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use std::marker::PhantomData;
use rustc_data_structures::snapshot_vec as sv;
use rustc_data_structures::undo_log::{Rollback, UndoLogs};
use rustc_data_structures::unify as ut;
use rustc_middle::infer::unify_key::RegionVidKey;
use rustc_middle::ty::{self, OpaqueHiddenType, OpaqueTypeKey};
use crate::{
infer::{region_constraints, type_variable, InferCtxtInner},
traits,
};
pub struct Snapshot<'tcx> {
pub(crate) undo_len: usize,
_marker: PhantomData<&'tcx ()>,
}
/// Records the "undo" data for a single operation that affects some form of inference variable.
#[derive(Clone)]
pub(crate) enum UndoLog<'tcx> {
OpaqueTypes(OpaqueTypeKey<'tcx>, Option<OpaqueHiddenType<'tcx>>),
TypeVariables(type_variable::UndoLog<'tcx>),
ConstUnificationTable(sv::UndoLog<ut::Delegate<ty::ConstVid<'tcx>>>),
IntUnificationTable(sv::UndoLog<ut::Delegate<ty::IntVid>>),
FloatUnificationTable(sv::UndoLog<ut::Delegate<ty::FloatVid>>),
RegionConstraintCollector(region_constraints::UndoLog<'tcx>),
RegionUnificationTable(sv::UndoLog<ut::Delegate<RegionVidKey<'tcx>>>),
ProjectionCache(traits::UndoLog<'tcx>),
PushRegionObligation,
}
macro_rules! impl_from {
($($ctor: ident ($ty: ty),)*) => {
$(
impl<'tcx> From<$ty> for UndoLog<'tcx> {
fn from(x: $ty) -> Self {
UndoLog::$ctor(x.into())
}
}
)*
}
}
// Upcast from a single kind of "undoable action" to the general enum
impl_from! {
RegionConstraintCollector(region_constraints::UndoLog<'tcx>),
TypeVariables(type_variable::UndoLog<'tcx>),
TypeVariables(sv::UndoLog<ut::Delegate<type_variable::TyVidEqKey<'tcx>>>),
TypeVariables(sv::UndoLog<ut::Delegate<ty::TyVid>>),
TypeVariables(sv::UndoLog<type_variable::Delegate>),
TypeVariables(type_variable::Instantiate),
IntUnificationTable(sv::UndoLog<ut::Delegate<ty::IntVid>>),
FloatUnificationTable(sv::UndoLog<ut::Delegate<ty::FloatVid>>),
ConstUnificationTable(sv::UndoLog<ut::Delegate<ty::ConstVid<'tcx>>>),
RegionUnificationTable(sv::UndoLog<ut::Delegate<RegionVidKey<'tcx>>>),
ProjectionCache(traits::UndoLog<'tcx>),
}
/// The Rollback trait defines how to rollback a particular action.
impl<'tcx> Rollback<UndoLog<'tcx>> for InferCtxtInner<'tcx> {
fn reverse(&mut self, undo: UndoLog<'tcx>) {
match undo {
UndoLog::OpaqueTypes(key, idx) => self.opaque_type_storage.remove(key, idx),
UndoLog::TypeVariables(undo) => self.type_variable_storage.reverse(undo),
UndoLog::ConstUnificationTable(undo) => self.const_unification_storage.reverse(undo),
UndoLog::IntUnificationTable(undo) => self.int_unification_storage.reverse(undo),
UndoLog::FloatUnificationTable(undo) => self.float_unification_storage.reverse(undo),
UndoLog::RegionConstraintCollector(undo) => {
self.region_constraint_storage.as_mut().unwrap().reverse(undo)
}
UndoLog::RegionUnificationTable(undo) => {
self.region_constraint_storage.as_mut().unwrap().unification_table.reverse(undo)
}
UndoLog::ProjectionCache(undo) => self.projection_cache.reverse(undo),
UndoLog::PushRegionObligation => {
self.region_obligations.pop();
}
}
}
}
/// The combined undo log for all the various unification tables. For each change to the storage
/// for any kind of inference variable, we record an UndoLog entry in the vector here.
