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//! Lexical region resolution.
use crate::infer::region_constraints::Constraint;
use crate::infer::region_constraints::GenericKind;
use crate::infer::region_constraints::RegionConstraintData;
use crate::infer::region_constraints::VarInfos;
use crate::infer::region_constraints::VerifyBound;
use crate::infer::RegionRelations;
use crate::infer::RegionVariableOrigin;
use crate::infer::SubregionOrigin;
use rustc_data_structures::fx::FxHashSet;
use rustc_data_structures::graph::implementation::{
Direction, Graph, NodeIndex, INCOMING, OUTGOING,
};
use rustc_data_structures::intern::Interned;
use rustc_index::{IndexSlice, IndexVec};
use rustc_middle::ty::fold::TypeFoldable;
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_middle::ty::{ReEarlyBound, ReErased, ReError, ReFree, ReStatic};
use rustc_middle::ty::{ReLateBound, RePlaceholder, ReVar};
use rustc_middle::ty::{Region, RegionVid};
use rustc_span::Span;
use std::fmt;
use super::outlives::test_type_match;
/// This function performs lexical region resolution given a complete
/// set of constraints and variable origins. It performs a fixed-point
/// iteration to find region values which satisfy all constraints,
/// assuming such values can be found. It returns the final values of
/// all the variables as well as a set of errors that must be reported.
#[instrument(level = "debug", skip(region_rels, var_infos, data))]
pub(crate) fn resolve<'tcx>(
param_env: ty::ParamEnv<'tcx>,
region_rels: &RegionRelations<'_, 'tcx>,
var_infos: VarInfos,
data: RegionConstraintData<'tcx>,
) -> (LexicalRegionResolutions<'tcx>, Vec<RegionResolutionError<'tcx>>) {
let mut errors = vec![];
let mut resolver = LexicalResolver { param_env, region_rels, var_infos, data };
let values = resolver.infer_variable_values(&mut errors);
(values, errors)
}
/// Contains the result of lexical region resolution. Offers methods
/// to lookup up the final value of a region variable.
#[derive(Clone)]
pub struct LexicalRegionResolutions<'tcx> {
pub(crate) values: IndexVec<RegionVid, VarValue<'tcx>>,
}
#[derive(Copy, Clone, Debug)]
pub(crate) enum VarValue<'tcx> {
/// Empty lifetime is for data that is never accessed. We tag the
/// empty lifetime with a universe -- the idea is that we don't
/// want `exists<'a> { forall<'b> { 'b: 'a } }` to be satisfiable.
/// Therefore, the `'empty` in a universe `U` is less than all
/// regions visible from `U`, but not less than regions not visible
/// from `U`.
Empty(ty::UniverseIndex),
Value(Region<'tcx>),
ErrorValue,
}
#[derive(Clone, Debug)]
pub enum RegionResolutionError<'tcx> {
/// `ConcreteFailure(o, a, b)`:
///
/// `o` requires that `a <= b`, but this does not hold
ConcreteFailure(SubregionOrigin<'tcx>, Region<'tcx>, Region<'tcx>),
/// `GenericBoundFailure(p, s, a)`:
///
/// The parameter/associated-type `p` must be known to outlive the lifetime
/// `a` (but none of the known bounds are sufficient).
GenericBoundFailure(SubregionOrigin<'tcx>, GenericKind<'tcx>, Region<'tcx>),
/// `SubSupConflict(v, v_origin, sub_origin, sub_r, sup_origin, sup_r)`:
///
/// Could not infer a value for `v` (which has origin `v_origin`)
/// because `sub_r <= v` (due to `sub_origin`) but `v <= sup_r` (due to `sup_origin`) and
/// `sub_r <= sup_r` does not hold.
SubSupConflict(
RegionVid,
RegionVariableOrigin,
SubregionOrigin<'tcx>,
Region<'tcx>,
SubregionOrigin<'tcx>,
Region<'tcx>,
Vec<Span>, // All the influences on a given value that didn't meet its constraints.
