1 use std::marker::PhantomData;
3 use rustc_data_structures::snapshot_vec as sv;
4 use rustc_data_structures::undo_log::{Rollback, UndoLogs};
5 use rustc_data_structures::unify as ut;
6 use rustc_middle::infer::unify_key::RegionVidKey;
10 infer::{region_constraints, type_variable, InferCtxtInner},
14 pub struct Snapshot<'tcx> {
15 pub(crate) undo_len: usize,
16 _marker: PhantomData<&'tcx ()>,
19 /// Records the "undo" data for a single operation that affects some form of inference variable.
20 pub(crate) enum UndoLog<'tcx> {
21 TypeVariables(type_variable::UndoLog<'tcx>),
22 ConstUnificationTable(sv::UndoLog<ut::Delegate<ty::ConstVid<'tcx>>>),
23 IntUnificationTable(sv::UndoLog<ut::Delegate<ty::IntVid>>),
24 FloatUnificationTable(sv::UndoLog<ut::Delegate<ty::FloatVid>>),
25 RegionConstraintCollector(region_constraints::UndoLog<'tcx>),
26 RegionUnificationTable(sv::UndoLog<ut::Delegate<RegionVidKey<'tcx>>>),
27 ProjectionCache(traits::UndoLog<'tcx>),
31 macro_rules! impl_from {
32 ($($ctor: ident ($ty: ty),)*) => {
34 impl<'tcx> From<$ty> for UndoLog<'tcx> {
35 fn from(x: $ty) -> Self {
36 UndoLog::$ctor(x.into())
43 // Upcast from a single kind of "undoable action" to the general enum
45 RegionConstraintCollector(region_constraints::UndoLog<'tcx>),
46 TypeVariables(type_variable::UndoLog<'tcx>),
48 TypeVariables(sv::UndoLog<ut::Delegate<type_variable::TyVidEqKey<'tcx>>>),
49 TypeVariables(sv::UndoLog<ut::Delegate<ty::TyVid>>),
50 TypeVariables(sv::UndoLog<type_variable::Delegate>),
51 TypeVariables(type_variable::Instantiate),
53 IntUnificationTable(sv::UndoLog<ut::Delegate<ty::IntVid>>),
55 FloatUnificationTable(sv::UndoLog<ut::Delegate<ty::FloatVid>>),
57 ConstUnificationTable(sv::UndoLog<ut::Delegate<ty::ConstVid<'tcx>>>),
59 RegionUnificationTable(sv::UndoLog<ut::Delegate<RegionVidKey<'tcx>>>),
60 ProjectionCache(traits::UndoLog<'tcx>),
63 /// The Rollback trait defines how to rollback a particular action.
64 impl<'tcx> Rollback<UndoLog<'tcx>> for InferCtxtInner<'tcx> {
65 fn reverse(&mut self, undo: UndoLog<'tcx>) {
67 UndoLog::TypeVariables(undo) => self.type_variable_storage.reverse(undo),
68 UndoLog::ConstUnificationTable(undo) => self.const_unification_storage.reverse(undo),
69 UndoLog::IntUnificationTable(undo) => self.int_unification_storage.reverse(undo),
70 UndoLog::FloatUnificationTable(undo) => self.float_unification_storage.reverse(undo),
71 UndoLog::RegionConstraintCollector(undo) => {
72 self.region_constraint_storage.as_mut().unwrap().reverse(undo)
74 UndoLog::RegionUnificationTable(undo) => {
75 self.region_constraint_storage.as_mut().unwrap().unification_table.reverse(undo)
77 UndoLog::ProjectionCache(undo) => self.projection_cache.reverse(undo),
78 UndoLog::PushRegionObligation => {
79 self.region_obligations.pop();
85 /// The combined undo log for all the various unification tables. For each change to the storage
86 /// for any kind of inference variable, we record an UndoLog entry in the vector here.
