1 use rustc_data_structures::frozen::Frozen;
2 use rustc_data_structures::transitive_relation::TransitiveRelation;
3 use rustc_infer::infer::canonical::QueryRegionConstraints;
4 use rustc_infer::infer::free_regions::FreeRegionRelations;
5 use rustc_infer::infer::outlives;
6 use rustc_infer::infer::region_constraints::GenericKind;
7 use rustc_infer::infer::InferCtxt;
8 use rustc_middle::mir::ConstraintCategory;
9 use rustc_middle::traits::query::OutlivesBound;
10 use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt};
11 use rustc_span::DUMMY_SP;
12 use rustc_trait_selection::traits::query::type_op::{self, TypeOp};
14 use type_op::TypeOpOutput;
18 type_check::constraint_conversion,
19 type_check::{Locations, MirTypeckRegionConstraints},
20 universal_regions::UniversalRegions,
24 crate struct UniversalRegionRelations<'tcx> {
25 universal_regions: Rc<UniversalRegions<'tcx>>,
27 /// Stores the outlives relations that are known to hold from the
28 /// implied bounds, in-scope where-clauses, and that sort of
30 outlives: TransitiveRelation<RegionVid>,
32 /// This is the `<=` relation; that is, if `a: b`, then `b <= a`,
33 /// and we store that here. This is useful when figuring out how
34 /// to express some local region in terms of external regions our
35 /// caller will understand.
36 inverse_outlives: TransitiveRelation<RegionVid>,
39 /// Each RBP `('a, GK)` indicates that `GK: 'a` can be assumed to
40 /// be true. These encode relationships like `T: 'a` that are
41 /// added via implicit bounds.
43 /// Each region here is guaranteed to be a key in the `indices`
44 /// map. We use the "original" regions (i.e., the keys from the
45 /// map, and not the values) because the code in
46 /// `process_registered_region_obligations` has some special-cased
47 /// logic expecting to see (e.g.) `ReStatic`, and if we supplied
48 /// our special inference variable there, we would mess that up.
49 type RegionBoundPairs<'tcx> = Vec<(ty::Region<'tcx>, GenericKind<'tcx>)>;
51 /// As part of computing the free region relations, we also have to
52 /// normalize the input-output types, which we then need later. So we
53 /// return those. This vector consists of first the input types and
54 /// then the output type as the last element.
55 type NormalizedInputsAndOutput<'tcx> = Vec<Ty<'tcx>>;
57 crate struct CreateResult<'tcx> {
58 crate universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
59 crate region_bound_pairs: RegionBoundPairs<'tcx>,
60 crate normalized_inputs_and_output: NormalizedInputsAndOutput<'tcx>,
64 infcx: &InferCtxt<'_, 'tcx>,
65 param_env: ty::ParamEnv<'tcx>,
66 implicit_region_bound: Option<ty::Region<'tcx>>,
67 universal_regions: &Rc<UniversalRegions<'tcx>>,
68 constraints: &mut MirTypeckRegionConstraints<'tcx>,
69 ) -> CreateResult<'tcx> {
70 UniversalRegionRelationsBuilder {
73 implicit_region_bound,
75 universal_regions: universal_regions.clone(),
76 region_bound_pairs: Vec::new(),
77 relations: UniversalRegionRelations {
78 universal_regions: universal_regions.clone(),
79 outlives: Default::default(),
80 inverse_outlives: Default::default(),
86 impl UniversalRegionRelations<'tcx> {
87 /// Records in the `outlives_relation` (and
88 /// `inverse_outlives_relation`) that `fr_a: fr_b`. Invoked by the
90 fn relate_universal_regions(&mut self, fr_a: RegionVid, fr_b: RegionVid) {
91 debug!("relate_universal_regions: fr_a={:?} outlives fr_b={:?}", fr_a, fr_b);
92 self.outlives.add(fr_a, fr_b);
93 self.inverse_outlives.add(fr_b, fr_a);
96 /// Given two universal regions, returns the postdominating
97 /// upper-bound (effectively the least upper bound).
99 /// (See `TransitiveRelation::postdom_upper_bound` for details on
100 /// the postdominating upper bound in general.)
101 crate fn postdom_upper_bound(&self, fr1: RegionVid, fr2: RegionVid) -> RegionVid {
102 assert!(self.universal_regions.is_universal_region(fr1));
103 assert!(self.universal_regions.is_universal_region(fr2));
106 .postdom_upper_bound(&fr1, &fr2)
107 .unwrap_or(&self.universal_regions.fr_static)
110 /// Finds an "upper bound" for `fr` that is not local. In other
111 /// words, returns the smallest (*) known region `fr1` that (a)
112 /// outlives `fr` and (b) is not local.
114 /// (*) If there are multiple competing choices, we return all of them.
115 crate fn non_local_upper_bounds(&'a self, fr: &'a RegionVid) -> Vec<&'a RegionVid> {
116 debug!("non_local_upper_bound(fr={:?})", fr);
117 let res = self.non_local_bounds(&self.inverse_outlives, fr);
118 assert!(!res.is_empty(), "can't find an upper bound!?");
122 /// Returns the "postdominating" bound of the set of
123 /// `non_local_upper_bounds` for the given region.
