1 //! The region check is a final pass that runs over the AST after we have 2 //! inferred the type constraints but before we have actually finalized 3 //! the types. Its purpose is to embed a variety of region constraints. 4 //! Inserting these constraints as a separate pass is good because (1) it 5 //! localizes the code that has to do with region inference and (2) often 6 //! we cannot know what constraints are needed until the basic types have 7 //! been inferred. 8 //! 9 //! ### Interaction with the borrow checker 10 //! 11 //! In general, the job of the borrowck module (which runs later) is to 12 //! check that all soundness criteria are met, given a particular set of 13 //! regions. The job of *this* module is to anticipate the needs of the 14 //! borrow checker and infer regions that will satisfy its requirements. 15 //! It is generally true that the inference doesn't need to be sound, 16 //! meaning that if there is a bug and we inferred bad regions, the borrow 17 //! checker should catch it. This is not entirely true though; for 18 //! example, the borrow checker doesn't check subtyping, and it doesn't 19 //! check that region pointers are always live when they are used. It 20 //! might be worthwhile to fix this so that borrowck serves as a kind of 21 //! verification step -- that would add confidence in the overall 22 //! correctness of the compiler, at the cost of duplicating some type 23 //! checks and effort. 24 //! 25 //! ### Inferring the duration of borrows, automatic and otherwise 26 //! 27 //! Whenever we introduce a borrowed pointer, for example as the result of 28 //! a borrow expression `let x = &data`, the lifetime of the pointer `x` 29 //! is always specified as a region inference variable. `regionck` has the 30 //! job of adding constraints such that this inference variable is as 31 //! narrow as possible while still accommodating all uses (that is, every 32 //! dereference of the resulting pointer must be within the lifetime). 33 //! 34 //! #### Reborrows 35 //! 36 //! Generally speaking, `regionck` does NOT try to ensure that the data 37 //! `data` will outlive the pointer `x`. That is the job of borrowck. The 38 //! one exception is when "re-borrowing" the contents of another borrowed 39 //! pointer. For example, imagine you have a borrowed pointer `b` with 40 //! lifetime `L1` and you have an expression `&*b`. The result of this 41 //! expression will be another borrowed pointer with lifetime `L2` (which is 42 //! an inference variable). The borrow checker is going to enforce the 43 //! constraint that `L2 < L1`, because otherwise you are re-borrowing data 44 //! for a lifetime larger than the original loan. However, without the 45 //! routines in this module, the region inferencer would not know of this 46 //! dependency and thus it might infer the lifetime of `L2` to be greater 47 //! than `L1` (issue #3148). 48 //! 49 //! There are a number of troublesome scenarios in the tests 50 //! `region-dependent-*.rs`, but here is one example: 51 //! 52 //! struct Foo { i: i32 } 53 //! struct Bar { foo: Foo } 54 //! fn get_i<'a>(x: &'a Bar) -> &'a i32 { 55 //! let foo = &x.foo; // Lifetime L1 56 //! &foo.i // Lifetime L2 57 //! } 58 //! 59 //! Note that this comes up either with `&` expressions, `ref` 60 //! bindings, and `autorefs`, which are the three ways to introduce 61 //! a borrow. 62 //! 63 //! The key point here is that when you are borrowing a value that 64 //! is "guaranteed" by a borrowed pointer, you must link the 65 //! lifetime of that borrowed pointer (`L1`, here) to the lifetime of 66 //! the borrow itself (`L2`). What do I mean by "guaranteed" by a 67 //! borrowed pointer? I mean any data that is reached by first 68 //! dereferencing a borrowed pointer and then either traversing 69 //! interior offsets or boxes. We say that the guarantor 70 //! of such data is the region of the borrowed pointer that was 71 //! traversed. This is essentially the same as the ownership 72 //! relation, except that a borrowed pointer never owns its 73 //! contents. 