),
/// Indicates a `'b: 'a` constraint where `'a` is in a universe that
/// cannot name the placeholder `'b`.
UpperBoundUniverseConflict(
RegionVid,
RegionVariableOrigin,
ty::UniverseIndex, // the universe index of the region variable
SubregionOrigin<'tcx>, // cause of the constraint
Region<'tcx>, // the placeholder `'b`
),
}
impl<'tcx> RegionResolutionError<'tcx> {
pub fn origin(&self) -> &SubregionOrigin<'tcx> {
match self {
RegionResolutionError::ConcreteFailure(origin, _, _)
| RegionResolutionError::GenericBoundFailure(origin, _, _)
| RegionResolutionError::SubSupConflict(_, _, origin, _, _, _, _)
| RegionResolutionError::UpperBoundUniverseConflict(_, _, _, origin, _) => origin,
}
}
}
struct RegionAndOrigin<'tcx> {
region: Region<'tcx>,
origin: SubregionOrigin<'tcx>,
}
type RegionGraph<'tcx> = Graph<(), Constraint<'tcx>>;
struct LexicalResolver<'cx, 'tcx> {
param_env: ty::ParamEnv<'tcx>,
region_rels: &'cx RegionRelations<'cx, 'tcx>,
var_infos: VarInfos,
data: RegionConstraintData<'tcx>,
}
impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
fn tcx(&self) -> TyCtxt<'tcx> {
self.region_rels.tcx
}
fn infer_variable_values(
&mut self,
errors: &mut Vec<RegionResolutionError<'tcx>>,
) -> LexicalRegionResolutions<'tcx> {
let mut var_data = self.construct_var_data();
if cfg!(debug_assertions) {
self.dump_constraints();
}
self.expansion(&mut var_data);
self.collect_errors(&mut var_data, errors);
self.collect_var_errors(&var_data, errors);
var_data
}
fn num_vars(&self) -> usize {
self.var_infos.len()
}
/// Initially, the value for all variables is set to `'empty`, the
/// empty region. The `expansion` phase will grow this larger.
fn construct_var_data(&self) -> LexicalRegionResolutions<'tcx> {
LexicalRegionResolutions {
values: IndexVec::from_fn_n(
|vid| {
let vid_universe = self.var_infos[vid].universe;
VarValue::Empty(vid_universe)
},
self.num_vars(),
),
}
}
#[instrument(level = "debug", skip(self))]
fn dump_constraints(&self) {
for (idx, (constraint, _)) in self.data.constraints.iter().enumerate() {
debug!("Constraint {} => {:?}", idx, constraint);
}
}
fn expansion(&self, var_values: &mut LexicalRegionResolutions<'tcx>) {
// In the first pass, we expand region vids according to constraints we
// have previously found. In the second pass, we loop through the region
// vids we expanded and expand *across* region vids (effectively
// "expanding" new `RegSubVar` constraints).
// Tracks the `VarSubVar` constraints generated for each region vid. We
// later use this to expand across vids.
let mut constraints = IndexVec::from_elem(Vec::new(), &var_values.values);
// Tracks the changed region vids.
let mut changes = Vec::new();
for constraint in self.data.constraints.keys() {
match *constraint {
Constraint::RegSubVar(a_region, b_vid) => {
let b_data = var_values.value_mut(b_vid);
if self.expand_node(a_region, b_vid, b_data) {
changes.push(b_vid);
}
}
Constraint::VarSubVar(a_vid, b_vid) => match *var_values.value(a_vid) {
VarValue::ErrorValue => continue,
VarValue::Empty(a_universe) => {
let b_data = var_values.value_mut(b_vid);
let changed = match *b_data {
VarValue::Empty(b_universe) => {
// Empty regions are ordered according to the universe
// they are associated with.
let ui = a_universe.min(b_universe);
debug!(
"Expanding value of {:?} \
from empty lifetime with universe {:?} \
to empty lifetime with universe {:?}",
b_vid, b_universe, ui
);
*b_data = VarValue::Empty(ui);
true
}
VarValue::Value(cur_region) => {
match *cur_region {
// If this empty region is from a universe that can name the
// placeholder universe, then the LUB is the Placeholder region
// (which is the cur_region). Otherwise, the LUB is the Static
// lifetime.
