InferOk { obligations: inferred_obligations, value: () }) => {
obligations.extend(inferred_obligations);
ProjectAndUnifyResult::Holds(obligations)
}
Err(err) => {
debug!("equating types encountered error {:?}", err);
ProjectAndUnifyResult::MismatchedProjectionTypes(MismatchedProjectionTypes { err })
}
}
}
/// As `normalize`, but with a custom depth.
pub(crate) fn normalize_with_depth<'a, 'b, 'tcx, T>(
selcx: &'a mut SelectionContext<'b, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
cause: ObligationCause<'tcx>,
depth: usize,
value: T,
) -> Normalized<'tcx, T>
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
let mut obligations = Vec::new();
let value = normalize_with_depth_to(selcx, param_env, cause, depth, value, &mut obligations);
Normalized { value, obligations }
}
#[instrument(level = "info", skip(selcx, param_env, cause, obligations))]
pub(crate) fn normalize_with_depth_to<'a, 'b, 'tcx, T>(
selcx: &'a mut SelectionContext<'b, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
cause: ObligationCause<'tcx>,
depth: usize,
value: T,
obligations: &mut Vec<PredicateObligation<'tcx>>,
) -> T
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
debug!(obligations.len = obligations.len());
let mut normalizer = AssocTypeNormalizer::new(selcx, param_env, cause, depth, obligations);
let result = ensure_sufficient_stack(|| normalizer.fold(value));
debug!(?result, obligations.len = normalizer.obligations.len());
debug!(?normalizer.obligations,);
result
}
#[instrument(level = "info", skip(selcx, param_env, cause, obligations))]
pub(crate) fn try_normalize_with_depth_to<'a, 'b, 'tcx, T>(
selcx: &'a mut SelectionContext<'b, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
cause: ObligationCause<'tcx>,
depth: usize,
value: T,
obligations: &mut Vec<PredicateObligation<'tcx>>,
) -> T
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
debug!(obligations.len = obligations.len());
let mut normalizer = AssocTypeNormalizer::new_without_eager_inference_replacement(
selcx,
param_env,
cause,
depth,
obligations,
);
let result = ensure_sufficient_stack(|| normalizer.fold(value));
debug!(?result, obligations.len = normalizer.obligations.len());
debug!(?normalizer.obligations,);
result
}
pub(crate) fn needs_normalization<'tcx, T: TypeVisitable<TyCtxt<'tcx>>>(
value: &T,
reveal: Reveal,
) -> bool {
match reveal {
Reveal::UserFacing => value.has_type_flags(
ty::TypeFlags::HAS_TY_PROJECTION
| ty::TypeFlags::HAS_TY_INHERENT
| ty::TypeFlags::HAS_CT_PROJECTION,
),
Reveal::All => value.has_type_flags(
ty::TypeFlags::HAS_TY_PROJECTION
| ty::TypeFlags::HAS_TY_INHERENT
| ty::TypeFlags::HAS_TY_OPAQUE
| ty::TypeFlags::HAS_CT_PROJECTION,
),
}
}
struct AssocTypeNormalizer<'a, 'b, 'tcx> {
selcx: &'a mut SelectionContext<'b, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
cause: ObligationCause<'tcx>,
obligations: &'a mut Vec<PredicateObligation<'tcx>>,
depth: usize,
universes: Vec<Option<ty::UniverseIndex>>,
/// If true, when a projection is unable to be completed, an inference
/// variable will be created and an obligation registered to project to that
/// inference variable. Also, constants will be eagerly evaluated.
eager_inference_replacement: bool,
}
impl<'a, 'b, 'tcx> AssocTypeNormalizer<'a, 'b, 'tcx> {
fn new(
selcx: &'a mut SelectionContext<'b, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
cause: ObligationCause<'tcx>,
depth: usize,
obligations: &'a mut Vec<PredicateObligation<'tcx>>,
) -> AssocTypeNormalizer<'a, 'b, 'tcx> {
debug_assert!(!selcx.infcx.next_trait_solver());
AssocTypeNormalizer {
selcx,
param_env,
cause,
obligations,
depth,
universes: vec![],
eager_inference_replacement: true,
}
}
fn new_without_eager_inference_replacement(
selcx: &'a mut SelectionContext<'b, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
cause: ObligationCause<'tcx>,
depth: usize,
obligations: &'a mut Vec<PredicateObligation<'tcx>>,
) -> AssocTypeNormalizer<'a, 'b, 'tcx> {
AssocTypeNormalizer {
selcx,
param_env,
cause,
obligations,
depth,
universes: vec![],
eager_inference_replacement: false,
}
}
fn fold<T: TypeFoldable<TyCtxt<'tcx>>>(&mut self, value: T) -> T {
let value = self.selcx.infcx.resolve_vars_if_possible(value);
debug!(?value);
assert!(
!value.has_escaping_bound_vars(),
"Normalizing {value:?} without wrapping in a `Binder`"
);
if !needs_normalization(&value, self.param_env.reveal()) {
value
} else {
value.fold_with(self)
}
}
}
impl<'a, 'b, 'tcx> TypeFolder<TyCtxt<'tcx>> for AssocTypeNormalizer<'a, 'b, 'tcx> {
fn interner(&self) -> TyCtxt<'tcx> {
self.selcx.tcx()
}
fn fold_binder<T: TypeFoldable<TyCtxt<'tcx>>>(
&mut self,
t: ty::Binder<'tcx, T>,
) -> ty::Binder<'tcx, T> {
self.universes.push(None);
let t = t.super_fold_with(self);
self.universes.pop();
t
}
fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
if !needs_normalization(&ty, self.param_env.reveal()) {
return ty;
}
let (kind, data) = match *ty.kind() {
ty::Alias(kind, alias_ty) => (kind, alias_ty),
_ => return ty.super_fold_with(self),
};
// We try to be a little clever here as a performance optimization in
// cases where there are nested projections under binders.
// For example:
// ```
// for<'a> fn(<T as Foo>::One<'a, Box<dyn Bar<'a, Item=<T as Foo>::Two<'a>>>>)
// ```
// We normalize the args on the projection before the projecting, but
// if we're naive, we'll
// replace bound vars on inner, project inner, replace placeholders on inner,
// replace bound vars on outer, project outer, replace placeholders on outer
//
// However, if we're a bit more clever, we can replace the bound vars
// on the entire type before normalizing nested projections, meaning we
// replace bound vars on outer, project inner,
// project outer, replace placeholders on outer
//
// This is possible because the inner `'a` will already be a placeholder
// when we need to normalize the inner projection
//
// On the other hand, this does add a bit of complexity, since we only
// replace bound vars if the current type is a `Projection` and we need
// to make sure we don't forget to fold the args regardless.
match kind {
ty::Opaque => {
// Only normalize `impl Trait` outside of type inference, usually in codegen.
match self.param_env.reveal() {
Reveal::UserFacing => ty.super_fold_with(self),
Reveal::All => {
let recursion_limit = self.interner().recursion_limit();
if !recursion_limit.value_within_limit(self.depth) {
self.selcx.infcx.err_ctxt().report_overflow_error(
&ty,
self.cause.span,
true,
|_| {},
);
}
let args = data.args.fold_with(self);
let generic_ty = self.interner().type_of(data.def_id);
let concrete_ty = generic_ty.instantiate(self.interner(), args);
self.depth += 1;
let folded_ty = self.fold_ty(concrete_ty);
self.depth -= 1;
folded_ty
}
}
}
ty::Projection if !data.has_escaping_bound_vars() => {
// This branch is *mostly* just an optimization: when we don't
// have escaping bound vars, we don't need to replace them with
// placeholders (see branch below). *Also*, we know that we can
// register an obligation to *later* project, since we know
// there won't be bound vars there.
let data = data.fold_with(self);
let normalized_ty = if self.eager_inference_replacement {
normalize_projection_type(
self.selcx,
self.param_env,
data,
self.cause.clone(),
self.depth,
&mut self.obligations,
)
} else {
opt_normalize_projection_type(
self.selcx,
self.param_env,
data,
self.cause.clone(),
self.depth,
&mut self.obligations,
)
.ok()
.flatten()
.unwrap_or_else(|| ty.super_fold_with(self).into())
};
debug!(
?self.depth,
?ty,
?normalized_ty,
obligations.len = ?self.obligations.len(),
"AssocTypeNormalizer: normalized type"
);
normalized_ty.ty().unwrap()
}
ty::Projection => {
// If there are escaping bound vars, we temporarily replace the
// bound vars with placeholders. Note though, that in the case
// that we still can't project for whatever reason (e.g. self
// type isn't known enough), we *can't* register an obligation
// and return an inference variable (since then that obligation
// would have bound vars and that's a can of worms). Instead,
// we just give up and fall back to pretending like we never tried!