74 75 use crate::check::dropck; 76 use crate::check::FnCtxt; 77 use crate::mem_categorization as mc; 78 use crate::middle::region; 79 use crate::outlives::outlives_bounds::InferCtxtExt as _; 80 use rustc_data_structures::stable_set::FxHashSet; 81 use rustc_hir as hir; 82 use rustc_hir::def_id::LocalDefId; 83 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor}; 84 use rustc_hir::PatKind; 85 use rustc_infer::infer::outlives::env::OutlivesEnvironment; 86 use rustc_infer::infer::{self, InferCtxt, RegionObligation, RegionckMode}; 87 use rustc_middle::hir::place::{PlaceBase, PlaceWithHirId}; 88 use rustc_middle::ty::adjustment; 89 use rustc_middle::ty::{self, Ty}; 90 use rustc_span::Span; 91 use std::ops::Deref; 92 93 // a variation on try that just returns unit 94 macro_rules! ignore_err { 95 ($e:expr) => { 96 match $e { 97 Ok(e) => e, 98 Err(_) => { 99 debug!("ignoring mem-categorization error!"); 100 return (); 101 } 102 } 103 }; 104 } 105 106 pub(crate) trait OutlivesEnvironmentExt<'tcx> { add_implied_bounds( &mut self, infcx: &InferCtxt<'a, 'tcx>, fn_sig_tys: FxHashSet<Ty<'tcx>>, body_id: hir::HirId, span: Span, )107 fn add_implied_bounds( 108 &mut self, 109 infcx: &InferCtxt<'a, 'tcx>, 110 fn_sig_tys: FxHashSet<Ty<'tcx>>, 111 body_id: hir::HirId, 112 span: Span, 113 ); 114 } 115 116 impl<'tcx> OutlivesEnvironmentExt<'tcx> for OutlivesEnvironment<'tcx> { 117 /// This method adds "implied bounds" into the outlives environment. 118 /// Implied bounds are outlives relationships that we can deduce 119 /// on the basis that certain types must be well-formed -- these are 120 /// either the types that appear in the function signature or else 121 /// the input types to an impl. For example, if you have a function 122 /// like 123 /// 124 /// ``` 125 /// fn foo<'a, 'b, T>(x: &'a &'b [T]) { } 126 /// ``` 127 /// 128 /// we can assume in the caller's body that `'b: 'a` and that `T: 129 /// 'b` (and hence, transitively, that `T: 'a`). This method would 130 /// add those assumptions into the outlives-environment. 131 /// 132 /// Tests: `src/test/ui/regions/regions-free-region-ordering-*.rs` add_implied_bounds( &mut self, infcx: &InferCtxt<'a, 'tcx>, fn_sig_tys: FxHashSet<Ty<'tcx>>, body_id: hir::HirId, span: Span, )133 fn add_implied_bounds( 134 &mut self, 135 infcx: &InferCtxt<'a, 'tcx>, 136 fn_sig_tys: FxHashSet<Ty<'tcx>>, 137 body_id: hir::HirId, 138 span: Span, 139 ) { 140 debug!("add_implied_bounds()"); 141 142 for ty in fn_sig_tys { 143 let ty = infcx.resolve_vars_if_possible(ty); 144 debug!("add_implied_bounds: ty = {}", ty); 145 let implied_bounds = infcx.implied_outlives_bounds(self.param_env, body_id, ty, span); 146 self.add_outlives_bounds(Some(infcx), implied_bounds) 147 } 148 } 149 } 150 151 /////////////////////////////////////////////////////////////////////////// 152 // PUBLIC ENTRY POINTS 153 154 impl<'a, 'tcx> FnCtxt<'a, 'tcx> { regionck_expr(&self, body: &'tcx hir::Body<'tcx>)155 pub fn regionck_expr(&self, body: &'tcx hir::Body<'tcx>) { 156 let subject = self.tcx.hir().body_owner_def_id(body.id()); 157 let id = body.value.hir_id; 158 let mut rcx = RegionCtxt::new(self, id, Subject(subject), self.param_env); 159 160 // There are no add'l implied bounds when checking a 161 // standalone expr (e.g., the `E` in a type like `[u32; E]`). 162 rcx.outlives_environment.save_implied_bounds(id); 163 164 if !self.errors_reported_since_creation() { 165 // regionck assumes typeck succeeded 166 rcx.visit_body(body); 167 rcx.visit_region_obligations(id); 168 } 169 rcx.resolve_regions_and_report_errors(RegionckMode::for_item_body(self.tcx)); 170 } 171 172 /// Region checking during the WF phase for items. `wf_tys` are the 173 /// types from which we should derive implied bounds, if any. regionck_item(&self, item_id: hir::HirId, span: Span, wf_tys: FxHashSet<Ty<'tcx>>)174 pub fn regionck_item(&self, item_id: hir::HirId, span: Span, wf_tys: FxHashSet<Ty<'tcx>>) { 175 debug!("regionck_item(item.id={:?}, wf_tys={:?})", item_id, wf_tys); 176 let subject = self.tcx.hir().local_def_id(item_id); 177 let mut rcx = RegionCtxt::new(self, item_id, Subject(subject), self.param_env); 178 rcx.outlives_environment.add_implied_bounds(self, wf_tys, item_id, span); 179 rcx.outlives_environment.save_implied_bounds(item_id); 180 rcx.visit_region_obligations(item_id); 181 rcx.resolve_regions_and_report_errors(RegionckMode::default()); 182 } 183 184 /// Region check a function body. Not invoked on closures, but 185 /// only on the "root" fn item (in which closures may be 186 /// embedded). Walks the function body and adds various add'l 187 /// constraints that are needed for region inference. This is 188 /// separated both to isolate "pure" region constraints from the 189 /// rest of type check and because sometimes we need type 190 /// inference to have completed before we can determine which 191 /// constraints to add. regionck_fn( &self, fn_id: hir::HirId, body: &'tcx hir::Body<'tcx>, span: Span, wf_tys: FxHashSet<Ty<'tcx>>, )192 pub(crate) fn regionck_fn( 193 &self, 194 fn_id: hir::HirId, 195 body: &'tcx hir::Body<'tcx>, 196 span: Span, 197 wf_tys: FxHashSet<Ty<'tcx>>, 198 ) { 199 debug!