87 pub(crate) struct InferCtxtUndoLogs<'tcx> {
88 logs: Vec<UndoLog<'tcx>>,
89 num_open_snapshots: usize,
92 impl Default for InferCtxtUndoLogs<'_> {
93 fn default() -> Self {
94 Self { logs: Default::default(), num_open_snapshots: Default::default() }
98 /// The UndoLogs trait defines how we undo a particular kind of action (of type T). We can undo any
99 /// action that is convertable into an UndoLog (per the From impls above).
100 impl<'tcx, T> UndoLogs<T> for InferCtxtUndoLogs<'tcx>
102 UndoLog<'tcx>: From<T>,
105 fn num_open_snapshots(&self) -> usize {
106 self.num_open_snapshots
110 fn push(&mut self, undo: T) {
111 if self.in_snapshot() {
112 self.logs.push(undo.into())
116 fn clear(&mut self) {
118 self.num_open_snapshots = 0;
121 fn extend<J>(&mut self, undos: J)
124 J: IntoIterator<Item = T>,
126 if self.in_snapshot() {
127 self.logs.extend(undos.into_iter().map(UndoLog::from))
132 impl<'tcx> InferCtxtInner<'tcx> {
133 pub fn rollback_to(&mut self, snapshot: Snapshot<'tcx>) {
134 debug!("rollback_to({})", snapshot.undo_len);
135 self.undo_log.assert_open_snapshot(&snapshot);
137 while self.undo_log.logs.len() > snapshot.undo_len {
138 let undo = self.undo_log.logs.pop().unwrap();
142 if self.undo_log.num_open_snapshots == 1 {
143 // The root snapshot. It's safe to clear the undo log because
144 // there's no snapshot further out that we might need to roll back
146 assert!(snapshot.undo_len == 0);
147 self.undo_log.logs.clear();
150 self.undo_log.num_open_snapshots -= 1;
153 pub fn commit(&mut self, snapshot: Snapshot<'tcx>) {
154 debug!("commit({})", snapshot.undo_len);
156 if self.undo_log.num_open_snapshots == 1 {
157 // The root snapshot. It's safe to clear the undo log because
158 // there's no snapshot further out that we might need to roll back
160 assert!(snapshot.undo_len == 0);
161 self.undo_log.logs.clear();
164 self.undo_log.num_open_snapshots -= 1;
168 impl<'tcx> InferCtxtUndoLogs<'tcx> {
169 pub fn start_snapshot(&mut self) -> Snapshot<'tcx> {
170 self.num_open_snapshots += 1;
171 Snapshot { undo_len: self.logs.len(), _marker: PhantomData }
174 pub(crate) fn region_constraints_in_snapshot(
177 ) -> impl Iterator<Item = &'_ region_constraints::UndoLog<'tcx>> + Clone {
178 self.logs[s.undo_len..].iter().filter_map(|log| match log {
179 UndoLog::RegionConstraintCollector(log) => Some(log),
184 pub(crate) fn region_constraints(
186 ) -> impl Iterator<Item = &'_ region_constraints::UndoLog<'tcx>> + Clone {
187 self.logs.iter().filter_map(|log| match log {
188 UndoLog::RegionConstraintCollector(log) => Some(log),
193 fn assert_open_snapshot(&self, snapshot: &Snapshot<'tcx>) {
194 // Failures here may indicate a failure to follow a stack discipline.
195 assert!(self.logs.len() >= snapshot.undo_len);
196 assert!(self.num_open_snapshots > 0);
200 impl<'tcx> std::ops::Index<usize> for InferCtxtUndoLogs<'tcx> {
201 type Output = UndoLog<'tcx>;
203 fn index(&self, key: usize) -> &Self::Output {
208 impl<'tcx> std::ops::IndexMut<usize> for InferCtxtUndoLogs<'tcx> {
209 fn index_mut(&mut self, key: usize) -> &mut Self::Output {