#[derive(Clone)]
pub(crate) struct InferCtxtUndoLogs<'tcx> {
logs: Vec<UndoLog<'tcx>>,
num_open_snapshots: usize,
}
impl Default for InferCtxtUndoLogs<'_> {
fn default() -> Self {
Self { logs: Default::default(), num_open_snapshots: Default::default() }
}
}
/// The UndoLogs trait defines how we undo a particular kind of action (of type T). We can undo any
/// action that is convertible into an UndoLog (per the From impls above).
impl<'tcx, T> UndoLogs<T> for InferCtxtUndoLogs<'tcx>
where
UndoLog<'tcx>: From<T>,
{
#[inline]
fn num_open_snapshots(&self) -> usize {
self.num_open_snapshots
}
#[inline]
fn push(&mut self, undo: T) {
if self.in_snapshot() {
self.logs.push(undo.into())
}
}
fn clear(&mut self) {
self.logs.clear();
self.num_open_snapshots = 0;
}
fn extend<J>(&mut self, undos: J)
where
Self: Sized,
J: IntoIterator<Item = T>,
{
if self.in_snapshot() {
self.logs.extend(undos.into_iter().map(UndoLog::from))
}
}
}
impl<'tcx> InferCtxtInner<'tcx> {
pub fn rollback_to(&mut self, snapshot: Snapshot<'tcx>) {
debug!("rollback_to({})", snapshot.undo_len);
self.undo_log.assert_open_snapshot(&snapshot);
while self.undo_log.logs.len() > snapshot.undo_len {
let undo = self.undo_log.logs.pop().unwrap();
self.reverse(undo);
}
if self.undo_log.num_open_snapshots == 1 {
// The root snapshot. It's safe to clear the undo log because
// there's no snapshot further out that we might need to roll back
// to.
assert!(snapshot.undo_len == 0);
self.undo_log.logs.clear();
}
self.undo_log.num_open_snapshots -= 1;
}
pub fn commit(&mut self, snapshot: Snapshot<'tcx>) {
debug!("commit({})", snapshot.undo_len);
if self.undo_log.num_open_snapshots == 1 {
// The root snapshot. It's safe to clear the undo log because
// there's no snapshot further out that we might need to roll back
// to.
assert!(snapshot.undo_len == 0);
self.undo_log.logs.clear();
}
self.undo_log.num_open_snapshots -= 1;
}
}
impl<'tcx> InferCtxtUndoLogs<'tcx> {
pub fn start_snapshot(&mut self) -> Snapshot<'tcx> {
self.num_open_snapshots += 1;
Snapshot { undo_len: self.logs.len(), _marker: PhantomData }
}
pub(crate) fn region_constraints_in_snapshot(
&self,
s: &Snapshot<'tcx>,
) -> impl Iterator<Item = &'_ region_constraints::UndoLog<'tcx>> + Clone {
self.logs[s.undo_len..].iter().filter_map(|log| match log {
UndoLog::RegionConstraintCollector(log) => Some(log),
_ => None,
})
}
pub(crate) fn opaque_types_in_snapshot(&self, s: &Snapshot<'tcx>) -> bool {
self.logs[s.undo_len..].iter().any(|log| matches!(log, UndoLog::OpaqueTypes(..)))
}
pub(crate) fn region_constraints(
&self,
) -> impl Iterator<Item = &'_ region_constraints::UndoLog<'tcx>> + Clone {
self.logs.iter().filter_map(|log| match log {
UndoLog::RegionConstraintCollector(log) => Some(log),
_ => None,
})
}
fn assert_open_snapshot(&self, snapshot: &Snapshot<'tcx>) {
// Failures here may indicate a failure to follow a stack discipline.
assert!(self.logs.len() >= snapshot.undo_len);
assert!(self.num_open_snapshots > 0);
}
}
impl<'tcx> std::ops::Index<usize> for InferCtxtUndoLogs<'tcx> {
type Output = UndoLog<'tcx>;
fn index(&self, key: usize) -> &Self::Output {
&self.logs[key]
}
}
impl<'tcx> std::ops::IndexMut<usize> for InferCtxtUndoLogs<'tcx> {
fn index_mut(&mut self, key: usize) -> &mut Self::Output {
&mut self.logs[key]
}
}
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