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//! See `README.md`.
use self::CombineMapType::*;
use self::UndoLog::*;
use super::{
InferCtxtUndoLogs, MiscVariable, RegionVariableOrigin, Rollback, Snapshot, SubregionOrigin,
};
use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::intern::Interned;
use rustc_data_structures::sync::Lrc;
use rustc_data_structures::undo_log::UndoLogs;
use rustc_data_structures::unify as ut;
use rustc_index::IndexVec;
use rustc_middle::infer::unify_key::{RegionVidKey, UnifiedRegion};
use rustc_middle::ty::ReStatic;
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_middle::ty::{ReLateBound, ReVar};
use rustc_middle::ty::{Region, RegionVid};
use rustc_span::Span;
use std::collections::BTreeMap;
use std::ops::Range;
use std::{cmp, fmt, mem};
mod leak_check;
pub use rustc_middle::infer::MemberConstraint;
#[derive(Clone, Default)]
pub struct RegionConstraintStorage<'tcx> {
/// For each `RegionVid`, the corresponding `RegionVariableOrigin`.
var_infos: IndexVec<RegionVid, RegionVariableInfo>,
data: RegionConstraintData<'tcx>,
/// For a given pair of regions (R1, R2), maps to a region R3 that
/// is designated as their LUB (edges R1 <= R3 and R2 <= R3
/// exist). This prevents us from making many such regions.
lubs: CombineMap<'tcx>,
/// For a given pair of regions (R1, R2), maps to a region R3 that
/// is designated as their GLB (edges R3 <= R1 and R3 <= R2
/// exist). This prevents us from making many such regions.
glbs: CombineMap<'tcx>,
/// When we add a R1 == R2 constraint, we currently add (a) edges
/// R1 <= R2 and R2 <= R1 and (b) we unify the two regions in this
/// table. You can then call `opportunistic_resolve_var` early
/// which will map R1 and R2 to some common region (i.e., either
/// R1 or R2). This is important when fulfillment, dropck and other such
/// code is iterating to a fixed point, because otherwise we sometimes
/// would wind up with a fresh stream of region variables that have been
/// equated but appear distinct.
pub(super) unification_table: ut::UnificationTableStorage<RegionVidKey<'tcx>>,
/// a flag set to true when we perform any unifications; this is used
/// to micro-optimize `take_and_reset_data`
any_unifications: bool,
}
pub struct RegionConstraintCollector<'a, 'tcx> {
storage: &'a mut RegionConstraintStorage<'tcx>,
undo_log: &'a mut InferCtxtUndoLogs<'tcx>,
}
impl<'tcx> std::ops::Deref for RegionConstraintCollector<'_, 'tcx> {
type Target = RegionConstraintStorage<'tcx>;
#[inline]
fn deref(&self) -> &RegionConstraintStorage<'tcx> {
self.storage
}
}
impl<'tcx> std::ops::DerefMut for RegionConstraintCollector<'_, 'tcx> {
#[inline]
fn deref_mut(&mut self) -> &mut RegionConstraintStorage<'tcx> {
self.storage
}
}
pub type VarInfos = IndexVec<RegionVid, RegionVariableInfo>;
/// The full set of region constraints gathered up by the collector.
/// Describes constraints between the region variables and other
/// regions, as well as other conditions that must be verified, or
/// assumptions that can be made.
#[derive(Debug, Default, Clone)]
pub struct RegionConstraintData<'tcx> {
/// Constraints of the form `A <= B`, where either `A` or `B` can
/// be a region variable (or neither, as it happens).
pub constraints: BTreeMap<Constraint<'tcx>, SubregionOrigin<'tcx>>,
/// Constraints of the form `R0 member of [R1, ..., Rn]`, meaning that
/// `R0` must be equal to one of the regions `R1..Rn`. These occur
/// with `impl Trait` quite frequently.
pub member_constraints: Vec<MemberConstraint<'tcx>>,
/// A "verify" is something that we need to verify after inference
/// is done, but which does not directly affect inference in any
/// way.
///
/// An example is a `A <= B` where neither `A` nor `B` are
/// inference variables.
pub verifys: Vec<Verify<'tcx>>,
}
/// Represents a constraint that influences the inference process.
#[derive(Clone, Copy, PartialEq, Eq, Debug, PartialOrd, Ord)]
pub enum Constraint<'tcx> {
/// A region variable is a subregion of another.