//
// Note: this isn't necessarily the final approach here; we may
// want to figure out how to register obligations with escaping vars
// or handle this some other way.
let infcx = self.selcx.infcx;
let (data, mapped_regions, mapped_types, mapped_consts) =
BoundVarReplacer::replace_bound_vars(infcx, &mut self.universes, data);
let data = data.fold_with(self);
let normalized_ty = opt_normalize_projection_type(
self.selcx,
self.param_env,
data,
self.cause.clone(),
self.depth,
&mut self.obligations,
)
.ok()
.flatten()
.map(|term| term.ty().unwrap())
.map(|normalized_ty| {
PlaceholderReplacer::replace_placeholders(
infcx,
mapped_regions,
mapped_types,
mapped_consts,
&self.universes,
normalized_ty,
)
})
.unwrap_or_else(|| ty.super_fold_with(self));
debug!(
?self.depth,
?ty,
?normalized_ty,
obligations.len = ?self.obligations.len(),
"AssocTypeNormalizer: normalized type"
);
normalized_ty
}
ty::Weak => {
let recursion_limit = self.interner().recursion_limit();
if !recursion_limit.value_within_limit(self.depth) {
self.selcx.infcx.err_ctxt().report_overflow_error(
&ty,
self.cause.span,
false,
|diag| {
diag.note(crate::fluent_generated::trait_selection_ty_alias_overflow);
},
);
}
let infcx = self.selcx.infcx;
self.obligations.extend(
infcx.tcx.predicates_of(data.def_id).instantiate_own(infcx.tcx, data.args).map(
|(mut predicate, span)| {
if data.has_escaping_bound_vars() {
(predicate, ..) = BoundVarReplacer::replace_bound_vars(
infcx,
&mut self.universes,
predicate,
);
}
let mut cause = self.cause.clone();
cause.map_code(|code| {
ObligationCauseCode::TypeAlias(code, span, data.def_id)
});
Obligation::new(infcx.tcx, cause, self.param_env, predicate)
},
),
);
self.depth += 1;
let res = infcx
.tcx
.type_of(data.def_id)
.instantiate(infcx.tcx, data.args)
.fold_with(self);
self.depth -= 1;
res
}
ty::Inherent if !data.has_escaping_bound_vars() => {
// This branch is *mostly* just an optimization: when we don't
// have escaping bound vars, we don't need to replace them with
// placeholders (see branch below). *Also*, we know that we can
// register an obligation to *later* project, since we know
// there won't be bound vars there.
let data = data.fold_with(self);
// FIXME(inherent_associated_types): Do we need to honor `self.eager_inference_replacement`
// here like `ty::Projection`?
normalize_inherent_projection(
self.selcx,
self.param_env,
data,
self.cause.clone(),
self.depth,
&mut self.obligations,
)
}
ty::Inherent => {
let infcx = self.selcx.infcx;
let (data, mapped_regions, mapped_types, mapped_consts) =
BoundVarReplacer::replace_bound_vars(infcx, &mut self.universes, data);
let data = data.fold_with(self);
let ty = normalize_inherent_projection(
self.selcx,
self.param_env,
data,
self.cause.clone(),
self.depth,
&mut self.obligations,
);
PlaceholderReplacer::replace_placeholders(
infcx,
mapped_regions,
mapped_types,
mapped_consts,
&self.universes,
ty,
)
}
}
}
#[instrument(skip(self), level = "debug")]
fn fold_const(&mut self, constant: ty::Const<'tcx>) -> ty::Const<'tcx> {
let tcx = self.selcx.tcx();
if tcx.features().generic_const_exprs
|| !needs_normalization(&constant, self.param_env.reveal())
{
constant
} else {
let constant = constant.super_fold_with(self);
debug!(?constant, ?self.param_env);
with_replaced_escaping_bound_vars(
self.selcx.infcx,
&mut self.universes,
constant,
|constant| constant.normalize(tcx, self.param_env),
)
}
}
#[inline]
fn fold_predicate(&mut self, p: ty::Predicate<'tcx>) -> ty::Predicate<'tcx> {
if p.allow_normalization() && needs_normalization(&p, self.param_env.reveal()) {
p.super_fold_with(self)
} else {
p
}
}
}
pub struct BoundVarReplacer<'me, 'tcx> {
infcx: &'me InferCtxt<'tcx>,
// These three maps track the bound variable that were replaced by placeholders. It might be
// nice to remove these since we already have the `kind` in the placeholder; we really just need
// the `var` (but we *could* bring that into scope if we were to track them as we pass them).
mapped_regions: BTreeMap<ty::PlaceholderRegion, ty::BoundRegion>,
mapped_types: BTreeMap<ty::PlaceholderType, ty::BoundTy>,
mapped_consts: BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar>,
// The current depth relative to *this* folding, *not* the entire normalization. In other words,
// the depth of binders we've passed here.
current_index: ty::DebruijnIndex,
// The `UniverseIndex` of the binding levels above us. These are optional, since we are lazy:
// we don't actually create a universe until we see a bound var we have to replace.
universe_indices: &'me mut Vec<Option<ty::UniverseIndex>>,
}
/// Executes `f` on `value` after replacing all escaping bound variables with placeholders
/// and then replaces these placeholders with the original bound variables in the result.
///
/// In most places, bound variables should be replaced right when entering a binder, making
/// this function unnecessary. However, normalization currently does not do that, so we have
/// to do this lazily.
///
/// You should not add any additional uses of this function, at least not without first
/// discussing it with t-types.
///
/// FIXME(@lcnr): We may even consider experimenting with eagerly replacing bound vars during
/// normalization as well, at which point this function will be unnecessary and can be removed.
pub fn with_replaced_escaping_bound_vars<
'a,
'tcx,
T: TypeFoldable<TyCtxt<'tcx>>,
R: TypeFoldable<TyCtxt<'tcx>>,
>(
infcx: &'a InferCtxt<'tcx>,
universe_indices: &'a mut Vec<Option<ty::UniverseIndex>>,
value: T,
f: impl FnOnce(T) -> R,
) -> R {
if value.has_escaping_bound_vars() {
let (value, mapped_regions, mapped_types, mapped_consts) =
BoundVarReplacer::replace_bound_vars(infcx, universe_indices, value);
let result = f(value);
PlaceholderReplacer::replace_placeholders(
infcx,
mapped_regions,
mapped_types,
mapped_consts,
universe_indices,
result,
)
} else {
f(value)
}
}
impl<'me, 'tcx> BoundVarReplacer<'me, 'tcx> {
/// Returns `Some` if we *were* able to replace bound vars. If there are any bound vars that
/// use a binding level above `universe_indices.len()`, we fail.
