rustc_infer/infer/snapshot/
mod.rs

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1use rustc_data_structures::undo_log::UndoLogs;
2use rustc_middle::ty;
3use tracing::{debug, instrument};
4
5use super::InferCtxt;
6use super::region_constraints::RegionSnapshot;
7
8pub(crate) mod fudge;
9pub(crate) mod undo_log;
10
11use undo_log::{Snapshot, UndoLog};
12
13#[must_use = "once you start a snapshot, you should always consume it"]
14pub struct CombinedSnapshot<'tcx> {
15    pub(super) undo_snapshot: Snapshot<'tcx>,
16    region_constraints_snapshot: RegionSnapshot,
17    universe: ty::UniverseIndex,
18}
19
20struct VariableLengths {
21    region_constraints_len: usize,
22    type_var_len: usize,
23    int_var_len: usize,
24    float_var_len: usize,
25    const_var_len: usize,
26}
27
28impl<'tcx> InferCtxt<'tcx> {
29    fn variable_lengths(&self) -> VariableLengths {
30        let mut inner = self.inner.borrow_mut();
31        VariableLengths {
32            region_constraints_len: inner.unwrap_region_constraints().num_region_vars(),
33            type_var_len: inner.type_variables().num_vars(),
34            int_var_len: inner.int_unification_table().len(),
35            float_var_len: inner.float_unification_table().len(),
36            const_var_len: inner.const_unification_table().len(),
37        }
38    }
39
40    pub fn in_snapshot(&self) -> bool {
41        UndoLogs::<UndoLog<'tcx>>::in_snapshot(&self.inner.borrow_mut().undo_log)
42    }
43
44    pub fn num_open_snapshots(&self) -> usize {
45        UndoLogs::<UndoLog<'tcx>>::num_open_snapshots(&self.inner.borrow_mut().undo_log)
46    }
47
48    fn start_snapshot(&self) -> CombinedSnapshot<'tcx> {
49        debug!("start_snapshot()");
50
51        let mut inner = self.inner.borrow_mut();
52
53        CombinedSnapshot {
54            undo_snapshot: inner.undo_log.start_snapshot(),
55            region_constraints_snapshot: inner.unwrap_region_constraints().start_snapshot(),
56            universe: self.universe(),
57        }
58    }
59
60    #[instrument(skip(self, snapshot), level = "debug")]
61    fn rollback_to(&self, snapshot: CombinedSnapshot<'tcx>) {
62        let CombinedSnapshot { undo_snapshot, region_constraints_snapshot, universe } = snapshot;
63
64        self.universe.set(universe);
65
66        let mut inner = self.inner.borrow_mut();
67        inner.rollback_to(undo_snapshot);
68        inner.unwrap_region_constraints().rollback_to(region_constraints_snapshot);
69    }
70
71    #[instrument(skip(self, snapshot), level = "debug")]
72    fn commit_from(&self, snapshot: CombinedSnapshot<'tcx>) {
73        let CombinedSnapshot { undo_snapshot, region_constraints_snapshot: _, universe: _ } =
74            snapshot;
75
76        self.inner.borrow_mut().commit(undo_snapshot);
77    }
78
79    /// Execute `f` and commit the bindings if closure `f` returns `Ok(_)`.
80    #[instrument(skip(self, f), level = "debug")]
81    pub fn commit_if_ok<T, E, F>(&self, f: F) -> Result<T, E>
82    where
83        F: FnOnce(&CombinedSnapshot<'tcx>) -> Result<T, E>,
84    {
85        let snapshot = self.start_snapshot();
86        let r = f(&snapshot);
87        debug!("commit_if_ok() -- r.is_ok() = {}", r.is_ok());
88        match r {
89            Ok(_) => {
90                self.commit_from(snapshot);
91            }
92            Err(_) => {
93                self.rollback_to(snapshot);
94            }
95        }
96        r
97    }
98
99    /// Execute `f` then unroll any bindings it creates.
100    #[instrument(skip(self, f), level = "debug")]
101    pub fn probe<R, F>(&self, f: F) -> R
102    where
103        F: FnOnce(&CombinedSnapshot<'tcx>) -> R,
104    {
105        let snapshot = self.start_snapshot();
106        let r = f(&snapshot);
107        self.rollback_to(snapshot);
108        r
109    }
110
111    /// Scan the constraints produced since `snapshot` and check whether
112    /// we added any region constraints.
113    pub fn region_constraints_added_in_snapshot(&self, snapshot: &CombinedSnapshot<'tcx>) -> bool {
114        self.inner
115            .borrow_mut()
116            .unwrap_region_constraints()
117            .region_constraints_added_in_snapshot(&snapshot.undo_snapshot)
118    }
119
120    pub fn opaque_types_added_in_snapshot(&self, snapshot: &CombinedSnapshot<'tcx>) -> bool {
121        self.inner.borrow().undo_log.opaque_types_in_snapshot(&snapshot.undo_snapshot)
122    }
123}
rustc_infer/infer/snapshot/mod.rs

rustc_infer/infer/snapshot/
mod.rs