RePlaceholder(placeholder)
if !a_universe.can_name(placeholder.universe) =>
{
let lub = self.tcx().lifetimes.re_static;
debug!(
"Expanding value of {:?} from {:?} to {:?}",
b_vid, cur_region, lub
);
*b_data = VarValue::Value(lub);
true
}
_ => false,
}
}
VarValue::ErrorValue => false,
};
if changed {
changes.push(b_vid);
}
match b_data {
VarValue::Value(Region(Interned(ReStatic, _)))
| VarValue::ErrorValue => (),
_ => {
constraints[a_vid].push((a_vid, b_vid));
constraints[b_vid].push((a_vid, b_vid));
}
}
}
VarValue::Value(a_region) => {
let b_data = var_values.value_mut(b_vid);
if self.expand_node(a_region, b_vid, b_data) {
changes.push(b_vid);
}
match b_data {
VarValue::Value(Region(Interned(ReStatic, _)))
| VarValue::ErrorValue => (),
_ => {
constraints[a_vid].push((a_vid, b_vid));
constraints[b_vid].push((a_vid, b_vid));
}
}
}
},
Constraint::RegSubReg(..) | Constraint::VarSubReg(..) => {
// These constraints are checked after expansion
// is done, in `collect_errors`.
continue;
}
}
}
while let Some(vid) = changes.pop() {
constraints[vid].retain(|&(a_vid, b_vid)| {
let VarValue::Value(a_region) = *var_values.value(a_vid) else {
return false;
};
let b_data = var_values.value_mut(b_vid);
if self.expand_node(a_region, b_vid, b_data) {
changes.push(b_vid);
}
!matches!(
b_data,
VarValue::Value(Region(Interned(ReStatic, _))) | VarValue::ErrorValue
)
});
}
}
/// Expands the value of the region represented with `b_vid` with current
/// value `b_data` to the lub of `b_data` and `a_region`. The corresponds
/// with the constraint `'?b: 'a` (`'a <: '?b`), where `'a` is some known
/// region and `'?b` is some region variable.
fn expand_node(
&self,
a_region: Region<'tcx>,
b_vid: RegionVid,
b_data: &mut VarValue<'tcx>,
) -> bool {
debug!("expand_node({:?}, {:?} == {:?})", a_region, b_vid, b_data);
match *b_data {
VarValue::Empty(empty_ui) => {
let lub = match *a_region {
RePlaceholder(placeholder) => {
// If this empty region is from a universe that can
// name the placeholder, then the placeholder is
// larger; otherwise, the only ancestor is `'static`.
if empty_ui.can_name(placeholder.universe) {
ty::Region::new_placeholder(self.tcx(), placeholder)
} else {
self.tcx().lifetimes.re_static
}
}
_ => a_region,
};
debug!("Expanding value of {:?} from empty lifetime to {:?}", b_vid, lub);
*b_data = VarValue::Value(lub);
true
}
VarValue::Value(cur_region) => {
// This is a specialized version of the `lub_concrete_regions`
// check below for a common case, here purely as an
// optimization.
let b_universe = self.var_infos[b_vid].universe;
let mut lub = self.lub_concrete_regions(a_region, cur_region);
if lub == cur_region {
return false;
}
// Watch out for `'b: !1` relationships, where the
// universe of `'b` can't name the placeholder `!1`. In
// that case, we have to grow `'b` to be `'static` for the
// relationship to hold. This is obviously a kind of sub-optimal
// choice -- in the future, when we incorporate a knowledge
// of the parameter environment, we might be able to find a
// tighter bound than `'static`.