pub fn replace_bound_vars<T: TypeFoldable<TyCtxt<'tcx>>>(
infcx: &'me InferCtxt<'tcx>,
universe_indices: &'me mut Vec<Option<ty::UniverseIndex>>,
value: T,
) -> (
T,
BTreeMap<ty::PlaceholderRegion, ty::BoundRegion>,
BTreeMap<ty::PlaceholderType, ty::BoundTy>,
BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar>,
) {
let mapped_regions: BTreeMap<ty::PlaceholderRegion, ty::BoundRegion> = BTreeMap::new();
let mapped_types: BTreeMap<ty::PlaceholderType, ty::BoundTy> = BTreeMap::new();
let mapped_consts: BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar> = BTreeMap::new();
let mut replacer = BoundVarReplacer {
infcx,
mapped_regions,
mapped_types,
mapped_consts,
current_index: ty::INNERMOST,
universe_indices,
};
let value = value.fold_with(&mut replacer);
(value, replacer.mapped_regions, replacer.mapped_types, replacer.mapped_consts)
}
fn universe_for(&mut self, debruijn: ty::DebruijnIndex) -> ty::UniverseIndex {
let infcx = self.infcx;
let index =
self.universe_indices.len() + self.current_index.as_usize() - debruijn.as_usize() - 1;
let universe = self.universe_indices[index].unwrap_or_else(|| {
for i in self.universe_indices.iter_mut().take(index + 1) {
*i = i.or_else(|| Some(infcx.create_next_universe()))
}
self.universe_indices[index].unwrap()
});
universe
}
}
impl<'tcx> TypeFolder<TyCtxt<'tcx>> for BoundVarReplacer<'_, 'tcx> {
fn interner(&self) -> TyCtxt<'tcx> {
self.infcx.tcx
}
fn fold_binder<T: TypeFoldable<TyCtxt<'tcx>>>(
&mut self,
t: ty::Binder<'tcx, T>,
) -> ty::Binder<'tcx, T> {
self.current_index.shift_in(1);
let t = t.super_fold_with(self);
self.current_index.shift_out(1);
t
}
fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
match *r {
ty::ReLateBound(debruijn, _)
if debruijn.as_usize() + 1
> self.current_index.as_usize() + self.universe_indices.len() =>
{
bug!("Bound vars outside of `self.universe_indices`");
}
ty::ReLateBound(debruijn, br) if debruijn >= self.current_index => {
let universe = self.universe_for(debruijn);
let p = ty::PlaceholderRegion { universe, bound: br };
self.mapped_regions.insert(p, br);
ty::Region::new_placeholder(self.infcx.tcx, p)
}
_ => r,
}
}
fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
match *t.kind() {
ty::Bound(debruijn, _)
if debruijn.as_usize() + 1
> self.current_index.as_usize() + self.universe_indices.len() =>
{
bug!("Bound vars outside of `self.universe_indices`");
}
ty::Bound(debruijn, bound_ty) if debruijn >= self.current_index => {
let universe = self.universe_for(debruijn);
let p = ty::PlaceholderType { universe, bound: bound_ty };
self.mapped_types.insert(p, bound_ty);
Ty::new_placeholder(self.infcx.tcx, p)
}
_ if t.has_vars_bound_at_or_above(self.current_index) => t.super_fold_with(self),
_ => t,
}
}
fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
match ct.kind() {
ty::ConstKind::Bound(debruijn, _)
if debruijn.as_usize() + 1
> self.current_index.as_usize() + self.universe_indices.len() =>
{
bug!("Bound vars outside of `self.universe_indices`");
}
ty::ConstKind::Bound(debruijn, bound_const) if debruijn >= self.current_index => {
let universe = self.universe_for(debruijn);
let p = ty::PlaceholderConst { universe, bound: bound_const };
self.mapped_consts.insert(p, bound_const);
ty::Const::new_placeholder(self.infcx.tcx, p, ct.ty())
}
_ => ct.super_fold_with(self),
}
}
fn fold_predicate(&mut self, p: ty::Predicate<'tcx>) -> ty::Predicate<'tcx> {
if p.has_vars_bound_at_or_above(self.current_index) { p.super_fold_with(self) } else { p }
}
}
/// The inverse of [`BoundVarReplacer`]: replaces placeholders with the bound vars from which they came.
pub struct PlaceholderReplacer<'me, 'tcx> {
infcx: &'me InferCtxt<'tcx>,
mapped_regions: BTreeMap<ty::PlaceholderRegion, ty::BoundRegion>,
mapped_types: BTreeMap<ty::PlaceholderType, ty::BoundTy>,
mapped_consts: BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar>,
universe_indices: &'me [Option<ty::UniverseIndex>],
current_index: ty::DebruijnIndex,
}
impl<'me, 'tcx> PlaceholderReplacer<'me, 'tcx> {
pub fn replace_placeholders<T: TypeFoldable<TyCtxt<'tcx>>>(
infcx: &'me InferCtxt<'tcx>,
mapped_regions: BTreeMap<ty::PlaceholderRegion, ty::BoundRegion>,
mapped_types: BTreeMap<ty::PlaceholderType, ty::BoundTy>,
mapped_consts: BTreeMap<ty::PlaceholderConst<'tcx>, ty::BoundVar>,
universe_indices: &'me [Option<ty::UniverseIndex>],
value: T,
) -> T {
let mut replacer = PlaceholderReplacer {
infcx,
mapped_regions,
mapped_types,
mapped_consts,
universe_indices,
current_index: ty::INNERMOST,
};
value.fold_with(&mut replacer)
}
}
impl<'tcx> TypeFolder<TyCtxt<'tcx>> for PlaceholderReplacer<'_, 'tcx> {
fn interner(&self) -> TyCtxt<'tcx> {
self.infcx.tcx
}
fn fold_binder<T: TypeFoldable<TyCtxt<'tcx>>>(
&mut self,
t: ty::Binder<'tcx, T>,
) -> ty::Binder<'tcx, T> {
if !t.has_placeholders() && !t.has_infer_regions() {
return t;
}
self.current_index.shift_in(1);
let t = t.super_fold_with(self);
self.current_index.shift_out(1);
t
}
fn fold_region(&mut self, r0: ty::Region<'tcx>) -> ty::Region<'tcx> {
let r1 = match *r0 {
ty::ReVar(vid) => self
.infcx
.inner
.borrow_mut()
.unwrap_region_constraints()
.opportunistic_resolve_var(self.infcx.tcx, vid),
_ => r0,
};
let r2 = match *r1 {
ty::RePlaceholder(p) => {
let replace_var = self.mapped_regions.get(&p);
match replace_var {
Some(replace_var) => {
let index = self
.universe_indices
.iter()
.position(|u| matches!(u, Some(pu) if *pu == p.universe))
.unwrap_or_else(|| bug!("Unexpected placeholder universe."));
let db = ty::DebruijnIndex::from_usize(
self.universe_indices.len() - index + self.current_index.as_usize() - 1,
);
ty::Region::new_late_bound(self.interner(), db, *replace_var)
}
None => r1,
}
}
_ => r1,
};
debug!(?r0, ?r1, ?r2, "fold_region");
r2
}
fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
match *ty.kind() {
ty::Placeholder(p) => {
let replace_var = self.mapped_types.get(&p);
match replace_var {
Some(replace_var) => {
let index = self
.universe_indices
.iter()
.position(|u| matches!(u, Some(pu) if *pu == p.universe))
.unwrap_or_else(|| bug!("Unexpected placeholder universe."));
let db = ty::DebruijnIndex::from_usize(
self.universe_indices.len() - index + self.current_index.as_usize() - 1,
);
Ty::new_bound(self.infcx.tcx, db, *replace_var)
}
None => ty,
}
}
_ if ty.has_placeholders() || ty.has_infer_regions() => ty.super_fold_with(self),
_ => ty,
}
}
fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
if let ty::ConstKind::Placeholder(p) = ct.kind() {
let replace_var = self.mapped_consts.get(&p);
match replace_var {
Some(replace_var) => {
let index = self
.universe_indices
.iter()
.position(|u| matches!(u, Some(pu) if *pu == p.universe))
.unwrap_or_else(|| bug!("Unexpected placeholder universe."));
let db = ty::DebruijnIndex::from_usize(
self.universe_indices.len() - index + self.current_index.as_usize() - 1,
);
ty::Const::new_bound(self.infcx.tcx, db, *replace_var, ct.ty())
}
None => ct,
}
} else {
ct.super_fold_with(self)
}
}
}
/// The guts of `normalize`: normalize a specific projection like `<T
/// as Trait>::Item`. The result is always a type (and possibly
/// additional obligations). If ambiguity arises, which implies that
/// there are unresolved type variables in the projection, we will
/// substitute a fresh type variable `$X` and generate a new
/// obligation `<T as Trait>::Item == $X` for later.
pub fn normalize_projection_type<'a, 'b, 'tcx>(
selcx: &'a mut SelectionContext<'b, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
projection_ty: ty::AliasTy<'tcx>,
cause: ObligationCause<'tcx>,
depth: usize,
obligations: &mut Vec<PredicateObligation<'tcx>>,
) -> Term<'tcx> {
opt_normalize_projection_type(
selcx,
param_env,
projection_ty,
cause.clone(),
depth,
obligations,
)
.ok()
.flatten()
.unwrap_or_else(move || {
// if we bottom out in ambiguity, create a type variable
// and a deferred predicate to resolve this when more type
// information is available.
selcx.infcx.infer_projection(param_env, projection_ty, cause, depth + 1, obligations).into()
})
}
/// The guts of `normalize`: normalize a specific projection like `<T
/// as Trait>::Item`. The result is always a type (and possibly
/// additional obligations). Returns `None` in the case of ambiguity,
/// which indicates that there are unbound type variables.
///
/// This function used to return `Option<NormalizedTy<'tcx>>`, which contains a
/// `Ty<'tcx>` and an obligations vector. But that obligation vector was very
/// often immediately appended to another obligations vector. So now this
/// function takes an obligations vector and appends to it directly, which is
/// slightly uglier but avoids the need for an extra short-lived allocation.
