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//! Code for the 'normalization' query. This consists of a wrapper
//! which folds deeply, invoking the underlying
//! `normalize_projection_ty` query when it encounters projections.
use crate::infer::at::At;
use crate::infer::canonical::OriginalQueryValues;
use crate::infer::{InferCtxt, InferOk};
use crate::traits::error_reporting::TypeErrCtxtExt;
use crate::traits::project::{needs_normalization, BoundVarReplacer, PlaceholderReplacer};
use crate::traits::{ObligationCause, PredicateObligation, Reveal};
use rustc_data_structures::sso::SsoHashMap;
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_infer::traits::Normalized;
use rustc_middle::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeSuperFoldable};
use rustc_middle::ty::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt};
use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitor};
use rustc_span::DUMMY_SP;
use std::ops::ControlFlow;
use super::NoSolution;
pub use rustc_middle::traits::query::NormalizationResult;
pub trait QueryNormalizeExt<'tcx> {
/// Normalize a value using the `QueryNormalizer`.
///
/// This normalization should *only* be used when the projection does not
/// have possible ambiguity or may not be well-formed.
///
/// After codegen, when lifetimes do not matter, it is preferable to instead
/// use [`TyCtxt::normalize_erasing_regions`], which wraps this procedure.
fn query_normalize<T>(self, value: T) -> Result<Normalized<'tcx, T>, NoSolution>
where
T: TypeFoldable<TyCtxt<'tcx>>;
}
impl<'cx, 'tcx> QueryNormalizeExt<'tcx> for At<'cx, 'tcx> {
/// Normalize `value` in the context of the inference context,
/// yielding a resulting type, or an error if `value` cannot be
/// normalized. If you don't care about regions, you should prefer
/// `normalize_erasing_regions`, which is more efficient.
///
/// If the normalization succeeds and is unambiguous, returns back
/// the normalized value along with various outlives relations (in
/// the form of obligations that must be discharged).
///
/// N.B., this will *eventually* be the main means of
/// normalizing, but for now should be used only when we actually
/// know that normalization will succeed, since error reporting
/// and other details are still "under development".
fn query_normalize<T>(self, value: T) -> Result<Normalized<'tcx, T>, NoSolution>
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
debug!(
"normalize::<{}>(value={:?}, param_env={:?}, cause={:?})",
std::any::type_name::<T>(),
value,
self.param_env,
self.cause,
);
// This is actually a consequence by the way `normalize_erasing_regions` works currently.
// Because it needs to call the `normalize_generic_arg_after_erasing_regions`, it folds
// through tys and consts in a `TypeFoldable`. Importantly, it skips binders, leaving us
// with trying to normalize with escaping bound vars.
//
// Here, we just add the universes that we *would* have created had we passed through the binders.
//
// We *could* replace escaping bound vars eagerly here, but it doesn't seem really necessary.
// The rest of the code is already set up to be lazy about replacing bound vars,
// and only when we actually have to normalize.
