rustc_trait_selection/traits/normalize.rs
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//! Deeply normalize types using the old trait solver.
use rustc_data_structures::stack::ensure_sufficient_stack;
use rustc_infer::infer::at::At;
use rustc_infer::infer::{InferCtxt, InferOk};
use rustc_infer::traits::{
FromSolverError, Normalized, Obligation, PredicateObligations, TraitEngine,
};
use rustc_macros::extension;
use rustc_middle::traits::{ObligationCause, ObligationCauseCode};
use rustc_middle::ty::{
self, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitable, TypeVisitableExt,
TypingMode,
};
use tracing::{debug, instrument};
use super::{
BoundVarReplacer, PlaceholderReplacer, SelectionContext, project,
with_replaced_escaping_bound_vars,
};
use crate::error_reporting::InferCtxtErrorExt;
use crate::error_reporting::traits::OverflowCause;
use crate::solve::NextSolverError;
#[extension(pub trait NormalizeExt<'tcx>)]
impl<'tcx> At<'_, '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, value: T) -> InferOk<'tcx, T> {
if self.infcx.next_trait_solver() {
InferOk { value, obligations: PredicateObligations::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 }
}
}
/// 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.
///
/// 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(-Znext-solver): For performance reasons, we currently reuse an existing
/// fulfillment context in the old solver. Once we have removed the old solver, we
/// can remove the `fulfill_cx` parameter on this function.
fn deeply_normalize<T, E>(
self,
value: T,
fulfill_cx: &mut dyn TraitEngine<'tcx, E>,
) -> Result<T, Vec<E>>
where
T: TypeFoldable<TyCtxt<'tcx>>,
E: FromSolverError<'tcx, NextSolverError<'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) }
}
}
}
/// 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 = PredicateObligations::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 PredicateObligations<'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(|| AssocTypeNormalizer::fold(&mut normalizer, value));
debug!(?result, obligations.len = normalizer.obligations.len());
debug!(?normalizer.obligations,);
result
}
pub(super) fn needs_normalization<'tcx, T: TypeVisitable<TyCtxt<'tcx>>>(
infcx: &InferCtxt<'tcx>,
param_env_for_debug_assertion: ty::ParamEnv<'tcx>,
value: &T,
) -> bool {
let mut flags = ty::TypeFlags::HAS_ALIAS;
// Opaques are treated as rigid with `Reveal::UserFacing`,
// so we can ignore those.
match infcx.typing_mode(param_env_for_debug_assertion) {
TypingMode::Coherence | TypingMode::Analysis { defining_opaque_types: _ } => {
flags.remove(ty::TypeFlags::HAS_TY_OPAQUE)
}
TypingMode::PostAnalysis => {}
}
value.has_type_flags(flags)
}
struct AssocTypeNormalizer<'a, 'b, 'tcx> {
selcx: &'a mut SelectionContext<'b, 'tcx>,
param_env: ty::ParamEnv<'tcx>,
cause: ObligationCause<'tcx>,
obligations: &'a mut PredicateObligations<'tcx>,
depth: usize,
universes: Vec<Option<ty::UniverseIndex>>,
}
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 PredicateObligations<'tcx>,
) -> AssocTypeNormalizer<'a, 'b, 'tcx> {
debug_assert!(!selcx.infcx.next_trait_solver());
AssocTypeNormalizer { selcx, param_env, cause, obligations, depth, universes: vec![] }
}
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(self.selcx.infcx, self.param_env, &value) {
value
} else {
value.fold_with(self)
}
}
}
impl<'a, 'b, 'tcx> TypeFolder<TyCtxt<'tcx>> for AssocTypeNormalizer<'a, 'b, 'tcx> {
fn cx(&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(self.selcx.infcx, self.param_env, &ty) {
return ty;
}
let (kind, data) = match *ty.kind() {
ty::Alias(kind, data) => (kind, data),
_ => 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.selcx.infcx.typing_mode(self.param_env) {
TypingMode::Coherence | TypingMode::Analysis { defining_opaque_types: _ } => {
ty.super_fold_with(self)
}
TypingMode::PostAnalysis => {
let recursion_limit = self.cx().recursion_limit();
if !recursion_limit.value_within_limit(self.depth) {
self.selcx.infcx.err_ctxt().report_overflow_error(
OverflowCause::DeeplyNormalize(data.into()),
self.cause.span,
true,
|_| {},
);
}
let args = data.args.fold_with(self);
let generic_ty = self.cx().type_of(data.def_id);
let concrete_ty = generic_ty.instantiate(self.cx(), 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 = project::normalize_projection_ty(
self.selcx,
self.param_env,
data,
self.cause.clone(),
self.depth,
self.obligations,
);
debug!(
?self.depth,
?ty,
?normalized_ty,
obligations.len = ?self.obligations.len(),
"AssocTypeNormalizer: normalized type"
);
normalized_ty.expect_type()
}
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 = project::opt_normalize_projection_term(
self.selcx,
self.param_env,
data.into(),
self.cause.clone(),
self.depth,
self.obligations,
)
.ok()
.flatten()
.map(|term| term.expect_type())
.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.cx().recursion_limit();
if !recursion_limit.value_within_limit(self.depth) {
self.selcx.infcx.err_ctxt().report_overflow_error(
OverflowCause::DeeplyNormalize(data.into()),
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);
project::normalize_inherent_projection(
self.selcx,
self.param_env,
data,
self.cause.clone(),
self.depth,
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 = project::normalize_inherent_projection(
self.selcx,
self.param_env,
data,
self.cause.clone(),
self.depth,
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(self.selcx.infcx, self.param_env, &constant)
{
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_internal(tcx, self.param_env),
)
}
}
#[inline]
fn fold_predicate(&mut self, p: ty::Predicate<'tcx>) -> ty::Predicate<'tcx> {
if p.allow_normalization() && needs_normalization(self.selcx.infcx, self.param_env, &p) {
p.super_fold_with(self)
} else {
p
}
}
}