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1 | // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT |
2 | // file at the top-level directory of this distribution and at | |
3 | // http://rust-lang.org/COPYRIGHT. | |
4 | // | |
5 | // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | |
6 | // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | |
7 | // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | |
8 | // option. This file may not be copied, modified, or distributed | |
9 | // except according to those terms. | |
10 | ||
11 | //! The region check is a final pass that runs over the AST after we have | |
12 | //! inferred the type constraints but before we have actually finalized | |
13 | //! the types. Its purpose is to embed a variety of region constraints. | |
14 | //! Inserting these constraints as a separate pass is good because (1) it | |
15 | //! localizes the code that has to do with region inference and (2) often | |
16 | //! we cannot know what constraints are needed until the basic types have | |
17 | //! been inferred. | |
18 | //! | |
19 | //! ### Interaction with the borrow checker | |
20 | //! | |
21 | //! In general, the job of the borrowck module (which runs later) is to | |
22 | //! check that all soundness criteria are met, given a particular set of | |
23 | //! regions. The job of *this* module is to anticipate the needs of the | |
24 | //! borrow checker and infer regions that will satisfy its requirements. | |
25 | //! It is generally true that the inference doesn't need to be sound, | |
26 | //! meaning that if there is a bug and we inferred bad regions, the borrow | |
27 | //! checker should catch it. This is not entirely true though; for | |
28 | //! example, the borrow checker doesn't check subtyping, and it doesn't | |
29 | //! check that region pointers are always live when they are used. It | |
30 | //! might be worthwhile to fix this so that borrowck serves as a kind of | |
31 | //! verification step -- that would add confidence in the overall | |
32 | //! correctness of the compiler, at the cost of duplicating some type | |
33 | //! checks and effort. | |
34 | //! | |
35 | //! ### Inferring the duration of borrows, automatic and otherwise | |
36 | //! | |
37 | //! Whenever we introduce a borrowed pointer, for example as the result of | |
38 | //! a borrow expression `let x = &data`, the lifetime of the pointer `x` | |
39 | //! is always specified as a region inference variable. `regionck` has the | |
40 | //! job of adding constraints such that this inference variable is as | |
41 | //! narrow as possible while still accommodating all uses (that is, every | |
42 | //! dereference of the resulting pointer must be within the lifetime). | |
43 | //! | |
44 | //! #### Reborrows | |
45 | //! | |
46 | //! Generally speaking, `regionck` does NOT try to ensure that the data | |
47 | //! `data` will outlive the pointer `x`. That is the job of borrowck. The | |
48 | //! one exception is when "re-borrowing" the contents of another borrowed | |
49 | //! pointer. For example, imagine you have a borrowed pointer `b` with | |
50 | //! lifetime L1 and you have an expression `&*b`. The result of this | |
51 | //! expression will be another borrowed pointer with lifetime L2 (which is | |
52 | //! an inference variable). The borrow checker is going to enforce the | |
53 | //! constraint that L2 < L1, because otherwise you are re-borrowing data | |
54 | //! for a lifetime larger than the original loan. However, without the | |
55 | //! routines in this module, the region inferencer would not know of this | |
56 | //! dependency and thus it might infer the lifetime of L2 to be greater | |
57 | //! than L1 (issue #3148). | |
58 | //! | |
59 | //! There are a number of troublesome scenarios in the tests | |
60 | //! `region-dependent-*.rs`, but here is one example: | |
61 | //! | |
92a42be0 | 62 | //! struct Foo { i: i32 } |
1a4d82fc | 63 | //! struct Bar { foo: Foo } |
9cc50fc6 | 64 | //! fn get_i<'a>(x: &'a Bar) -> &'a i32 { |
1a4d82fc JJ |
65 | //! let foo = &x.foo; // Lifetime L1 |
66 | //! &foo.i // Lifetime L2 | |
67 | //! } | |
68 | //! | |
69 | //! Note that this comes up either with `&` expressions, `ref` | |
70 | //! bindings, and `autorefs`, which are the three ways to introduce | |
71 | //! a borrow. | |
72 | //! | |
73 | //! The key point here is that when you are borrowing a value that | |
74 | //! is "guaranteed" by a borrowed pointer, you must link the | |
75 | //! lifetime of that borrowed pointer (L1, here) to the lifetime of | |
76 | //! the borrow itself (L2). What do I mean by "guaranteed" by a | |
77 | //! borrowed pointer? I mean any data that is reached by first | |
78 | //! dereferencing a borrowed pointer and then either traversing | |
62682a34 | 79 | //! interior offsets or boxes. We say that the guarantor |
b039eaaf | 80 | //! of such data is the region of the borrowed pointer that was |
1a4d82fc JJ |
81 | //! traversed. This is essentially the same as the ownership |
82 | //! relation, except that a borrowed pointer never owns its | |
83 | //! contents. | |
84 | ||
85aaf69f | 85 | use check::dropck; |
1a4d82fc | 86 | use check::FnCtxt; |
bd371182 | 87 | use middle::free_region::FreeRegionMap; |
1a4d82fc | 88 | use middle::mem_categorization as mc; |
92a42be0 | 89 | use middle::mem_categorization::Categorization; |
9cc50fc6 | 90 | use middle::region::{self, CodeExtent}; |
54a0048b SL |
91 | use rustc::ty::subst::Substs; |
92 | use rustc::traits; | |
a7813a04 XL |
93 | use rustc::ty::{self, Ty, MethodCall, TypeFoldable}; |
94 | use rustc::infer::{self, GenericKind, InferOk, SubregionOrigin, TypeOrigin, VerifyBound}; | |
54a0048b SL |
95 | use hir::pat_util; |
96 | use rustc::ty::adjustment; | |
97 | use rustc::ty::wf::ImpliedBound; | |
1a4d82fc | 98 | |
85aaf69f | 99 | use std::mem; |
a7813a04 | 100 | use std::ops::Deref; |
e9174d1e | 101 | use syntax::ast; |
3157f602 | 102 | use syntax_pos::Span; |
54a0048b SL |
103 | use rustc::hir::intravisit::{self, Visitor}; |
104 | use rustc::hir::{self, PatKind}; | |
1a4d82fc | 105 | |
1a4d82fc JJ |
106 | use self::SubjectNode::Subject; |
107 | ||
108 | // a variation on try that just returns unit | |
109 | macro_rules! ignore_err { | |
110 | ($e:expr) => (match $e { Ok(e) => e, Err(_) => return () }) | |
111 | } | |
112 | ||
113 | /////////////////////////////////////////////////////////////////////////// | |
114 | // PUBLIC ENTRY POINTS | |
115 | ||
a7813a04 XL |
116 | impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> { |
117 | pub fn regionck_expr(&self, e: &hir::Expr) { | |
118 | let mut rcx = RegionCtxt::new(self, RepeatingScope(e.id), e.id, Subject(e.id)); | |
119 | if self.err_count_since_creation() == 0 { | |
120 | // regionck assumes typeck succeeded | |
121 | rcx.visit_expr(e); | |
122 | rcx.visit_region_obligations(e.id); | |
123 | } | |
124 | rcx.resolve_regions_and_report_errors(); | |
1a4d82fc | 125 | } |
1a4d82fc | 126 | |
a7813a04 XL |
127 | /// Region checking during the WF phase for items. `wf_tys` are the |
128 | /// types from which we should derive implied bounds, if any. | |
129 | pub fn regionck_item(&self, | |
130 | item_id: ast::NodeId, | |
131 | span: Span, | |
132 | wf_tys: &[Ty<'tcx>]) { | |
133 | debug!("regionck_item(item.id={:?}, wf_tys={:?}", item_id, wf_tys); | |
134 | let mut rcx = RegionCtxt::new(self, RepeatingScope(item_id), item_id, Subject(item_id)); | |
135 | rcx.free_region_map.relate_free_regions_from_predicates( | |
136 | &self.parameter_environment.caller_bounds); | |
137 | rcx.relate_free_regions(wf_tys, item_id, span); | |
138 | rcx.visit_region_obligations(item_id); | |
139 | rcx.resolve_regions_and_report_errors(); | |
1a4d82fc JJ |
140 | } |
141 | ||
a7813a04 XL |
142 | pub fn regionck_fn(&self, |
143 | fn_id: ast::NodeId, | |
a7813a04 XL |
144 | decl: &hir::FnDecl, |
145 | blk: &hir::Block) { | |
146 | debug!("regionck_fn(id={})", fn_id); | |
147 | let mut rcx = RegionCtxt::new(self, RepeatingScope(blk.id), blk.id, Subject(fn_id)); | |
148 | ||
149 | if self.err_count_since_creation() == 0 { | |
150 | // regionck assumes typeck succeeded | |
5bcae85e | 151 | rcx.visit_fn_body(fn_id, decl, blk, self.tcx.map.span(fn_id)); |
a7813a04 XL |
152 | } |
153 | ||
154 | rcx.free_region_map.relate_free_regions_from_predicates( | |
155 | &self.parameter_environment.caller_bounds); | |
bd371182 | 156 | |
a7813a04 | 157 | rcx.resolve_regions_and_report_errors(); |
bd371182 | 158 | |
a7813a04 XL |
159 | // For the top-level fn, store the free-region-map. We don't store |
160 | // any map for closures; they just share the same map as the | |
161 | // function that created them. | |
162 | self.tcx.store_free_region_map(fn_id, rcx.free_region_map); | |
163 | } | |
1a4d82fc JJ |
164 | } |
165 | ||
1a4d82fc JJ |
166 | /////////////////////////////////////////////////////////////////////////// |
167 | // INTERNALS | |
168 | ||
a7813a04 XL |
169 | pub struct RegionCtxt<'a, 'gcx: 'a+'tcx, 'tcx: 'a> { |
170 | pub fcx: &'a FnCtxt<'a, 'gcx, 'tcx>, | |
1a4d82fc | 171 | |
9e0c209e | 172 | region_bound_pairs: Vec<(&'tcx ty::Region, GenericKind<'tcx>)>, |
1a4d82fc | 173 | |
bd371182 AL |
174 | free_region_map: FreeRegionMap, |
175 | ||
85aaf69f SL |
176 | // id of innermost fn body id |
177 | body_id: ast::NodeId, | |
178 | ||
9cc50fc6 SL |
179 | // call_site scope of innermost fn |
180 | call_site_scope: Option<CodeExtent>, | |
181 | ||
1a4d82fc JJ |
182 | // id of innermost fn or loop |
183 | repeating_scope: ast::NodeId, | |
184 | ||
185 | // id of AST node being analyzed (the subject of the analysis). | |
186 | subject: SubjectNode, | |
85aaf69f | 187 | |
1a4d82fc JJ |
188 | } |
189 | ||
a7813a04 XL |
190 | impl<'a, 'gcx, 'tcx> Deref for RegionCtxt<'a, 'gcx, 'tcx> { |
191 | type Target = FnCtxt<'a, 'gcx, 'tcx>; | |
192 | fn deref(&self) -> &Self::Target { | |
193 | &self.fcx | |
194 | } | |
195 | } | |
196 | ||
c34b1796 | 197 | pub struct RepeatingScope(ast::NodeId); |
1a4d82fc JJ |
198 | pub enum SubjectNode { Subject(ast::NodeId), None } |
199 | ||
a7813a04 XL |
200 | impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> { |
