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universal_regions.rs
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universal_regions.rs
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// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Code to extract the universally quantified regions declared on a
//! function and the relationships between them. For example:
//!
//! ```
//! fn foo<'a, 'b, 'c: 'b>() { }
//! ```
//!
//! here we would be returning a map assigning each of `{'a, 'b, 'c}`
//! to an index, as well as the `FreeRegionMap` which can compute
//! relationships between them.
//!
//! The code in this file doesn't *do anything* with those results; it
//! just returns them for other code to use.
use rustc::hir::{BodyOwnerKind, HirId};
use rustc::hir::def_id::DefId;
use rustc::infer::{InferCtxt, NLLRegionVariableOrigin};
use rustc::infer::region_constraints::GenericKind;
use rustc::infer::outlives::bounds::{self, OutlivesBound};
use rustc::infer::outlives::free_region_map::FreeRegionRelations;
use rustc::ty::{self, RegionVid, Ty, TyCtxt};
use rustc::ty::fold::TypeFoldable;
use rustc::ty::subst::Substs;
use rustc::util::nodemap::FxHashMap;
use rustc_data_structures::indexed_vec::{Idx, IndexVec};
use rustc_data_structures::transitive_relation::TransitiveRelation;
use std::iter;
use syntax::ast;
use super::ToRegionVid;
#[derive(Debug)]
pub struct UniversalRegions<'tcx> {
indices: UniversalRegionIndices<'tcx>,
/// The vid assigned to `'static`
pub fr_static: RegionVid,
/// A special region vid created to represent the current MIR fn
/// body. It will outlive the entire CFG but it will not outlive
/// any other universal regions.
pub fr_fn_body: RegionVid,
/// We create region variables such that they are ordered by their
/// `RegionClassification`. The first block are globals, then
/// externals, then locals. So things from:
/// - `FIRST_GLOBAL_INDEX..first_extern_index` are global;
/// - `first_extern_index..first_local_index` are external; and
/// - first_local_index..num_universals` are local.
first_extern_index: usize,
/// See `first_extern_index`.
first_local_index: usize,
/// The total number of universal region variables instantiated.
num_universals: usize,
/// The "defining" type for this function, with all universal
/// regions instantiated. For a closure or generator, this is the
/// closure type, but for a top-level function it's the `TyFnDef`.
pub defining_ty: DefiningTy<'tcx>,
/// The return type of this function, with all regions replaced by
/// their universal `RegionVid` equivalents.
///
/// NB. Associated types in this type have not been normalized,
/// as the name suggests. =)
pub unnormalized_output_ty: Ty<'tcx>,
/// The fully liberated input types of this function, with all
/// regions replaced by their universal `RegionVid` equivalents.
///
/// NB. Associated types in these types have not been normalized,
/// as the name suggests. =)
pub unnormalized_input_tys: &'tcx [Ty<'tcx>],
/// Each RBP `('a, GK)` indicates that `GK: 'a` can be assumed to
/// be true. These encode relationships like `T: 'a` that are
/// added via implicit bounds.
///
/// Each region here is guaranteed to be a key in the `indices`
/// map. We use the "original" regions (i.e., the keys from the
/// map, and not the values) because the code in
/// `process_registered_region_obligations` has some special-cased
/// logic expecting to see (e.g.) `ReStatic`, and if we supplied
/// our special inference variable there, we would mess that up.
pub region_bound_pairs: Vec<(ty::Region<'tcx>, GenericKind<'tcx>)>,
pub yield_ty: Option<Ty<'tcx>>,
relations: UniversalRegionRelations,
}
/// The "defining type" for this MIR. The key feature of the "defining
/// type" is that it contains the information needed to derive all the
/// universal regions that are in scope as well as the types of the
/// inputs/output from the MIR. In general, early-bound universal
/// regions appear free in the defining type and late-bound regions
/// appear bound in the signature.
#[derive(Copy, Clone, Debug)]
pub enum DefiningTy<'tcx> {
/// The MIR is a closure. The signature is found via
/// `ClosureSubsts::closure_sig_ty`.
Closure(DefId, ty::ClosureSubsts<'tcx>),
/// The MIR is a generator. The signature is that generators take
/// no parameters and return the result of
/// `ClosureSubsts::generator_return_ty`.