//
// (This might e.g. arise from being asked to prove `for<'a> { 'b: 'a }`.)
if let ty::RePlaceholder(p) = *lub && b_universe.cannot_name(p.universe) {
lub = self.tcx().lifetimes.re_static;
}
debug!("Expanding value of {:?} from {:?} to {:?}", b_vid, cur_region, lub);
*b_data = VarValue::Value(lub);
true
}
VarValue::ErrorValue => false,
}
}
/// True if `a <= b`.
fn sub_region_values(&self, a: VarValue<'tcx>, b: VarValue<'tcx>) -> bool {
match (a, b) {
// Error region is `'static`
(VarValue::ErrorValue, _) | (_, VarValue::ErrorValue) => return true,
(VarValue::Empty(a_ui), VarValue::Empty(b_ui)) => {
// Empty regions are ordered according to the universe
// they are associated with.
a_ui.min(b_ui) == b_ui
}
(VarValue::Value(a), VarValue::Empty(_)) => {
match *a {
// this is always on an error path,
// so it doesn't really matter if it's shorter or longer than an empty region
ReError(_) => false,
ReLateBound(..) | ReErased => {
bug!("cannot relate region: {:?}", a);
}
ReVar(v_id) => {
span_bug!(
self.var_infos[v_id].origin.span(),
"lub_concrete_regions invoked with non-concrete region: {:?}",
a
);
}
ReStatic | ReEarlyBound(_) | ReFree(_) => {
// nothing lives longer than `'static`
// All empty regions are less than early-bound, free,
// and scope regions.
false
}
RePlaceholder(_) => {
// The LUB is either `a` or `'static`
false
}
}
}
(VarValue::Empty(a_ui), VarValue::Value(b)) => {
match *b {
// this is always on an error path,
// so it doesn't really matter if it's shorter or longer than an empty region
ReError(_) => false,
ReLateBound(..) | ReErased => {
bug!("cannot relate region: {:?}", b);
}
ReVar(v_id) => {
span_bug!(
self.var_infos[v_id].origin.span(),
"lub_concrete_regions invoked with non-concrete regions: {:?}",
b
);
}
ReStatic | ReEarlyBound(_) | ReFree(_) => {
// nothing lives longer than `'static`
// All empty regions are less than early-bound, free,
// and scope regions.
true
}
RePlaceholder(placeholder) => {
// If this empty region is from a universe that can
// name the placeholder, then the placeholder is
// larger; otherwise, the only ancestor is `'static`.
return a_ui.can_name(placeholder.universe);
}
}
}
(VarValue::Value(a), VarValue::Value(b)) => self.sub_concrete_regions(a, b),
}
}
/// True if `a <= b`, but not defined over inference variables.
#[instrument(level = "trace", skip(self))]
fn sub_concrete_regions(&self, a: Region<'tcx>, b: Region<'tcx>) -> bool {
let tcx = self.tcx();
let sub_free_regions = |r1, r2| self.region_rels.free_regions.sub_free_regions(tcx, r1, r2);
// Check for the case where we know that `'b: 'static` -- in that case,
// `a <= b` for all `a`.
let b_free_or_static = b.is_free_or_static();
if b_free_or_static && sub_free_regions(tcx.lifetimes.re_static, b) {
return true;
}
// If both `a` and `b` are free, consult the declared
// relationships. Note that this can be more precise than the
// `lub` relationship defined below, since sometimes the "lub"
// is actually the `postdom_upper_bound` (see
// `TransitiveRelation` for more details).
let a_free_or_static = a.is_free_or_static();
if a_free_or_static && b_free_or_static {
return sub_free_regions(a, b);
}
// For other cases, leverage the LUB code to find the LUB and
// check if it is equal to `b`.
self.lub_concrete_regions(a, b) == b
}
/// Returns the least-upper-bound of `a` and `b`; i.e., the
/// smallest region `c` such that `a <= c` and `b <= c`.
///
/// Neither `a` nor `b` may be an inference variable (hence the
/// term "concrete regions").