201 | pub fn new(fcx: &'a FnCtxt<'a, 'gcx, 'tcx>, | |
1a4d82fc | 202 | initial_repeating_scope: RepeatingScope, |
85aaf69f | 203 | initial_body_id: ast::NodeId, |
a7813a04 | 204 | subject: SubjectNode) -> RegionCtxt<'a, 'gcx, 'tcx> { |
85aaf69f | 205 | let RepeatingScope(initial_repeating_scope) = initial_repeating_scope; |
a7813a04 XL |
206 | RegionCtxt { |
207 | fcx: fcx, | |
208 | repeating_scope: initial_repeating_scope, | |
209 | body_id: initial_body_id, | |
210 | call_site_scope: None, | |
211 | subject: subject, | |
212 | region_bound_pairs: Vec::new(), | |
213 | free_region_map: FreeRegionMap::new(), | |
85aaf69f | 214 | } |
1a4d82fc JJ |
215 | } |
216 | ||
9cc50fc6 SL |
217 | fn set_call_site_scope(&mut self, call_site_scope: Option<CodeExtent>) -> Option<CodeExtent> { |
218 | mem::replace(&mut self.call_site_scope, call_site_scope) | |
219 | } | |
220 | ||
85aaf69f SL |
221 | fn set_body_id(&mut self, body_id: ast::NodeId) -> ast::NodeId { |
222 | mem::replace(&mut self.body_id, body_id) | |
223 | } | |
224 | ||
225 | fn set_repeating_scope(&mut self, scope: ast::NodeId) -> ast::NodeId { | |
226 | mem::replace(&mut self.repeating_scope, scope) | |
1a4d82fc JJ |
227 | } |
228 | ||
229 | /// Try to resolve the type for the given node, returning t_err if an error results. Note that | |
230 | /// we never care about the details of the error, the same error will be detected and reported | |
231 | /// in the writeback phase. | |
232 | /// | |
233 | /// Note one important point: we do not attempt to resolve *region variables* here. This is | |
234 | /// because regionck is essentially adding constraints to those region variables and so may yet | |
235 | /// influence how they are resolved. | |
236 | /// | |
237 | /// Consider this silly example: | |
238 | /// | |
239 | /// ``` | |
92a42be0 SL |
240 | /// fn borrow(x: &i32) -> &i32 {x} |
241 | /// fn foo(x: @i32) -> i32 { // block: B | |
1a4d82fc JJ |
242 | /// let b = borrow(x); // region: <R0> |
243 | /// *b | |
244 | /// } | |
245 | /// ``` | |
246 | /// | |
c34b1796 | 247 | /// Here, the region of `b` will be `<R0>`. `<R0>` is constrained to be some subregion of the |
1a4d82fc JJ |
248 | /// block B and some superregion of the call. If we forced it now, we'd choose the smaller |
249 | /// region (the call). But that would make the *b illegal. Since we don't resolve, the type | |
92a42be0 | 250 | /// of b will be `&<R0>.i32` and then `*b` will require that `<R0>` be bigger than the let and |
1a4d82fc JJ |
251 | /// the `*b` expression, so we will effectively resolve `<R0>` to be the block B. |
252 | pub fn resolve_type(&self, unresolved_ty: Ty<'tcx>) -> Ty<'tcx> { | |
a7813a04 | 253 | self.resolve_type_vars_if_possible(&unresolved_ty) |
1a4d82fc JJ |
254 | } |
255 | ||
256 | /// Try to resolve the type for the given node. | |
257 | fn resolve_node_type(&self, id: ast::NodeId) -> Ty<'tcx> { | |
a7813a04 | 258 | let t = self.node_ty(id); |
1a4d82fc JJ |
259 | self.resolve_type(t) |
260 | } | |
261 | ||
1a4d82fc | 262 | /// Try to resolve the type for the given node. |
e9174d1e | 263 | pub fn resolve_expr_type_adjusted(&mut self, expr: &hir::Expr) -> Ty<'tcx> { |
c30ab7b3 SL |
264 | let ty = self.tables.borrow().expr_ty_adjusted(expr); |
265 | self.resolve_type(ty) | |
1a4d82fc JJ |
266 | } |
267 | ||
268 | fn visit_fn_body(&mut self, | |
9cc50fc6 | 269 | id: ast::NodeId, // the id of the fn itself |
e9174d1e SL |
270 | fn_decl: &hir::FnDecl, |
271 | body: &hir::Block, | |
85aaf69f | 272 | span: Span) |
1a4d82fc JJ |
273 | { |
274 | // When we enter a function, we can derive | |
85aaf69f | 275 | debug!("visit_fn_body(id={})", id); |
1a4d82fc | 276 | |
a7813a04 | 277 | let call_site = self.tcx.region_maps.lookup_code_extent( |
9cc50fc6 SL |
278 | region::CodeExtentData::CallSiteScope { fn_id: id, body_id: body.id }); |
279 | let old_call_site_scope = self.set_call_site_scope(Some(call_site)); | |
280 | ||
92a42be0 | 281 | let fn_sig = { |
a7813a04 | 282 | let fn_sig_map = &self.tables.borrow().liberated_fn_sigs; |
92a42be0 SL |
283 | match fn_sig_map.get(&id) { |
284 | Some(f) => f.clone(), | |
285 | None => { | |
54a0048b | 286 | bug!("No fn-sig entry for id={}", id); |
92a42be0 | 287 | } |
1a4d82fc JJ |
288 | } |
289 | }; | |
290 | ||
bd371182 AL |
291 | let old_region_bounds_pairs_len = self.region_bound_pairs.len(); |
292 | ||
92a42be0 SL |
293 | // Collect the types from which we create inferred bounds. |
294 | // For the return type, if diverging, substitute `bool` just | |
295 | // because it will have no effect. | |
296 | // | |
9cc50fc6 | 297 | // FIXME(#27579) return types should not be implied bounds |
92a42be0 SL |
298 | let fn_sig_tys: Vec<_> = |
299 | fn_sig.inputs.iter() | |
300 | .cloned() | |
5bcae85e | 301 | .chain(Some(fn_sig.output)) |
92a42be0 SL |
302 | .collect(); |
303 | ||
85aaf69f | 304 | let old_body_id = self.set_body_id(body.id); |
92a42be0 | 305 | self.relate_free_regions(&fn_sig_tys[..], body.id, span); |
a7813a04 XL |
306 | self.link_fn_args(self.tcx.region_maps.node_extent(body.id), |
307 | &fn_decl.inputs[..]); | |
1a4d82fc JJ |
308 | self.visit_block(body); |
309 | self.visit_region_obligations(body.id); | |
bd371182 | 310 | |
9cc50fc6 SL |
311 | let call_site_scope = self.call_site_scope.unwrap(); |
312 | debug!("visit_fn_body body.id {} call_site_scope: {:?}", | |
313 | body.id, call_site_scope); | |
9e0c209e | 314 | let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope)); |
a7813a04 XL |
315 | self.type_of_node_must_outlive(infer::CallReturn(span), |
316 | body.id, | |
9e0c209e | 317 | call_site_region); |
9cc50fc6 | 318 | |
bd371182 AL |
319 | self.region_bound_pairs.truncate(old_region_bounds_pairs_len); |
320 | ||
85aaf69f | 321 | self.set_body_id(old_body_id); |
9cc50fc6 | 322 | self.set_call_site_scope(old_call_site_scope); |
1a4d82fc JJ |
323 | } |
324 | ||
325 | fn visit_region_obligations(&mut self, node_id: ast::NodeId) | |
326 | { | |
327 | debug!("visit_region_obligations: node_id={}", node_id); | |
85aaf69f SL |
328 | |
329 | // region checking can introduce new pending obligations | |
330 | // which, when processed, might generate new region | |
331 | // obligations. So make sure we process those. | |
a7813a04 | 332 | self.select_all_obligations_or_error(); |
85aaf69f SL |
333 | |
334 | // Make a copy of the region obligations vec because we'll need | |
335 | // to be able to borrow the fulfillment-cx below when projecting. | |
336 | let region_obligations = | |
a7813a04 | 337 | self.fulfillment_cx |
c1a9b12d SL |
338 | .borrow() |
339 | .region_obligations(node_id) | |
340 | .to_vec(); | |
85aaf69f SL |
341 | |
342 | for r_o in ®ion_obligations { | |
e9174d1e SL |
343 | debug!("visit_region_obligations: r_o={:?} cause={:?}", |
344 | r_o, r_o.cause); | |
1a4d82fc | 345 | let sup_type = self.resolve_type(r_o.sup_type); |
c30ab7b3 | 346 | let origin = self.code_to_origin(&r_o.cause, sup_type); |
a7813a04 | 347 | self.type_must_outlive(origin, sup_type, r_o.sub_region); |
1a4d82fc | 348 | } |
85aaf69f SL |
349 | |
350 | // Processing the region obligations should not cause the list to grow further: | |
351 | assert_eq!(region_obligations.len(), | |
a7813a04 | 352 | self.fulfillment_cx.borrow().region_obligations(node_id).len()); |
e9174d1e SL |
353 | } |
354 | ||
355 | fn code_to_origin(&self, | |
c30ab7b3 SL |
356 | cause: &traits::ObligationCause<'tcx>, |
357 | sup_type: Ty<'tcx>) | |
e9174d1e | 358 | -> SubregionOrigin<'tcx> { |
c30ab7b3 SL |
359 | SubregionOrigin::from_obligation_cause(cause, |
360 | || infer::RelateParamBound(cause.span, sup_type)) | |
e9174d1e SL |
361 | } |
362 | ||
1a4d82fc JJ |
363 | /// This method populates the region map's `free_region_map`. It walks over the transformed |
364 | /// argument and return types for each function just before we check the body of that function, | |
365 | /// looking for types where you have a borrowed pointer to other borrowed data (e.g., `&'a &'b | |
c34b1796 | 366 | /// [usize]`. We do not allow references to outlive the things they point at, so we can assume |
1a4d82fc JJ |
367 | /// that `'a <= 'b`. This holds for both the argument and return types, basically because, on |
368 | /// the caller side, the caller is responsible for checking that the type of every expression | |
369 | /// (including the actual values for the arguments, as well as the return type of the fn call) | |
370 | /// is well-formed. | |
371 | /// | |
372 | /// Tests: `src/test/compile-fail/regions-free-region-ordering-*.rs` | |
373 | fn relate_free_regions(&mut self, | |
374 | fn_sig_tys: &[Ty<'tcx>], | |
85aaf69f SL |
375 | body_id: ast::NodeId, |
376 | span: Span) { | |
1a4d82fc | 377 | debug!("relate_free_regions >>"); |
1a4d82fc | 378 | |
85aaf69f | 379 | for &ty in fn_sig_tys { |
1a4d82fc | 380 | let ty = self.resolve_type(ty); |
62682a34 | 381 | debug!("relate_free_regions(t={:?})", ty); |
a7813a04 | 382 | let implied_bounds = ty::wf::implied_bounds(self, body_id, ty, span); |
bd371182 AL |
383 | |
384 | // Record any relations between free regions that we observe into the free-region-map. | |
e9174d1e | 385 | self.free_region_map.relate_free_regions_from_implied_bounds(&implied_bounds); |
bd371182 AL |
386 | |
387 | // But also record other relationships, such as `T:'x`, | |
388 | // that don't go into the free-region-map but which we use | |
389 | // here. | |
e9174d1e | 390 | for implication in implied_bounds { |
62682a34 | 391 | debug!("implication: {:?}", implication); |
85aaf69f | 392 | match implication { |
9e0c209e SL |
393 | ImpliedBound::RegionSubRegion(&ty::ReFree(free_a), |
394 | &ty::ReVar(vid_b)) => { | |
a7813a04 | 395 | self.add_given(free_a, vid_b); |
1a4d82fc | 396 | } |
e9174d1e SL |
397 | ImpliedBound::RegionSubParam(r_a, param_b) => { |
398 | self.region_bound_pairs.push((r_a, GenericKind::Param(param_b))); | |
c34b1796 | 399 | } |
e9174d1e SL |
400 | ImpliedBound::RegionSubProjection(r_a, projection_b) => { |
401 | self.region_bound_pairs.push((r_a, GenericKind::Projection(projection_b))); | |
402 | } | |
403 | ImpliedBound::RegionSubRegion(..) => { | |
1a4d82fc JJ |
404 | // In principle, we could record (and take |