Generator(DefId, ty::ClosureSubsts<'tcx>, ty::GeneratorInterior<'tcx>),
/// The MIR is a fn item with the given def-id and substs. The signature
/// of the function can be bound then with the `fn_sig` query.
FnDef(DefId, &'tcx Substs<'tcx>),
/// The MIR represents some form of constant. The signature then
/// is that it has no inputs and a single return value, which is
/// the value of the constant.
Const(Ty<'tcx>),
}
#[derive(Debug)]
struct UniversalRegionIndices<'tcx> {
/// For those regions that may appear in the parameter environment
/// ('static and early-bound regions), we maintain a map from the
/// `ty::Region` to the internal `RegionVid` we are using. This is
/// used because trait matching and type-checking will feed us
/// region constraints that reference those regions and we need to
/// be able to map them our internal `RegionVid`. This is
/// basically equivalent to a `Substs`, except that it also
/// contains an entry for `ReStatic` -- it might be nice to just
/// use a substs, and then handle `ReStatic` another way.
indices: FxHashMap<ty::Region<'tcx>, RegionVid>,
}
#[derive(Debug)]
struct UniversalRegionRelations {
/// Stores the outlives relations that are known to hold from the
/// implied bounds, in-scope where clauses, and that sort of
/// thing.
outlives: TransitiveRelation<RegionVid>,
/// This is the `<=` relation; that is, if `a: b`, then `b <= a`,
/// and we store that here. This is useful when figuring out how
/// to express some local region in terms of external regions our
/// caller will understand.
inverse_outlives: TransitiveRelation<RegionVid>,
}
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
pub enum RegionClassification {
/// A **global** region is one that can be named from
/// anywhere. There is only one, `'static`.
Global,
/// An **external** region is only relevant for closures. In that
/// case, it refers to regions that are free in the closure type
/// -- basically, something bound in the surrounding context.
///
/// Consider this example:
///
/// ```
/// fn foo<'a, 'b>(a: &'a u32, b: &'b u32, c: &'static u32) {
/// let closure = for<'x> |x: &'x u32| { .. };
/// ^^^^^^^ pretend this were legal syntax
/// for declaring a late-bound region in
/// a closure signature
/// }
/// ```
///
/// Here, the lifetimes `'a` and `'b` would be **external** to the
/// closure.
///
/// If we are not analyzing a closure, there are no external
/// lifetimes.
External,
/// A **local** lifetime is one about which we know the full set
/// of relevant constraints (that is, relationships to other named
/// regions). For a closure, this includes any region bound in
/// the closure's signature. For a fn item, this includes all
/// regions other than global ones.
///
/// Continuing with the example from `External`, if we were
/// analyzing the closure, then `'x` would be local (and `'a` and
/// `'b` are external). If we are analyzing the function item
/// `foo`, then `'a` and `'b` are local (and `'x` is not in
/// scope).
Local,
}
const FIRST_GLOBAL_INDEX: usize = 0;
impl<'tcx> UniversalRegions<'tcx> {
/// Creates a new and fully initialized `UniversalRegions` that
/// contains indices for all the free regions found in the given
/// MIR -- that is, all the regions that appear in the function's
/// signature. This will also compute the relationships that are
/// known between those regions.
pub fn new(
infcx: &InferCtxt<'_, '_, 'tcx>,
mir_def_id: DefId,
param_env: ty::ParamEnv<'tcx>,
) -> Self {
let tcx = infcx.tcx;
let mir_node_id = tcx.hir.as_local_node_id(mir_def_id).unwrap();
let mir_hir_id = tcx.hir.node_to_hir_id(mir_node_id);
UniversalRegionsBuilder {
infcx,
mir_def_id,
mir_node_id,
mir_hir_id,
param_env,
region_bound_pairs: vec![],
relations: UniversalRegionRelations {
outlives: TransitiveRelation::new(),
inverse_outlives: TransitiveRelation::new(),
},
}.build()
}
/// Given a reference to a closure type, extracts all the values
/// from its free regions and returns a vector with them. This is
/// used when the closure's creator checks that the
/// `ClosureRegionRequirements` are met. The requirements from
/// `ClosureRegionRequirements` are expressed in terms of
/// `RegionVid` entries that map into the returned vector `V`: so
/// if the `ClosureRegionRequirements` contains something like
/// `'1: '2`, then the caller would impose the constraint that
/// `V[1]: V[2]`.