#[instrument(level = "debug", skip(selcx, param_env, cause, obligations))]
fn opt_normalize_projection_type<'a, 'b, 'tcx>(
selcx: &'a mut SelectionContext<'b, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
projection_ty: ty::AliasTy<'tcx>,
cause: ObligationCause<'tcx>,
depth: usize,
obligations: &mut Vec<PredicateObligation<'tcx>>,
) -> Result<Option<Term<'tcx>>, InProgress> {
let infcx = selcx.infcx;
debug_assert!(!selcx.infcx.next_trait_solver());
// Don't use the projection cache in intercrate mode -
// the `infcx` may be re-used between intercrate in non-intercrate
// mode, which could lead to using incorrect cache results.
let use_cache = !selcx.is_intercrate();
let projection_ty = infcx.resolve_vars_if_possible(projection_ty);
let cache_key = ProjectionCacheKey::new(projection_ty);
// FIXME(#20304) For now, I am caching here, which is good, but it
// means we don't capture the type variables that are created in
// the case of ambiguity. Which means we may create a large stream
// of such variables. OTOH, if we move the caching up a level, we
// would not benefit from caching when proving `T: Trait<U=Foo>`
// bounds. It might be the case that we want two distinct caches,
// or else another kind of cache entry.
let cache_result = if use_cache {
infcx.inner.borrow_mut().projection_cache().try_start(cache_key)
} else {
Ok(())
};
match cache_result {
Ok(()) => debug!("no cache"),
Err(ProjectionCacheEntry::Ambiguous) => {
// If we found ambiguity the last time, that means we will continue
// to do so until some type in the key changes (and we know it
// hasn't, because we just fully resolved it).
debug!("found cache entry: ambiguous");
return Ok(None);
}
Err(ProjectionCacheEntry::InProgress) => {
// Under lazy normalization, this can arise when
// bootstrapping. That is, imagine an environment with a
// where-clause like `A::B == u32`. Now, if we are asked
// to normalize `A::B`, we will want to check the
// where-clauses in scope. So we will try to unify `A::B`
// with `A::B`, which can trigger a recursive
// normalization.
debug!("found cache entry: in-progress");
// Cache that normalizing this projection resulted in a cycle. This
// should ensure that, unless this happens within a snapshot that's
// rolled back, fulfillment or evaluation will notice the cycle.
if use_cache {
infcx.inner.borrow_mut().projection_cache().recur(cache_key);
}
return Err(InProgress);
}
Err(ProjectionCacheEntry::Recur) => {
debug!("recur cache");
return Err(InProgress);
}
Err(ProjectionCacheEntry::NormalizedTy { ty, complete: _ }) => {
// This is the hottest path in this function.
//
// If we find the value in the cache, then return it along
// with the obligations that went along with it. Note
// that, when using a fulfillment context, these
// obligations could in principle be ignored: they have
// already been registered when the cache entry was
// created (and hence the new ones will quickly be
// discarded as duplicated). But when doing trait
// evaluation this is not the case, and dropping the trait
// evaluations can causes ICEs (e.g., #43132).
debug!(?ty, "found normalized ty");
obligations.extend(ty.obligations);
return Ok(Some(ty.value));
}
Err(ProjectionCacheEntry::Error) => {
debug!("opt_normalize_projection_type: found error");
let result = normalize_to_error(selcx, param_env, projection_ty, cause, depth);
obligations.extend(result.obligations);
return Ok(Some(result.value.into()));
}
}
let obligation =
Obligation::with_depth(selcx.tcx(), cause.clone(), depth, param_env, projection_ty);
match project(selcx, &obligation) {
Ok(Projected::Progress(Progress {
term: projected_term,
obligations: mut projected_obligations,
})) => {
// if projection succeeded, then what we get out of this
// is also non-normalized (consider: it was derived from
// an impl, where-clause etc) and hence we must
// re-normalize it
let projected_term = selcx.infcx.resolve_vars_if_possible(projected_term);
let result = if projected_term.has_projections() {
let mut normalizer = AssocTypeNormalizer::new(
selcx,
param_env,
cause,
depth + 1,
&mut projected_obligations,
);
let normalized_ty = normalizer.fold(projected_term);
let mut deduped = SsoHashSet::with_capacity(projected_obligations.len());
projected_obligations.retain(|obligation| deduped.insert(obligation.clone()));
Normalized { value: normalized_ty, obligations: projected_obligations }
} else {
Normalized { value: projected_term, obligations: projected_obligations }
};
if use_cache {
infcx.inner.borrow_mut().projection_cache().insert_term(cache_key, result.clone());
}
obligations.extend(result.obligations);
Ok(Some(result.value))
}
Ok(Projected::NoProgress(projected_ty)) => {
let result = Normalized { value: projected_ty, obligations: vec![] };
if use_cache {
infcx.inner.borrow_mut().projection_cache().insert_term(cache_key, result.clone());
}
// No need to extend `obligations`.
Ok(Some(result.value))
}
Err(ProjectionError::TooManyCandidates) => {
debug!("opt_normalize_projection_type: too many candidates");
if use_cache {
infcx.inner.borrow_mut().projection_cache().ambiguous(cache_key);
}
Ok(None)
}
Err(ProjectionError::TraitSelectionError(_)) => {
debug!("opt_normalize_projection_type: ERROR");
// if we got an error processing the `T as Trait` part,
// just return `ty::err` but add the obligation `T :
// Trait`, which when processed will cause the error to be
// reported later
if use_cache {
infcx.inner.borrow_mut().projection_cache().error(cache_key);
}
let result = normalize_to_error(selcx, param_env, projection_ty, cause, depth);
obligations.extend(result.obligations);
Ok(Some(result.value.into()))
}
}
}
/// If we are projecting `<T as Trait>::Item`, but `T: Trait` does not
/// hold. In various error cases, we cannot generate a valid
/// normalized projection. Therefore, we create an inference variable
/// return an associated obligation that, when fulfilled, will lead to
/// an error.
///
/// Note that we used to return `Error` here, but that was quite
/// dubious -- the premise was that an error would *eventually* be
/// reported, when the obligation was processed. But in general once
/// you see an `Error` you are supposed to be able to assume that an
/// error *has been* reported, so that you can take whatever heuristic
/// paths you want to take. To make things worse, it was possible for
/// cycles to arise, where you basically had a setup like `<MyType<$0>
/// as Trait>::Foo == $0`. Here, normalizing `<MyType<$0> as
/// Trait>::Foo>` to `[type error]` would lead to an obligation of
/// `<MyType<[type error]> as Trait>::Foo`. We are supposed to report
/// an error for this obligation, but we legitimately should not,
/// because it contains `[type error]`. Yuck! (See issue #29857 for
/// one case where this arose.)
fn normalize_to_error<'a, 'tcx>(
selcx: &mut SelectionContext<'a, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
projection_ty: ty::AliasTy<'tcx>,
cause: ObligationCause<'tcx>,
depth: usize,
) -> NormalizedTy<'tcx> {
let trait_ref = ty::Binder::dummy(projection_ty.trait_ref(selcx.tcx()));
let trait_obligation = Obligation {
cause,
recursion_depth: depth,
param_env,
predicate: trait_ref.to_predicate(selcx.tcx()),
};
let tcx = selcx.infcx.tcx;
let new_value = selcx.infcx.next_ty_var(TypeVariableOrigin {
kind: TypeVariableOriginKind::NormalizeProjectionType,
span: tcx.def_span(projection_ty.def_id),
});
Normalized { value: new_value, obligations: vec![trait_obligation] }
}
/// Confirm and normalize the given inherent projection.
#[instrument(level = "debug", skip(selcx, param_env, cause, obligations))]
pub fn normalize_inherent_projection<'a, 'b, 'tcx>(
selcx: &'a mut SelectionContext<'b, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
alias_ty: ty::AliasTy<'tcx>,
cause: ObligationCause<'tcx>,
depth: usize,
obligations: &mut Vec<PredicateObligation<'tcx>>,
) -> Ty<'tcx> {
let tcx = selcx.tcx();
if !tcx.recursion_limit().value_within_limit(depth) {
// Halt compilation because it is important that overflows never be masked.
tcx.sess.emit_fatal(InherentProjectionNormalizationOverflow {
span: cause.span,
ty: alias_ty.to_string(),
});
}
let args = compute_inherent_assoc_ty_args(
selcx,
param_env,
alias_ty,
cause.clone(),
depth,
obligations,
);
// Register the obligations arising from the impl and from the associated type itself.
let predicates = tcx.predicates_of(alias_ty.def_id).instantiate(tcx, args);
for (predicate, span) in predicates {
let predicate = normalize_with_depth_to(
selcx,
param_env,
cause.clone(),
depth + 1,
predicate,
obligations,
);
let nested_cause = ObligationCause::new(
cause.span,
cause.body_id,
// FIXME(inherent_associated_types): Since we can't pass along the self type to the
// cause code, inherent projections will be printed with identity substitutions in
// diagnostics which is not ideal.