("regionck_fn(id={})", fn_id); 200 let subject = self.tcx.hir().body_owner_def_id(body.id()); 201 let hir_id = body.value.hir_id; 202 let mut rcx = RegionCtxt::new(self, hir_id, Subject(subject), self.param_env); 203 // We need to add the implied bounds from the function signature 204 rcx.outlives_environment.add_implied_bounds(self, wf_tys, fn_id, span); 205 rcx.outlives_environment.save_implied_bounds(fn_id); 206 207 if !self.errors_reported_since_creation() { 208 // regionck assumes typeck succeeded 209 rcx.visit_fn_body(fn_id, body, self.tcx.hir().span(fn_id)); 210 } 211 212 rcx.resolve_regions_and_report_errors(RegionckMode::for_item_body(self.tcx)); 213 } 214 } 215 216 /////////////////////////////////////////////////////////////////////////// 217 // INTERNALS 218 219 pub struct RegionCtxt<'a, 'tcx> { 220 pub fcx: &'a FnCtxt<'a, 'tcx>, 221 222 pub region_scope_tree: &'tcx region::ScopeTree, 223 224 outlives_environment: OutlivesEnvironment<'tcx>, 225 226 // id of innermost fn body id 227 body_id: hir::HirId, 228 body_owner: LocalDefId, 229 230 // id of AST node being analyzed (the subject of the analysis). 231 subject_def_id: LocalDefId, 232 } 233 234 impl<'a, 'tcx> Deref for RegionCtxt<'a, 'tcx> { 235 type Target = FnCtxt<'a, 'tcx>; deref(&self) -> &Self::Target236 fn deref(&self) -> &Self::Target { 237 self.fcx 238 } 239 } 240 241 pub struct Subject(LocalDefId); 242 243 impl<'a, 'tcx> RegionCtxt<'a, 'tcx> { new( fcx: &'a FnCtxt<'a, 'tcx>, initial_body_id: hir::HirId, Subject(subject): Subject, param_env: ty::ParamEnv<'tcx>, ) -> RegionCtxt<'a, 'tcx>244 pub fn new( 245 fcx: &'a FnCtxt<'a, 'tcx>, 246 initial_body_id: hir::HirId, 247 Subject(subject): Subject, 248 param_env: ty::ParamEnv<'tcx>, 249 ) -> RegionCtxt<'a, 'tcx> { 250 let region_scope_tree = fcx.tcx.region_scope_tree(subject); 251 let outlives_environment = OutlivesEnvironment::new(param_env); 252 RegionCtxt { 253 fcx, 254 region_scope_tree, 255 body_id: initial_body_id, 256 body_owner: subject, 257 subject_def_id: subject, 258 outlives_environment, 259 } 260 } 261 262 /// Try to resolve the type for the given node, returning `t_err` if an error results. Note that 263 /// we never care about the details of the error, the same error will be detected and reported 264 /// in the writeback phase. 265 /// 266 /// Note one important point: we do not attempt to resolve *region variables* here. This is 267 /// because regionck is essentially adding constraints to those region variables and so may yet 268 /// influence how they are resolved. 269 /// 270 /// Consider this silly example: 271 /// 272 /// ``` 273 /// fn borrow(x: &i32) -> &i32 {x} 274 /// fn foo(x: @i32) -> i32 { // block: B 275 /// let b = borrow(x); // region: <R0> 276 /// *b 277 /// } 278 /// ``` 279 /// 280 /// Here, the region of `b` will be `<R0>`. `<R0>` is constrained to be some subregion of the 281 /// block B and some superregion of the call. If we forced it now, we'd choose the smaller 282 /// region (the call). But that would make the *b illegal. Since we don't resolve, the type 283 /// of b will be `&<R0>.i32` and then `*b` will require that `<R0>` be bigger than the let and 284 /// the `*b` expression, so we will effectively resolve `<R0>` to be the block B. resolve_type(&self, unresolved_ty: Ty<'tcx>) -> Ty<'tcx>285 pub fn resolve_type(&self, unresolved_ty: Ty<'tcx>) -> Ty<'tcx> { 286 self.resolve_vars_if_possible(unresolved_ty) 287 } 288 289 /// Try to resolve the type for the given node. resolve_node_type(&self, id: hir::HirId) -> Ty<'tcx>290 fn resolve_node_type(&self, id: hir::HirId) -> Ty<'tcx> { 291 let t = self.node_ty(id); 292 self.resolve_type(t) 293 } 294 295 /// This is the "main" function when region-checking a function item or a 296 /// closure within a function item. It begins by updating various fields 297 /// (e.g., `outlives_environment`) to be appropriate to the function and 298 /// then adds constraints derived from the function body. 299 /// 300 /// Note that it does **not** restore the state of the fields that 301 /// it updates! This is intentional, since -- for the main 302 /// function -- we wish to be able to read the final 303 /// `outlives_environment` and other fields from the caller. For 304 /// closures, however, we save and restore any "scoped state" 305 /// before we invoke this function. (See `visit_fn` in the 306 /// `intravisit::Visitor` impl below.) visit_fn_body( &mut self, id: hir::HirId, body: &'tcx hir::Body<'tcx>, span: Span, )307 fn visit_fn_body( 308 &mut self, 309 id: hir::HirId, // the id of the fn itself 310 body: &'tcx hir::Body<'tcx>, 311 span: Span, 312 ) { 313 // When we enter a function, we can derive 314 debug!