VarSubVar(RegionVid, RegionVid),
/// A concrete region is a subregion of region variable.
RegSubVar(Region<'tcx>, RegionVid),
/// A region variable is a subregion of a concrete region. This does not
/// directly affect inference, but instead is checked after
/// inference is complete.
VarSubReg(RegionVid, Region<'tcx>),
/// A constraint where neither side is a variable. This does not
/// directly affect inference, but instead is checked after
/// inference is complete.
RegSubReg(Region<'tcx>, Region<'tcx>),
}
impl Constraint<'_> {
pub fn involves_placeholders(&self) -> bool {
match self {
Constraint::VarSubVar(_, _) => false,
Constraint::VarSubReg(_, r) | Constraint::RegSubVar(r, _) => r.is_placeholder(),
Constraint::RegSubReg(r, s) => r.is_placeholder() || s.is_placeholder(),
}
}
}
#[derive(Debug, Clone)]
pub struct Verify<'tcx> {
pub kind: GenericKind<'tcx>,
pub origin: SubregionOrigin<'tcx>,
pub region: Region<'tcx>,
pub bound: VerifyBound<'tcx>,
}
#[derive(Copy, Clone, PartialEq, Eq, Hash, TypeFoldable, TypeVisitable)]
pub enum GenericKind<'tcx> {
Param(ty::ParamTy),
Alias(ty::AliasTy<'tcx>),
}
/// Describes the things that some `GenericKind` value `G` is known to
/// outlive. Each variant of `VerifyBound` can be thought of as a
/// function:
/// ```ignore (pseudo-rust)
/// fn(min: Region) -> bool { .. }
/// ```
/// where `true` means that the region `min` meets that `G: min`.
/// (False means nothing.)
///
/// So, for example, if we have the type `T` and we have in scope that
/// `T: 'a` and `T: 'b`, then the verify bound might be:
/// ```ignore (pseudo-rust)
/// fn(min: Region) -> bool {
/// ('a: min) || ('b: min)
/// }
/// ```
/// This is described with an `AnyRegion('a, 'b)` node.
#[derive(Debug, Clone, TypeFoldable, TypeVisitable)]
pub enum VerifyBound<'tcx> {
/// See [`VerifyIfEq`] docs
IfEq(ty::Binder<'tcx, VerifyIfEq<'tcx>>),
/// Given a region `R`, expands to the function:
///
/// ```ignore (pseudo-rust)
/// fn(min) -> bool {
/// R: min
/// }
/// ```
///
/// This is used when we can establish that `G: R` -- therefore,
/// if `R: min`, then by transitivity `G: min`.
OutlivedBy(Region<'tcx>),
/// Given a region `R`, true if it is `'empty`.
IsEmpty,
/// Given a set of bounds `B`, expands to the function:
///
/// ```ignore (pseudo-rust)
/// fn(min) -> bool {
/// exists (b in B) { b(min) }
/// }
/// ```
///
/// In other words, if we meet some bound in `B`, that suffices.
/// This is used when all the bounds in `B` are known to apply to `G`.
AnyBound(Vec<VerifyBound<'tcx>>),
/// Given a set of bounds `B`, expands to the function:
///
/// ```ignore (pseudo-rust)
/// fn(min) -> bool {
/// forall (b in B) { b(min) }
/// }
/// ```
///
/// In other words, if we meet *all* bounds in `B`, that suffices.
/// This is used when *some* bound in `B` is known to suffice, but
/// we don't know which.
AllBounds(Vec<VerifyBound<'tcx>>),
}
/// This is a "conditional bound" that checks the result of inference
/// and supplies a bound if it ended up being relevant. It's used in situations
/// like this:
///
/// ```rust,ignore (pseudo-Rust)
/// fn foo<'a, 'b, T: SomeTrait<'a>>
/// where
/// <T as SomeTrait<'a>>::Item: 'b
/// ```
///
/// If we have an obligation like `<T as SomeTrait<'?x>>::Item: 'c`, then
/// we don't know yet whether it suffices to show that `'b: 'c`. If `'?x` winds
/// up being equal to `'a`, then the where-clauses on function applies, and
/// in that case we can show `'b: 'c`. But if `'?x` winds up being something
/// else, the bound isn't relevant.
///
/// In the [`VerifyBound`], this struct is enclosed in `Binder` to account
/// for cases like
///
/// ```rust,ignore (pseudo-Rust)
/// where for<'a> <T as SomeTrait<'a>::Item: 'a
/// ```
///
/// The idea is that we have to find some instantiation of `'a` that can
/// make `<T as SomeTrait<'a>>::Item` equal to the final value of `G`,
/// the generic we are checking.