#[instrument(level = "trace", skip(self), ret)]
fn lub_concrete_regions(&self, a: Region<'tcx>, b: Region<'tcx>) -> Region<'tcx> {
match (*a, *b) {
(ReLateBound(..), _) | (_, ReLateBound(..)) | (ReErased, _) | (_, ReErased) => {
bug!("cannot relate region: LUB({:?}, {:?})", a, b);
}
(ReVar(v_id), _) | (_, ReVar(v_id)) => {
span_bug!(
self.var_infos[v_id].origin.span(),
"lub_concrete_regions invoked with non-concrete \
regions: {:?}, {:?}",
a,
b
);
}
(ReError(_), _) => a,
(_, ReError(_)) => b,
(ReStatic, _) | (_, ReStatic) => {
// nothing lives longer than `'static`
self.tcx().lifetimes.re_static
}
(ReEarlyBound(_) | ReFree(_), ReEarlyBound(_) | ReFree(_)) => {
self.region_rels.lub_free_regions(a, b)
}
// For these types, we cannot define any additional
// relationship:
(RePlaceholder(..), _) | (_, RePlaceholder(..)) => {
if a == b {
a
} else {
self.tcx().lifetimes.re_static
}
}
}
}
/// After expansion is complete, go and check upper bounds (i.e.,
/// cases where the region cannot grow larger than a fixed point)
/// and check that they are satisfied.
#[instrument(skip(self, var_data, errors))]
fn collect_errors(
&self,
var_data: &mut LexicalRegionResolutions<'tcx>,
errors: &mut Vec<RegionResolutionError<'tcx>>,
) {
for (constraint, origin) in &self.data.constraints {
debug!(?constraint, ?origin);
match *constraint {
Constraint::RegSubVar(..) | Constraint::VarSubVar(..) => {
// Expansion will ensure that these constraints hold. Ignore.
}
Constraint::RegSubReg(sub, sup) => {
if self.sub_concrete_regions(sub, sup) {
continue;
}
debug!(
"region error at {:?}: \
cannot verify that {:?} <= {:?}",
origin, sub, sup
);
errors.push(RegionResolutionError::ConcreteFailure(
(*origin).clone(),
sub,
sup,
));
}
Constraint::VarSubReg(a_vid, b_region) => {
let a_data = var_data.value_mut(a_vid);
debug!("contraction: {:?} == {:?}, {:?}", a_vid, a_data, b_region);
let VarValue::Value(a_region) = *a_data else {
continue;
};
// Do not report these errors immediately:
// instead, set the variable value to error and
// collect them later.
if !self.sub_concrete_regions(a_region, b_region) {
debug!(
"region error at {:?}: \
cannot verify that {:?}={:?} <= {:?}",
origin, a_vid, a_region, b_region
);
*a_data = VarValue::ErrorValue;
}
}
}
}
for verify in &self.data.verifys {
debug!("collect_errors: verify={:?}", verify);
let sub = var_data.normalize(self.tcx(), verify.region);
let verify_kind_ty = verify.kind.to_ty(self.tcx());
let verify_kind_ty = var_data.normalize(self.tcx(), verify_kind_ty);
if self.bound_is_met(&verify.bound, var_data, verify_kind_ty, sub) {
continue;
}
debug!(
"collect_errors: region error at {:?}: \
cannot verify that {:?} <= {:?}",
verify.origin, verify.region, verify.bound
);
errors.push(RegionResolutionError::GenericBoundFailure(
verify.origin.clone(),
verify.kind,
sub,
));
}
}
/// Go over the variables that were declared to be error variables
/// and create a `RegionResolutionError` for each of them.
fn collect_var_errors(
&self,
var_data: &LexicalRegionResolutions<'tcx>,
errors: &mut Vec<RegionResolutionError<'tcx>>,
) {
debug!("collect_var_errors, var_data = {:#?}", var_data.values);
// This is the best way that I have found to suppress
// duplicate and related errors. Basically we keep a set of
// flags for every node. Whenever an error occurs, we will
// walk some portion of the graph looking to find pairs of
// conflicting regions to report to the user. As we walk, we
// trip the flags from false to true, and if we find that
// we've already reported an error involving any particular
// node we just stop and don't report the current error. The
// idea is to report errors that derive from independent
// regions of the graph, but not those that derive from
// overlapping locations.
let mut dup_vec = IndexVec::from_elem_n(None, self.num_vars());
// Only construct the graph when necessary, because it's moderately
// expensive.
let mut graph = None;
for (node_vid, value) in var_data.values.iter_enumerated() {
match *value {
VarValue::Empty(_) | VarValue::Value(_) => { /* Inference successful */ }
VarValue::ErrorValue => {
// Inference impossible: this value contains
// inconsistent constraints.