pub fn closure_mapping(
infcx: &InferCtxt<'_, '_, 'tcx>,
closure_ty: Ty<'tcx>,
expected_num_vars: usize,
) -> IndexVec<RegionVid, ty::Region<'tcx>> {
let mut region_mapping = IndexVec::with_capacity(expected_num_vars);
region_mapping.push(infcx.tcx.types.re_static);
infcx.tcx.for_each_free_region(&closure_ty, |fr| {
region_mapping.push(fr);
});
assert_eq!(
region_mapping.len(),
expected_num_vars,
"index vec had unexpected number of variables"
);
region_mapping
}
/// True if `r` is a member of this set of universal regions.
pub fn is_universal_region(&self, r: RegionVid) -> bool {
(FIRST_GLOBAL_INDEX..self.num_universals).contains(r.index())
}
/// Classifies `r` as a universal region, returning `None` if this
/// is not a member of this set of universal regions.
pub fn region_classification(&self, r: RegionVid) -> Option<RegionClassification> {
let index = r.index();
if (FIRST_GLOBAL_INDEX..self.first_extern_index).contains(index) {
Some(RegionClassification::Global)
} else if (self.first_extern_index..self.first_local_index).contains(index) {
Some(RegionClassification::External)
} else if (self.first_local_index..self.num_universals).contains(index) {
Some(RegionClassification::Local)
} else {
None
}
}
/// Returns an iterator over all the RegionVids corresponding to
/// universally quantified free regions.
pub fn universal_regions(&self) -> impl Iterator<Item = RegionVid> {
(FIRST_GLOBAL_INDEX..self.num_universals).map(RegionVid::new)
}
/// True if `r` is classified as an local region.
pub fn is_local_free_region(&self, r: RegionVid) -> bool {
self.region_classification(r) == Some(RegionClassification::Local)
}
/// Returns the number of universal regions created in any category.
pub fn len(&self) -> usize {
self.num_universals
}
/// Given two universal regions, returns the postdominating
/// upper-bound (effectively the least upper bound).
///
/// (See `TransitiveRelation::postdom_upper_bound` for details on
/// the postdominating upper bound in general.)
pub fn postdom_upper_bound(&self, fr1: RegionVid, fr2: RegionVid) -> RegionVid {
assert!(self.is_universal_region(fr1));
assert!(self.is_universal_region(fr2));
*self.relations
.inverse_outlives
.postdom_upper_bound(&fr1, &fr2)
.unwrap_or(&self.fr_static)
}
/// Finds an "upper bound" for `fr` that is not local. In other
/// words, returns the smallest (*) known region `fr1` that (a)
/// outlives `fr` and (b) is not local. This cannot fail, because
/// we will always find `'static` at worst.
///
/// (*) If there are multiple competing choices, we pick the "postdominating"
/// one. See `TransitiveRelation::postdom_upper_bound` for details.
pub fn non_local_upper_bound(&self, fr: RegionVid) -> RegionVid {
debug!("non_local_upper_bound(fr={:?})", fr);
self.non_local_bound(&self.relations.inverse_outlives, fr)
.unwrap_or(self.fr_static)
}
/// Finds a "lower bound" for `fr` that is not local. In other
/// words, returns the largest (*) known region `fr1` that (a) is
/// outlived by `fr` and (b) is not local. This cannot fail,
/// because we will always find `'static` at worst.
///
/// (*) If there are multiple competing choices, we pick the "postdominating"
/// one. See `TransitiveRelation::postdom_upper_bound` for details.
pub fn non_local_lower_bound(&self, fr: RegionVid) -> Option<RegionVid> {
debug!("non_local_lower_bound(fr={:?})", fr);
self.non_local_bound(&self.relations.outlives, fr)
}
/// Returns the number of global plus external universal regions.