///
/// ```ignore (pseudo-rust)
/// fn(min) -> bool {
/// exists<'a> {
/// if G == K {
/// B(min)
/// } else {
/// false
/// }
/// }
/// }
/// ```
#[derive(Debug, Copy, Clone, TypeFoldable, TypeVisitable)]
pub struct VerifyIfEq<'tcx> {
/// Type which must match the generic `G`
pub ty: Ty<'tcx>,
/// Bound that applies if `ty` is equal.
pub bound: Region<'tcx>,
}
#[derive(Copy, Clone, PartialEq, Eq, Hash)]
pub(crate) struct TwoRegions<'tcx> {
a: Region<'tcx>,
b: Region<'tcx>,
}
#[derive(Copy, Clone, PartialEq)]
pub(crate) enum UndoLog<'tcx> {
/// We added `RegionVid`.
AddVar(RegionVid),
/// We added the given `constraint`.
AddConstraint(Constraint<'tcx>),
/// We added the given `verify`.
AddVerify(usize),
/// We added a GLB/LUB "combination variable".
AddCombination(CombineMapType, TwoRegions<'tcx>),
}
#[derive(Copy, Clone, PartialEq)]
pub(crate) enum CombineMapType {
Lub,
Glb,
}
type CombineMap<'tcx> = FxHashMap<TwoRegions<'tcx>, RegionVid>;
#[derive(Debug, Clone, Copy)]
pub struct RegionVariableInfo {
pub origin: RegionVariableOrigin,
pub universe: ty::UniverseIndex,
}
pub struct RegionSnapshot {
any_unifications: bool,
}
impl<'tcx> RegionConstraintStorage<'tcx> {
pub fn new() -> Self {
Self::default()
}
#[inline]
pub(crate) fn with_log<'a>(
&'a mut self,
undo_log: &'a mut InferCtxtUndoLogs<'tcx>,
) -> RegionConstraintCollector<'a, 'tcx> {
RegionConstraintCollector { storage: self, undo_log }
}
fn rollback_undo_entry(&mut self, undo_entry: UndoLog<'tcx>) {
match undo_entry {
AddVar(vid) => {
self.var_infos.pop().unwrap();
assert_eq!(self.var_infos.len(), vid.index() as usize);
}
AddConstraint(ref constraint) => {
self.data.constraints.remove(constraint);
}
AddVerify(index) => {
self.data.verifys.pop();
assert_eq!(self.data.verifys.len(), index);
}
AddCombination(Glb, ref regions) => {
self.glbs.remove(regions);
}
AddCombination(Lub, ref regions) => {
self.lubs.remove(regions);
}
}
}
}
impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
pub fn num_region_vars(&self) -> usize {
self.var_infos.len()
}
pub fn region_constraint_data(&self) -> &RegionConstraintData<'tcx> {
&self.data
}
/// Once all the constraints have been gathered, extract out the final data.
///
/// Not legal during a snapshot.
pub fn into_infos_and_data(self) -> (VarInfos, RegionConstraintData<'tcx>) {
assert!(!UndoLogs::<super::UndoLog<'_>>::in_snapshot(&self.undo_log));
(mem::take(&mut self.storage.var_infos), mem::take(&mut self.storage.data))
}
/// Takes (and clears) the current set of constraints. Note that
/// the set of variables remains intact, but all relationships
/// between them are reset. This is used during NLL checking to
/// grab the set of constraints that arose from a particular
/// operation.
///
/// We don't want to leak relationships between variables between
/// points because just because (say) `r1 == r2` was true at some
/// point P in the graph doesn't imply that it will be true at
/// some other point Q, in NLL.