//
// I think that in this case we should report an
// error now -- unlike the case above, we can't
// wait to see whether the user needs the result
// of this variable. The reason is that the mere
// existence of this variable implies that the
// region graph is inconsistent, whether or not it
// is used.
//
// For example, we may have created a region
// variable that is the GLB of two other regions
// which do not have a GLB. Even if that variable
// is not used, it implies that those two regions
// *should* have a GLB.
//
// At least I think this is true. It may be that
// the mere existence of a conflict in a region
// variable that is not used is not a problem, so
// if this rule starts to create problems we'll
// have to revisit this portion of the code and
// think hard about it. =) -- nikomatsakis
// Obtain the spans for all the places that can
// influence the constraints on this value for
// richer diagnostics in `static_impl_trait`.
let g = graph.get_or_insert_with(|| self.construct_graph());
self.collect_error_for_expanding_node(g, &mut dup_vec, node_vid, errors);
}
}
}
}
fn construct_graph(&self) -> RegionGraph<'tcx> {
let num_vars = self.num_vars();
let mut graph = Graph::new();
for _ in 0..num_vars {
graph.add_node(());
}
// Issue #30438: two distinct dummy nodes, one for incoming
// edges (dummy_source) and another for outgoing edges
// (dummy_sink). In `dummy -> a -> b -> dummy`, using one
// dummy node leads one to think (erroneously) there exists a
// path from `b` to `a`. Two dummy nodes sidesteps the issue.
let dummy_source = graph.add_node(());
let dummy_sink = graph.add_node(());
for constraint in self.data.constraints.keys() {
match *constraint {
Constraint::VarSubVar(a_id, b_id) => {
graph.add_edge(
NodeIndex(a_id.index() as usize),
NodeIndex(b_id.index() as usize),
*constraint,
);
}
Constraint::RegSubVar(_, b_id) => {
graph.add_edge(dummy_source, NodeIndex(b_id.index() as usize), *constraint);
}
Constraint::VarSubReg(a_id, _) => {
graph.add_edge(NodeIndex(a_id.index() as usize), dummy_sink, *constraint);
}
Constraint::RegSubReg(..) => {
// this would be an edge from `dummy_source` to
// `dummy_sink`; just ignore it.
}
}
}
graph
}
fn collect_error_for_expanding_node(
&self,
graph: &RegionGraph<'tcx>,
dup_vec: &mut IndexSlice<RegionVid, Option<RegionVid>>,
node_idx: RegionVid,
errors: &mut Vec<RegionResolutionError<'tcx>>,
) {
// Errors in expanding nodes result from a lower-bound that is
// not contained by an upper-bound.
let (mut lower_bounds, lower_vid_bounds, lower_dup) =
self.collect_bounding_regions(graph, node_idx, INCOMING, Some(dup_vec));
let (mut upper_bounds, _, upper_dup) =
self.collect_bounding_regions(graph, node_idx, OUTGOING, Some(dup_vec));
if lower_dup || upper_dup {
return;
}
// We place free regions first because we are special casing
// SubSupConflict(ReFree, ReFree) when reporting error, and so
// the user will more likely get a specific suggestion.