// Consider creating separate cause codes for this specific situation.
if span.is_dummy() {
super::ItemObligation(alias_ty.def_id)
} else {
super::BindingObligation(alias_ty.def_id, span)
},
);
obligations.push(Obligation::with_depth(
tcx,
nested_cause,
depth + 1,
param_env,
predicate,
));
}
let ty = tcx.type_of(alias_ty.def_id).instantiate(tcx, args);
let mut ty = selcx.infcx.resolve_vars_if_possible(ty);
if ty.has_projections() {
ty = normalize_with_depth_to(selcx, param_env, cause.clone(), depth + 1, ty, obligations);
}
ty
}
pub fn compute_inherent_assoc_ty_args<'a, 'b, 'tcx>(
selcx: &'a mut SelectionContext<'b, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
alias_ty: ty::AliasTy<'tcx>,
cause: ObligationCause<'tcx>,
depth: usize,
obligations: &mut Vec<PredicateObligation<'tcx>>,
) -> ty::GenericArgsRef<'tcx> {
let tcx = selcx.tcx();
let impl_def_id = tcx.parent(alias_ty.def_id);
let impl_args = selcx.infcx.fresh_args_for_item(cause.span, impl_def_id);
let mut impl_ty = tcx.type_of(impl_def_id).instantiate(tcx, impl_args);
if !selcx.infcx.next_trait_solver() {
impl_ty = normalize_with_depth_to(
selcx,
param_env,
cause.clone(),
depth + 1,
impl_ty,
obligations,
);
}
// Infer the generic parameters of the impl by unifying the
// impl type with the self type of the projection.
let self_ty = alias_ty.self_ty();
match selcx.infcx.at(&cause, param_env).eq(DefineOpaqueTypes::No, impl_ty, self_ty) {
Ok(mut ok) => obligations.append(&mut ok.obligations),
Err(_) => {
tcx.sess.delay_span_bug(
cause.span,
format!(
"{self_ty:?} was a subtype of {impl_ty:?} during selection but now it is not"
),
);
}
}
alias_ty.rebase_inherent_args_onto_impl(impl_args, tcx)
}
enum Projected<'tcx> {
Progress(Progress<'tcx>),
NoProgress(ty::Term<'tcx>),
}
struct Progress<'tcx> {
term: ty::Term<'tcx>,
obligations: Vec<PredicateObligation<'tcx>>,
}
impl<'tcx> Progress<'tcx> {
fn error(tcx: TyCtxt<'tcx>, guar: ErrorGuaranteed) -> Self {
Progress { term: Ty::new_error(tcx, guar).into(), obligations: vec![] }
}
fn with_addl_obligations(mut self, mut obligations: Vec<PredicateObligation<'tcx>>) -> Self {
self.obligations.append(&mut obligations);
self
}
}
/// Computes the result of a projection type (if we can).
///
/// IMPORTANT:
/// - `obligation` must be fully normalized
#[instrument(level = "info", skip(selcx))]
fn project<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
) -> Result<Projected<'tcx>, ProjectionError<'tcx>> {
if !selcx.tcx().recursion_limit().value_within_limit(obligation.recursion_depth) {
// This should really be an immediate error, but some existing code
// relies on being able to recover from this.
return Err(ProjectionError::TraitSelectionError(SelectionError::Overflow(
OverflowError::Canonical,
)));
}
if let Err(guar) = obligation.predicate.error_reported() {
return Ok(Projected::Progress(Progress::error(selcx.tcx(), guar)));
}
let mut candidates = ProjectionCandidateSet::None;
// Make sure that the following procedures are kept in order. ParamEnv
// needs to be first because it has highest priority, and Select checks
// the return value of push_candidate which assumes it's ran at last.
assemble_candidates_from_param_env(selcx, obligation, &mut candidates);
assemble_candidates_from_trait_def(selcx, obligation, &mut candidates);
assemble_candidates_from_object_ty(selcx, obligation, &mut candidates);
if let ProjectionCandidateSet::Single(ProjectionCandidate::Object(_)) = candidates {
// Avoid normalization cycle from selection (see
// `assemble_candidates_from_object_ty`).
// FIXME(lazy_normalization): Lazy normalization should save us from
// having to special case this.
} else {
assemble_candidates_from_impls(selcx, obligation, &mut candidates);
};
match candidates {
ProjectionCandidateSet::Single(candidate) => {
Ok(Projected::Progress(confirm_candidate(selcx, obligation, candidate)))
}
ProjectionCandidateSet::None => {
let tcx = selcx.tcx();
let term = match tcx.def_kind(obligation.predicate.def_id) {
DefKind::AssocTy => {
Ty::new_projection(tcx, obligation.predicate.def_id, obligation.predicate.args)
.into()
}
DefKind::AssocConst => ty::Const::new_unevaluated(
tcx,
ty::UnevaluatedConst::new(
obligation.predicate.def_id,
obligation.predicate.args,
),
tcx.type_of(obligation.predicate.def_id)
.instantiate(tcx, obligation.predicate.args),
)
.into(),
kind => {
bug!("unknown projection def-id: {}", kind.descr(obligation.predicate.def_id))
}
};
Ok(Projected::NoProgress(term))
}
// Error occurred while trying to processing impls.
ProjectionCandidateSet::Error(e) => Err(ProjectionError::TraitSelectionError(e)),
// Inherent ambiguity that prevents us from even enumerating the
// candidates.
ProjectionCandidateSet::Ambiguous => Err(ProjectionError::TooManyCandidates),
}
}
/// The first thing we have to do is scan through the parameter
/// environment to see whether there are any projection predicates
/// there that can answer this question.
fn assemble_candidates_from_param_env<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
candidate_set: &mut ProjectionCandidateSet<'tcx>,
) {
assemble_candidates_from_predicates(
selcx,
obligation,
candidate_set,
ProjectionCandidate::ParamEnv,
obligation.param_env.caller_bounds().iter(),
false,
);
}
/// In the case of a nested projection like `<<A as Foo>::FooT as Bar>::BarT`, we may find
/// that the definition of `Foo` has some clues:
///
/// ```ignore (illustrative)
/// trait Foo {
/// type FooT : Bar<BarT=i32>
/// }
/// ```
///
/// Here, for example, we could conclude that the result is `i32`.
fn assemble_candidates_from_trait_def<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
candidate_set: &mut ProjectionCandidateSet<'tcx>,
) {
debug!("assemble_candidates_from_trait_def(..)");
let tcx = selcx.tcx();
// Check whether the self-type is itself a projection.
// If so, extract what we know from the trait and try to come up with a good answer.
let bounds = match *obligation.predicate.self_ty().kind() {
// Excluding IATs and type aliases here as they don't have meaningful item bounds.
ty::Alias(ty::Projection | ty::Opaque, ref data) => {
tcx.item_bounds(data.def_id).instantiate(tcx, data.args)
}
ty::Infer(ty::TyVar(_)) => {
// If the self-type is an inference variable, then it MAY wind up
// being a projected type, so induce an ambiguity.
candidate_set.mark_ambiguous();
return;
}
_ => return,
};
assemble_candidates_from_predicates(
selcx,
obligation,
candidate_set,
ProjectionCandidate::TraitDef,
bounds.iter(),
true,
);
}
/// In the case of a trait object like
/// `<dyn Iterator<Item = ()> as Iterator>::Item` we can use the existential
/// predicate in the trait object.
///
/// We don't go through the select candidate for these bounds to avoid cycles:
/// In the above case, `dyn Iterator<Item = ()>: Iterator` would create a
/// nested obligation of `<dyn Iterator<Item = ()> as Iterator>::Item: Sized`,
/// this then has to be normalized without having to prove
/// `dyn Iterator<Item = ()>: Iterator` again.
fn assemble_candidates_from_object_ty<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
candidate_set: &mut ProjectionCandidateSet<'tcx>,
) {
debug!("assemble_candidates_from_object_ty(..)");
let tcx = selcx.tcx();
if !tcx.trait_def(obligation.predicate.trait_def_id(tcx)).implement_via_object {
return;
}
let self_ty = obligation.predicate.self_ty();
let object_ty = selcx.infcx.shallow_resolve(self_ty);
let data = match object_ty.kind() {
ty::Dynamic(data, ..) => data,
ty::Infer(ty::TyVar(_)) => {
// If the self-type is an inference variable, then it MAY wind up
// being an object type, so induce an ambiguity.
