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project.rs
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project.rs
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//! Code for projecting associated types out of trait references.
use super::specialization_graph;
use super::translate_substs;
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::{
ImplSourceClosureData, ImplSourceFnPointerData, ImplSourceFutureData, ImplSourceGeneratorData,
ImplSourceUserDefinedData,
};
use super::{Normalized, NormalizedTy, ProjectionCacheEntry, ProjectionCacheKey};
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::def_id::DefId;
use rustc_hir::lang_items::LangItem;
use rustc_infer::infer::at::At;
use rustc_infer::infer::resolve::OpportunisticRegionResolver;
use rustc_infer::traits::ImplSourceBuiltinData;
use rustc_middle::traits::select::OverflowError;
use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
use rustc_middle::ty::visit::{MaxUniverse, TypeVisitable};
use rustc_middle::ty::DefIdTree;
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<'tcx>>(&self, t: T) -> InferOk<'tcx, T>;
}
impl<'tcx> NormalizeExt<'tcx> for At<'_, 'tcx> {
fn normalize<T: TypeFoldable<'tcx>>(&self, value: T) -> InferOk<'tcx, T> {
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 }
}
}
/// 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>),
ImplTraitInTrait(ImplTraitInTraitCandidate<'tcx>),
}
#[derive(PartialEq, Eq, Debug)]
enum ImplTraitInTraitCandidate<'tcx> {
// The `impl Trait` from a trait function's default body
Trait,
// A concrete type provided from a trait's `impl Trait` from an impl
Impl(ImplSourceUserDefinedData<'tcx, PredicateObligation<'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.replace_bound_vars_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 src/test/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);
match infcx.at(&obligation.cause, obligation.param_env).eq(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<'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<'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<'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<'tcx>>(value: &T, reveal: Reveal) -> bool {
match reveal {
Reveal::UserFacing => value
.has_type_flags(ty::TypeFlags::HAS_TY_PROJECTION | ty::TypeFlags::HAS_CT_PROJECTION),
Reveal::All => value.has_type_flags(
ty::TypeFlags::HAS_TY_PROJECTION
| 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> {
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<'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 {:?} without wrapping in a `Binder`",
value
);
if !needs_normalization(&value, self.param_env.reveal()) {
value
} else {
value.fold_with(self)
}
}
}
impl<'a, 'b, 'tcx> TypeFolder<'tcx> for AssocTypeNormalizer<'a, 'b, 'tcx> {
fn tcx<'c>(&'c self) -> TyCtxt<'tcx> {
self.selcx.tcx()
}
fn fold_binder<T: TypeFoldable<'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;
}
// 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 substs 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 substs regardless.
match *ty.kind() {
// This is really important. While we *can* handle this, this has
// severe performance implications for large opaque types with
// late-bound regions. See `issue-88862` benchmark.
ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. })
if !substs.has_escaping_bound_vars() =>
{
// 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.tcx().recursion_limit();
if !recursion_limit.value_within_limit(self.depth) {
self.selcx.infcx.err_ctxt().report_overflow_error(
&ty,
self.cause.span,
true,
|_| {},
);
}
let substs = substs.fold_with(self);
let generic_ty = self.tcx().bound_type_of(def_id);
let concrete_ty = generic_ty.subst(self.tcx(), substs);
self.depth += 1;
let folded_ty = self.fold_ty(concrete_ty);
self.depth -= 1;
folded_ty
}
}
}
ty::Alias(ty::Projection, data) 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::Alias(ty::Projection, data) => {
// 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.super_fold_with(self),
}
}
#[instrument(skip(self), level = "debug")]
fn fold_const(&mut self, constant: ty::Const<'tcx>) -> ty::Const<'tcx> {
let tcx = self.selcx.tcx();
if tcx.lazy_normalization() || !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.eval(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<'tcx>, R: TypeFoldable<'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<'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<'tcx> for BoundVarReplacer<'_, 'tcx> {
fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
self.infcx.tcx
}
fn fold_binder<T: TypeFoldable<'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, name: br.kind };
self.mapped_regions.insert(p, br);
self.infcx.tcx.mk_region(ty::RePlaceholder(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, name: bound_ty.var };
self.mapped_types.insert(p, bound_ty);
self.infcx.tcx.mk_ty(ty::Placeholder(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, name: bound_const };
self.mapped_consts.insert(p, bound_const);
self.infcx.tcx.mk_const(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<'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<'tcx> for PlaceholderReplacer<'_, 'tcx> {
fn tcx<'b>(&'b self) -> TyCtxt<'tcx> {
self.infcx.tcx
}
fn fold_binder<T: TypeFoldable<'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(_) => self
.infcx
.inner
.borrow_mut()
.unwrap_region_constraints()
.opportunistic_resolve_region(self.infcx.tcx, r0),
_ => 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,
);
self.tcx().mk_region(ty::ReLateBound(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,
);
self.tcx().mk_ty(ty::Bound(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,
);
self.tcx().mk_const(ty::ConstKind::Bound(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>,