124 crate fn non_local_upper_bound(&self, fr: RegionVid) -> RegionVid {
125 let upper_bounds = self.non_local_upper_bounds(&fr);
127 // In case we find more than one, reduce to one for
128 // convenience. This is to prevent us from generating more
129 // complex constraints, but it will cause spurious errors.
130 let post_dom = self.inverse_outlives.mutual_immediate_postdominator(upper_bounds);
132 debug!("non_local_bound: post_dom={:?}", post_dom);
135 .and_then(|&post_dom| {
136 // If the mutual immediate postdom is not local, then
137 // there is no non-local result we can return.
138 if !self.universal_regions.is_local_free_region(post_dom) {
144 .unwrap_or(self.universal_regions.fr_static)
147 /// Finds a "lower bound" for `fr` that is not local. In other
148 /// words, returns the largest (*) known region `fr1` that (a) is
149 /// outlived by `fr` and (b) is not local.
151 /// (*) If there are multiple competing choices, we pick the "postdominating"
152 /// one. See `TransitiveRelation::postdom_upper_bound` for details.
153 crate fn non_local_lower_bound(&self, fr: RegionVid) -> Option<RegionVid> {
154 debug!("non_local_lower_bound(fr={:?})", fr);
155 let lower_bounds = self.non_local_bounds(&self.outlives, &fr);
157 // In case we find more than one, reduce to one for
158 // convenience. This is to prevent us from generating more
159 // complex constraints, but it will cause spurious errors.
160 let post_dom = self.outlives.mutual_immediate_postdominator(lower_bounds);
162 debug!("non_local_bound: post_dom={:?}", post_dom);
164 post_dom.and_then(|&post_dom| {
165 // If the mutual immediate postdom is not local, then
166 // there is no non-local result we can return.
167 if !self.universal_regions.is_local_free_region(post_dom) {
175 /// Helper for `non_local_upper_bounds` and `non_local_lower_bounds`.
176 /// Repeatedly invokes `postdom_parent` until we find something that is not
177 /// local. Returns `None` if we never do so.
178 fn non_local_bounds<'a>(
180 relation: &'a TransitiveRelation<RegionVid>,
182 ) -> Vec<&'a RegionVid> {
183 // This method assumes that `fr0` is one of the universally
184 // quantified region variables.
185 assert!(self.universal_regions.is_universal_region(*fr0));
187 let mut external_parents = vec![];
188 let mut queue = vec![fr0];
190 // Keep expanding `fr` into its parents until we reach
191 // non-local regions.
192 while let Some(fr) = queue.pop() {
193 if !self.universal_regions.is_local_free_region(*fr) {
194 external_parents.push(fr);
198 queue.extend(relation.parents(fr));
201 debug!("non_local_bound: external_parents={:?}", external_parents);
206 /// Returns `true` if fr1 is known to outlive fr2.
208 /// This will only ever be true for universally quantified regions.
209 crate fn outlives(&self, fr1: RegionVid, fr2: RegionVid) -> bool {
210 self.outlives.contains(&fr1, &fr2)
213 /// Returns a vector of free regions `x` such that `fr1: x` is
215 crate fn regions_outlived_by(&self, fr1: RegionVid) -> Vec<&RegionVid> {
216 self.outlives.reachable_from(&fr1)
219 /// Returns the _non-transitive_ set of known `outlives` constraints between free regions.
220 crate fn known_outlives(&self) -> impl Iterator<Item = (&RegionVid, &RegionVid)> {
221 self.outlives.base_edges()
225 struct UniversalRegionRelationsBuilder<'this, 'tcx> {
226 infcx: &'this InferCtxt<'this, 'tcx>,
227 param_env: ty::ParamEnv<'tcx>,
228 universal_regions: Rc<UniversalRegions<'tcx>>,
229 implicit_region_bound: Option<ty::Region<'tcx>>,
230 constraints: &'this mut MirTypeckRegionConstraints<'tcx>,
233 relations: UniversalRegionRelations<'tcx>,
234 region_bound_pairs: RegionBoundPairs<'tcx>,
237 impl UniversalRegionRelationsBuilder<'cx, 'tcx> {
238 crate fn create(mut self) -> CreateResult<'tcx> {
239 let unnormalized_input_output_tys = self
241 .unnormalized_input_tys
244 .chain(Some(self.universal_regions.unnormalized_output_ty));
246 // For each of the input/output types:
247 // - Normalize the type. This will create some region
248 // constraints, which we buffer up because we are
249 // not ready to process them yet.
250 // - Then compute the implied bounds. This will adjust
251 // the `region_bound_pairs` and so forth.
252 // - After this is done, we'll process the constraints, once
253 // the `relations` is built.