405 | // advantage of) every relationship here, but | |
406 | // we are also free not to -- it simply means | |
407 | // strictly less that we can successfully type | |
408 | // check. (It may also be that we should | |
409 | // revise our inference system to be more | |
410 | // general and to make use of *every* | |
411 | // relationship that arises here, but | |
412 | // presently we do not.) | |
413 | } | |
1a4d82fc JJ |
414 | } |
415 | } | |
416 | } | |
417 | ||
418 | debug!("<< relate_free_regions"); | |
419 | } | |
420 | ||
421 | fn resolve_regions_and_report_errors(&self) { | |
422 | let subject_node_id = match self.subject { | |
423 | Subject(s) => s, | |
424 | SubjectNode::None => { | |
54a0048b SL |
425 | bug!("cannot resolve_regions_and_report_errors \ |
426 | without subject node"); | |
1a4d82fc JJ |
427 | } |
428 | }; | |
429 | ||
a7813a04 XL |
430 | self.fcx.resolve_regions_and_report_errors(&self.free_region_map, |
431 | subject_node_id); | |
432 | } | |
433 | ||
434 | fn constrain_bindings_in_pat(&mut self, pat: &hir::Pat) { | |
435 | let tcx = self.tcx; | |
436 | debug!("regionck::visit_pat(pat={:?})", pat); | |
3157f602 | 437 | pat_util::pat_bindings(pat, |_, id, span, _| { |
a7813a04 XL |
438 | // If we have a variable that contains region'd data, that |
439 | // data will be accessible from anywhere that the variable is | |
440 | // accessed. We must be wary of loops like this: | |
441 | // | |
442 | // // from src/test/compile-fail/borrowck-lend-flow.rs | |
443 | // let mut v = box 3, w = box 4; | |
444 | // let mut x = &mut w; | |
445 | // loop { | |
446 | // **x += 1; // (2) | |
447 | // borrow(v); //~ ERROR cannot borrow | |
448 | // x = &mut v; // (1) | |
449 | // } | |
450 | // | |
451 | // Typically, we try to determine the region of a borrow from | |
452 | // those points where it is dereferenced. In this case, one | |
453 | // might imagine that the lifetime of `x` need only be the | |
454 | // body of the loop. But of course this is incorrect because | |
455 | // the pointer that is created at point (1) is consumed at | |
456 | // point (2), meaning that it must be live across the loop | |
457 | // iteration. The easiest way to guarantee this is to require | |
458 | // that the lifetime of any regions that appear in a | |
459 | // variable's type enclose at least the variable's scope. | |
460 | ||
461 | let var_scope = tcx.region_maps.var_scope(id); | |
9e0c209e | 462 | let var_region = self.tcx.mk_region(ty::ReScope(var_scope)); |
a7813a04 XL |
463 | |
464 | let origin = infer::BindingTypeIsNotValidAtDecl(span); | |
9e0c209e | 465 | self.type_of_node_must_outlive(origin, id, var_region); |
a7813a04 XL |
466 | |
467 | let typ = self.resolve_node_type(id); | |
468 | dropck::check_safety_of_destructor_if_necessary(self, typ, span, var_scope); | |
469 | }) | |
1a4d82fc JJ |
470 | } |
471 | } | |
472 | ||
a7813a04 | 473 | impl<'a, 'gcx, 'tcx, 'v> Visitor<'v> for RegionCtxt<'a, 'gcx, 'tcx> { |
1a4d82fc JJ |
474 | // (..) FIXME(#3238) should use visit_pat, not visit_arm/visit_local, |
475 | // However, right now we run into an issue whereby some free | |
476 | // regions are not properly related if they appear within the | |
477 | // types of arguments that must be inferred. This could be | |
478 | // addressed by deferring the construction of the region | |
479 | // hierarchy, and in particular the relationships between free | |
480 | // regions, until regionck, as described in #3238. | |
481 | ||
92a42be0 | 482 | fn visit_fn(&mut self, _fk: intravisit::FnKind<'v>, fd: &'v hir::FnDecl, |
e9174d1e | 483 | b: &'v hir::Block, span: Span, id: ast::NodeId) { |
85aaf69f | 484 | self.visit_fn_body(id, fd, b, span) |
1a4d82fc JJ |
485 | } |
486 | ||
1a4d82fc JJ |
487 | //visit_pat: visit_pat, // (..) see above |
488 | ||
a7813a04 XL |
489 | fn visit_arm(&mut self, arm: &hir::Arm) { |
490 | // see above | |
491 | for p in &arm.pats { | |
492 | self.constrain_bindings_in_pat(p); | |
493 | } | |
494 | intravisit::walk_arm(self, arm); | |
1a4d82fc JJ |
495 | } |
496 | ||
a7813a04 XL |
497 | fn visit_local(&mut self, l: &hir::Local) { |
498 | // see above | |
499 | self.constrain_bindings_in_pat(&l.pat); | |
500 | self.link_local(l); | |
501 | intravisit::walk_local(self, l); | |
502 | } | |
1a4d82fc | 503 | |
a7813a04 XL |
504 | fn visit_expr(&mut self, expr: &hir::Expr) { |
505 | debug!("regionck::visit_expr(e={:?}, repeating_scope={})", | |
506 | expr, self.repeating_scope); | |
507 | ||
508 | // No matter what, the type of each expression must outlive the | |
509 | // scope of that expression. This also guarantees basic WF. | |
510 | let expr_ty = self.resolve_node_type(expr.id); | |
511 | // the region corresponding to this expression | |
9e0c209e | 512 | let expr_region = self.tcx.node_scope_region(expr.id); |
a7813a04 XL |
513 | self.type_must_outlive(infer::ExprTypeIsNotInScope(expr_ty, expr.span), |
514 | expr_ty, expr_region); | |
515 | ||
516 | let method_call = MethodCall::expr(expr.id); | |
517 | let opt_method_callee = self.tables.borrow().method_map.get(&method_call).cloned(); | |
518 | let has_method_map = opt_method_callee.is_some(); | |
519 | ||
520 | // If we are calling a method (either explicitly or via an | |
521 | // overloaded operator), check that all of the types provided as | |
522 | // arguments for its type parameters are well-formed, and all the regions | |
523 | // provided as arguments outlive the call. | |
524 | if let Some(callee) = opt_method_callee { | |
525 | let origin = match expr.node { | |
526 | hir::ExprMethodCall(..) => | |
527 | infer::ParameterOrigin::MethodCall, | |
528 | hir::ExprUnary(op, _) if op == hir::UnDeref => | |
529 | infer::ParameterOrigin::OverloadedDeref, | |
530 | _ => | |
531 | infer::ParameterOrigin::OverloadedOperator | |
532 | }; | |
1a4d82fc | 533 | |
a7813a04 XL |
534 | self.substs_wf_in_scope(origin, &callee.substs, expr.span, expr_region); |
535 | self.type_must_outlive(infer::ExprTypeIsNotInScope(callee.ty, expr.span), | |
536 | callee.ty, expr_region); | |
537 | } | |
1a4d82fc | 538 | |
a7813a04 XL |
539 | // Check any autoderefs or autorefs that appear. |
540 | let adjustment = self.tables.borrow().adjustments.get(&expr.id).map(|a| a.clone()); | |
541 | if let Some(adjustment) = adjustment { | |
542 | debug!("adjustment={:?}", adjustment); | |
c30ab7b3 SL |
543 | match adjustment.kind { |
544 | adjustment::Adjust::DerefRef { autoderefs, ref autoref, .. } => { | |
a7813a04 XL |
545 | let expr_ty = self.resolve_node_type(expr.id); |
546 | self.constrain_autoderefs(expr, autoderefs, expr_ty); | |
547 | if let Some(ref autoref) = *autoref { | |
548 | self.link_autoref(expr, autoderefs, autoref); | |
549 | ||
550 | // Require that the resulting region encompasses | |
551 | // the current node. | |
552 | // | |
553 | // FIXME(#6268) remove to support nested method calls | |
554 | self.type_of_node_must_outlive(infer::AutoBorrow(expr.span), | |
555 | expr.id, expr_region); | |
556 | } | |
557 | } | |
558 | /* | |
9e0c209e | 559 | adjustment::AutoObject(_, ref bounds, ..) => { |
a7813a04 XL |
560 | // Determine if we are casting `expr` to a trait |
561 | // instance. If so, we have to be sure that the type | |
562 | // of the source obeys the new region bound. | |
563 | let source_ty = self.resolve_node_type(expr.id); | |
564 | self.type_must_outlive(infer::RelateObjectBound(expr.span), | |
565 | source_ty, bounds.region_bound); | |
1a4d82fc | 566 | } |
a7813a04 XL |
567 | */ |
568 | _ => {} | |
1a4d82fc | 569 | } |
a7813a04 XL |
570 | |
571 | // If necessary, constrain destructors in the unadjusted form of this | |
572 | // expression. | |
573 | let cmt_result = { | |
574 | let mc = mc::MemCategorizationContext::new(self); | |
575 | mc.cat_expr_unadjusted(expr) | |
576 | }; | |
577 | match cmt_result { | |
578 | Ok(head_cmt) => { | |
579 | self.check_safety_of_rvalue_destructor_if_necessary(head_cmt, | |
580 | expr.span); | |
581 | } | |
582 | Err(..) => { | |
583 | self.tcx.sess.delay_span_bug(expr.span, "cat_expr_unadjusted Errd"); | |
584 | } | |
1a4d82fc | 585 | } |
1a4d82fc | 586 | } |
85aaf69f | 587 | |
a7813a04 XL |
588 | // If necessary, constrain destructors in this expression. This will be |
589 | // the adjusted form if there is an adjustment. | |
85aaf69f | 590 | let cmt_result = { |
a7813a04 XL |
591 | let mc = mc::MemCategorizationContext::new(self); |
592 | mc.cat_expr(expr) | |
85aaf69f SL |
593 | }; |
594 | match cmt_result { | |
595 | Ok(head_cmt) => { | |
a7813a04 | 596 | self.check_safety_of_rvalue_destructor_if_necessary(head_cmt, expr.span); |
85aaf69f SL |
597 | } |
598 | Err(..) => { | |
a7813a04 | 599 | self.tcx.sess.delay_span_bug(expr.span, "cat_expr Errd"); |
85aaf69f SL |
600 | } |
601 | } | |
85aaf69f | 602 | |
a7813a04 XL |
603 | debug!("regionck::visit_expr(e={:?}, repeating_scope={}) - visiting subexprs", |
604 | expr, self.repeating_scope); | |
605 | match expr.node { | |
606 | hir::ExprPath(..) => { | |
607 | self.fcx.opt_node_ty_substs(expr.id, |item_substs| { | |
608 | let origin = infer::ParameterOrigin::Path; | |
609 | self.substs_wf_in_scope(origin, &item_substs.substs, expr.span, expr_region); | |
610 | }); | |
1a4d82fc JJ |
611 | } |
612 | ||
a7813a04 XL |
613 | hir::ExprCall(ref callee, ref args) => { |
614 | if has_method_map { | |
615 | self.constrain_call(expr, Some(&callee), | |
616 | args.iter().map(|e| &**e), false); | |
617 | } else { | |
618 | self.constrain_callee(callee.id, expr, &callee); | |
619 | self.constrain_call(expr, None, | |
620 | args.iter().map(|e| &**e), false); | |
621 | } | |
1a4d82fc | 622 | |
a7813a04 XL |
623 | intravisit::walk_expr(self, expr); |
624 | } | |
1a4d82fc | 625 | |
9e0c209e | 626 | hir::ExprMethodCall(.., ref args) => { |
a7813a04 XL |
627 | self.constrain_call(expr, Some(&args[0]), |
628 | args[1..].iter().map(|e| &**e), false); | |
1a4d82fc | 629 | |
a7813a04 | 630 | intravisit::walk_expr(self, expr); |
1a4d82fc JJ |
631 | } |
632 | ||
a7813a04 XL |
633 | hir::ExprAssignOp(_, ref lhs, ref rhs) => { |
634 | if has_method_map { | |
635 | self.constrain_call(expr, Some(&lhs), | |