("visit_fn_body(id={:?})", id); 315 316 let body_id = body.id(); 317 self.body_id = body_id.hir_id; 318 self.body_owner = self.tcx.hir().body_owner_def_id(body_id); 319 320 let fn_sig = { 321 match self.typeck_results.borrow().liberated_fn_sigs().get(id) { 322 Some(f) => *f, 323 None => { 324 bug!("No fn-sig entry for id={:?}", id); 325 } 326 } 327 }; 328 329 // Collect the types from which we create inferred bounds. 330 // For the return type, if diverging, substitute `bool` just 331 // because it will have no effect. 332 // 333 // FIXME(#27579) return types should not be implied bounds 334 let fn_sig_tys: FxHashSet<_> = 335 fn_sig.inputs().iter().cloned().chain(Some(fn_sig.output())).collect(); 336 337 self.outlives_environment.add_implied_bounds(self.fcx, fn_sig_tys, body_id.hir_id, span); 338 self.outlives_environment.save_implied_bounds(body_id.hir_id); 339 self.link_fn_params(body.params); 340 self.visit_body(body); 341 self.visit_region_obligations(body_id.hir_id); 342 } 343 visit_inline_const(&mut self, id: hir::HirId, body: &'tcx hir::Body<'tcx>)344 fn visit_inline_const(&mut self, id: hir::HirId, body: &'tcx hir::Body<'tcx>) { 345 debug!("visit_inline_const(id={:?})", id); 346 347 // Save state of current function. We will restore afterwards. 348 let old_body_id = self.body_id; 349 let old_body_owner = self.body_owner; 350 let env_snapshot = self.outlives_environment.push_snapshot_pre_typeck_child(); 351 352 let body_id = body.id(); 353 self.body_id = body_id.hir_id; 354 self.body_owner = self.tcx.hir().body_owner_def_id(body_id); 355 356 self.outlives_environment.save_implied_bounds(body_id.hir_id); 357 358 self.visit_body(body); 359 self.visit_region_obligations(body_id.hir_id); 360 361 // Restore state from previous function. 362 self.outlives_environment.pop_snapshot_post_typeck_child(env_snapshot); 363 self.body_id = old_body_id; 364 self.body_owner = old_body_owner; 365 } 366 visit_region_obligations(&mut self, hir_id: hir::HirId)367 fn visit_region_obligations(&mut self, hir_id: hir::HirId) { 368 debug!("visit_region_obligations: hir_id={:?}", hir_id); 369 370 // region checking can introduce new pending obligations 371 // which, when processed, might generate new region 372 // obligations. So make sure we process those. 373 self.select_all_obligations_or_error(); 374 } 375 resolve_regions_and_report_errors(&self, mode: RegionckMode)376 fn resolve_regions_and_report_errors(&self, mode: RegionckMode) { 377 self.infcx.process_registered_region_obligations( 378 self.outlives_environment.region_bound_pairs_map(), 379 Some(self.tcx.lifetimes.re_root_empty), 380 self.param_env, 381 ); 382 383 self.fcx.resolve_regions_and_report_errors( 384 self.subject_def_id.to_def_id(), 385 &self.outlives_environment, 386 mode, 387 ); 388 } 389 constrain_bindings_in_pat(&mut self, pat: &hir::Pat<'_>)390 fn constrain_bindings_in_pat(&mut self, pat: &hir::Pat<'_>) { 391 debug!("regionck::visit_pat(pat={:?})", pat); 392 pat.each_binding(|_, hir_id, span, _| { 393 let typ = self.resolve_node_type(hir_id); 394 let body_id = self.body_id; 395 dropck::check_drop_obligations(self, typ, span, body_id); 396 }) 397 } 398 } 399 400 impl<'a, 'tcx> Visitor<'tcx> for RegionCtxt<'a, 'tcx> { 401 // (..) FIXME(#3238) should use visit_pat, not visit_arm/visit_local, 402 // However, right now we run into an issue whereby some free 403 // regions are not properly related if they appear within the 404 // types of arguments that must be inferred. This could be 405 // addressed by deferring the construction of the region 406 // hierarchy, and in particular the relationships between free 407 // regions, until regionck, as described in #3238. 