candidate_set.mark_ambiguous();
return;
}
_ => return,
};
let env_predicates = data
.projection_bounds()
.filter(|bound| bound.item_def_id() == obligation.predicate.def_id)
.map(|p| p.with_self_ty(tcx, object_ty).to_predicate(tcx));
assemble_candidates_from_predicates(
selcx,
obligation,
candidate_set,
ProjectionCandidate::Object,
env_predicates,
false,
);
}
#[instrument(
level = "debug",
skip(selcx, candidate_set, ctor, env_predicates, potentially_unnormalized_candidates)
)]
fn assemble_candidates_from_predicates<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
candidate_set: &mut ProjectionCandidateSet<'tcx>,
ctor: fn(ty::PolyProjectionPredicate<'tcx>) -> ProjectionCandidate<'tcx>,
env_predicates: impl Iterator<Item = ty::Clause<'tcx>>,
potentially_unnormalized_candidates: bool,
) {
let infcx = selcx.infcx;
for predicate in env_predicates {
let bound_predicate = predicate.kind();
if let ty::ClauseKind::Projection(data) = predicate.kind().skip_binder() {
let data = bound_predicate.rebind(data);
if data.projection_def_id() != obligation.predicate.def_id {
continue;
}
let is_match = infcx.probe(|_| {
selcx.match_projection_projections(
obligation,
data,
potentially_unnormalized_candidates,
)
});
match is_match {
ProjectionMatchesProjection::Yes => {
candidate_set.push_candidate(ctor(data));
if potentially_unnormalized_candidates
&& !obligation.predicate.has_non_region_infer()
{
// HACK: Pick the first trait def candidate for a fully
// inferred predicate. This is to allow duplicates that
// differ only in normalization.
return;
}
}
ProjectionMatchesProjection::Ambiguous => {
candidate_set.mark_ambiguous();
}
ProjectionMatchesProjection::No => {}
}
}
}
}
#[instrument(level = "debug", skip(selcx, obligation, candidate_set))]
fn assemble_candidates_from_impls<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
candidate_set: &mut ProjectionCandidateSet<'tcx>,
) {
// If we are resolving `<T as TraitRef<...>>::Item == Type`,
// start out by selecting the predicate `T as TraitRef<...>`:
let trait_ref = obligation.predicate.trait_ref(selcx.tcx());
let trait_obligation = obligation.with(selcx.tcx(), trait_ref);
let _ = selcx.infcx.commit_if_ok(|_| {
let impl_source = match selcx.select(&trait_obligation) {
Ok(Some(impl_source)) => impl_source,
Ok(None) => {
candidate_set.mark_ambiguous();
return Err(());
}
Err(e) => {
debug!(error = ?e, "selection error");
candidate_set.mark_error(e);
return Err(());
}
};
let eligible = match &impl_source {
ImplSource::UserDefined(impl_data) => {
// We have to be careful when projecting out of an
// impl because of specialization. If we are not in
// codegen (i.e., projection mode is not "any"), and the
// impl's type is declared as default, then we disable
// projection (even if the trait ref is fully
// monomorphic). In the case where trait ref is not
// fully monomorphic (i.e., includes type parameters),
// this is because those type parameters may
// ultimately be bound to types from other crates that
// may have specialized impls we can't see. In the
// case where the trait ref IS fully monomorphic, this
// is a policy decision that we made in the RFC in
// order to preserve flexibility for the crate that
// defined the specializable impl to specialize later
// for existing types.
//
// In either case, we handle this by not adding a
// candidate for an impl if it contains a `default`
// type.
//
// NOTE: This should be kept in sync with the similar code in
// `rustc_ty_utils::instance::resolve_associated_item()`.
let node_item =
specialization_graph::assoc_def(selcx.tcx(), impl_data.impl_def_id, obligation.predicate.def_id)
.map_err(|ErrorGuaranteed { .. }| ())?;
if node_item.is_final() {
// Non-specializable items are always projectable.
true
} else {
// Only reveal a specializable default if we're past type-checking
// and the obligation is monomorphic, otherwise passes such as
// transmute checking and polymorphic MIR optimizations could
// get a result which isn't correct for all monomorphizations.
if obligation.param_env.reveal() == Reveal::All {
// NOTE(eddyb) inference variables can resolve to parameters, so
// assume `poly_trait_ref` isn't monomorphic, if it contains any.
let poly_trait_ref = selcx.infcx.resolve_vars_if_possible(trait_ref);
!poly_trait_ref.still_further_specializable()
} else {
debug!(
assoc_ty = ?selcx.tcx().def_path_str(node_item.item.def_id),
?obligation.predicate,
"assemble_candidates_from_impls: not eligible due to default",
);
false
}
}
}
ImplSource::Builtin(BuiltinImplSource::Misc, _) => {
// While a builtin impl may be known to exist, the associated type may not yet
// be known. Any type with multiple potential associated types is therefore
// not eligible.
let self_ty = selcx.infcx.shallow_resolve(obligation.predicate.self_ty());
let lang_items = selcx.tcx().lang_items();
if [lang_items.gen_trait(), lang_items.future_trait()].contains(&Some(trait_ref.def_id))
|| selcx.tcx().fn_trait_kind_from_def_id(trait_ref.def_id).is_some()
{
true
} else if lang_items.discriminant_kind_trait() == Some(trait_ref.def_id) {
match self_ty.kind() {
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Adt(..)
| ty::Foreign(_)
| ty::Str
| ty::Array(..)
| ty::Slice(_)
| ty::RawPtr(..)
| ty::Ref(..)
| ty::FnDef(..)
| ty::FnPtr(..)
| ty::Dynamic(..)
| ty::Closure(..)
| ty::Generator(..)
| ty::GeneratorWitness(..)
| ty::Never
| ty::Tuple(..)
// Integers and floats always have `u8` as their discriminant.
| ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(..)) => true,
// type parameters, opaques, and unnormalized projections have pointer
// metadata if they're known (e.g. by the param_env) to be sized
ty::Param(_)
| ty::Alias(..)
| ty::Bound(..)
| ty::Placeholder(..)
| ty::Infer(..)
| ty::Error(_) => false,
}
} else if lang_items.pointee_trait() == Some(trait_ref.def_id) {
let tail = selcx.tcx().struct_tail_with_normalize(
self_ty,
|ty| {
// We throw away any obligations we get from this, since we normalize
// and confirm these obligations once again during confirmation
normalize_with_depth(
selcx,
obligation.param_env,
obligation.cause.clone(),
obligation.recursion_depth + 1,
ty,
)
.value
},
|| {},
);
match tail.kind() {
ty::Bool
| ty::Char
| ty::Int(_)
| ty::Uint(_)
| ty::Float(_)
| ty::Str
| ty::Array(..)
| ty::Slice(_)
| ty::RawPtr(..)
| ty::Ref(..)
| ty::FnDef(..)
| ty::FnPtr(..)
| ty::Dynamic(..)
| ty::Closure(..)
| ty::Generator(..)
| ty::GeneratorWitness(..)
| ty::Never
// Extern types have unit metadata, according to RFC 2850
| ty::Foreign(_)
// If returned by `struct_tail_without_normalization` this is a unit struct
// without any fields, or not a struct, and therefore is Sized.
| ty::Adt(..)
// If returned by `struct_tail_without_normalization` this is the empty tuple.
| ty::Tuple(..)
// Integers and floats are always Sized, and so have unit type metadata.
| ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(..)) => true,
// type parameters, opaques, and unnormalized projections have pointer
// metadata if they're known (e.g. by the param_env) to be sized
ty::Param(_) | ty::Alias(..)
if selcx.infcx.predicate_must_hold_modulo_regions(
&obligation.with(
selcx.tcx(),
ty::TraitRef::from_lang_item(selcx.tcx(), LangItem::Sized, obligation.cause.span(),[self_ty]),
),
) =>
{
true
}
// FIXME(compiler-errors): are Bound and Placeholder types ever known sized?
ty::Param(_)
| ty::Alias(..)
| ty::Bound(..)
| ty::Placeholder(..)
| ty::Infer(..)
| ty::Error(_) => {
if tail.has_infer_types() {
candidate_set.mark_ambiguous();
}
false
}
}
} else {
bug!("unexpected builtin trait with associated type: {trait_ref:?}")
}
}
ImplSource::Param(..) => {
// This case tell us nothing about the value of an
// associated type. Consider:
//
// ```
// trait SomeTrait { type Foo; }
// fn foo<T:SomeTrait>(...) { }
// ```
//
// If the user writes `<T as SomeTrait>::Foo`, then the `T
// : SomeTrait` binding does not help us decide what the
// type `Foo` is (at least, not more specifically than
// what we already knew).