636 | Some(&**rhs).into_iter(), false); | |
637 | } | |
1a4d82fc | 638 | |
a7813a04 XL |
639 | intravisit::walk_expr(self, expr); |
640 | } | |
1a4d82fc | 641 | |
a7813a04 XL |
642 | hir::ExprIndex(ref lhs, ref rhs) if has_method_map => { |
643 | self.constrain_call(expr, Some(&lhs), | |
644 | Some(&**rhs).into_iter(), true); | |
1a4d82fc | 645 | |
a7813a04 XL |
646 | intravisit::walk_expr(self, expr); |
647 | }, | |
1a4d82fc | 648 | |
a7813a04 XL |
649 | hir::ExprBinary(op, ref lhs, ref rhs) if has_method_map => { |
650 | let implicitly_ref_args = !op.node.is_by_value(); | |
1a4d82fc | 651 | |
a7813a04 XL |
652 | // As `expr_method_call`, but the call is via an |
653 | // overloaded op. Note that we (sadly) currently use an | |
654 | // implicit "by ref" sort of passing style here. This | |
655 | // should be converted to an adjustment! | |
656 | self.constrain_call(expr, Some(&lhs), | |
657 | Some(&**rhs).into_iter(), implicitly_ref_args); | |
1a4d82fc | 658 | |
a7813a04 | 659 | intravisit::walk_expr(self, expr); |
85aaf69f | 660 | } |
85aaf69f | 661 | |
a7813a04 XL |
662 | hir::ExprBinary(_, ref lhs, ref rhs) => { |
663 | // If you do `x OP y`, then the types of `x` and `y` must | |
664 | // outlive the operation you are performing. | |
665 | let lhs_ty = self.resolve_expr_type_adjusted(&lhs); | |
666 | let rhs_ty = self.resolve_expr_type_adjusted(&rhs); | |
667 | for &ty in &[lhs_ty, rhs_ty] { | |
668 | self.type_must_outlive(infer::Operand(expr.span), | |
669 | ty, expr_region); | |
670 | } | |
671 | intravisit::walk_expr(self, expr); | |
672 | } | |
1a4d82fc | 673 | |
a7813a04 XL |
674 | hir::ExprUnary(op, ref lhs) if has_method_map => { |
675 | let implicitly_ref_args = !op.is_by_value(); | |
1a4d82fc | 676 | |
a7813a04 XL |
677 | // As above. |
678 | self.constrain_call(expr, Some(&lhs), | |
679 | None::<hir::Expr>.iter(), implicitly_ref_args); | |
1a4d82fc | 680 | |
a7813a04 | 681 | intravisit::walk_expr(self, expr); |
1a4d82fc JJ |
682 | } |
683 | ||
a7813a04 XL |
684 | hir::ExprUnary(hir::UnDeref, ref base) => { |
685 | // For *a, the lifetime of a must enclose the deref | |
686 | let method_call = MethodCall::expr(expr.id); | |
687 | let base_ty = match self.tables.borrow().method_map.get(&method_call) { | |
688 | Some(method) => { | |
689 | self.constrain_call(expr, Some(&base), | |
690 | None::<hir::Expr>.iter(), true); | |
691 | // late-bound regions in overloaded method calls are instantiated | |
692 | let fn_ret = self.tcx.no_late_bound_regions(&method.ty.fn_ret()); | |
5bcae85e | 693 | fn_ret.unwrap() |
a7813a04 XL |
694 | } |
695 | None => self.resolve_node_type(base.id) | |
696 | }; | |
697 | if let ty::TyRef(r_ptr, _) = base_ty.sty { | |
9e0c209e | 698 | self.mk_subregion_due_to_dereference(expr.span, expr_region, r_ptr); |
a7813a04 | 699 | } |
1a4d82fc | 700 | |
a7813a04 XL |
701 | intravisit::walk_expr(self, expr); |
702 | } | |
1a4d82fc | 703 | |
a7813a04 XL |
704 | hir::ExprIndex(ref vec_expr, _) => { |
705 | // For a[b], the lifetime of a must enclose the deref | |
706 | let vec_type = self.resolve_expr_type_adjusted(&vec_expr); | |
707 | self.constrain_index(expr, vec_type); | |
1a4d82fc | 708 | |
a7813a04 XL |
709 | intravisit::walk_expr(self, expr); |
710 | } | |
1a4d82fc | 711 | |
a7813a04 XL |
712 | hir::ExprCast(ref source, _) => { |
713 | // Determine if we are casting `source` to a trait | |
714 | // instance. If so, we have to be sure that the type of | |
715 | // the source obeys the trait's region bound. | |
716 | self.constrain_cast(expr, &source); | |
717 | intravisit::walk_expr(self, expr); | |
718 | } | |
1a4d82fc | 719 | |
a7813a04 XL |
720 | hir::ExprAddrOf(m, ref base) => { |
721 | self.link_addr_of(expr, m, &base); | |
722 | ||
723 | // Require that when you write a `&expr` expression, the | |
724 | // resulting pointer has a lifetime that encompasses the | |
725 | // `&expr` expression itself. Note that we constraining | |
726 | // the type of the node expr.id here *before applying | |
727 | // adjustments*. | |
728 | // | |
729 | // FIXME(#6268) nested method calls requires that this rule change | |
730 | let ty0 = self.resolve_node_type(expr.id); | |
731 | self.type_must_outlive(infer::AddrOf(expr.span), ty0, expr_region); | |
732 | intravisit::walk_expr(self, expr); | |
733 | } | |
1a4d82fc | 734 | |
a7813a04 XL |
735 | hir::ExprMatch(ref discr, ref arms, _) => { |
736 | self.link_match(&discr, &arms[..]); | |
1a4d82fc | 737 | |
a7813a04 XL |
738 | intravisit::walk_expr(self, expr); |
739 | } | |
1a4d82fc | 740 | |
9e0c209e | 741 | hir::ExprClosure(.., ref body, _) => { |
a7813a04 XL |
742 | self.check_expr_fn_block(expr, &body); |
743 | } | |
1a4d82fc | 744 | |
a7813a04 XL |
745 | hir::ExprLoop(ref body, _) => { |
746 | let repeating_scope = self.set_repeating_scope(body.id); | |
747 | intravisit::walk_expr(self, expr); | |
748 | self.set_repeating_scope(repeating_scope); | |
749 | } | |
1a4d82fc | 750 | |
a7813a04 XL |
751 | hir::ExprWhile(ref cond, ref body, _) => { |
752 | let repeating_scope = self.set_repeating_scope(cond.id); | |
753 | self.visit_expr(&cond); | |
1a4d82fc | 754 | |
a7813a04 XL |
755 | self.set_repeating_scope(body.id); |
756 | self.visit_block(&body); | |
1a4d82fc | 757 | |
a7813a04 XL |
758 | self.set_repeating_scope(repeating_scope); |
759 | } | |
1a4d82fc | 760 | |
a7813a04 XL |
761 | hir::ExprRet(Some(ref ret_expr)) => { |
762 | let call_site_scope = self.call_site_scope; | |
763 | debug!("visit_expr ExprRet ret_expr.id {} call_site_scope: {:?}", | |
764 | ret_expr.id, call_site_scope); | |
9e0c209e | 765 | let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope.unwrap())); |
a7813a04 XL |
766 | self.type_of_node_must_outlive(infer::CallReturn(ret_expr.span), |
767 | ret_expr.id, | |
9e0c209e | 768 | call_site_region); |
a7813a04 XL |
769 | intravisit::walk_expr(self, expr); |
770 | } | |
9cc50fc6 | 771 | |
a7813a04 XL |
772 | _ => { |
773 | intravisit::walk_expr(self, expr); | |
774 | } | |
1a4d82fc JJ |
775 | } |
776 | } | |
777 | } | |
778 | ||
a7813a04 XL |
779 | impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> { |
780 | fn constrain_cast(&mut self, | |
781 | cast_expr: &hir::Expr, | |
782 | source_expr: &hir::Expr) | |
783 | { | |
784 | debug!("constrain_cast(cast_expr={:?}, source_expr={:?})", | |
785 | cast_expr, | |
786 | source_expr); | |
1a4d82fc | 787 | |
a7813a04 XL |
788 | let source_ty = self.resolve_node_type(source_expr.id); |
789 | let target_ty = self.resolve_node_type(cast_expr.id); | |
1a4d82fc | 790 | |
a7813a04 XL |
791 | self.walk_cast(cast_expr, source_ty, target_ty); |
792 | } | |
1a4d82fc | 793 | |
a7813a04 XL |
794 | fn walk_cast(&mut self, |
795 | cast_expr: &hir::Expr, | |
796 | from_ty: Ty<'tcx>, | |
797 | to_ty: Ty<'tcx>) { | |
62682a34 SL |
798 | debug!("walk_cast(from_ty={:?}, to_ty={:?})", |
799 | from_ty, | |
800 | to_ty); | |
1a4d82fc | 801 | match (&from_ty.sty, &to_ty.sty) { |
62682a34 SL |
802 | /*From:*/ (&ty::TyRef(from_r, ref from_mt), |
803 | /*To: */ &ty::TyRef(to_r, ref to_mt)) => { | |
1a4d82fc | 804 | // Target cannot outlive source, naturally. |
9e0c209e | 805 | self.sub_regions(infer::Reborrow(cast_expr.span), to_r, from_r); |
a7813a04 | 806 | self.walk_cast(cast_expr, from_mt.ty, to_mt.ty); |
1a4d82fc JJ |
807 | } |
808 | ||
809 | /*From:*/ (_, | |
9e0c209e | 810 | /*To: */ &ty::TyTrait(ref obj)) => { |
1a4d82fc JJ |
811 | // When T is existentially quantified as a trait |
812 | // `Foo+'to`, it must outlive the region bound `'to`. | |
a7813a04 | 813 | self.type_must_outlive(infer::RelateObjectBound(cast_expr.span), |
9e0c209e | 814 | from_ty, obj.region_bound); |
1a4d82fc JJ |
815 | } |
816 | ||
62682a34 SL |
817 | /*From:*/ (&ty::TyBox(from_referent_ty), |
818 | /*To: */ &ty::TyBox(to_referent_ty)) => { | |
a7813a04 | 819 | self.walk_cast(cast_expr, from_referent_ty, to_referent_ty); |
1a4d82fc JJ |
820 | } |
821 | ||
822 | _ => { } | |
823 | } | |
824 | } | |
1a4d82fc | 825 | |
a7813a04 XL |
826 | fn check_expr_fn_block(&mut self, |
827 | expr: &hir::Expr, | |
828 | body: &hir::Block) { | |
829 | let repeating_scope = self.set_repeating_scope(body.id); | |
830 | intravisit::walk_expr(self, expr); | |
831 | self.set_repeating_scope(repeating_scope); | |
832 | } | |
1a4d82fc | 833 | |
a7813a04 XL |
834 | fn constrain_callee(&mut self, |
835 | callee_id: ast::NodeId, | |
836 | _call_expr: &hir::Expr, | |
837 | _callee_expr: &hir::Expr) { | |
838 | let callee_ty = self.resolve_node_type(callee_id); | |
839 | match callee_ty.sty { | |
840 | ty::TyFnDef(..) | ty::TyFnPtr(_) => { } | |
841 | _ => { | |
842 | // this should not happen, but it does if the program is | |
843 | // erroneous | |
844 | // | |
845 | // bug!( | |
846 | // callee_expr.span, | |
847 | // "Calling non-function: {}", | |
848 | // callee_ty); | |
849 | } | |
1a4d82fc JJ |
850 | } |
851 | } | |
1a4d82fc | 852 | |
a7813a04 XL |
853 | fn constrain_call<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self, |
854 | call_expr: &hir::Expr, | |
855 | receiver: Option<&hir::Expr>, | |
856 | arg_exprs: I, | |
857 | implicitly_ref_args: bool) { | |
858 | //! Invoked on every call site (i.e., normal calls, method calls, | |
859 | //! and overloaded operators). Constrains the regions which appear | |
860 | //! in the type of the function. Also constrains the regions that | |
861 | //! appear in the arguments appropriately. | |
862 | ||
863 | debug!("constrain_call(call_expr={:?}, \ | |
864 | receiver={:?}, \ | |
865 | implicitly_ref_args={})", | |
866 | call_expr, | |
867 | receiver, | |
868 | implicitly_ref_args); | |
869 | ||
870 | // `callee_region` is the scope representing the time in which the | |
871 | // call occurs. | |
872 | // | |
873 | // FIXME(#6268) to support nested method calls, should be callee_id | |
874 | let callee_scope = self.tcx.region_maps.node_extent(call_expr.id); | |
9e0c209e | 875 | let callee_region = self.tcx.mk_region(ty::ReScope(callee_scope)); |
a7813a04 XL |
876 | |
877 | debug!("callee_region={:?}", callee_region); | |
878 | ||
879 | for arg_expr in arg_exprs { | |
880 | debug!("Argument: {:?}", arg_expr); | |
881 | ||