408 409 type Map = intravisit::ErasedMap<'tcx>; 410 nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map>411 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { 412 NestedVisitorMap::None 413 } 414 visit_fn( &mut self, fk: intravisit::FnKind<'tcx>, _: &'tcx hir::FnDecl<'tcx>, body_id: hir::BodyId, span: Span, hir_id: hir::HirId, )415 fn visit_fn( 416 &mut self, 417 fk: intravisit::FnKind<'tcx>, 418 _: &'tcx hir::FnDecl<'tcx>, 419 body_id: hir::BodyId, 420 span: Span, 421 hir_id: hir::HirId, 422 ) { 423 assert!( 424 matches!(fk, intravisit::FnKind::Closure), 425 "visit_fn invoked for something other than a closure" 426 ); 427 428 // Save state of current function before invoking 429 // `visit_fn_body`. We will restore afterwards. 430 let old_body_id = self.body_id; 431 let old_body_owner = self.body_owner; 432 let env_snapshot = self.outlives_environment.push_snapshot_pre_typeck_child(); 433 434 let body = self.tcx.hir().body(body_id); 435 self.visit_fn_body(hir_id, body, span); 436 437 // Restore state from previous function. 438 self.outlives_environment.pop_snapshot_post_typeck_child(env_snapshot); 439 self.body_id = old_body_id; 440 self.body_owner = old_body_owner; 441 } 442 443 //visit_pat: visit_pat, // (..) see above 444 visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>)445 fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) { 446 // see above 447 self.constrain_bindings_in_pat(arm.pat); 448 intravisit::walk_arm(self, arm); 449 } 450 visit_local(&mut self, l: &'tcx hir::Local<'tcx>)451 fn visit_local(&mut self, l: &'tcx hir::Local<'tcx>) { 452 // see above 453 self.constrain_bindings_in_pat(l.pat); 454 self.link_local(l); 455 intravisit::walk_local(self, l); 456 } 457 visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>)458 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) { 459 // Check any autoderefs or autorefs that appear. 460 let cmt_result = self.constrain_adjustments(expr); 461 462 // If necessary, constrain destructors in this expression. This will be 463 // the adjusted form if there is an adjustment. 464 match cmt_result { 465 Ok(head_cmt) => { 466 self.check_safety_of_rvalue_destructor_if_necessary(&head_cmt, expr.span); 467 } 468 Err(..) => { 469 self.tcx.sess.delay_span_bug(expr.span, "cat_expr Errd"); 470 } 471 } 472 473 match expr.kind { 474 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, m, ref base) => { 475 self.link_addr_of(expr, m, base); 476 477 intravisit::walk_expr(self, expr); 478 } 479 480 hir::ExprKind::Match(ref discr, arms, _) => { 481 self.link_match(discr, arms); 482 483 intravisit::walk_expr(self, expr); 484 } 485 486 hir::ExprKind::ConstBlock(anon_const) => { 487 let body = self.tcx.hir().body(anon_const.body); 488 self.visit_inline_const(anon_const.hir_id, body); 489 } 490 491 _ => intravisit::walk_expr(self, expr), 492 } 493 } 494 } 495 496 impl<'a, 'tcx> RegionCtxt<'a, 'tcx> { 497 /// Creates a temporary `MemCategorizationContext` and pass it to the closure. with_mc<F, R>(&self, f: F) -> R where F: for<'b> FnOnce(mc::MemCategorizationContext<'b, 'tcx>) -> R,498 fn with_mc<F, R>(&self, f: F) -> R 499 where 500 F: for<'b> FnOnce(mc::MemCategorizationContext<'b, 'tcx>) -> R, 501 { 502 f(mc::MemCategorizationContext::new( 503 &self.infcx, 504 self.outlives_environment.param_env, 505 self.body_owner, 506 &self.typeck_results.borrow(), 507 )) 508 } 509 510 /// Invoked on any adjustments that occur. Checks that if this is a region pointer being 511 /// dereferenced, the lifetime of the pointer includes the deref expr. constrain_adjustments( &mut self, expr: &hir::Expr<'_>, ) -> mc::McResult<PlaceWithHirId<'tcx>>512 fn constrain_adjustments( 513 &mut self, 514 expr: &hir::Expr<'_>, 515 ) -> mc::McResult<PlaceWithHirId<'tcx>> { 516 debug!("constrain_adjustments(expr={:?})", expr); 517 518 let mut place = self.with_mc(|mc| mc.cat_expr_unadjusted(expr))?; 519 520 let typeck_results = self.typeck_results.borrow(); 521 let adjustments = typeck_results.expr_adjustments(expr); 522 if adjustments.is_empty() { 523 return Ok(place); 524 } 525 526 debug!("constrain_adjustments: adjustments={:?}", adjustments); 527 528 // If necessary, constrain destructors in the unadjusted form of this 529 // expression. 530 self.check_safety_of_rvalue_destructor_if_necessary(&place, expr.span); 531 532 for adjustment in adjustments { 533 debug!("constrain_adjustments: adjustment={:?}, place={:?