///
/// Not legal during a snapshot.
pub fn take_and_reset_data(&mut self) -> RegionConstraintData<'tcx> {
assert!(!UndoLogs::<super::UndoLog<'_>>::in_snapshot(&self.undo_log));
// If you add a new field to `RegionConstraintCollector`, you
// should think carefully about whether it needs to be cleared
// or updated in some way.
let RegionConstraintStorage {
var_infos: _,
data,
lubs,
glbs,
unification_table: _,
any_unifications,
} = self.storage;
// Clear the tables of (lubs, glbs), so that we will create
// fresh regions if we do a LUB operation. As it happens,
// LUB/GLB are not performed by the MIR type-checker, which is
// the one that uses this method, but it's good to be correct.
lubs.clear();
glbs.clear();
let data = mem::take(data);
// Clear all unifications and recreate the variables a "now
// un-unified" state. Note that when we unify `a` and `b`, we
// also insert `a <= b` and a `b <= a` edges, so the
// `RegionConstraintData` contains the relationship here.
if *any_unifications {
*any_unifications = false;
self.unification_table_mut().reset_unifications(|_| UnifiedRegion::new(None));
}
data
}
pub fn data(&self) -> &RegionConstraintData<'tcx> {
&self.data
}
pub(super) fn start_snapshot(&mut self) -> RegionSnapshot {
debug!("RegionConstraintCollector: start_snapshot");
RegionSnapshot { any_unifications: self.any_unifications }
}
pub(super) fn rollback_to(&mut self, snapshot: RegionSnapshot) {
debug!("RegionConstraintCollector: rollback_to({:?})", snapshot);
self.any_unifications = snapshot.any_unifications;
}
pub(super) fn new_region_var(
&mut self,
universe: ty::UniverseIndex,
origin: RegionVariableOrigin,
) -> RegionVid {
let vid = self.var_infos.push(RegionVariableInfo { origin, universe });
let u_vid = self.unification_table_mut().new_key(UnifiedRegion::new(None));
assert_eq!(vid, u_vid.vid);
self.undo_log.push(AddVar(vid));
debug!("created new region variable {:?} in {:?} with origin {:?}", vid, universe, origin);
vid
}
/// Returns the universe for the given variable.
pub(super) fn var_universe(&self, vid: RegionVid) -> ty::UniverseIndex {
self.var_infos[vid].universe
}
/// Returns the origin for the given variable.
pub(super) fn var_origin(&self, vid: RegionVid) -> RegionVariableOrigin {
self.var_infos[vid].origin
}
fn add_constraint(&mut self, constraint: Constraint<'tcx>, origin: SubregionOrigin<'tcx>) {
// cannot add constraints once regions are resolved
debug!("RegionConstraintCollector: add_constraint({:?})", constraint);
// never overwrite an existing (constraint, origin) - only insert one if it isn't
// present in the map yet. This prevents origins from outside the snapshot being
// replaced with "less informative" origins e.g., during calls to `can_eq`
let undo_log = &mut self.undo_log;
self.storage.data.constraints.entry(constraint).or_insert_with(|| {
undo_log.push(AddConstraint(constraint));
origin
});
}
fn add_verify(&mut self, verify: Verify<'tcx>) {
// cannot add verifys once regions are resolved
debug!("RegionConstraintCollector: add_verify({:?})", verify);
// skip no-op cases known to be satisfied
if let VerifyBound::AllBounds(ref bs) = verify.bound && bs.is_empty() {
return;
}
let index = self.data.verifys.len();
self.data.verifys.push(verify);
self.undo_log.push(AddVerify(index));
}
pub(super) fn make_eqregion(
&mut self,
origin: SubregionOrigin<'tcx>,
sub: Region<'tcx>,
sup: Region<'tcx>,
) {
if sub != sup {
// Eventually, it would be nice to add direct support for
// equating regions.
