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use crate::infer::free_regions::FreeRegionMap;
use crate::infer::GenericKind;
use crate::traits::query::OutlivesBound;
use rustc_data_structures::fx::FxIndexSet;
use rustc_data_structures::transitive_relation::TransitiveRelationBuilder;
use rustc_middle::ty::{self, Region};
use super::explicit_outlives_bounds;
/// The `OutlivesEnvironment` collects information about what outlives
/// what in a given type-checking setting. For example, if we have a
/// where-clause like `where T: 'a` in scope, then the
/// `OutlivesEnvironment` would record that (in its
/// `region_bound_pairs` field). Similarly, it contains methods for
/// processing and adding implied bounds into the outlives
/// environment.
///
/// Other code at present does not typically take a
/// `&OutlivesEnvironment`, but rather takes some of its fields (e.g.,
/// `process_registered_region_obligations` wants the
/// region-bound-pairs). There is no mistaking it: the current setup
/// of tracking region information is quite scattered! The
/// `OutlivesEnvironment`, for example, needs to sometimes be combined
/// with the `middle::RegionRelations`, to yield a full picture of how
/// (lexical) lifetimes interact. However, I'm reluctant to do more
/// refactoring here, since the setup with NLL is quite different.
/// For example, NLL has no need of `RegionRelations`, and is solely
/// interested in the `OutlivesEnvironment`. -nmatsakis
#[derive(Clone)]
pub struct OutlivesEnvironment<'tcx> {
pub param_env: ty::ParamEnv<'tcx>,
free_region_map: FreeRegionMap<'tcx>,
// Contains the implied region bounds in scope for our current body.
//
// Example:
//
// ```
// fn foo<'a, 'b, T>(x: &'a T, y: &'b ()) {
// bar(x, y, |y: &'b T| { .. } // body B1)
// } // body B0
// ```
//
// Here, when checking the body B0, the list would be `[T: 'a]`, because we
// infer that `T` must outlive `'a` from the implied bounds on the
// fn declaration.
//
// For the body B1 however, the list would be `[T: 'a, T: 'b]`, because we
// also can see that -- within the closure body! -- `T` must
// outlive `'b`. This is not necessarily true outside the closure
// body, since the closure may never be called.
region_bound_pairs: RegionBoundPairs<'tcx>,
}
/// Builder of OutlivesEnvironment.
#[derive(Debug)]
struct OutlivesEnvironmentBuilder<'tcx> {
param_env: ty::ParamEnv<'tcx>,
region_relation: TransitiveRelationBuilder<Region<'tcx>>,
region_bound_pairs: RegionBoundPairs<'tcx>,
}
/// "Region-bound pairs" tracks outlives relations that are known to
/// be true, either because of explicit where-clauses like `T: 'a` or
/// because of implied bounds.
pub type RegionBoundPairs<'tcx> =
FxIndexSet<ty::OutlivesPredicate<GenericKind<'tcx>, Region<'tcx>>>;
impl<'tcx> OutlivesEnvironment<'tcx> {
/// Create a builder using `ParamEnv` and add explicit outlives bounds into it.
fn builder(param_env: ty::ParamEnv<'tcx>) -> OutlivesEnvironmentBuilder<'tcx> {
let mut builder = OutlivesEnvironmentBuilder {
param_env,
region_relation: Default::default(),
region_bound_pairs: Default::default(),
};
builder.add_outlives_bounds(explicit_outlives_bounds(param_env));
builder
}
#[inline]
/// Create a new `OutlivesEnvironment` without extra outlives bounds.
pub fn new(param_env: ty::ParamEnv<'tcx>) -> Self {
Self::builder(param_env).build()
}
/// Create a new `OutlivesEnvironment` with extra outlives bounds.
pub fn with_bounds(
param_env: ty::ParamEnv<'tcx>,
extra_bounds: impl IntoIterator<Item = OutlivesBound<'tcx>>,
) -> Self {
let mut builder = Self::builder(param_env);
builder.add_outlives_bounds(extra_bounds);
builder.build()
}
/// Borrows current value of the `free_region_map`.
pub fn free_region_map(&self) -> &FreeRegionMap<'tcx> {
&self.free_region_map
}
/// Borrows current `region_bound_pairs`.
pub fn region_bound_pairs(&self) -> &RegionBoundPairs<'tcx> {
&self.region_bound_pairs
}
}
impl<'tcx> OutlivesEnvironmentBuilder<'tcx> {
#[inline]
#[instrument(level = "debug")]
fn build(self) -> OutlivesEnvironment<'tcx> {
OutlivesEnvironment {
param_env: self.param_env,
free_region_map: FreeRegionMap { relation: self.region_relation.freeze() },
region_bound_pairs: self.region_bound_pairs,
}
}
/// Processes outlives bounds that are known to hold, whether from implied or other sources.
fn add_outlives_bounds<I>(&mut self, outlives_bounds: I)
where
I: IntoIterator<Item = OutlivesBound<'tcx>>,
{
// Record relationships such as `T:'x` that don't go into the
// free-region-map but which we use here.
for outlives_bound in outlives_bounds {
debug!("add_outlives_bounds: outlives_bound={:?}", outlives_bound);
match outlives_bound {
OutlivesBound::RegionSubParam(r_a, param_b) => {
self.region_bound_pairs
.insert(ty::OutlivesPredicate(GenericKind::Param(param_b), r_a));
}
OutlivesBound::RegionSubAlias(r_a, alias_b) => {
self.region_bound_pairs
.insert(ty::OutlivesPredicate(GenericKind::Alias(alias_b), r_a));
}
OutlivesBound::RegionSubRegion(r_a, r_b) => match (*r_a, *r_b) {
(
ty::ReStatic | ty::ReEarlyParam(_) | ty::ReLateParam(_),
ty::ReStatic | ty::ReEarlyParam(_) | ty::ReLateParam(_),
) => self.region_relation.add(r_a, r_b),
(ty::ReError(_), _) | (_, ty::ReError(_)) => {}
// FIXME(#109628): We shouldn't have existential variables in implied bounds.
// Panic here once the linked issue is resolved!
(ty::ReVar(_), _) | (_, ty::ReVar(_)) => {}
_ => bug!("add_outlives_bounds: unexpected regions: ({r_a:?}, {r_b:?})"),
},
}
}
}
}
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