}", adjustment, place); 534 535 if let adjustment::Adjust::Deref(Some(deref)) = adjustment.kind { 536 self.link_region( 537 expr.span, 538 deref.region, 539 ty::BorrowKind::from_mutbl(deref.mutbl), 540 &place, 541 ); 542 } 543 544 if let adjustment::Adjust::Borrow(ref autoref) = adjustment.kind { 545 self.link_autoref(expr, &place, autoref); 546 } 547 548 place = self.with_mc(|mc| mc.cat_expr_adjusted(expr, place, adjustment))?; 549 } 550 551 Ok(place) 552 } 553 check_safety_of_rvalue_destructor_if_necessary( &mut self, place_with_id: &PlaceWithHirId<'tcx>, span: Span, )554 fn check_safety_of_rvalue_destructor_if_necessary( 555 &mut self, 556 place_with_id: &PlaceWithHirId<'tcx>, 557 span: Span, 558 ) { 559 if let PlaceBase::Rvalue = place_with_id.place.base { 560 if place_with_id.place.projections.is_empty() { 561 let typ = self.resolve_type(place_with_id.place.ty()); 562 let body_id = self.body_id; 563 dropck::check_drop_obligations(self, typ, span, body_id); 564 } 565 } 566 } 567 /// Adds constraints to inference such that `T: 'a` holds (or 568 /// reports an error if it cannot). 569 /// 570 /// # Parameters 571 /// 572 /// - `origin`, the reason we need this constraint 573 /// - `ty`, the type `T` 574 /// - `region`, the region `'a` type_must_outlive( &self, origin: infer::SubregionOrigin<'tcx>, ty: Ty<'tcx>, region: ty::Region<'tcx>, )575 pub fn type_must_outlive( 576 &self, 577 origin: infer::SubregionOrigin<'tcx>, 578 ty: Ty<'tcx>, 579 region: ty::Region<'tcx>, 580 ) { 581 self.infcx.register_region_obligation( 582 self.body_id, 583 RegionObligation { sub_region: region, sup_type: ty, origin }, 584 ); 585 } 586 587 /// Computes the guarantor for an expression `&base` and then ensures that the lifetime of the 588 /// resulting pointer is linked to the lifetime of its guarantor (if any). link_addr_of( &mut self, expr: &hir::Expr<'_>, mutability: hir::Mutability, base: &hir::Expr<'_>, )589 fn link_addr_of( 590 &mut self, 591 expr: &hir::Expr<'_>, 592 mutability: hir::Mutability, 593 base: &hir::Expr<'_>, 594 ) { 595 debug!("link_addr_of(expr={:?}, base={:?})", expr, base); 596 597 let cmt = ignore_err!(self.with_mc(|mc| mc.cat_expr(base))); 598 599 debug!("link_addr_of: cmt={:?}", cmt); 600 601 self.link_region_from_node_type(expr.span, expr.hir_id, mutability, &cmt); 602 } 603 604 /// Computes the guarantors for any ref bindings in a `let` and 605 /// then ensures that the lifetime of the resulting pointer is 606 /// linked to the lifetime of the initialization expression. link_local(&self, local: &hir::Local<'_>)607 fn link_local(&self, local: &hir::Local<'_>) { 608 debug!("regionck::for_local()"); 609 let init_expr = match local.init { 610 None => { 611 return; 612 } 613 Some(expr) => &*expr, 614 }; 615 let discr_cmt = ignore_err!(self.with_mc(|mc| mc.cat_expr(init_expr))); 616 self.link_pattern(discr_cmt, local.pat); 617 } 618 619 /// Computes the guarantors for any ref bindings in a match and 620 /// then ensures that the lifetime of the resulting pointer is 621 /// linked to the lifetime of its guarantor (if any). link_match(&self, discr: &hir::Expr<'_>, arms: &[hir::Arm<'_>])622 fn link_match(&self, discr: &hir::Expr<'_>, arms: &[hir::Arm<'_>]) { 623 debug!("regionck::for_match()"); 624 let discr_cmt = ignore_err!(self.with_mc(|mc| mc.cat_expr(discr))); 625 debug!("discr_cmt={:?}", discr_cmt); 626 for arm in arms { 627 self.link_pattern(discr_cmt.clone(), arm.pat); 628 } 629 } 630 631 /// Computes the guarantors for any ref bindings in a match and 632 /// then ensures that the lifetime of the resulting pointer is 633 /// linked to the lifetime of its guarantor (if any). link_fn_params(&self, params: &[hir::Param<'_>])634 fn link_fn_params(&self, params: &[hir::Param<'_>]) { 635 for param in params { 636 let param_ty = self.node_ty(param.hir_id); 637 let param_cmt = 638 self.with_mc(|mc| mc.cat_rvalue(param.hir_id, param.pat.span, param_ty)); 639 debug!("param_ty={:?} param_cmt={:?} param={:?}", param_ty, param_cmt, param); 640 self.link_pattern(param_cmt, param.pat); 641 } 642 } 643 644 /// Link lifetimes of any ref bindings in `root_pat` to the pointers found 645 /// in the discriminant, if needed. link_pattern(&self, discr_cmt: PlaceWithHirId<'tcx>, root_pat: &hir::Pat<'_>)646 fn link_pattern(&self, discr_cmt: PlaceWithHirId<'tcx>, root_pat: &hir::Pat<'_>) { 647 debug!("link_pattern(discr_cmt={:?}, root_pat={:?})", discr_cmt, root_pat); 648 ignore_err!