self.make_subregion(origin.clone(), sub, sup);
self.make_subregion(origin, sup, sub);
match (sub, sup) {
(Region(Interned(ReVar(sub), _)), Region(Interned(ReVar(sup), _))) => {
debug!("make_eqregion: unifying {:?} with {:?}", sub, sup);
self.unification_table_mut().union(*sub, *sup);
self.any_unifications = true;
}
(Region(Interned(ReVar(vid), _)), value)
| (value, Region(Interned(ReVar(vid), _))) => {
debug!("make_eqregion: unifying {:?} with {:?}", vid, value);
self.unification_table_mut().union_value(*vid, UnifiedRegion::new(Some(value)));
self.any_unifications = true;
}
(_, _) => {}
}
}
}
pub(super) fn member_constraint(
&mut self,
key: ty::OpaqueTypeKey<'tcx>,
definition_span: Span,
hidden_ty: Ty<'tcx>,
member_region: ty::Region<'tcx>,
choice_regions: &Lrc<Vec<ty::Region<'tcx>>>,
) {
debug!("member_constraint({:?} in {:#?})", member_region, choice_regions);
if choice_regions.iter().any(|&r| r == member_region) {
return;
}
self.data.member_constraints.push(MemberConstraint {
key,
definition_span,
hidden_ty,
member_region,
choice_regions: choice_regions.clone(),
});
}
#[instrument(skip(self, origin), level = "debug")]
pub(super) fn make_subregion(
&mut self,
origin: SubregionOrigin<'tcx>,
sub: Region<'tcx>,
sup: Region<'tcx>,
) {
// cannot add constraints once regions are resolved
debug!("origin = {:#?}", origin);
match (*sub, *sup) {
(ReLateBound(..), _) | (_, ReLateBound(..)) => {
span_bug!(origin.span(), "cannot relate bound region: {:?} <= {:?}", sub, sup);
}
(_, ReStatic) => {
// all regions are subregions of static, so we can ignore this
}
(ReVar(sub_id), ReVar(sup_id)) => {
self.add_constraint(Constraint::VarSubVar(sub_id, sup_id), origin);
}
(_, ReVar(sup_id)) => {
self.add_constraint(Constraint::RegSubVar(sub, sup_id), origin);
}
(ReVar(sub_id), _) => {
self.add_constraint(Constraint::VarSubReg(sub_id, sup), origin);
}
_ => {
self.add_constraint(Constraint::RegSubReg(sub, sup), origin);
}
}
}
pub(super) fn verify_generic_bound(
&mut self,
origin: SubregionOrigin<'tcx>,
kind: GenericKind<'tcx>,
sub: Region<'tcx>,
bound: VerifyBound<'tcx>,
) {
self.add_verify(Verify { kind, origin, region: sub, bound });
}
pub(super) fn lub_regions(
&mut self,
tcx: TyCtxt<'tcx>,
origin: SubregionOrigin<'tcx>,
a: Region<'tcx>,
b: Region<'tcx>,
) -> Region<'tcx> {
// cannot add constraints once regions are resolved
debug!("RegionConstraintCollector: lub_regions({:?}, {:?})", a, b);
if a.is_static() || b.is_static() {
a // nothing lives longer than static
} else if a == b {
a // LUB(a,a) = a
} else {
self.combine_vars(tcx, Lub, a, b, origin)
}
}
pub(super) fn glb_regions(
&mut self,
tcx: TyCtxt<'tcx>,
origin: SubregionOrigin<'tcx>,
a: Region<'tcx>,
b: Region<'tcx>,
) -> Region<'tcx> {
// cannot add constraints once regions are resolved
debug!("RegionConstraintCollector: glb_regions({:?}, {:?})", a, b);
if a.is_static() {
b // static lives longer than everything else
} else if b.is_static() {
a // static lives longer than everything else
} else if a == b {
a // GLB(a,a) = a
} else {
self.combine_vars(tcx, Glb, a, b, origin)
}
}
/// Resolves a region var to its value in the unification table, if it exists.
/// Otherwise, it is resolved to the root `ReVar` in the table.
pub fn opportunistic_resolve_var(
&mut self,
tcx: TyCtxt<'tcx>,
vid: ty::RegionVid,
) -> ty::Region<'tcx> {
let mut ut = self.unification_table_mut(); // FIXME(rust-lang/ena#42): unnecessary mut
let root_vid = ut.find(vid).vid;
let resolved = ut
.probe_value(root_vid)
.get_value_ignoring_universes()
.unwrap_or_else(|| ty::Region::new_var(tcx, root_vid));
// Don't resolve a variable to a region that it cannot name.
if self.var_universe(vid).can_name(self.universe(resolved)) {
resolved
} else {
ty::Region::new_var(tcx, vid)
}
}
fn combine_map(&mut self, t: CombineMapType) -> &mut CombineMap<'tcx> {
match t {
Glb => &mut self.glbs,
Lub => &mut self.lubs,
}
}
fn combine_vars(
&mut self,
tcx: TyCtxt<'tcx>,
t: CombineMapType,
a: Region<'tcx>,
b: Region<'tcx>,
origin: SubregionOrigin<'tcx>,
) -> Region<'tcx> {
let vars = TwoRegions { a, b };
if let Some(&c) = self.combine_map(t).get(&vars) {
return ty::Region::new_var(tcx, c);
}
let a_universe = self.universe(a);
let b_universe = self.universe(b);
let c_universe = cmp::max(a_universe, b_universe);
let c = self.new_region_var(c_universe, MiscVariable(origin.span()));
self.combine_map(t).insert(vars, c);
self.undo_log.push(AddCombination(t, vars));
let new_r = ty::Region::new_var(tcx, c);
for old_r in [a, b] {
match t {
Glb => self.make_subregion(origin.clone(), new_r, old_r),
Lub => self.make_subregion(origin.clone(), old_r, new_r),
}
}
debug!("combine_vars() c={:?}", c);
new_r
}
pub fn universe(&self, region: Region<'tcx>) -> ty::UniverseIndex {
match *region {
ty::ReStatic
| ty::ReErased
| ty::ReFree(..)