let universes = if value.has_escaping_bound_vars() {
let mut max_visitor =
MaxEscapingBoundVarVisitor { outer_index: ty::INNERMOST, escaping: 0 };
value.visit_with(&mut max_visitor);
vec![None; max_visitor.escaping]
} else {
vec![]
};
if self.infcx.next_trait_solver() {
match crate::solve::deeply_normalize_with_skipped_universes(self, value, universes) {
Ok(value) => return Ok(Normalized { value, obligations: vec![] }),
Err(_errors) => {
return Err(NoSolution);
}
}
}
if !needs_normalization(&value, self.param_env.reveal()) {
return Ok(Normalized { value, obligations: vec![] });
}
let mut normalizer = QueryNormalizer {
infcx: self.infcx,
cause: self.cause,
param_env: self.param_env,
obligations: vec![],
cache: SsoHashMap::new(),
anon_depth: 0,
universes,
};
let result = value.try_fold_with(&mut normalizer);
info!(
"normalize::<{}>: result={:?} with {} obligations",
std::any::type_name::<T>(),
result,
normalizer.obligations.len(),
);
debug!(
"normalize::<{}>: obligations={:?}",
std::any::type_name::<T>(),
normalizer.obligations,
);
result.map(|value| Normalized { value, obligations: normalizer.obligations })
}
}
// Visitor to find the maximum escaping bound var
struct MaxEscapingBoundVarVisitor {
// The index which would count as escaping
outer_index: ty::DebruijnIndex,
escaping: usize,
}
impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for MaxEscapingBoundVarVisitor {
fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>(
&mut self,
t: &ty::Binder<'tcx, T>,
) -> ControlFlow<Self::BreakTy> {
self.outer_index.shift_in(1);
let result = t.super_visit_with(self);
self.outer_index.shift_out(1);
result
}
#[inline]
fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
if t.outer_exclusive_binder() > self.outer_index {
self.escaping = self
.escaping
.max(t.outer_exclusive_binder().as_usize() - self.outer_index.as_usize());
}
ControlFlow::Continue(())
}
#[inline]
fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
match *r {
ty::ReLateBound(debruijn, _) if debruijn > self.outer_index => {
self.escaping =
self.escaping.max(debruijn.as_usize() - self.outer_index.as_usize());
}
_ => {}
}
ControlFlow::Continue(())
}
fn visit_const(&mut self, ct: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
match ct.kind() {
ty::ConstKind::Bound(debruijn, _) if debruijn >= self.outer_index => {
self.escaping =
self.escaping.max(debruijn.as_usize() - self.outer_index.as_usize());
ControlFlow::Continue(())
}
_ => ct.super_visit_with(self),
}
}
}
struct QueryNormalizer<'cx, 'tcx> {
infcx: &'cx InferCtxt<'tcx>,
cause: &'cx ObligationCause<'tcx>,
param_env: ty::ParamEnv<'tcx>,
obligations: Vec<PredicateObligation<'tcx>>,
cache: SsoHashMap<Ty<'tcx>, Ty<'tcx>>,
anon_depth: usize,
universes: Vec<Option<ty::UniverseIndex>>,
}
impl<'cx, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for QueryNormalizer<'cx, 'tcx> {
type Error = NoSolution;
fn interner(&self) -> TyCtxt<'tcx> {
self.infcx.tcx
}
fn try_fold_binder<T: TypeFoldable<TyCtxt<'tcx>>>(
&mut self,
t: ty::Binder<'tcx, T>,
) -> Result<ty::Binder<'tcx, T>, Self::Error> {
self.universes.push(None);
let t = t.try_super_fold_with(self);
self.universes.pop();
t
}
#[instrument(level = "debug", skip(self))]
fn try_fold_ty(&mut self, ty: Ty<'tcx>) -> Result<Ty<'tcx>, Self::Error> {
if !needs_normalization(&ty, self.param_env.reveal()) {
return Ok(ty);
}
if let Some(ty) = self.cache.get(&ty) {
return Ok(*ty);
}
let (kind, data) = match *ty.kind() {
ty::Alias(kind, data) => (kind, data),
_ => {
let res = ty.try_super_fold_with(self)?;
self.cache.insert(ty, res);
return Ok(res);
}
};
// See note in `rustc_trait_selection::traits::project` about why we
// wait to fold the args.
// Wrap this in a closure so we don't accidentally return from the outer function
let res = match kind {
ty::Opaque => {
// Only normalize `impl Trait` outside of type inference, usually in codegen.
match self.param_env.reveal() {
Reveal::UserFacing => ty.try_super_fold_with(self)?,
Reveal::All => {
let args = data.args.try_fold_with(self)?;
let recursion_limit = self.interner().recursion_limit();
if !recursion_limit.value_within_limit(self.anon_depth) {
// A closure or generator may have itself as in its upvars.
// This should be checked handled by the recursion check for opaque
// types, but we may end up here before that check can happen.
// In that case, we delay a bug to mark the trip, and continue without
// revealing the opaque.
self.infcx
.err_ctxt()
.build_overflow_error(&ty, self.cause.span, true)
.delay_as_bug();
return ty.try_super_fold_with(self);
}
let generic_ty = self.interner().type_of(data.def_id);
let concrete_ty = generic_ty.instantiate(self.interner(), args);
self.anon_depth += 1;
if concrete_ty == ty {
bug!(
"infinite recursion generic_ty: {:#?}, args: {:#?}, \
concrete_ty: {:#?}, ty: {:#?}",
generic_ty,
args,
concrete_ty,
ty
);
}
let folded_ty = ensure_sufficient_stack(|| self.try_fold_ty(concrete_ty));
self.anon_depth -= 1;
folded_ty?