//
// But wait, you say! What about an example like this:
//
// ```
// fn bar<T:SomeTrait<Foo=usize>>(...) { ... }
// ```
//
// Doesn't the `T : SomeTrait<Foo=usize>` predicate help
// resolve `T::Foo`? And of course it does, but in fact
// that single predicate is desugared into two predicates
// in the compiler: a trait predicate (`T : SomeTrait`) and a
// projection. And the projection where clause is handled
// in `assemble_candidates_from_param_env`.
false
}
ImplSource::Builtin(BuiltinImplSource::Object { .. }, _) => {
// Handled by the `Object` projection candidate. See
// `assemble_candidates_from_object_ty` for an explanation of
// why we special case object types.
false
}
ImplSource::Builtin(BuiltinImplSource::TraitUpcasting { .. }, _)
| ImplSource::Builtin(BuiltinImplSource::TupleUnsizing, _) => {
// These traits have no associated types.
selcx.tcx().sess.delay_span_bug(
obligation.cause.span,
format!("Cannot project an associated type from `{impl_source:?}`"),
);
return Err(());
}
};
if eligible {
if candidate_set.push_candidate(ProjectionCandidate::Select(impl_source)) {
Ok(())
} else {
Err(())
}
} else {
Err(())
}
});
}
fn confirm_candidate<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
candidate: ProjectionCandidate<'tcx>,
) -> Progress<'tcx> {
debug!(?obligation, ?candidate, "confirm_candidate");
let mut progress = match candidate {
ProjectionCandidate::ParamEnv(poly_projection)
| ProjectionCandidate::Object(poly_projection) => {
confirm_param_env_candidate(selcx, obligation, poly_projection, false)
}
ProjectionCandidate::TraitDef(poly_projection) => {
confirm_param_env_candidate(selcx, obligation, poly_projection, true)
}
ProjectionCandidate::Select(impl_source) => {
confirm_select_candidate(selcx, obligation, impl_source)
}
};
// When checking for cycle during evaluation, we compare predicates with
// "syntactic" equality. Since normalization generally introduces a type
// with new region variables, we need to resolve them to existing variables
// when possible for this to work. See `auto-trait-projection-recursion.rs`
// for a case where this matters.
if progress.term.has_infer_regions() {
progress.term = progress.term.fold_with(&mut OpportunisticRegionResolver::new(selcx.infcx));
}
progress
}
fn confirm_select_candidate<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
impl_source: Selection<'tcx>,
) -> Progress<'tcx> {
match impl_source {
ImplSource::UserDefined(data) => confirm_impl_candidate(selcx, obligation, data),
ImplSource::Builtin(BuiltinImplSource::Misc, data) => {
let trait_def_id = obligation.predicate.trait_def_id(selcx.tcx());
let lang_items = selcx.tcx().lang_items();
if lang_items.gen_trait() == Some(trait_def_id) {
confirm_generator_candidate(selcx, obligation, data)
} else if lang_items.future_trait() == Some(trait_def_id) {
confirm_future_candidate(selcx, obligation, data)
} else if selcx.tcx().fn_trait_kind_from_def_id(trait_def_id).is_some() {
if obligation.predicate.self_ty().is_closure() {
confirm_closure_candidate(selcx, obligation, data)
} else {
confirm_fn_pointer_candidate(selcx, obligation, data)
}
} else {
confirm_builtin_candidate(selcx, obligation, data)
}
}
ImplSource::Builtin(BuiltinImplSource::Object { .. }, _)
| ImplSource::Param(..)
| ImplSource::Builtin(BuiltinImplSource::TraitUpcasting { .. }, _)
| ImplSource::Builtin(BuiltinImplSource::TupleUnsizing, _) => {
// we don't create Select candidates with this kind of resolution
span_bug!(
obligation.cause.span,
"Cannot project an associated type from `{:?}`",
impl_source
)
}
}
}
fn confirm_generator_candidate<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
nested: Vec<PredicateObligation<'tcx>>,
) -> Progress<'tcx> {
let ty::Generator(_, args, _) =
selcx.infcx.shallow_resolve(obligation.predicate.self_ty()).kind()
else {
unreachable!()
};
let gen_sig = args.as_generator().poly_sig();
let Normalized { value: gen_sig, obligations } = normalize_with_depth(
selcx,
obligation.param_env,
obligation.cause.clone(),
obligation.recursion_depth + 1,
gen_sig,
);
debug!(?obligation, ?gen_sig, ?obligations, "confirm_generator_candidate");
let tcx = selcx.tcx();
let gen_def_id = tcx.require_lang_item(LangItem::Generator, None);
let predicate = super::util::generator_trait_ref_and_outputs(
tcx,
gen_def_id,
obligation.predicate.self_ty(),
gen_sig,
)
.map_bound(|(trait_ref, yield_ty, return_ty)| {
let name = tcx.associated_item(obligation.predicate.def_id).name;
let ty = if name == sym::Return {
return_ty
} else if name == sym::Yield {
yield_ty
} else {
bug!()
};
ty::ProjectionPredicate {
projection_ty: tcx.mk_alias_ty(obligation.predicate.def_id, trait_ref.args),
term: ty.into(),
}
});
confirm_param_env_candidate(selcx, obligation, predicate, false)
.with_addl_obligations(nested)
.with_addl_obligations(obligations)
}
fn confirm_future_candidate<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
nested: Vec<PredicateObligation<'tcx>>,
) -> Progress<'tcx> {
let ty::Generator(_, args, _) =
selcx.infcx.shallow_resolve(obligation.predicate.self_ty()).kind()
else {
unreachable!()
};
let gen_sig = args.as_generator().poly_sig();
let Normalized { value: gen_sig, obligations } = normalize_with_depth(
selcx,
obligation.param_env,
obligation.cause.clone(),
obligation.recursion_depth + 1,
gen_sig,
);
debug!(?obligation, ?gen_sig, ?obligations, "confirm_future_candidate");
let tcx = selcx.tcx();
let fut_def_id = tcx.require_lang_item(LangItem::Future, None);
let predicate = super::util::future_trait_ref_and_outputs(
tcx,
fut_def_id,
obligation.predicate.self_ty(),
gen_sig,
)
.map_bound(|(trait_ref, return_ty)| {
debug_assert_eq!(tcx.associated_item(obligation.predicate.def_id).name, sym::Output);
ty::ProjectionPredicate {
projection_ty: tcx.mk_alias_ty(obligation.predicate.def_id, trait_ref.args),
term: return_ty.into(),
}
});
confirm_param_env_candidate(selcx, obligation, predicate, false)
.with_addl_obligations(nested)
.with_addl_obligations(obligations)
}
fn confirm_builtin_candidate<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
data: Vec<PredicateObligation<'tcx>>,
) -> Progress<'tcx> {
let tcx = selcx.tcx();
let self_ty = obligation.predicate.self_ty();
let args = tcx.mk_args(&[self_ty.into()]);
let lang_items = tcx.lang_items();
let item_def_id = obligation.predicate.def_id;
let trait_def_id = tcx.trait_of_item(item_def_id).unwrap();
let (term, obligations) = if lang_items.discriminant_kind_trait() == Some(trait_def_id) {
let discriminant_def_id = tcx.require_lang_item(LangItem::Discriminant, None);
assert_eq!(discriminant_def_id, item_def_id);
(self_ty.discriminant_ty(tcx).into(), Vec::new())
} else if lang_items.pointee_trait() == Some(trait_def_id) {
let metadata_def_id = tcx.require_lang_item(LangItem::Metadata, None);
assert_eq!(metadata_def_id, item_def_id);
let mut obligations = Vec::new();
let (metadata_ty, check_is_sized) = self_ty.ptr_metadata_ty(tcx, |ty| {
normalize_with_depth_to(
selcx,
obligation.param_env,
obligation.cause.clone(),
obligation.recursion_depth + 1,
ty,
&mut obligations,
)
});
if check_is_sized {
let sized_predicate = ty::TraitRef::from_lang_item(
tcx,
LangItem::Sized,
obligation.cause.span(),
[self_ty],
);
obligations.push(obligation.with(tcx, sized_predicate));
}
(metadata_ty.into(), obligations)
} else {
bug!("unexpected builtin trait with associated type: {:?}", obligation.predicate);
};
let predicate =
ty::ProjectionPredicate { projection_ty: tcx.mk_alias_ty(item_def_id, args), term };
confirm_param_env_candidate(selcx, obligation, ty::Binder::dummy(predicate), false)
.with_addl_obligations(obligations)
.with_addl_obligations(data)
}
fn confirm_fn_pointer_candidate<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
nested: Vec<PredicateObligation<'tcx>>,
) -> Progress<'tcx> {
let fn_type = selcx.infcx.shallow_resolve(obligation.predicate.self_ty());
let sig = fn_type.fn_sig(selcx.tcx());
let Normalized { value: sig, obligations } = normalize_with_depth(
selcx,
obligation.param_env,
obligation.cause.clone(),