fn region_order_key(x: &RegionAndOrigin<'_>) -> u8 {
match *x.region {
ReEarlyBound(_) => 0,
ReFree(_) => 1,
_ => 2,
}
}
lower_bounds.sort_by_key(region_order_key);
upper_bounds.sort_by_key(region_order_key);
let node_universe = self.var_infos[node_idx].universe;
for lower_bound in &lower_bounds {
let effective_lower_bound = if let ty::RePlaceholder(p) = *lower_bound.region {
if node_universe.cannot_name(p.universe) {
self.tcx().lifetimes.re_static
} else {
lower_bound.region
}
} else {
lower_bound.region
};
for upper_bound in &upper_bounds {
if !self.sub_concrete_regions(effective_lower_bound, upper_bound.region) {
let origin = self.var_infos[node_idx].origin;
debug!(
"region inference error at {:?} for {:?}: SubSupConflict sub: {:?} \
sup: {:?}",
origin, node_idx, lower_bound.region, upper_bound.region
);
errors.push(RegionResolutionError::SubSupConflict(
node_idx,
origin,
lower_bound.origin.clone(),
lower_bound.region,
upper_bound.origin.clone(),
upper_bound.region,
vec![],
));
return;
}
}
}
// If we have a scenario like `exists<'a> { forall<'b> { 'b:
// 'a } }`, we wind up without any lower-bound -- all we have
// are placeholders as upper bounds, but the universe of the
// variable `'a`, or some variable that `'a` has to outlive, doesn't
// permit those placeholders.
//
// We only iterate to find the min, which means it doesn't cause reproducibility issues
#[allow(rustc::potential_query_instability)]
let min_universe = lower_vid_bounds
.into_iter()
.map(|vid| self.var_infos[vid].universe)
.min()
.expect("lower_vid_bounds should at least include `node_idx`");
for upper_bound in &upper_bounds {
if let ty::RePlaceholder(p) = *upper_bound.region {
if min_universe.cannot_name(p.universe) {
let origin = self.var_infos[node_idx].origin;
errors.push(RegionResolutionError::UpperBoundUniverseConflict(
node_idx,
origin,
min_universe,
upper_bound.origin.clone(),
upper_bound.region,
));
return;
}
}
}
// Errors in earlier passes can yield error variables without
// resolution errors here; delay ICE in favor of those errors.
self.tcx().sess.delay_span_bug(
self.var_infos[node_idx].origin.span(),
format!(
"collect_error_for_expanding_node() could not find \
error for var {node_idx:?} in universe {node_universe:?}, lower_bounds={lower_bounds:#?}, \
upper_bounds={upper_bounds:#?}"
),
);
}
/// Collects all regions that "bound" the variable `orig_node_idx` in the
/// given direction.
///
/// If `dup_vec` is `Some` it's used to track duplicates between successive
/// calls of this function.
///
/// The return tuple fields are:
/// - a list of all concrete regions bounding the given region.
/// - the set of all region variables bounding the given region.
/// - a `bool` that's true if the returned region variables overlap with
/// those returned by a previous call for another region.
fn collect_bounding_regions(
&self,
graph: &RegionGraph<'tcx>,
orig_node_idx: RegionVid,
dir: Direction,
mut dup_vec: Option<&mut IndexSlice<RegionVid, Option<RegionVid>>>,
) -> (Vec<RegionAndOrigin<'tcx>>, FxHashSet<RegionVid>, bool) {
struct WalkState<'tcx> {
set: FxHashSet<RegionVid>,
stack: Vec<RegionVid>,
result: Vec<RegionAndOrigin<'tcx>>,
dup_found: bool,
}
let mut state = WalkState {
set: Default::default(),
stack: vec![orig_node_idx],
result: Vec::new(),
dup_found: false,
};
state.set.insert(orig_node_idx);
// to start off the process, walk the source node in the
// direction specified
process_edges(&self.data, &mut state, graph, orig_node_idx, dir);