/// For closures, these are the regions that appear free in the
/// closure type (versus those bound in the closure
/// signature). They are therefore the regions between which the
/// closure may impose constraints that its creator must verify.
pub fn num_global_and_external_regions(&self) -> usize {
self.first_local_index
}
/// Helper for `non_local_upper_bound` and
/// `non_local_lower_bound`. Repeatedly invokes `postdom_parent`
/// until we find something that is not local. Returns None if we
/// never do so.
fn non_local_bound(
&self,
relation: &TransitiveRelation<RegionVid>,
fr0: RegionVid,
) -> Option<RegionVid> {
// This method assumes that `fr0` is one of the universally
// quantified region variables.
assert!(self.is_universal_region(fr0));
let mut external_parents = vec![];
let mut queue = vec![&fr0];
// Keep expanding `fr` into its parents until we reach
// non-local regions.
while let Some(fr) = queue.pop() {
if !self.is_local_free_region(*fr) {
external_parents.push(fr);
continue;
}
queue.extend(relation.parents(fr));
}
debug!("non_local_bound: external_parents={:?}", external_parents);
// In case we find more than one, reduce to one for
// convenience. This is to prevent us from generating more
// complex constraints, but it will cause spurious errors.
let post_dom = relation
.mutual_immediate_postdominator(external_parents)
.cloned();
debug!("non_local_bound: post_dom={:?}", post_dom);
post_dom.and_then(|post_dom| {
// If the mutual immediate postdom is not local, then
// there is no non-local result we can return.
if !self.is_local_free_region(post_dom) {
Some(post_dom)
} else {
None
}
})
}
/// True if fr1 is known to outlive fr2.
///
/// This will only ever be true for universally quantified regions.
pub fn outlives(&self, fr1: RegionVid, fr2: RegionVid) -> bool {
self.relations.outlives.contains(&fr1, &fr2)
}
/// Returns a vector of free regions `x` such that `fr1: x` is
/// known to hold.
pub fn regions_outlived_by(&self, fr1: RegionVid) -> Vec<&RegionVid> {
self.relations.outlives.reachable_from(&fr1)
}
/// Get an iterator over all the early-bound regions that have names.
pub fn named_universal_regions<'s>(
&'s self,
) -> impl Iterator<Item = (ty::Region<'tcx>, ty::RegionVid)> + 's {
self.indices.indices.iter().map(|(&r, &v)| (r, v))
}
/// See `UniversalRegionIndices::to_region_vid`.
pub fn to_region_vid(&self, r: ty::Region<'tcx>) -> RegionVid {
self.indices.to_region_vid(r)
}
}
struct UniversalRegionsBuilder<'cx, 'gcx: 'tcx, 'tcx: 'cx> {
infcx: &'cx InferCtxt<'cx, 'gcx, 'tcx>,
mir_def_id: DefId,
mir_hir_id: HirId,
mir_node_id: ast::NodeId,
param_env: ty::ParamEnv<'tcx>,
region_bound_pairs: Vec<(ty::Region<'tcx>, GenericKind<'tcx>)>,
relations: UniversalRegionRelations,
}
const FR: NLLRegionVariableOrigin = NLLRegionVariableOrigin::FreeRegion;
impl<'cx, 'gcx, 'tcx> UniversalRegionsBuilder<'cx, 'gcx, 'tcx> {
fn build(mut self) -> UniversalRegions<'tcx> {
debug!("build(mir_def_id={:?})", self.mir_def_id);
let param_env = self.param_env;
debug!("build: param_env={:?}", param_env);
assert_eq!(FIRST_GLOBAL_INDEX, self.infcx.num_region_vars());
// Create the "global" region that is always free in all contexts: 'static.
let fr_static = self.infcx.next_nll_region_var(FR).to_region_vid();
// We've now added all the global regions. The next ones we
// add will be external.
let first_extern_index = self.infcx.num_region_vars();
let defining_ty = self.defining_ty();
debug!("build: defining_ty={:?}", defining_ty);
let mut indices = self.compute_indices(fr_static, defining_ty);
debug!("build: indices={:?}", indices);
let bound_inputs_and_output = self.compute_inputs_and_output(&indices, defining_ty);
// "Liberate" the late-bound regions. These correspond to
// "local" free regions.
let first_local_index = self.infcx.num_region_vars();
let inputs_and_output = self.infcx.replace_bound_regions_with_nll_infer_vars(
FR,
self.mir_def_id,
&bound_inputs_and_output,
&mut indices,
);
let fr_fn_body = self.infcx.next_nll_region_var(FR).to_region_vid();
let num_universals = self.infcx.num_region_vars();
// Insert the facts we know from the predicates. Why? Why not.
self.add_outlives_bounds(&indices, bounds::explicit_outlives_bounds(param_env));
// Add the implied bounds from inputs and outputs.