882 | // ensure that any regions appearing in the argument type are | |
883 | // valid for at least the lifetime of the function: | |
884 | self.type_of_node_must_outlive(infer::CallArg(arg_expr.span), | |
885 | arg_expr.id, callee_region); | |
886 | ||
887 | // unfortunately, there are two means of taking implicit | |
888 | // references, and we need to propagate constraints as a | |
889 | // result. modes are going away and the "DerefArgs" code | |
890 | // should be ported to use adjustments | |
891 | if implicitly_ref_args { | |
892 | self.link_by_ref(arg_expr, callee_scope); | |
893 | } | |
1a4d82fc | 894 | } |
1a4d82fc | 895 | |
a7813a04 XL |
896 | // as loop above, but for receiver |
897 | if let Some(r) = receiver { | |
898 | debug!("receiver: {:?}", r); | |
899 | self.type_of_node_must_outlive(infer::CallRcvr(r.span), | |
900 | r.id, callee_region); | |
901 | if implicitly_ref_args { | |
902 | self.link_by_ref(&r, callee_scope); | |
903 | } | |
1a4d82fc JJ |
904 | } |
905 | } | |
1a4d82fc | 906 | |
a7813a04 XL |
907 | /// Invoked on any auto-dereference that occurs. Checks that if this is a region pointer being |
908 | /// dereferenced, the lifetime of the pointer includes the deref expr. | |
909 | fn constrain_autoderefs(&mut self, | |
910 | deref_expr: &hir::Expr, | |
911 | derefs: usize, | |
912 | mut derefd_ty: Ty<'tcx>) | |
913 | { | |
914 | debug!("constrain_autoderefs(deref_expr={:?}, derefs={}, derefd_ty={:?})", | |
915 | deref_expr, | |
916 | derefs, | |
917 | derefd_ty); | |
1a4d82fc | 918 | |
9e0c209e | 919 | let r_deref_expr = self.tcx.node_scope_region(deref_expr.id); |
a7813a04 XL |
920 | for i in 0..derefs { |
921 | let method_call = MethodCall::autoderef(deref_expr.id, i as u32); | |
922 | debug!("constrain_autoderefs: method_call={:?} (of {:?} total)", method_call, derefs); | |
1a4d82fc | 923 | |
a7813a04 XL |
924 | let method = self.tables.borrow().method_map.get(&method_call).map(|m| m.clone()); |
925 | ||
926 | derefd_ty = match method { | |
927 | Some(method) => { | |
928 | debug!("constrain_autoderefs: #{} is overloaded, method={:?}", | |
929 | i, method); | |
930 | ||
931 | let origin = infer::ParameterOrigin::OverloadedDeref; | |
932 | self.substs_wf_in_scope(origin, method.substs, deref_expr.span, r_deref_expr); | |
933 | ||
c30ab7b3 | 934 | // Treat overloaded autoderefs as if an AutoBorrow adjustment |
a7813a04 XL |
935 | // was applied on the base type, as that is always the case. |
936 | let fn_sig = method.ty.fn_sig(); | |
937 | let fn_sig = // late-bound regions should have been instantiated | |
938 | self.tcx.no_late_bound_regions(fn_sig).unwrap(); | |
939 | let self_ty = fn_sig.inputs[0]; | |
940 | let (m, r) = match self_ty.sty { | |
941 | ty::TyRef(r, ref m) => (m.mutbl, r), | |
942 | _ => { | |
943 | span_bug!( | |
944 | deref_expr.span, | |
945 | "bad overloaded deref type {:?}", | |
946 | method.ty) | |
947 | } | |
948 | }; | |
949 | ||
950 | debug!("constrain_autoderefs: receiver r={:?} m={:?}", | |
951 | r, m); | |
952 | ||
953 | { | |
954 | let mc = mc::MemCategorizationContext::new(self); | |
955 | let self_cmt = ignore_err!(mc.cat_expr_autoderefd(deref_expr, i)); | |
956 | debug!("constrain_autoderefs: self_cmt={:?}", | |
957 | self_cmt); | |
958 | self.link_region(deref_expr.span, r, | |
959 | ty::BorrowKind::from_mutbl(m), self_cmt); | |
960 | } | |
1a4d82fc | 961 | |
a7813a04 XL |
962 | // Specialized version of constrain_call. |
963 | self.type_must_outlive(infer::CallRcvr(deref_expr.span), | |
964 | self_ty, r_deref_expr); | |
5bcae85e SL |
965 | self.type_must_outlive(infer::CallReturn(deref_expr.span), |
966 | fn_sig.output, r_deref_expr); | |
967 | fn_sig.output | |
1a4d82fc | 968 | } |
a7813a04 XL |
969 | None => derefd_ty |
970 | }; | |
1a4d82fc | 971 | |
a7813a04 XL |
972 | if let ty::TyRef(r_ptr, _) = derefd_ty.sty { |
973 | self.mk_subregion_due_to_dereference(deref_expr.span, | |
9e0c209e | 974 | r_deref_expr, r_ptr); |
a7813a04 | 975 | } |
1a4d82fc | 976 | |
a7813a04 XL |
977 | match derefd_ty.builtin_deref(true, ty::NoPreference) { |
978 | Some(mt) => derefd_ty = mt.ty, | |
979 | /* if this type can't be dereferenced, then there's already an error | |
980 | in the session saying so. Just bail out for now */ | |
981 | None => break | |
982 | } | |
1a4d82fc JJ |
983 | } |
984 | } | |
1a4d82fc | 985 | |
a7813a04 XL |
986 | pub fn mk_subregion_due_to_dereference(&mut self, |
987 | deref_span: Span, | |
9e0c209e SL |
988 | minimum_lifetime: &'tcx ty::Region, |
989 | maximum_lifetime: &'tcx ty::Region) { | |
a7813a04 XL |
990 | self.sub_regions(infer::DerefPointer(deref_span), |
991 | minimum_lifetime, maximum_lifetime) | |
992 | } | |
1a4d82fc | 993 | |
a7813a04 XL |
994 | fn check_safety_of_rvalue_destructor_if_necessary(&mut self, |
995 | cmt: mc::cmt<'tcx>, | |
996 | span: Span) { | |
997 | match cmt.cat { | |
998 | Categorization::Rvalue(region) => { | |
9e0c209e | 999 | match *region { |
a7813a04 XL |
1000 | ty::ReScope(rvalue_scope) => { |
1001 | let typ = self.resolve_type(cmt.ty); | |
1002 | dropck::check_safety_of_destructor_if_necessary(self, | |
1003 | typ, | |
1004 | span, | |
1005 | rvalue_scope); | |
1006 | } | |
1007 | ty::ReStatic => {} | |
9e0c209e | 1008 | _ => { |
a7813a04 XL |
1009 | span_bug!(span, |
1010 | "unexpected rvalue region in rvalue \ | |
1011 | destructor safety checking: `{:?}`", | |
1012 | region); | |
1013 | } | |
85aaf69f SL |
1014 | } |
1015 | } | |
a7813a04 | 1016 | _ => {} |
85aaf69f | 1017 | } |
85aaf69f | 1018 | } |
1a4d82fc | 1019 | |
a7813a04 XL |
1020 | /// Invoked on any index expression that occurs. Checks that if this is a slice |
1021 | /// being indexed, the lifetime of the pointer includes the deref expr. | |
1022 | fn constrain_index(&mut self, | |
1023 | index_expr: &hir::Expr, | |
1024 | indexed_ty: Ty<'tcx>) | |
1025 | { | |
1026 | debug!("constrain_index(index_expr=?, indexed_ty={}", | |
1027 | self.ty_to_string(indexed_ty)); | |
1028 | ||
1029 | let r_index_expr = ty::ReScope(self.tcx.region_maps.node_extent(index_expr.id)); | |
1030 | if let ty::TyRef(r_ptr, mt) = indexed_ty.sty { | |
1031 | match mt.ty.sty { | |
1032 | ty::TySlice(_) | ty::TyStr => { | |
1033 | self.sub_regions(infer::IndexSlice(index_expr.span), | |
9e0c209e | 1034 | self.tcx.mk_region(r_index_expr), r_ptr); |
a7813a04 XL |
1035 | } |
1036 | _ => {} | |
1a4d82fc | 1037 | } |
1a4d82fc JJ |
1038 | } |
1039 | } | |
1a4d82fc | 1040 | |
a7813a04 XL |
1041 | /// Guarantees that any lifetimes which appear in the type of the node `id` (after applying |
1042 | /// adjustments) are valid for at least `minimum_lifetime` | |
1043 | fn type_of_node_must_outlive(&mut self, | |
1044 | origin: infer::SubregionOrigin<'tcx>, | |
1045 | id: ast::NodeId, | |
9e0c209e | 1046 | minimum_lifetime: &'tcx ty::Region) |
a7813a04 | 1047 | { |
a7813a04 XL |
1048 | // Try to resolve the type. If we encounter an error, then typeck |
1049 | // is going to fail anyway, so just stop here and let typeck | |
1050 | // report errors later on in the writeback phase. | |
1051 | let ty0 = self.resolve_node_type(id); | |
c30ab7b3 SL |
1052 | let ty = self.tables.borrow().adjustments.get(&id).map_or(ty0, |adj| adj.target); |
1053 | let ty = self.resolve_type(ty); | |
a7813a04 XL |
1054 | debug!("constrain_regions_in_type_of_node(\ |
1055 | ty={}, ty0={}, id={}, minimum_lifetime={:?})", | |
1056 | ty, ty0, | |
1057 | id, minimum_lifetime); | |
1058 | self.type_must_outlive(origin, ty, minimum_lifetime); | |
1059 | } | |
1a4d82fc | 1060 | |
a7813a04 XL |
1061 | /// Computes the guarantor for an expression `&base` and then ensures that the lifetime of the |
1062 | /// resulting pointer is linked to the lifetime of its guarantor (if any). | |
1063 | fn link_addr_of(&mut self, expr: &hir::Expr, | |
1064 | mutability: hir::Mutability, base: &hir::Expr) { | |
1065 | debug!("link_addr_of(expr={:?}, base={:?})", expr, base); | |
1a4d82fc | 1066 | |
a7813a04 XL |
1067 | let cmt = { |
1068 | let mc = mc::MemCategorizationContext::new(self); | |
1069 | ignore_err!(mc.cat_expr(base)) | |
1070 | }; | |
1a4d82fc | 1071 | |
a7813a04 | 1072 | debug!("link_addr_of: cmt={:?}", cmt); |
1a4d82fc | 1073 | |
a7813a04 XL |
1074 | self.link_region_from_node_type(expr.span, expr.id, mutability, cmt); |
1075 | } | |
1a4d82fc | 1076 | |
a7813a04 XL |
1077 | /// Computes the guarantors for any ref bindings in a `let` and |
1078 | /// then ensures that the lifetime of the resulting pointer is | |
1079 | /// linked to the lifetime of the initialization expression. | |
1080 | fn link_local(&self, local: &hir::Local) { | |
1081 | debug!("regionck::for_local()"); | |
1082 | let init_expr = match local.init { | |
1083 | None => { return; } | |
1084 | Some(ref expr) => &**expr, | |
1085 | }; | |
1086 | let mc = mc::MemCategorizationContext::new(self); | |
1087 | let discr_cmt = ignore_err!(mc.cat_expr(init_expr)); | |
1088 | self.link_pattern(mc, discr_cmt, &local.pat); | |
1089 | } | |
1a4d82fc | 1090 | |
a7813a04 XL |
1091 | /// Computes the guarantors for any ref bindings in a match and |
1092 | /// then ensures that the lifetime of the resulting pointer is | |
1093 | /// linked to the lifetime of its guarantor (if any). | |
1094 | fn link_match(&self, discr: &hir::Expr, arms: &[hir::Arm]) { | |
1095 | debug!("regionck::for_match()"); | |
1096 | let mc = mc::MemCategorizationContext::new(self); | |
1097 | let discr_cmt = ignore_err!(mc.cat_expr(discr)); | |
1098 | debug!("discr_cmt={:?}", discr_cmt); | |
1099 | for arm in arms { | |
1100 | for root_pat in &arm.pats { | |
1101 | self.link_pattern(mc, discr_cmt.clone(), &root_pat); | |
1102 | } | |
1a4d82fc JJ |
1103 | } |
1104 | } | |
1a4d82fc | 1105 | |
a7813a04 XL |
1106 | /// Computes the guarantors for any ref bindings in a match and |
1107 | /// then ensures that the lifetime of the resulting pointer is | |
1108 | /// linked to the lifetime of its guarantor (if any). | |
1109 | fn link_fn_args(&self, body_scope: CodeExtent, args: &[hir::Arg]) { | |
1110 | debug!("regionck::link_fn_args(body_scope={:?})", body_scope); | |
1111 | let mc = mc::MemCategorizationContext::new(self); | |
1112 | for arg in args { | |
1113 | let arg_ty = self.node_ty(arg.id); | |