(self.with_mc(|mc| { 649 mc.cat_pattern(discr_cmt, root_pat, |sub_cmt, hir::Pat { kind, span, hir_id, .. }| { 650 // `ref x` pattern 651 if let PatKind::Binding(..) = kind { 652 if let Some(ty::BindByReference(mutbl)) = 653 mc.typeck_results.extract_binding_mode(self.tcx.sess, *hir_id, *span) 654 { 655 self.link_region_from_node_type(*span, *hir_id, mutbl, sub_cmt); 656 } 657 } 658 }) 659 })); 660 } 661 662 /// Link lifetime of borrowed pointer resulting from autoref to lifetimes in the value being 663 /// autoref'd. link_autoref( &self, expr: &hir::Expr<'_>, expr_cmt: &PlaceWithHirId<'tcx>, autoref: &adjustment::AutoBorrow<'tcx>, )664 fn link_autoref( 665 &self, 666 expr: &hir::Expr<'_>, 667 expr_cmt: &PlaceWithHirId<'tcx>, 668 autoref: &adjustment::AutoBorrow<'tcx>, 669 ) { 670 debug!("link_autoref(autoref={:?}, expr_cmt={:?})", autoref, expr_cmt); 671 672 match *autoref { 673 adjustment::AutoBorrow::Ref(r, m) => { 674 self.link_region(expr.span, r, ty::BorrowKind::from_mutbl(m.into()), expr_cmt); 675 } 676 677 adjustment::AutoBorrow::RawPtr(_) => {} 678 } 679 } 680 681 /// Like `link_region()`, except that the region is extracted from the type of `id`, 682 /// which must be some reference (`&T`, `&str`, etc). link_region_from_node_type( &self, span: Span, id: hir::HirId, mutbl: hir::Mutability, cmt_borrowed: &PlaceWithHirId<'tcx>, )683 fn link_region_from_node_type( 684 &self, 685 span: Span, 686 id: hir::HirId, 687 mutbl: hir::Mutability, 688 cmt_borrowed: &PlaceWithHirId<'tcx>, 689 ) { 690 debug!( 691 "link_region_from_node_type(id={:?}, mutbl={:?}, cmt_borrowed={:?})", 692 id, mutbl, cmt_borrowed 693 ); 694 695 let rptr_ty = self.resolve_node_type(id); 696 if let ty::Ref(r, _, _) = rptr_ty.kind() { 697 debug!("rptr_ty={}", rptr_ty); 698 self.link_region(span, r, ty::BorrowKind::from_mutbl(mutbl), cmt_borrowed); 699 } 700 } 701 702 /// Informs the inference engine that `borrow_cmt` is being borrowed with 703 /// kind `borrow_kind` and lifetime `borrow_region`. 704 /// In order to ensure borrowck is satisfied, this may create constraints 705 /// between regions, as explained in `link_reborrowed_region()`. link_region( &self, span: Span, borrow_region: ty::Region<'tcx>, borrow_kind: ty::BorrowKind, borrow_place: &PlaceWithHirId<'tcx>, )706 fn link_region( 707 &self, 708 span: Span, 709 borrow_region: ty::Region<'tcx>, 710 borrow_kind: ty::BorrowKind, 711 borrow_place: &PlaceWithHirId<'tcx>, 712 ) { 713 let origin = infer::DataBorrowed(borrow_place.place.ty(), span); 714 self.type_must_outlive(origin, borrow_place.place.ty(), borrow_region); 715 716 for pointer_ty in borrow_place.place.deref_tys() { 717 debug!( 718 "link_region(borrow_region={:?}, borrow_kind={:?}, pointer_ty={:?})", 719 borrow_region, borrow_kind, borrow_place 720 ); 721 match *pointer_ty.kind() { 722 ty::RawPtr(_) => return, 723 ty::Ref(ref_region, _, ref_mutability) => { 724 if self.link_reborrowed_region(span, borrow_region, ref_region, ref_mutability) 725 { 726 return; 727 } 728 } 729 _ => assert!(pointer_ty.is_box(), "unexpected built-in deref type {}", pointer_ty), 730 } 731 } 732 if let PlaceBase::Upvar(upvar_id) = borrow_place.place.base { 733 self.link_upvar_region(span, borrow_region, upvar_id); 734 } 735 } 736 737 /// This is the most complicated case: the path being borrowed is 738 /// itself the referent of a borrowed pointer. Let me give an 739 /// example fragment of code to make clear(er) the situation: 740 /// 741 /// ```ignore (incomplete Rust code) 742 /// let r: &'a mut T = ...; // the original reference "r" has lifetime 'a 743 /// ... 744 /// &'z *r // the reborrow has lifetime 'z 745 /// ``` 746 /// 747 /// Now, in this case, our primary job is to add the inference 748 /// constraint that `'z <= 'a`. Given this setup, let's clarify the 749 /// parameters in (roughly) terms of the example: 750 /// 751 /// ```plain,ignore (pseudo-Rust) 752 /// A borrow of: `& 'z bk * r` where `r` has type `& 'a bk T` 753 /// borrow_region ^~ ref_region ^~ 754 /// borrow_kind ^~ ref_kind ^~ 755 /// ref_cmt ^ 756 /// ``` 757 /// 758 /// Here `bk` stands for some borrow-kind (e.g., `mut`, `uniq`, etc). 759 /// 760 /// There is a complication beyond the simple scenario I just painted: there 761 /// may in fact be more levels of reborrowing. In the example, I said the 762 /// borrow was like `&'z *r`, but it might in fact be a borrow like 763 /// `&'z **q` where `q` has type `&'a &'b mut T`. In that case, we want to 764 /// ensure that `'z <= 'a` and `'z <= 'b`. 