for ty in inputs_and_output {
debug!("build: input_or_output={:?}", ty);
self.add_implied_bounds(&indices, ty);
}
// Finally:
// - outlives is reflexive, so `'r: 'r` for every region `'r`
// - `'static: 'r` for every region `'r`
// - `'r: 'fn_body` for every (other) universally quantified
// region `'r`, all of which are provided by our caller
for fr in (FIRST_GLOBAL_INDEX..num_universals).map(RegionVid::new) {
debug!(
"build: relating free region {:?} to itself and to 'static",
fr
);
self.relations.relate_universal_regions(fr, fr);
self.relations.relate_universal_regions(fr_static, fr);
self.relations.relate_universal_regions(fr, fr_fn_body);
}
let (unnormalized_output_ty, unnormalized_input_tys) =
inputs_and_output.split_last().unwrap();
debug!(
"build: global regions = {}..{}",
FIRST_GLOBAL_INDEX,
first_extern_index
);
debug!(
"build: extern regions = {}..{}",
first_extern_index,
first_local_index
);
debug!(
"build: local regions = {}..{}",
first_local_index,
num_universals
);
let yield_ty = match defining_ty {
DefiningTy::Generator(def_id, substs, _) => {
Some(substs.generator_yield_ty(def_id, self.infcx.tcx))
}
_ => None,
};
UniversalRegions {
indices,
fr_static,
fr_fn_body,
first_extern_index,
first_local_index,
num_universals,
defining_ty,
unnormalized_output_ty,
unnormalized_input_tys,
region_bound_pairs: self.region_bound_pairs,
yield_ty: yield_ty,
relations: self.relations,
}
}
/// Returns the "defining type" of the current MIR;
/// see `DefiningTy` for details.
fn defining_ty(&self) -> DefiningTy<'tcx> {
let tcx = self.infcx.tcx;
let closure_base_def_id = tcx.closure_base_def_id(self.mir_def_id);
let defining_ty = if self.mir_def_id == closure_base_def_id {
tcx.type_of(closure_base_def_id)
} else {
let tables = tcx.typeck_tables_of(self.mir_def_id);
tables.node_id_to_type(self.mir_hir_id)
};
let defining_ty = self.infcx
.replace_free_regions_with_nll_infer_vars(FR, &defining_ty);
match tcx.hir.body_owner_kind(self.mir_node_id) {
BodyOwnerKind::Fn => match defining_ty.sty {
ty::TyClosure(def_id, substs) => DefiningTy::Closure(def_id, substs),
ty::TyGenerator(def_id, substs, interior) => {
DefiningTy::Generator(def_id, substs, interior)
}
ty::TyFnDef(def_id, substs) => DefiningTy::FnDef(def_id, substs),
_ => span_bug!(
tcx.def_span(self.mir_def_id),
"expected defining type for `{:?}`: `{:?}`",
self.mir_def_id,
defining_ty
),
},
BodyOwnerKind::Const | BodyOwnerKind::Static(..) => DefiningTy::Const(defining_ty),
}
}
/// Builds a hashmap that maps from the universal regions that are
/// in scope (as a `ty::Region<'tcx>`) to their indices (as a
/// `RegionVid`). The map returned by this function contains only
/// the early-bound regions.
fn compute_indices(
&self,
fr_static: RegionVid,
defining_ty: DefiningTy<'tcx>,
) -> UniversalRegionIndices<'tcx> {
let tcx = self.infcx.tcx;
let gcx = tcx.global_tcx();
let closure_base_def_id = tcx.closure_base_def_id(self.mir_def_id);
let identity_substs = Substs::identity_for_item(gcx, closure_base_def_id);
let fr_substs = match defining_ty {
DefiningTy::Closure(_, substs) | DefiningTy::Generator(_, substs, _) => {
// In the case of closures, we rely on the fact that
// the first N elements in the ClosureSubsts are
// inherited from the `closure_base_def_id`.
// Therefore, when we zip together (below) with
// `identity_substs`, we will get only those regions
// that correspond to early-bound regions declared on
// the `closure_base_def_id`.
assert!(substs.substs.len() >= identity_substs.len());
assert_eq!(substs.substs.regions().count(), identity_substs.regions().count());
substs.substs
}
DefiningTy::FnDef(_, substs) => substs,
// When we encounter a constant body, just return whatever
// substitutions are in scope for that constant.