254 let mut normalized_inputs_and_output =
255 Vec::with_capacity(self.universal_regions.unnormalized_input_tys.len() + 1);
256 let constraint_sets: Vec<_> = unnormalized_input_output_tys
258 debug!("build: input_or_output={:?}", ty);
259 // We add implied bounds from both the unnormalized and normalized ty
261 let constraints_implied_1 = self.add_implied_bounds(ty);
262 let TypeOpOutput { output: norm_ty, constraints: constraints1, .. } = self
264 .and(type_op::normalize::Normalize::new(ty))
265 .fully_perform(self.infcx)
266 .unwrap_or_else(|_| {
270 .delay_span_bug(DUMMY_SP, &format!("failed to normalize {:?}", ty));
272 output: self.infcx.tcx.ty_error(),
274 canonicalized_query: None,
277 // Note: we need this in examples like
281 // fn foo(&self) -> &Self::Bar;
285 // fn foo(&self) ->&() {}
288 // Both &Self::Bar and &() are WF
289 let constraints_implied_2 =
290 if ty != norm_ty { self.add_implied_bounds(norm_ty) } else { None };
291 normalized_inputs_and_output.push(norm_ty);
292 constraints1.into_iter().chain(constraints_implied_1).chain(constraints_implied_2)
296 // Insert the facts we know from the predicates. Why? Why not.
297 let param_env = self.param_env;
298 self.add_outlives_bounds(outlives::explicit_outlives_bounds(param_env));
301 // - outlives is reflexive, so `'r: 'r` for every region `'r`
302 // - `'static: 'r` for every region `'r`
303 // - `'r: 'fn_body` for every (other) universally quantified
304 // region `'r`, all of which are provided by our caller
305 let fr_static = self.universal_regions.fr_static;
306 let fr_fn_body = self.universal_regions.fr_fn_body;
307 for fr in self.universal_regions.universal_regions() {
308 debug!("build: relating free region {:?} to itself and to 'static", fr);
309 self.relations.relate_universal_regions(fr, fr);
310 self.relations.relate_universal_regions(fr_static, fr);
311 self.relations.relate_universal_regions(fr, fr_fn_body);
314 for data in &constraint_sets {
315 constraint_conversion::ConstraintConversion::new(
317 &self.universal_regions,
318 &self.region_bound_pairs,
319 self.implicit_region_bound,
321 Locations::All(DUMMY_SP),
322 ConstraintCategory::Internal,
323 &mut self.constraints,
329 universal_region_relations: Frozen::freeze(self.relations),
330 region_bound_pairs: self.region_bound_pairs,
331 normalized_inputs_and_output,
335 /// Update the type of a single local, which should represent
336 /// either the return type of the MIR or one of its arguments. At
337 /// the same time, compute and add any implied bounds that come
339 fn add_implied_bounds(&mut self, ty: Ty<'tcx>) -> Option<Rc<QueryRegionConstraints<'tcx>>> {
340 debug!("add_implied_bounds(ty={:?})", ty);
341 let TypeOpOutput { output: bounds, constraints, .. } = self
343 .and(type_op::implied_outlives_bounds::ImpliedOutlivesBounds { ty })
344 .fully_perform(self.infcx)
345 .unwrap_or_else(|_| bug!("failed to compute implied bounds {:?}", ty));
346 self.add_outlives_bounds(bounds);
350 /// Registers the `OutlivesBound` items from `outlives_bounds` in
351 /// the outlives relation as well as the region-bound pairs
353 fn add_outlives_bounds<I>(&mut self, outlives_bounds: I)
355 I: IntoIterator<Item = OutlivesBound<'tcx>>,
357 for outlives_bound in outlives_bounds {
358 debug!("add_outlives_bounds(bound={:?})", outlives_bound);
360 match outlives_bound {
361 OutlivesBound::RegionSubRegion(r1, r2) => {
362 // `where Type:` is lowered to `where Type: 'empty` so that
363 // we check `Type` is well formed, but there's no use for
365 if let ty::ReEmpty(_) = r1 {
369 // The bound says that `r1 <= r2`; we store `r2: r1`.
370 let r1 = self.universal_regions.to_region_vid(r1);
371 let r2 = self.universal_regions.to_region_vid(r2);
372 self.relations.relate_universal_regions(r2, r1);
375 OutlivesBound::RegionSubParam(r_a, param_b) => {
376 self.region_bound_pairs.push((r_a, GenericKind::Param(param_b)));
379 OutlivesBound::RegionSubProjection(r_a, projection_b) => {
380 self.region_bound_pairs.push((r_a, GenericKind::Projection(projection_b)));
387 /// This trait is used by the `impl-trait` constraint code to abstract
388 /// over the `FreeRegionMap` from lexical regions and
389 /// `UniversalRegions` (from NLL)`.
390 impl<'tcx> FreeRegionRelations<'tcx> for UniversalRegionRelations<'tcx> {
394 shorter: ty::Region<'tcx>,
395 longer: ty::Region<'tcx>,
397 let shorter = shorter.to_region_vid();
398 assert!(self.universal_regions.is_universal_region(shorter));
399 let longer = longer.to_region_vid();
400 assert!(self.universal_regions.is_universal_region(longer));
401 self.outlives(longer, shorter)