while let Some(node_idx) = state.stack.pop() {
// check whether we've visited this node on some previous walk
if let Some(dup_vec) = &mut dup_vec {
if dup_vec[node_idx].is_none() {
dup_vec[node_idx] = Some(orig_node_idx);
} else if dup_vec[node_idx] != Some(orig_node_idx) {
state.dup_found = true;
}
debug!(
"collect_concrete_regions(orig_node_idx={:?}, node_idx={:?})",
orig_node_idx, node_idx
);
}
process_edges(&self.data, &mut state, graph, node_idx, dir);
}
let WalkState { result, dup_found, set, .. } = state;
return (result, set, dup_found);
fn process_edges<'tcx>(
this: &RegionConstraintData<'tcx>,
state: &mut WalkState<'tcx>,
graph: &RegionGraph<'tcx>,
source_vid: RegionVid,
dir: Direction,
) {
debug!("process_edges(source_vid={:?}, dir={:?})", source_vid, dir);
let source_node_index = NodeIndex(source_vid.index() as usize);
for (_, edge) in graph.adjacent_edges(source_node_index, dir) {
match edge.data {
Constraint::VarSubVar(from_vid, to_vid) => {
let opp_vid = if from_vid == source_vid { to_vid } else { from_vid };
if state.set.insert(opp_vid) {
state.stack.push(opp_vid);
}
}
Constraint::RegSubVar(region, _) | Constraint::VarSubReg(_, region) => {
state.result.push(RegionAndOrigin {
region,
origin: this.constraints.get(&edge.data).unwrap().clone(),
});
}
Constraint::RegSubReg(..) => panic!(
"cannot reach reg-sub-reg edge in region inference \
post-processing"
),
}
}
}
}
fn bound_is_met(
&self,
bound: &VerifyBound<'tcx>,
var_values: &LexicalRegionResolutions<'tcx>,
generic_ty: Ty<'tcx>,
min: ty::Region<'tcx>,
) -> bool {
if let ty::ReError(_) = *min {
return true;
}
match bound {
VerifyBound::IfEq(verify_if_eq_b) => {
let verify_if_eq_b = var_values.normalize(self.region_rels.tcx, *verify_if_eq_b);
match test_type_match::extract_verify_if_eq(
self.tcx(),
self.param_env,
&verify_if_eq_b,
generic_ty,
) {
Some(r) => {
self.bound_is_met(&VerifyBound::OutlivedBy(r), var_values, generic_ty, min)
}
None => false,
}
}
VerifyBound::OutlivedBy(r) => {
let a = match *min {
ty::ReVar(rid) => var_values.values[rid],
_ => VarValue::Value(min),
};
let b = match **r {
ty::ReVar(rid) => var_values.values[rid],
_ => VarValue::Value(*r),
};
self.sub_region_values(a, b)
}
VerifyBound::IsEmpty => match *min {
ty::ReVar(rid) => match var_values.values[rid] {
VarValue::ErrorValue => false,
VarValue::Empty(_) => true,
VarValue::Value(_) => false,
},
_ => false,
},
VerifyBound::AnyBound(bs) => {
bs.iter().any(|b| self.bound_is_met(b, var_values, generic_ty, min))
}
VerifyBound::AllBounds(bs) => {
bs.iter().all(|b| self.bound_is_met(b, var_values, generic_ty, min))
}
}
}
}
impl<'tcx> fmt::Debug for RegionAndOrigin<'tcx> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "RegionAndOrigin({:?},{:?})", self.region, self.origin)
}
}
impl<'tcx> LexicalRegionResolutions<'tcx> {
fn normalize<T>(&self, tcx: TyCtxt<'tcx>, value: T) -> T
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
tcx.fold_regions(value, |r, _db| self.resolve_region(tcx, r))
}
fn value(&self, rid: RegionVid) -> &VarValue<'tcx> {
&self.values[rid]
}
fn value_mut(&mut self, rid: RegionVid) -> &mut VarValue<'tcx> {
&mut self.values[rid]
}
pub(crate) fn resolve_region(
&self,
tcx: TyCtxt<'tcx>,
r: ty::Region<'tcx>,
) -> ty::Region<'tcx> {
let result = match *r {
ty::ReVar(rid) => match self.values[rid] {
VarValue::Empty(_) => r,
VarValue::Value(r) => r,
VarValue::ErrorValue => tcx.lifetimes.re_static,
},
_ => r,
};
debug!("resolve_region({:?}) = {:?}", r, result);
result
}
}