DefiningTy::Const(_) => {
identity_substs
}
};
let global_mapping = iter::once((gcx.types.re_static, fr_static));
let subst_mapping = identity_substs
.regions()
.zip(fr_substs.regions().map(|r| r.to_region_vid()));
UniversalRegionIndices {
indices: global_mapping.chain(subst_mapping).collect(),
}
}
fn compute_inputs_and_output(
&self,
indices: &UniversalRegionIndices<'tcx>,
defining_ty: DefiningTy<'tcx>,
) -> ty::Binder<&'tcx ty::Slice<Ty<'tcx>>> {
let tcx = self.infcx.tcx;
match defining_ty {
DefiningTy::Closure(def_id, substs) => {
assert_eq!(self.mir_def_id, def_id);
let closure_sig = substs.closure_sig_ty(def_id, tcx).fn_sig(tcx);
let inputs_and_output = closure_sig.inputs_and_output();
let closure_ty = tcx.closure_env_ty(def_id, substs).unwrap();
ty::Binder::fuse(
closure_ty,
inputs_and_output,
|closure_ty, inputs_and_output| {
// The "inputs" of the closure in the
// signature appear as a tuple. The MIR side
// flattens this tuple.
let (&output, tuplized_inputs) = inputs_and_output.split_last().unwrap();
assert_eq!(tuplized_inputs.len(), 1, "multiple closure inputs");
let inputs = match tuplized_inputs[0].sty {
ty::TyTuple(inputs, _) => inputs,
_ => bug!("closure inputs not a tuple: {:?}", tuplized_inputs[0]),
};
tcx.mk_type_list(
iter::once(closure_ty)
.chain(inputs.iter().cloned())
.chain(iter::once(output)),
)
},
)
}
DefiningTy::Generator(def_id, substs, interior) => {
assert_eq!(self.mir_def_id, def_id);
let output = substs.generator_return_ty(def_id, tcx);
let generator_ty = tcx.mk_generator(def_id, substs, interior);
let inputs_and_output = self.infcx.tcx.intern_type_list(&[generator_ty, output]);
ty::Binder::dummy(inputs_and_output)
}
DefiningTy::FnDef(def_id, _) => {
let sig = tcx.fn_sig(def_id);
let sig = indices.fold_to_region_vids(tcx, &sig);
sig.inputs_and_output()
}
// For a constant body, there are no inputs, and one
// "output" (the type of the constant).
DefiningTy::Const(ty) => ty::Binder::dummy(tcx.mk_type_list(iter::once(ty))),
}
}
/// Update the type of a single local, which should represent
/// either the return type of the MIR or one of its arguments. At
/// the same time, compute and add any implied bounds that come
/// from this local.
///
/// Assumes that `universal_regions` indices map is fully constructed.
fn add_implied_bounds(&mut self, indices: &UniversalRegionIndices<'tcx>, ty: Ty<'tcx>) {
debug!("add_implied_bounds(ty={:?})", ty);
let span = self.infcx.tcx.def_span(self.mir_def_id);
let bounds = self.infcx
.implied_outlives_bounds(self.param_env, self.mir_node_id, ty, span);
self.add_outlives_bounds(indices, bounds);
}
/// Registers the `OutlivesBound` items from `outlives_bounds` in
/// the outlives relation as well as the region-bound pairs
/// listing.
fn add_outlives_bounds<I>(&mut self, indices: &UniversalRegionIndices<'tcx>, outlives_bounds: I)
where
I: IntoIterator<Item = OutlivesBound<'tcx>>,
{
for outlives_bound in outlives_bounds {
debug!("add_outlives_bounds(bound={:?})", outlives_bound);
match outlives_bound {
OutlivesBound::RegionSubRegion(r1, r2) => {
// The bound says that `r1 <= r2`; we store `r2: r1`.
let r1 = indices.to_region_vid(r1);
let r2 = indices.to_region_vid(r2);
self.relations.relate_universal_regions(r2, r1);
}
OutlivesBound::RegionSubParam(r_a, param_b) => {
self.region_bound_pairs
.push((r_a, GenericKind::Param(param_b)));
}
OutlivesBound::RegionSubProjection(r_a, projection_b) => {
self.region_bound_pairs
.push((r_a, GenericKind::Projection(projection_b)));
}
}
}
}
}
impl UniversalRegionRelations {
/// Records in the `outlives_relation` (and
/// `inverse_outlives_relation`) that `fr_a: fr_b`.