obligation.recursion_depth + 1,
sig,
);
confirm_callable_candidate(selcx, obligation, sig, util::TupleArgumentsFlag::Yes)
.with_addl_obligations(nested)
.with_addl_obligations(obligations)
}
fn confirm_closure_candidate<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
nested: Vec<PredicateObligation<'tcx>>,
) -> Progress<'tcx> {
let ty::Closure(_, args) = selcx.infcx.shallow_resolve(obligation.predicate.self_ty()).kind()
else {
unreachable!()
};
let closure_sig = args.as_closure().sig();
let Normalized { value: closure_sig, obligations } = normalize_with_depth(
selcx,
obligation.param_env,
obligation.cause.clone(),
obligation.recursion_depth + 1,
closure_sig,
);
debug!(?obligation, ?closure_sig, ?obligations, "confirm_closure_candidate");
confirm_callable_candidate(selcx, obligation, closure_sig, util::TupleArgumentsFlag::No)
.with_addl_obligations(nested)
.with_addl_obligations(obligations)
}
fn confirm_callable_candidate<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
fn_sig: ty::PolyFnSig<'tcx>,
flag: util::TupleArgumentsFlag,
) -> Progress<'tcx> {
let tcx = selcx.tcx();
debug!(?obligation, ?fn_sig, "confirm_callable_candidate");
let fn_once_def_id = tcx.require_lang_item(LangItem::FnOnce, None);
let fn_once_output_def_id = tcx.require_lang_item(LangItem::FnOnceOutput, None);
let predicate = super::util::closure_trait_ref_and_return_type(
tcx,
fn_once_def_id,
obligation.predicate.self_ty(),
fn_sig,
flag,
)
.map_bound(|(trait_ref, ret_type)| ty::ProjectionPredicate {
projection_ty: tcx.mk_alias_ty(fn_once_output_def_id, trait_ref.args),
term: ret_type.into(),
});
confirm_param_env_candidate(selcx, obligation, predicate, true)
}
fn confirm_param_env_candidate<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
poly_cache_entry: ty::PolyProjectionPredicate<'tcx>,
potentially_unnormalized_candidate: bool,
) -> Progress<'tcx> {
let infcx = selcx.infcx;
let cause = &obligation.cause;
let param_env = obligation.param_env;
let cache_entry = infcx.instantiate_binder_with_fresh_vars(
cause.span,
LateBoundRegionConversionTime::HigherRankedType,
poly_cache_entry,
);
let cache_projection = cache_entry.projection_ty;
let mut nested_obligations = Vec::new();
let obligation_projection = obligation.predicate;
let obligation_projection = ensure_sufficient_stack(|| {
normalize_with_depth_to(
selcx,
obligation.param_env,
obligation.cause.clone(),
obligation.recursion_depth + 1,
obligation_projection,
&mut nested_obligations,
)
});
let cache_projection = if potentially_unnormalized_candidate {
ensure_sufficient_stack(|| {
normalize_with_depth_to(
selcx,
obligation.param_env,
obligation.cause.clone(),
obligation.recursion_depth + 1,
cache_projection,
&mut nested_obligations,
)
})
} else {
cache_projection
};
debug!(?cache_projection, ?obligation_projection);
match infcx.at(cause, param_env).eq(
DefineOpaqueTypes::No,
cache_projection,
obligation_projection,
) {
Ok(InferOk { value: _, obligations }) => {
nested_obligations.extend(obligations);
assoc_ty_own_obligations(selcx, obligation, &mut nested_obligations);
// FIXME(associated_const_equality): Handle consts here as well? Maybe this progress type should just take
// a term instead.
Progress { term: cache_entry.term, obligations: nested_obligations }
}
Err(e) => {
let msg = format!(
"Failed to unify obligation `{obligation:?}` with poly_projection `{poly_cache_entry:?}`: {e:?}",
);
debug!("confirm_param_env_candidate: {}", msg);
let err = Ty::new_error_with_message(infcx.tcx, obligation.cause.span, msg);
Progress { term: err.into(), obligations: vec![] }
}
}
}
fn confirm_impl_candidate<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
impl_impl_source: ImplSourceUserDefinedData<'tcx, PredicateObligation<'tcx>>,
) -> Progress<'tcx> {
let tcx = selcx.tcx();
let ImplSourceUserDefinedData { impl_def_id, args, mut nested } = impl_impl_source;
let assoc_item_id = obligation.predicate.def_id;
let trait_def_id = tcx.trait_id_of_impl(impl_def_id).unwrap();
let param_env = obligation.param_env;
let assoc_ty = match specialization_graph::assoc_def(tcx, impl_def_id, assoc_item_id) {
Ok(assoc_ty) => assoc_ty,
Err(guar) => return Progress::error(tcx, guar),
};
if !assoc_ty.item.defaultness(tcx).has_value() {
// This means that the impl is missing a definition for the
// associated type. This error will be reported by the type
// checker method `check_impl_items_against_trait`, so here we
// just return Error.
debug!(
"confirm_impl_candidate: no associated type {:?} for {:?}",
assoc_ty.item.name, obligation.predicate
);
return Progress { term: Ty::new_misc_error(tcx).into(), obligations: nested };
}
// If we're trying to normalize `<Vec<u32> as X>::A<S>` using
//`impl<T> X for Vec<T> { type A<Y> = Box<Y>; }`, then:
//
// * `obligation.predicate.args` is `[Vec<u32>, S]`
// * `args` is `[u32]`
// * `args` ends up as `[u32, S]`
let args = obligation.predicate.args.rebase_onto(tcx, trait_def_id, args);
let args = translate_args(selcx.infcx, param_env, impl_def_id, args, assoc_ty.defining_node);
let ty = tcx.type_of(assoc_ty.item.def_id);
let is_const = matches!(tcx.def_kind(assoc_ty.item.def_id), DefKind::AssocConst);
let term: ty::EarlyBinder<ty::Term<'tcx>> = if is_const {
let did = assoc_ty.item.def_id;
let identity_args = crate::traits::GenericArgs::identity_for_item(tcx, did);
let uv = ty::UnevaluatedConst::new(did, identity_args);
ty.map_bound(|ty| ty::Const::new_unevaluated(tcx, uv, ty).into())
} else {
ty.map_bound(|ty| ty.into())
};
if !check_args_compatible(tcx, assoc_ty.item, args) {
let err = Ty::new_error_with_message(
tcx,
obligation.cause.span,
"impl item and trait item have different parameters",
);
Progress { term: err.into(), obligations: nested }
} else {
assoc_ty_own_obligations(selcx, obligation, &mut nested);
Progress { term: term.instantiate(tcx, args), obligations: nested }
}
}
// Get obligations corresponding to the predicates from the where-clause of the
// associated type itself.
fn assoc_ty_own_obligations<'cx, 'tcx>(
selcx: &mut SelectionContext<'cx, 'tcx>,
obligation: &ProjectionTyObligation<'tcx>,
nested: &mut Vec<PredicateObligation<'tcx>>,
) {
let tcx = selcx.tcx();
let predicates = tcx
.predicates_of(obligation.predicate.def_id)
.instantiate_own(tcx, obligation.predicate.args);
for (predicate, span) in predicates {
let normalized = normalize_with_depth_to(
selcx,
obligation.param_env,
obligation.cause.clone(),
obligation.recursion_depth + 1,
predicate,
nested,
);
let nested_cause = if matches!(
obligation.cause.code(),
super::CompareImplItemObligation { .. }
| super::CheckAssociatedTypeBounds { .. }
| super::AscribeUserTypeProvePredicate(..)
) {
obligation.cause.clone()
} else if span.is_dummy() {
ObligationCause::new(
obligation.cause.span,
obligation.cause.body_id,
super::ItemObligation(obligation.predicate.def_id),
)
} else {
ObligationCause::new(
obligation.cause.span,
obligation.cause.body_id,
super::BindingObligation(obligation.predicate.def_id, span),
)
};
nested.push(Obligation::with_depth(
tcx,
nested_cause,
obligation.recursion_depth + 1,
obligation.param_env,
normalized,
));
}
}
pub(crate) trait ProjectionCacheKeyExt<'cx, 'tcx>: Sized {
fn from_poly_projection_predicate(
selcx: &mut SelectionContext<'cx, 'tcx>,
predicate: ty::PolyProjectionPredicate<'tcx>,
) -> Option<Self>;
}
impl<'cx, 'tcx> ProjectionCacheKeyExt<'cx, 'tcx> for ProjectionCacheKey<'tcx> {
fn from_poly_projection_predicate(
selcx: &mut SelectionContext<'cx, 'tcx>,
predicate: ty::PolyProjectionPredicate<'tcx>,
) -> Option<Self> {
let infcx = selcx.infcx;
// We don't do cross-snapshot caching of obligations with escaping regions,
// so there's no cache key to use
predicate.no_bound_vars().map(|predicate| {
ProjectionCacheKey::new(
// We don't attempt to match up with a specific type-variable state
// from a specific call to `opt_normalize_projection_type` - if
// there's no precise match, the original cache entry is "stranded"
// anyway.
infcx.resolve_vars_if_possible(predicate.projection_ty),
)
})
}
}