9e0c209e | 1114 | let re_scope = self.tcx.mk_region(ty::ReScope(body_scope)); |
a7813a04 XL |
1115 | let arg_cmt = mc.cat_rvalue(arg.id, arg.ty.span, re_scope, arg_ty); |
1116 | debug!("arg_ty={:?} arg_cmt={:?} arg={:?}", | |
1117 | arg_ty, | |
1118 | arg_cmt, | |
1119 | arg); | |
1120 | self.link_pattern(mc, arg_cmt, &arg.pat); | |
1121 | } | |
1a4d82fc | 1122 | } |
1a4d82fc | 1123 | |
a7813a04 XL |
1124 | /// Link lifetimes of any ref bindings in `root_pat` to the pointers found |
1125 | /// in the discriminant, if needed. | |
1126 | fn link_pattern<'t>(&self, | |
1127 | mc: mc::MemCategorizationContext<'a, 'gcx, 'tcx>, | |
1128 | discr_cmt: mc::cmt<'tcx>, | |
1129 | root_pat: &hir::Pat) { | |
1130 | debug!("link_pattern(discr_cmt={:?}, root_pat={:?})", | |
1131 | discr_cmt, | |
1132 | root_pat); | |
3157f602 | 1133 | let _ = mc.cat_pattern(discr_cmt, root_pat, |_, sub_cmt, sub_pat| { |
a7813a04 XL |
1134 | match sub_pat.node { |
1135 | // `ref x` pattern | |
9e0c209e | 1136 | PatKind::Binding(hir::BindByRef(mutbl), ..) => { |
a7813a04 XL |
1137 | self.link_region_from_node_type(sub_pat.span, sub_pat.id, |
1138 | mutbl, sub_cmt); | |
1139 | } | |
a7813a04 | 1140 | _ => {} |
1a4d82fc | 1141 | } |
a7813a04 XL |
1142 | }); |
1143 | } | |
1a4d82fc | 1144 | |
a7813a04 XL |
1145 | /// Link lifetime of borrowed pointer resulting from autoref to lifetimes in the value being |
1146 | /// autoref'd. | |
1147 | fn link_autoref(&self, | |
1148 | expr: &hir::Expr, | |
1149 | autoderefs: usize, | |
c30ab7b3 | 1150 | autoref: &adjustment::AutoBorrow<'tcx>) |
a7813a04 XL |
1151 | { |
1152 | debug!("link_autoref(autoref={:?})", autoref); | |
1153 | let mc = mc::MemCategorizationContext::new(self); | |
1154 | let expr_cmt = ignore_err!(mc.cat_expr_autoderefd(expr, autoderefs)); | |
1155 | debug!("expr_cmt={:?}", expr_cmt); | |
1156 | ||
1157 | match *autoref { | |
c30ab7b3 | 1158 | adjustment::AutoBorrow::Ref(r, m) => { |
a7813a04 XL |
1159 | self.link_region(expr.span, r, |
1160 | ty::BorrowKind::from_mutbl(m), expr_cmt); | |
1161 | } | |
1a4d82fc | 1162 | |
c30ab7b3 | 1163 | adjustment::AutoBorrow::RawPtr(m) => { |
9e0c209e SL |
1164 | let r = self.tcx.node_scope_region(expr.id); |
1165 | self.link_region(expr.span, r, ty::BorrowKind::from_mutbl(m), expr_cmt); | |
a7813a04 | 1166 | } |
9346a6ac | 1167 | } |
1a4d82fc | 1168 | } |
1a4d82fc | 1169 | |
a7813a04 XL |
1170 | /// Computes the guarantor for cases where the `expr` is being passed by implicit reference and |
1171 | /// must outlive `callee_scope`. | |
1172 | fn link_by_ref(&self, | |
1173 | expr: &hir::Expr, | |
1174 | callee_scope: CodeExtent) { | |
1175 | debug!("link_by_ref(expr={:?}, callee_scope={:?})", | |
1176 | expr, callee_scope); | |
1177 | let mc = mc::MemCategorizationContext::new(self); | |
1178 | let expr_cmt = ignore_err!(mc.cat_expr(expr)); | |
9e0c209e SL |
1179 | let borrow_region = self.tcx.mk_region(ty::ReScope(callee_scope)); |
1180 | self.link_region(expr.span, borrow_region, ty::ImmBorrow, expr_cmt); | |
a7813a04 | 1181 | } |
1a4d82fc | 1182 | |
a7813a04 XL |
1183 | /// Like `link_region()`, except that the region is extracted from the type of `id`, |
1184 | /// which must be some reference (`&T`, `&str`, etc). | |
1185 | fn link_region_from_node_type(&self, | |
1186 | span: Span, | |
1187 | id: ast::NodeId, | |
1188 | mutbl: hir::Mutability, | |
1189 | cmt_borrowed: mc::cmt<'tcx>) { | |
1190 | debug!("link_region_from_node_type(id={:?}, mutbl={:?}, cmt_borrowed={:?})", | |
1191 | id, mutbl, cmt_borrowed); | |
1192 | ||
1193 | let rptr_ty = self.resolve_node_type(id); | |
9e0c209e | 1194 | if let ty::TyRef(r, _) = rptr_ty.sty { |
a7813a04 | 1195 | debug!("rptr_ty={}", rptr_ty); |
9e0c209e | 1196 | self.link_region(span, r, ty::BorrowKind::from_mutbl(mutbl), |
a7813a04 XL |
1197 | cmt_borrowed); |
1198 | } | |
1a4d82fc | 1199 | } |
1a4d82fc | 1200 | |
a7813a04 XL |
1201 | /// Informs the inference engine that `borrow_cmt` is being borrowed with |
1202 | /// kind `borrow_kind` and lifetime `borrow_region`. | |
1203 | /// In order to ensure borrowck is satisfied, this may create constraints | |
1204 | /// between regions, as explained in `link_reborrowed_region()`. | |
1205 | fn link_region(&self, | |
1206 | span: Span, | |
9e0c209e | 1207 | borrow_region: &'tcx ty::Region, |
a7813a04 XL |
1208 | borrow_kind: ty::BorrowKind, |
1209 | borrow_cmt: mc::cmt<'tcx>) { | |
1210 | let mut borrow_cmt = borrow_cmt; | |
1211 | let mut borrow_kind = borrow_kind; | |
1212 | ||
1213 | let origin = infer::DataBorrowed(borrow_cmt.ty, span); | |
9e0c209e | 1214 | self.type_must_outlive(origin, borrow_cmt.ty, borrow_region); |
a7813a04 XL |
1215 | |
1216 | loop { | |
1217 | debug!("link_region(borrow_region={:?}, borrow_kind={:?}, borrow_cmt={:?})", | |
1218 | borrow_region, | |
1219 | borrow_kind, | |
1220 | borrow_cmt); | |
1221 | match borrow_cmt.cat.clone() { | |
1222 | Categorization::Deref(ref_cmt, _, | |
1223 | mc::Implicit(ref_kind, ref_region)) | | |
1224 | Categorization::Deref(ref_cmt, _, | |
1225 | mc::BorrowedPtr(ref_kind, ref_region)) => { | |
1226 | match self.link_reborrowed_region(span, | |
1227 | borrow_region, borrow_kind, | |
1228 | ref_cmt, ref_region, ref_kind, | |
1229 | borrow_cmt.note) { | |
1230 | Some((c, k)) => { | |
1231 | borrow_cmt = c; | |
1232 | borrow_kind = k; | |
1233 | } | |
1234 | None => { | |
1235 | return; | |
1236 | } | |
1237 | } | |
1238 | } | |
1a4d82fc | 1239 | |
a7813a04 XL |
1240 | Categorization::Downcast(cmt_base, _) | |
1241 | Categorization::Deref(cmt_base, _, mc::Unique) | | |
1242 | Categorization::Interior(cmt_base, _) => { | |
1243 | // Borrowing interior or owned data requires the base | |
1244 | // to be valid and borrowable in the same fashion. | |
1245 | borrow_cmt = cmt_base; | |
1246 | borrow_kind = borrow_kind; | |
1247 | } | |
e9174d1e | 1248 | |
9e0c209e | 1249 | Categorization::Deref(.., mc::UnsafePtr(..)) | |
a7813a04 XL |
1250 | Categorization::StaticItem | |
1251 | Categorization::Upvar(..) | | |
1252 | Categorization::Local(..) | | |
1253 | Categorization::Rvalue(..) => { | |
1254 | // These are all "base cases" with independent lifetimes | |
1255 | // that are not subject to inference | |
1256 | return; | |
1257 | } | |
1258 | } | |
1259 | } | |
1260 | } | |
1261 | ||
1262 | /// This is the most complicated case: the path being borrowed is | |
1263 | /// itself the referent of a borrowed pointer. Let me give an | |
1264 | /// example fragment of code to make clear(er) the situation: | |
1265 | /// | |
1266 | /// let r: &'a mut T = ...; // the original reference "r" has lifetime 'a | |
1267 | /// ... | |
1268 | /// &'z *r // the reborrow has lifetime 'z | |
1269 | /// | |
1270 | /// Now, in this case, our primary job is to add the inference | |
1271 | /// constraint that `'z <= 'a`. Given this setup, let's clarify the | |
1272 | /// parameters in (roughly) terms of the example: | |
1273 | /// | |
1274 | /// A borrow of: `& 'z bk * r` where `r` has type `& 'a bk T` | |
1275 | /// borrow_region ^~ ref_region ^~ | |
1276 | /// borrow_kind ^~ ref_kind ^~ | |
1277 | /// ref_cmt ^ | |
1278 | /// | |
1279 | /// Here `bk` stands for some borrow-kind (e.g., `mut`, `uniq`, etc). | |
1280 | /// | |
1281 | /// Unfortunately, there are some complications beyond the simple | |
1282 | /// scenario I just painted: | |
1283 | /// | |
1284 | /// 1. The reference `r` might in fact be a "by-ref" upvar. In that | |
1285 | /// case, we have two jobs. First, we are inferring whether this reference | |
1286 | /// should be an `&T`, `&mut T`, or `&uniq T` reference, and we must | |
1287 | /// adjust that based on this borrow (e.g., if this is an `&mut` borrow, | |
1288 | /// then `r` must be an `&mut` reference). Second, whenever we link | |
1289 | /// two regions (here, `'z <= 'a`), we supply a *cause*, and in this | |
1290 | /// case we adjust the cause to indicate that the reference being | |
1291 | /// "reborrowed" is itself an upvar. This provides a nicer error message | |
1292 | /// should something go wrong. | |
1293 | /// | |
1294 | /// 2. There may in fact be more levels of reborrowing. In the | |
1295 | /// example, I said the borrow was like `&'z *r`, but it might | |
1296 | /// in fact be a borrow like `&'z **q` where `q` has type `&'a | |
1297 | /// &'b mut T`. In that case, we want to ensure that `'z <= 'a` | |
1298 | /// and `'z <= 'b`. This is explained more below. | |
1299 | /// | |
1300 | /// The return value of this function indicates whether we need to | |
1301 | /// recurse and process `ref_cmt` (see case 2 above). | |
1302 | fn link_reborrowed_region(&self, | |
1303 | span: Span, | |
9e0c209e | 1304 | borrow_region: &'tcx ty::Region, |
a7813a04 XL |
1305 | borrow_kind: ty::BorrowKind, |
1306 | ref_cmt: mc::cmt<'tcx>, | |
9e0c209e | 1307 | ref_region: &'tcx ty::Region, |
a7813a04 XL |
1308 | mut ref_kind: ty::BorrowKind, |
1309 | note: mc::Note) | |
1310 | -> Option<(mc::cmt<'tcx>, ty::BorrowKind)> | |
1311 | { | |
1312 | // Possible upvar ID we may need later to create an entry in the | |
1313 | // maybe link map. | |
1314 | ||
1315 | // Detect by-ref upvar `x`: | |
1316 | let cause = match note { | |
1317 | mc::NoteUpvarRef(ref upvar_id) => { | |
1318 | let upvar_capture_map = &self.tables.borrow_mut().upvar_capture_map; | |
1319 | match upvar_capture_map.get(upvar_id) { | |
1320 | Some(&ty::UpvarCapture::ByRef(ref upvar_borrow)) => { | |
1321 | // The mutability of the upvar may have been modified | |
1322 | // by the above adjustment, so update our local variable. | |
1323 | ref_kind = upvar_borrow.kind; | |
1324 | ||
1325 | infer::ReborrowUpvar(span, *upvar_id) | |
1a4d82fc | 1326 | } |
a7813a04 XL |
1327 | _ => { |
1328 | span_bug!( span, "Illegal upvar id: {:?}", upvar_id); | |
1a4d82fc JJ |
1329 | } |
1330 | } | |
1331 | } | |
a7813a04 XL |
1332 | mc::NoteClosureEnv(ref upvar_id) => { |
1333 | // We don't have any mutability changes to propagate, but | |
1334 | // we do want to note that an upvar reborrow caused this | |
1335 | // link | |
1336 | infer::ReborrowUpvar(span, *upvar_id) | |
1337 | } | |
1338 | _ => { | |
