rust/src/librustc_mir/borrow_check/nll/pick_constraints.rs

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use crate::rustc::ty::{self, Ty};
use rustc::hir::def_id::DefId;
use rustc::infer::region_constraints::PickConstraint;
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::indexed_vec::{Idx, IndexVec};
use std::hash::Hash;
use std::ops::Index;
/// Compactly stores a set of `pick R0 in [R1...Rn]` constraints,
/// indexed by the region R0.
crate struct PickConstraintSet<'tcx, R>
where
R: Copy + Hash + Eq,
{
/// Stores the first "pick" constraint for a given R0. This is an
/// index into the `constraints` vector below.
first_constraints: FxHashMap<R, NllPickConstraintIndex>,
/// Stores the data about each `pick R0 from [R1..Rn]` constraint.
/// These are organized into a linked list, so each constraint
/// contains the index of the next constraint with the same R0.
constraints: IndexVec<NllPickConstraintIndex, NllPickConstraint<'tcx>>,
/// Stores the `R1..Rn` regions for *all* sets. For any given
/// constraint, we keep two indices so that we can pull out a
/// slice.
option_regions: Vec<ty::RegionVid>,
}
/// Represents a `pick R0 in [R1..Rn]` constraint
crate struct NllPickConstraint<'tcx> {
next_constraint: Option<NllPickConstraintIndex>,
/// The opaque type whose hidden type is being inferred. (Used in error reporting.)
crate opaque_type_def_id: DefId,
/// The hidden type in which R0 appears. (Used in error reporting.)
crate hidden_ty: Ty<'tcx>,
/// The region R0.
crate pick_region_vid: ty::RegionVid,
/// Index of `R1` in `option_regions` vector from `PickConstraintSet`.
start_index: usize,
/// Index of `Rn` in `option_regions` vector from `PickConstraintSet`.
end_index: usize,
}
newtype_index! {
crate struct NllPickConstraintIndex {
DEBUG_FORMAT = "PickConstraintIndex({})"
}
}
impl Default for PickConstraintSet<'tcx, ty::RegionVid> {
fn default() -> Self {
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Self {
first_constraints: Default::default(),
constraints: Default::default(),
option_regions: Default::default(),
}
}
}
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impl<'tcx> PickConstraintSet<'tcx, ty::RegionVid> {
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crate fn push_constraint(
&mut self,
p_c: &PickConstraint<'tcx>,
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mut to_region_vid: impl FnMut(ty::Region<'tcx>) -> ty::RegionVid,
) {
debug!("push_constraint(p_c={:?})", p_c);
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let pick_region_vid: ty::RegionVid = to_region_vid(p_c.pick_region);
let next_constraint = self.first_constraints.get(&pick_region_vid).cloned();
let start_index = self.option_regions.len();
let end_index = start_index + p_c.option_regions.len();
debug!("push_constraint: pick_region_vid={:?}", pick_region_vid);
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let constraint_index = self.constraints.push(NllPickConstraint {
next_constraint,
pick_region_vid,
opaque_type_def_id: p_c.opaque_type_def_id,
hidden_ty: p_c.hidden_ty,
start_index,
end_index,
});
self.first_constraints.insert(pick_region_vid, constraint_index);
self.option_regions.extend(p_c.option_regions.iter().map(|&r| to_region_vid(r)));
}
}
impl<'tcx, R1> PickConstraintSet<'tcx, R1>
where
R1: Copy + Hash + Eq,
{
/// Remap the "pick region" key using `map_fn`, producing a new
/// pick-constraint set. This is used in the NLL code to map from
/// the original `RegionVid` to an scc index. In some cases, we
/// may have multiple R1 values mapping to the same R2 key -- that
/// is ok, the two sets will be merged.
crate fn into_mapped<R2>(self, mut map_fn: impl FnMut(R1) -> R2) -> PickConstraintSet<'tcx, R2>
where
R2: Copy + Hash + Eq,
{
// We can re-use most of the original data, just tweaking the
// linked list links a bit.
//
// For example if we had two keys Ra and Rb that both now wind
// up mapped to the same key S, we would append the linked
// list for Ra onto the end of the linked list for Rb (or vice
// versa) -- this basically just requires rewriting the final
// link from one list to point at the othe other (see
// `append_list`).
let PickConstraintSet { first_constraints, mut constraints, option_regions } = self;
let mut first_constraints2 = FxHashMap::default();
first_constraints2.reserve(first_constraints.len());
for (r1, start1) in first_constraints {
let r2 = map_fn(r1);
if let Some(&start2) = first_constraints2.get(&r2) {
append_list(&mut constraints, start1, start2);
}
first_constraints2.insert(r2, start1);
}
PickConstraintSet {
first_constraints: first_constraints2,
constraints,
option_regions,
}
}
}
impl<'tcx, R> PickConstraintSet<'tcx, R>
where
R: Copy + Hash + Eq,
{
crate fn all_indices(
&self,
) -> impl Iterator<Item = NllPickConstraintIndex> {
self.constraints.indices()
}
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/// Iterate down the constraint indices associated with a given
/// peek-region. You can then use `option_regions` and other
/// methods to access data.
crate fn indices(
&self,
pick_region_vid: R,
) -> impl Iterator<Item = NllPickConstraintIndex> + '_ {
let mut next = self.first_constraints.get(&pick_region_vid).cloned();
std::iter::from_fn(move || -> Option<NllPickConstraintIndex> {
if let Some(current) = next {
next = self.constraints[current].next_constraint;
Some(current)
} else {
None
}
})
}
/// Returns the "option regions" for a given pick constraint. This is the R1..Rn from
/// a constraint like:
///
/// ```
/// pick R0 in [R1..Rn]
/// ```
crate fn option_regions(&self, pci: NllPickConstraintIndex) -> &[ty::RegionVid] {
let NllPickConstraint { start_index, end_index, .. } = &self.constraints[pci];
&self.option_regions[*start_index..*end_index]
}
}
impl<'tcx, R> Index<NllPickConstraintIndex> for PickConstraintSet<'tcx, R>
where
R: Copy + Hash + Eq,
{
type Output = NllPickConstraint<'tcx>;
fn index(&self, i: NllPickConstraintIndex) -> &NllPickConstraint<'tcx> {
&self.constraints[i]
}
}
/// Given a linked list starting at `source_list` and another linked
/// list starting at `target_list`, modify `target_list` so that it is
/// followed by `source_list`.
///
/// Before:
///
/// ```
/// target_list: A -> B -> C -> (None)
/// source_list: D -> E -> F -> (None)
/// ```
///
/// After:
///
/// ```
/// target_list: A -> B -> C -> D -> E -> F -> (None)
/// ```
fn append_list(
constraints: &mut IndexVec<NllPickConstraintIndex, NllPickConstraint<'_>>,
target_list: NllPickConstraintIndex,
source_list: NllPickConstraintIndex,
) {
let mut p = target_list;
loop {
let mut r = &mut constraints[p];
match r.next_constraint {
Some(q) => p = q,
None => {
r.next_constraint = Some(source_list);
return;
}
}
}
}