fn relate_universal_regions(&mut self, fr_a: RegionVid, fr_b: RegionVid) {
debug!(
"relate_universal_regions: fr_a={:?} outlives fr_b={:?}",
fr_a,
fr_b
);
self.outlives.add(fr_a, fr_b);
self.inverse_outlives.add(fr_b, fr_a);
}
}
trait InferCtxtExt<'tcx> {
fn replace_free_regions_with_nll_infer_vars<T>(
&self,
origin: NLLRegionVariableOrigin,
value: &T,
) -> T
where
T: TypeFoldable<'tcx>;
fn replace_bound_regions_with_nll_infer_vars<T>(
&self,
origin: NLLRegionVariableOrigin,
all_outlive_scope: DefId,
value: &ty::Binder<T>,
indices: &mut UniversalRegionIndices<'tcx>,
) -> T
where
T: TypeFoldable<'tcx>;
}
impl<'cx, 'gcx, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'cx, 'gcx, 'tcx> {
fn replace_free_regions_with_nll_infer_vars<T>(
&self,
origin: NLLRegionVariableOrigin,
value: &T,
) -> T
where
T: TypeFoldable<'tcx>,
{
self.tcx.fold_regions(value, &mut false, |_region, _depth| {
self.next_nll_region_var(origin)
})
}
fn replace_bound_regions_with_nll_infer_vars<T>(
&self,
origin: NLLRegionVariableOrigin,
all_outlive_scope: DefId,
value: &ty::Binder<T>,
indices: &mut UniversalRegionIndices<'tcx>,
) -> T
where
T: TypeFoldable<'tcx>,
{
let (value, _map) = self.tcx.replace_late_bound_regions(value, |br| {
let liberated_region = self.tcx.mk_region(ty::ReFree(ty::FreeRegion {
scope: all_outlive_scope,
bound_region: br,
}));
let region_vid = self.next_nll_region_var(origin);
indices.insert_late_bound_region(liberated_region, region_vid.to_region_vid());
region_vid
});
value
}
}
impl<'tcx> UniversalRegionIndices<'tcx> {
/// Initially, the `UniversalRegionIndices` map contains only the
/// early-bound regions in scope. Once that is all setup, we come
/// in later and instantiate the late-bound regions, and then we
/// insert the `ReFree` version of those into the map as
/// well. These are used for error reporting.
fn insert_late_bound_region(&mut self, r: ty::Region<'tcx>,
vid: ty::RegionVid)
{
self.indices.insert(r, vid);
}
/// Converts `r` into a local inference variable: `r` can either
/// by a `ReVar` (i.e., already a reference to an inference
/// variable) or it can be `'static` or some early-bound
/// region. This is useful when taking the results from
/// type-checking and trait-matching, which may sometimes
/// reference those regions from the `ParamEnv`. It is also used
/// during initialization. Relies on the `indices` map having been
/// fully initialized.
pub fn to_region_vid(&self, r: ty::Region<'tcx>) -> RegionVid {
if let ty::ReVar(..) = r {
r.to_region_vid()
} else {
*self.indices.get(&r).unwrap_or_else(|| {
bug!("cannot convert `{:?}` to a region vid", r)
})
}
}
/// Replace all free regions in `value` with region vids, as
/// returned by `to_region_vid`.
pub fn fold_to_region_vids<T>(&self, tcx: TyCtxt<'_, '_, 'tcx>, value: &T) -> T
where
T: TypeFoldable<'tcx>,
{
tcx.fold_regions(value, &mut false, |region, _| {
tcx.mk_region(ty::ReVar(self.to_region_vid(region)))
})
}
}
/// This trait is used by the `impl-trait` constraint code to abstract
/// over the `FreeRegionMap` from lexical regions and
/// `UniversalRegions` (from NLL)`.
impl<'tcx> FreeRegionRelations<'tcx> for UniversalRegions<'tcx> {
fn sub_free_regions(&self, shorter: ty::Region<'tcx>, longer: ty::Region<'tcx>) -> bool {
let shorter = shorter.to_region_vid();
assert!(self.is_universal_region(shorter));
let longer = longer.to_region_vid();
assert!(self.is_universal_region(longer));
self.outlives(longer, shorter)
}
}