1339 | infer::Reborrow(span) | |
1340 | } | |
1341 | }; | |
1a4d82fc | 1342 | |
a7813a04 XL |
1343 | debug!("link_reborrowed_region: {:?} <= {:?}", |
1344 | borrow_region, | |
1345 | ref_region); | |
9e0c209e | 1346 | self.sub_regions(cause, borrow_region, ref_region); |
a7813a04 XL |
1347 | |
1348 | // If we end up needing to recurse and establish a region link | |
1349 | // with `ref_cmt`, calculate what borrow kind we will end up | |
1350 | // needing. This will be used below. | |
1351 | // | |
1352 | // One interesting twist is that we can weaken the borrow kind | |
1353 | // when we recurse: to reborrow an `&mut` referent as mutable, | |
1354 | // borrowck requires a unique path to the `&mut` reference but not | |
1355 | // necessarily a *mutable* path. | |
1356 | let new_borrow_kind = match borrow_kind { | |
1357 | ty::ImmBorrow => | |
1358 | ty::ImmBorrow, | |
1359 | ty::MutBorrow | ty::UniqueImmBorrow => | |
1360 | ty::UniqueImmBorrow | |
1361 | }; | |
1362 | ||
1363 | // Decide whether we need to recurse and link any regions within | |
1364 | // the `ref_cmt`. This is concerned for the case where the value | |
1365 | // being reborrowed is in fact a borrowed pointer found within | |
1366 | // another borrowed pointer. For example: | |
1367 | // | |
1368 | // let p: &'b &'a mut T = ...; | |
1369 | // ... | |
1370 | // &'z **p | |
1371 | // | |
1372 | // What makes this case particularly tricky is that, if the data | |
1373 | // being borrowed is a `&mut` or `&uniq` borrow, borrowck requires | |
1374 | // not only that `'z <= 'a`, (as before) but also `'z <= 'b` | |
1375 | // (otherwise the user might mutate through the `&mut T` reference | |
1376 | // after `'b` expires and invalidate the borrow we are looking at | |
1377 | // now). | |
1378 | // | |
1379 | // So let's re-examine our parameters in light of this more | |
1380 | // complicated (possible) scenario: | |
1381 | // | |
1382 | // A borrow of: `& 'z bk * * p` where `p` has type `&'b bk & 'a bk T` | |
1383 | // borrow_region ^~ ref_region ^~ | |
1384 | // borrow_kind ^~ ref_kind ^~ | |
1385 | // ref_cmt ^~~ | |
1386 | // | |
1387 | // (Note that since we have not examined `ref_cmt.cat`, we don't | |
1388 | // know whether this scenario has occurred; but I wanted to show | |
1389 | // how all the types get adjusted.) | |
1390 | match ref_kind { | |
1391 | ty::ImmBorrow => { | |
1392 | // The reference being reborrowed is a sharable ref of | |
1393 | // type `&'a T`. In this case, it doesn't matter where we | |
1394 | // *found* the `&T` pointer, the memory it references will | |
1395 | // be valid and immutable for `'a`. So we can stop here. | |
1396 | // | |
1397 | // (Note that the `borrow_kind` must also be ImmBorrow or | |
1398 | // else the user is borrowed imm memory as mut memory, | |
1399 | // which means they'll get an error downstream in borrowck | |
1400 | // anyhow.) | |
1401 | return None; | |
1a4d82fc JJ |
1402 | } |
1403 | ||
a7813a04 XL |
1404 | ty::MutBorrow | ty::UniqueImmBorrow => { |
1405 | // The reference being reborrowed is either an `&mut T` or | |
1406 | // `&uniq T`. This is the case where recursion is needed. | |
1407 | return Some((ref_cmt, new_borrow_kind)); | |
1a4d82fc JJ |
1408 | } |
1409 | } | |
1410 | } | |
1a4d82fc | 1411 | |
a7813a04 XL |
1412 | /// Checks that the values provided for type/region arguments in a given |
1413 | /// expression are well-formed and in-scope. | |
1414 | fn substs_wf_in_scope(&mut self, | |
1415 | origin: infer::ParameterOrigin, | |
1416 | substs: &Substs<'tcx>, | |
1417 | expr_span: Span, | |
9e0c209e | 1418 | expr_region: &'tcx ty::Region) { |
a7813a04 XL |
1419 | debug!("substs_wf_in_scope(substs={:?}, \ |
1420 | expr_region={:?}, \ | |
1421 | origin={:?}, \ | |
1422 | expr_span={:?})", | |
1423 | substs, expr_region, origin, expr_span); | |
1424 | ||
1425 | let origin = infer::ParameterInScope(origin, expr_span); | |
1426 | ||
9e0c209e | 1427 | for region in substs.regions() { |
a7813a04 | 1428 | self.sub_regions(origin.clone(), expr_region, region); |
1a4d82fc JJ |
1429 | } |
1430 | ||
9e0c209e | 1431 | for ty in substs.types() { |
a7813a04 XL |
1432 | let ty = self.resolve_type(ty); |
1433 | self.type_must_outlive(origin.clone(), ty, expr_region); | |
1a4d82fc JJ |
1434 | } |
1435 | } | |
1a4d82fc | 1436 | |
a7813a04 XL |
1437 | /// Ensures that type is well-formed in `region`, which implies (among |
1438 | /// other things) that all borrowed data reachable via `ty` outlives | |
1439 | /// `region`. | |
1440 | pub fn type_must_outlive(&self, | |
1441 | origin: infer::SubregionOrigin<'tcx>, | |
1442 | ty: Ty<'tcx>, | |
9e0c209e | 1443 | region: &'tcx ty::Region) |
a7813a04 XL |
1444 | { |
1445 | let ty = self.resolve_type(ty); | |
e9174d1e | 1446 | |
a7813a04 XL |
1447 | debug!("type_must_outlive(ty={:?}, region={:?}, origin={:?})", |
1448 | ty, | |
1449 | region, | |
1450 | origin); | |
e9174d1e | 1451 | |
a7813a04 | 1452 | assert!(!ty.has_escaping_regions()); |
e9174d1e | 1453 | |
c30ab7b3 | 1454 | let components = self.tcx.outlives_components(ty); |
a7813a04 XL |
1455 | self.components_must_outlive(origin, components, region); |
1456 | } | |
1457 | ||
1458 | fn components_must_outlive(&self, | |
1459 | origin: infer::SubregionOrigin<'tcx>, | |
1460 | components: Vec<ty::outlives::Component<'tcx>>, | |
9e0c209e | 1461 | region: &'tcx ty::Region) |
a7813a04 XL |
1462 | { |
1463 | for component in components { | |
1464 | let origin = origin.clone(); | |
1465 | match component { | |
1466 | ty::outlives::Component::Region(region1) => { | |
1467 | self.sub_regions(origin, region, region1); | |
1468 | } | |
1469 | ty::outlives::Component::Param(param_ty) => { | |
1470 | self.param_ty_must_outlive(origin, region, param_ty); | |
1471 | } | |
1472 | ty::outlives::Component::Projection(projection_ty) => { | |
1473 | self.projection_must_outlive(origin, region, projection_ty); | |
1474 | } | |
1475 | ty::outlives::Component::EscapingProjection(subcomponents) => { | |
1476 | self.components_must_outlive(origin, subcomponents, region); | |
1477 | } | |
1478 | ty::outlives::Component::UnresolvedInferenceVariable(v) => { | |
1479 | // ignore this, we presume it will yield an error | |
1480 | // later, since if a type variable is not resolved by | |
1481 | // this point it never will be | |
1482 | self.tcx.sess.delay_span_bug( | |
1483 | origin.span(), | |
1484 | &format!("unresolved inference variable in outlives: {:?}", v)); | |
1485 | } | |
1a4d82fc JJ |
1486 | } |
1487 | } | |
1488 | } | |
1a4d82fc | 1489 | |
a7813a04 XL |
1490 | fn param_ty_must_outlive(&self, |
1491 | origin: infer::SubregionOrigin<'tcx>, | |
9e0c209e | 1492 | region: &'tcx ty::Region, |
a7813a04 XL |
1493 | param_ty: ty::ParamTy) { |
1494 | debug!("param_ty_must_outlive(region={:?}, param_ty={:?}, origin={:?})", | |
1495 | region, param_ty, origin); | |
1a4d82fc | 1496 | |
a7813a04 XL |
1497 | let verify_bound = self.param_bound(param_ty); |
1498 | let generic = GenericKind::Param(param_ty); | |
1499 | self.verify_generic_bound(origin, generic, region, verify_bound); | |
e9174d1e | 1500 | } |
85aaf69f | 1501 | |
a7813a04 XL |
1502 | fn projection_must_outlive(&self, |
1503 | origin: infer::SubregionOrigin<'tcx>, | |
9e0c209e | 1504 | region: &'tcx ty::Region, |
a7813a04 XL |
1505 | projection_ty: ty::ProjectionTy<'tcx>) |
1506 | { | |
1507 | debug!("projection_must_outlive(region={:?}, projection_ty={:?}, origin={:?})", | |
1508 | region, projection_ty, origin); | |
1509 | ||
1510 | // This case is thorny for inference. The fundamental problem is | |
1511 | // that there are many cases where we have choice, and inference | |
1512 | // doesn't like choice (the current region inference in | |
1513 | // particular). :) First off, we have to choose between using the | |
1514 | // OutlivesProjectionEnv, OutlivesProjectionTraitDef, and | |
1515 | // OutlivesProjectionComponent rules, any one of which is | |
1516 | // sufficient. If there are no inference variables involved, it's | |
1517 | // not hard to pick the right rule, but if there are, we're in a | |
1518 | // bit of a catch 22: if we picked which rule we were going to | |
1519 | // use, we could add constraints to the region inference graph | |
1520 | // that make it apply, but if we don't add those constraints, the | |
1521 | // rule might not apply (but another rule might). For now, we err | |
1522 | // on the side of adding too few edges into the graph. | |
1523 | ||
1524 | // Compute the bounds we can derive from the environment or trait | |
1525 | // definition. We know that the projection outlives all the | |
1526 | // regions in this list. | |
1527 | let env_bounds = self.projection_declared_bounds(origin.span(), projection_ty); | |
1528 | ||
1529 | debug!("projection_must_outlive: env_bounds={:?}", | |
1530 | env_bounds); | |
1531 | ||
1532 | // If we know that the projection outlives 'static, then we're | |
1533 | // done here. | |
9e0c209e | 1534 | if env_bounds.contains(&&ty::ReStatic) { |
a7813a04 XL |
1535 | debug!("projection_must_outlive: 'static as declared bound"); |
1536 | return; | |
e9174d1e SL |
1537 | } |
1538 | ||
a7813a04 XL |
1539 | // If declared bounds list is empty, the only applicable rule is |
1540 | // OutlivesProjectionComponent. If there are inference variables, | |
1541 | // then, we can break down the outlives into more primitive | |
1542 | // components without adding unnecessary edges. | |
1543 | // | |
1544 | // If there are *no* inference variables, however, we COULD do | |
1545 | // this, but we choose not to, because the error messages are less | |
1546 | // good. For example, a requirement like `T::Item: 'r` would be | |
1547 | // translated to a requirement that `T: 'r`; when this is reported | |
1548 | // to the user, it will thus say "T: 'r must hold so that T::Item: | |
1549 | // 'r holds". But that makes it sound like the only way to fix | |
1550 | // the problem is to add `T: 'r`, which isn't true. So, if there are no | |
1551 | // inference variables, we use a verify constraint instead of adding | |
1552 | // edges, which winds up enforcing the same condition. | |