}
}
}
ty::Projection | ty::Inherent | ty::Weak => {
// See note in `rustc_trait_selection::traits::project`
let infcx = self.infcx;
let tcx = infcx.tcx;
// Just an optimization: When we don't have escaping bound vars,
// we don't need to replace them with placeholders.
let (data, maps) = if data.has_escaping_bound_vars() {
let (data, mapped_regions, mapped_types, mapped_consts) =
BoundVarReplacer::replace_bound_vars(infcx, &mut self.universes, data);
(data, Some((mapped_regions, mapped_types, mapped_consts)))
} else {
(data, None)
};
let data = data.try_fold_with(self)?;
let mut orig_values = OriginalQueryValues::default();
// HACK(matthewjasper) `'static` is special-cased in selection,
// so we cannot canonicalize it.
let c_data = infcx
.canonicalize_query_keep_static(self.param_env.and(data), &mut orig_values);
debug!("QueryNormalizer: c_data = {:#?}", c_data);
debug!("QueryNormalizer: orig_values = {:#?}", orig_values);
let result = match kind {
ty::Projection => tcx.normalize_projection_ty(c_data),
ty::Weak => tcx.normalize_weak_ty(c_data),
ty::Inherent => tcx.normalize_inherent_projection_ty(c_data),
_ => unreachable!(),
}?;
// We don't expect ambiguity.
if result.is_ambiguous() {
// Rustdoc normalizes possibly not well-formed types, so only
// treat this as a bug if we're not in rustdoc.
if !tcx.sess.opts.actually_rustdoc {
tcx.sess.delay_span_bug(
DUMMY_SP,
format!("unexpected ambiguity: {c_data:?} {result:?}"),
);
}
return Err(NoSolution);
}
let InferOk { value: result, obligations } = infcx
.instantiate_query_response_and_region_obligations(
self.cause,
self.param_env,
&orig_values,
result,
)?;
debug!("QueryNormalizer: result = {:#?}", result);
debug!("QueryNormalizer: obligations = {:#?}", obligations);
self.obligations.extend(obligations);
let res = if let Some((mapped_regions, mapped_types, mapped_consts)) = maps {
PlaceholderReplacer::replace_placeholders(
infcx,
mapped_regions,
mapped_types,
mapped_consts,
&self.universes,
result.normalized_ty,
)
} else {
result.normalized_ty
};
// `tcx.normalize_projection_ty` may normalize to a type that still has
// unevaluated consts, so keep normalizing here if that's the case.
// Similarly, `tcx.normalize_weak_ty` will only unwrap one layer of type
// and we need to continue folding it to reveal the TAIT behind it.
if res != ty
&& (res.has_type_flags(ty::TypeFlags::HAS_CT_PROJECTION) || kind == ty::Weak)
{
res.try_fold_with(self)?
} else {
res
}
}
};
self.cache.insert(ty, res);
Ok(res)
}
fn try_fold_const(
&mut self,
constant: ty::Const<'tcx>,
) -> Result<ty::Const<'tcx>, Self::Error> {
if !needs_normalization(&constant, self.param_env.reveal()) {
return Ok(constant);
}
let constant = constant.try_super_fold_with(self)?;
debug!(?constant, ?self.param_env);
Ok(crate::traits::project::with_replaced_escaping_bound_vars(
self.infcx,
&mut self.universes,
constant,
|constant| constant.normalize(self.infcx.tcx, self.param_env),
))
}
#[inline]
fn try_fold_predicate(
&mut self,
p: ty::Predicate<'tcx>,
) -> Result<ty::Predicate<'tcx>, Self::Error> {
if p.allow_normalization() && needs_normalization(&p, self.param_env.reveal()) {
p.try_super_fold_with(self)
} else {
Ok(p)
}
}
}