| ty::ReEarlyBound(..)
| ty::ReError(_) => ty::UniverseIndex::ROOT,
ty::RePlaceholder(placeholder) => placeholder.universe,
ty::ReVar(vid) => self.var_universe(vid),
ty::ReLateBound(..) => bug!("universe(): encountered bound region {:?}", region),
}
}
pub fn vars_since_snapshot(
&self,
value_count: usize,
) -> (Range<RegionVid>, Vec<RegionVariableOrigin>) {
let range = RegionVid::from(value_count)..RegionVid::from(self.unification_table.len());
(
range.clone(),
(range.start.index()..range.end.index())
.map(|index| self.var_infos[ty::RegionVid::from(index)].origin)
.collect(),
)
}
/// See `InferCtxt::region_constraints_added_in_snapshot`.
pub fn region_constraints_added_in_snapshot(&self, mark: &Snapshot<'tcx>) -> bool {
self.undo_log
.region_constraints_in_snapshot(mark)
.any(|&elt| matches!(elt, AddConstraint(_)))
}
#[inline]
fn unification_table_mut(&mut self) -> super::UnificationTable<'_, 'tcx, RegionVidKey<'tcx>> {
ut::UnificationTable::with_log(&mut self.storage.unification_table, self.undo_log)
}
}
impl fmt::Debug for RegionSnapshot {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "RegionSnapshot")
}
}
impl<'tcx> fmt::Debug for GenericKind<'tcx> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match *self {
GenericKind::Param(ref p) => write!(f, "{p:?}"),
GenericKind::Alias(ref p) => write!(f, "{p:?}"),
}
}
}
impl<'tcx> fmt::Display for GenericKind<'tcx> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match *self {
GenericKind::Param(ref p) => write!(f, "{p}"),
GenericKind::Alias(ref p) => write!(f, "{p}"),
}
}
}
impl<'tcx> GenericKind<'tcx> {
pub fn to_ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
match *self {
GenericKind::Param(ref p) => p.to_ty(tcx),
GenericKind::Alias(ref p) => p.to_ty(tcx),
}
}
}
impl<'tcx> VerifyBound<'tcx> {
pub fn must_hold(&self) -> bool {
match self {
VerifyBound::IfEq(..) => false,
VerifyBound::OutlivedBy(re) => re.is_static(),
VerifyBound::IsEmpty => false,
VerifyBound::AnyBound(bs) => bs.iter().any(|b| b.must_hold()),
VerifyBound::AllBounds(bs) => bs.iter().all(|b| b.must_hold()),
}
}
pub fn cannot_hold(&self) -> bool {
match self {
VerifyBound::IfEq(..) => false,
VerifyBound::IsEmpty => false,
VerifyBound::OutlivedBy(_) => false,
VerifyBound::AnyBound(bs) => bs.iter().all(|b| b.cannot_hold()),
VerifyBound::AllBounds(bs) => bs.iter().any(|b| b.cannot_hold()),
}
}
pub fn or(self, vb: VerifyBound<'tcx>) -> VerifyBound<'tcx> {
if self.must_hold() || vb.cannot_hold() {
self
} else if self.cannot_hold() || vb.must_hold() {
vb
} else {
VerifyBound::AnyBound(vec![self, vb])
}
}
}
impl<'tcx> RegionConstraintData<'tcx> {
/// Returns `true` if this region constraint data contains no constraints, and `false`
/// otherwise.
pub fn is_empty(&self) -> bool {
let RegionConstraintData { constraints, member_constraints, verifys } = self;
constraints.is_empty() && member_constraints.is_empty() && verifys.is_empty()
}
}
impl<'tcx> Rollback<UndoLog<'tcx>> for RegionConstraintStorage<'tcx> {
fn reverse(&mut self, undo: UndoLog<'tcx>) {
self.rollback_undo_entry(undo)
}
}