9e0c209e | 1553 | let needs_infer = projection_ty.trait_ref.needs_infer(); |
a7813a04 XL |
1554 | if env_bounds.is_empty() && needs_infer { |
1555 | debug!("projection_must_outlive: no declared bounds"); | |
e9174d1e | 1556 | |
9e0c209e | 1557 | for component_ty in projection_ty.trait_ref.substs.types() { |
a7813a04 XL |
1558 | self.type_must_outlive(origin.clone(), component_ty, region); |
1559 | } | |
1560 | ||
9e0c209e | 1561 | for r in projection_ty.trait_ref.substs.regions() { |
a7813a04 XL |
1562 | self.sub_regions(origin.clone(), region, r); |
1563 | } | |
e9174d1e | 1564 | |
e9174d1e | 1565 | return; |
85aaf69f | 1566 | } |
1a4d82fc | 1567 | |
a7813a04 XL |
1568 | // If we find that there is a unique declared bound `'b`, and this bound |
1569 | // appears in the trait reference, then the best action is to require that `'b:'r`, | |
1570 | // so do that. This is best no matter what rule we use: | |
1571 | // | |
1572 | // - OutlivesProjectionEnv or OutlivesProjectionTraitDef: these would translate to | |
1573 | // the requirement that `'b:'r` | |
1574 | // - OutlivesProjectionComponent: this would require `'b:'r` in addition to | |
1575 | // other conditions | |
1576 | if !env_bounds.is_empty() && env_bounds[1..].iter().all(|b| *b == env_bounds[0]) { | |
1577 | let unique_bound = env_bounds[0]; | |
1578 | debug!("projection_must_outlive: unique declared bound = {:?}", unique_bound); | |
9e0c209e | 1579 | if projection_ty.trait_ref.substs.regions().any(|r| env_bounds.contains(&r)) { |
a7813a04 XL |
1580 | debug!("projection_must_outlive: unique declared bound appears in trait ref"); |
1581 | self.sub_regions(origin.clone(), region, unique_bound); | |
1582 | return; | |
1583 | } | |
e9174d1e | 1584 | } |
a7813a04 XL |
1585 | |
1586 | // Fallback to verifying after the fact that there exists a | |
1587 | // declared bound, or that all the components appearing in the | |
1588 | // projection outlive; in some cases, this may add insufficient | |
1589 | // edges into the inference graph, leading to inference failures | |
1590 | // even though a satisfactory solution exists. | |
1591 | let verify_bound = self.projection_bound(origin.span(), env_bounds, projection_ty); | |
1592 | let generic = GenericKind::Projection(projection_ty); | |
1593 | self.verify_generic_bound(origin, generic.clone(), region, verify_bound); | |
1594 | } | |
1595 | ||
9e0c209e | 1596 | fn type_bound(&self, span: Span, ty: Ty<'tcx>) -> VerifyBound<'tcx> { |
a7813a04 XL |
1597 | match ty.sty { |
1598 | ty::TyParam(p) => { | |
1599 | self.param_bound(p) | |
1600 | } | |
1601 | ty::TyProjection(data) => { | |
1602 | let declared_bounds = self.projection_declared_bounds(span, data); | |
1603 | self.projection_bound(span, declared_bounds, data) | |
1604 | } | |
1605 | _ => { | |
1606 | self.recursive_type_bound(span, ty) | |
1607 | } | |
e9174d1e SL |
1608 | } |
1609 | } | |
e9174d1e | 1610 | |
9e0c209e | 1611 | fn param_bound(&self, param_ty: ty::ParamTy) -> VerifyBound<'tcx> { |
a7813a04 | 1612 | let param_env = &self.parameter_environment; |
e9174d1e | 1613 | |
a7813a04 XL |
1614 | debug!("param_bound(param_ty={:?})", |
1615 | param_ty); | |
e9174d1e | 1616 | |
a7813a04 | 1617 | let mut param_bounds = self.declared_generic_bounds_from_env(GenericKind::Param(param_ty)); |
e9174d1e | 1618 | |
a7813a04 XL |
1619 | // Add in the default bound of fn body that applies to all in |
1620 | // scope type parameters: | |
1621 | param_bounds.push(param_env.implicit_region_bound); | |
1a4d82fc | 1622 | |
a7813a04 XL |
1623 | VerifyBound::AnyRegion(param_bounds) |
1624 | } | |
e9174d1e | 1625 | |
a7813a04 XL |
1626 | fn projection_declared_bounds(&self, |
1627 | span: Span, | |
1628 | projection_ty: ty::ProjectionTy<'tcx>) | |
9e0c209e | 1629 | -> Vec<&'tcx ty::Region> |
a7813a04 XL |
1630 | { |
1631 | // First assemble bounds from where clauses and traits. | |
e9174d1e | 1632 | |
a7813a04 XL |
1633 | let mut declared_bounds = |
1634 | self.declared_generic_bounds_from_env(GenericKind::Projection(projection_ty)); | |
e9174d1e | 1635 | |
a7813a04 XL |
1636 | declared_bounds.extend_from_slice( |
1637 | &self.declared_projection_bounds_from_trait(span, projection_ty)); | |
e9174d1e | 1638 | |
a7813a04 XL |
1639 | declared_bounds |
1640 | } | |
e9174d1e | 1641 | |
a7813a04 XL |
1642 | fn projection_bound(&self, |
1643 | span: Span, | |
9e0c209e | 1644 | declared_bounds: Vec<&'tcx ty::Region>, |
a7813a04 | 1645 | projection_ty: ty::ProjectionTy<'tcx>) |
9e0c209e | 1646 | -> VerifyBound<'tcx> { |
a7813a04 XL |
1647 | debug!("projection_bound(declared_bounds={:?}, projection_ty={:?})", |
1648 | declared_bounds, projection_ty); | |
e9174d1e | 1649 | |
a7813a04 | 1650 | // see the extensive comment in projection_must_outlive |
e9174d1e | 1651 | |
a7813a04 XL |
1652 | let ty = self.tcx.mk_projection(projection_ty.trait_ref, projection_ty.item_name); |
1653 | let recursive_bound = self.recursive_type_bound(span, ty); | |
e9174d1e | 1654 | |
a7813a04 XL |
1655 | VerifyBound::AnyRegion(declared_bounds).or(recursive_bound) |
1656 | } | |
e9174d1e | 1657 | |
9e0c209e | 1658 | fn recursive_type_bound(&self, span: Span, ty: Ty<'tcx>) -> VerifyBound<'tcx> { |
a7813a04 | 1659 | let mut bounds = vec![]; |
e9174d1e | 1660 | |
a7813a04 XL |
1661 | for subty in ty.walk_shallow() { |
1662 | bounds.push(self.type_bound(span, subty)); | |
1663 | } | |
e9174d1e | 1664 | |
a7813a04 XL |
1665 | let mut regions = ty.regions(); |
1666 | regions.retain(|r| !r.is_bound()); // ignore late-bound regions | |
1667 | bounds.push(VerifyBound::AllRegions(regions)); | |
e9174d1e | 1668 | |
a7813a04 XL |
1669 | // remove bounds that must hold, since they are not interesting |
1670 | bounds.retain(|b| !b.must_hold()); | |
e9174d1e | 1671 | |
a7813a04 XL |
1672 | if bounds.len() == 1 { |
1673 | bounds.pop().unwrap() | |
1674 | } else { | |
1675 | VerifyBound::AllBounds(bounds) | |
1676 | } | |
e9174d1e | 1677 | } |
e9174d1e | 1678 | |
a7813a04 | 1679 | fn declared_generic_bounds_from_env(&self, generic: GenericKind<'tcx>) |
9e0c209e | 1680 | -> Vec<&'tcx ty::Region> |
a7813a04 XL |
1681 | { |
1682 | let param_env = &self.parameter_environment; | |
1683 | ||
1684 | // To start, collect bounds from user: | |
1685 | let mut param_bounds = self.tcx.required_region_bounds(generic.to_ty(self.tcx), | |
1686 | param_env.caller_bounds.clone()); | |
1687 | ||
1688 | // Next, collect regions we scraped from the well-formedness | |
1689 | // constraints in the fn signature. To do that, we walk the list | |
1690 | // of known relations from the fn ctxt. | |
1691 | // | |
1692 | // This is crucial because otherwise code like this fails: | |
1693 | // | |
1694 | // fn foo<'a, A>(x: &'a A) { x.bar() } | |
1695 | // | |
1696 | // The problem is that the type of `x` is `&'a A`. To be | |
1697 | // well-formed, then, A must be lower-generic by `'a`, but we | |
1698 | // don't know that this holds from first principles. | |
1699 | for &(r, p) in &self.region_bound_pairs { | |
1700 | debug!("generic={:?} p={:?}", | |
1701 | generic, | |
1702 | p); | |
1703 | if generic == p { | |
1704 | param_bounds.push(r); | |
1705 | } | |
1a4d82fc | 1706 | } |
1a4d82fc | 1707 | |
a7813a04 XL |
1708 | param_bounds |
1709 | } | |
85aaf69f | 1710 | |
a7813a04 XL |
1711 | fn declared_projection_bounds_from_trait(&self, |
1712 | span: Span, | |
1713 | projection_ty: ty::ProjectionTy<'tcx>) | |
9e0c209e | 1714 | -> Vec<&'tcx ty::Region> |
a7813a04 XL |
1715 | { |
1716 | debug!("projection_bounds(projection_ty={:?})", | |
1717 | projection_ty); | |
85aaf69f | 1718 | |
a7813a04 XL |
1719 | let ty = self.tcx.mk_projection(projection_ty.trait_ref.clone(), |
1720 | projection_ty.item_name); | |
85aaf69f | 1721 | |
a7813a04 XL |
1722 | // Say we have a projection `<T as SomeTrait<'a>>::SomeType`. We are interested |
1723 | // in looking for a trait definition like: | |
1724 | // | |
1725 | // ``` | |
1726 | // trait SomeTrait<'a> { | |
1727 | // type SomeType : 'a; | |
1728 | // } | |
1729 | // ``` | |
1730 | // | |
1731 | // we can thus deduce that `<T as SomeTrait<'a>>::SomeType : 'a`. | |
1732 | let trait_predicates = self.tcx.lookup_predicates(projection_ty.trait_ref.def_id); | |
9e0c209e | 1733 | assert_eq!(trait_predicates.parent, None); |
a7813a04 XL |
1734 | let predicates = trait_predicates.predicates.as_slice().to_vec(); |
1735 | traits::elaborate_predicates(self.tcx, predicates) | |
1736 | .filter_map(|predicate| { | |
1737 | // we're only interesting in `T : 'a` style predicates: | |
1738 | let outlives = match predicate { | |
1739 | ty::Predicate::TypeOutlives(data) => data, | |
1740 | _ => { return None; } | |
1741 | }; | |
85aaf69f | 1742 | |
a7813a04 XL |
1743 | debug!("projection_bounds: outlives={:?} (1)", |
1744 | outlives); | |
85aaf69f | 1745 | |
a7813a04 XL |
1746 | // apply the substitutions (and normalize any projected types) |
1747 | let outlives = self.instantiate_type_scheme(span, | |
1748 | projection_ty.trait_ref.substs, | |
1749 | &outlives); | |
85aaf69f | 1750 | |
a7813a04 | 1751 | debug!("projection_bounds: outlives={:?} (2)", |
62682a34 | 1752 | outlives); |
85aaf69f | 1753 | |
a7813a04 XL |
1754 | let region_result = self.commit_if_ok(|_| { |
1755 | let (outlives, _) = | |
1756 | self.replace_late_bound_regions_with_fresh_var( | |
1757 | span, | |
1758 | infer::AssocTypeProjection(projection_ty.item_name), | |
1759 | &outlives); | |
1760 | ||
1761 | debug!("projection_bounds: outlives={:?} (3)", | |
1762 | outlives); | |
1763 | ||
1764 | // check whether this predicate applies to our current projection | |
1765 | match self.eq_types(false, TypeOrigin::Misc(span), ty, outlives.0) { | |
1766 | Ok(InferOk { obligations, .. }) => { | |
1767 | // FIXME(#32730) propagate obligations | |
1768 | assert!(obligations.is_empty()); | |
1769 | Ok(outlives.1) | |
1770 | } | |
1771 | Err(_) => { Err(()) } | |
54a0048b | 1772 | } |
a7813a04 | 1773 | }); |
85aaf69f | 1774 | |
a7813a04 XL |
1775 | debug!("projection_bounds: region_result={:?}", |
1776 | region_result); | |
85aaf69f | 1777 | |
a7813a04 XL |
1778 | region_result.ok() |
1779 | }) | |
1780 | .collect() | |
1781 | } | |
85aaf69f | 1782 | } |