765 /// 766 /// The return value of this function indicates whether we *don't* need to 767 /// the recurse to the next reference up. 768 /// 769 /// This is explained more below. link_reborrowed_region( &self, span: Span, borrow_region: ty::Region<'tcx>, ref_region: ty::Region<'tcx>, ref_mutability: hir::Mutability, ) -> bool770 fn link_reborrowed_region( 771 &self, 772 span: Span, 773 borrow_region: ty::Region<'tcx>, 774 ref_region: ty::Region<'tcx>, 775 ref_mutability: hir::Mutability, 776 ) -> bool { 777 debug!("link_reborrowed_region: {:?} <= {:?}", borrow_region, ref_region); 778 self.sub_regions(infer::Reborrow(span), borrow_region, ref_region); 779 780 // Decide whether we need to recurse and link any regions within 781 // the `ref_cmt`. This is concerned for the case where the value 782 // being reborrowed is in fact a borrowed pointer found within 783 // another borrowed pointer. For example: 784 // 785 // let p: &'b &'a mut T = ...; 786 // ... 787 // &'z **p 788 // 789 // What makes this case particularly tricky is that, if the data 790 // being borrowed is a `&mut` or `&uniq` borrow, borrowck requires 791 // not only that `'z <= 'a`, (as before) but also `'z <= 'b` 792 // (otherwise the user might mutate through the `&mut T` reference 793 // after `'b` expires and invalidate the borrow we are looking at 794 // now). 795 // 796 // So let's re-examine our parameters in light of this more 797 // complicated (possible) scenario: 798 // 799 // A borrow of: `& 'z bk * * p` where `p` has type `&'b bk & 'a bk T` 800 // borrow_region ^~ ref_region ^~ 801 // borrow_kind ^~ ref_kind ^~ 802 // ref_cmt ^~~ 803 // 804 // (Note that since we have not examined `ref_cmt.cat`, we don't 805 // know whether this scenario has occurred; but I wanted to show 806 // how all the types get adjusted.) 807 match ref_mutability { 808 hir::Mutability::Not => { 809 // The reference being reborrowed is a shareable ref of 810 // type `&'a T`. In this case, it doesn't matter where we 811 // *found* the `&T` pointer, the memory it references will 812 // be valid and immutable for `'a`. So we can stop here. 813 true 814 } 815 816 hir::Mutability::Mut => { 817 // The reference being reborrowed is either an `&mut T`. This is 818 // the case where recursion is needed. 819 false 820 } 821 } 822 } 823 824 /// An upvar may be behind up to 2 references: 825 /// 826 /// * One can come from the reference to a "by-reference" upvar. 827 /// * Another one can come from the reference to the closure itself if it's 828 /// a `FnMut` or `Fn` closure. 829 /// 830 /// This function links the lifetimes of those references to the lifetime 831 /// of the borrow that's provided. See [RegionCtxt::link_reborrowed_region] for some 832 /// more explanation of this in the general case. 833 /// 834 /// We also supply a *cause*, and in this case we set the cause to 835 /// indicate that the reference being "reborrowed" is itself an upvar. This 836 /// provides a nicer error message should something go wrong. link_upvar_region( &self, span: Span, borrow_region: ty::Region<'tcx>, upvar_id: ty::UpvarId, )837 fn link_upvar_region( 838 &self, 839 span: Span, 840 borrow_region: ty::Region<'tcx>, 841 upvar_id: ty::UpvarId, 842 ) { 843 debug!("link_upvar_region(borrorw_region={:?}, upvar_id={:?}", borrow_region, upvar_id); 844 // A by-reference upvar can't be borrowed for longer than the 845 // upvar is borrowed from the environment. 846 let closure_local_def_id = upvar_id.closure_expr_id; 847 let mut all_captures_are_imm_borrow = true; 848 for captured_place in self 849 .typeck_results 850 .borrow() 851 .closure_min_captures 852 .get(&closure_local_def_id.to_def_id()) 853 .and_then(|root_var_min_cap| root_var_min_cap.get(&upvar_id.var_path.hir_id)) 854 .into_iter() 855 .flatten() 856 { 857 match captured_place.info.capture_kind { 858 ty::UpvarCapture::ByRef(upvar_borrow) => { 859 self.sub_regions( 860 infer::ReborrowUpvar(span, upvar_id), 861 borrow_region, 862 upvar_borrow.region, 863 ); 864 if let ty::ImmBorrow = upvar_borrow.kind { 865 debug!("link_upvar_region: capture by shared ref"); 866 } else { 867 all_captures_are_imm_borrow = false; 868 } 869 } 870 ty::UpvarCapture::ByValue(_) => { 871 all_captures_are_imm_borrow = false; 872 } 873 } 874 } 875 if all_captures_are_imm_borrow { 876 return; 877 } 878 let fn_hir_id = self.tcx.hir().local_def_id_to_hir_id(closure_local_def_id); 879 let ty = self.resolve_node_type(fn_hir_id); 880 debug!("link_upvar_region: ty={:?}", ty); 881 882 // A closure capture can't be borrowed for longer than the 883 // reference to the closure. 884 if let ty::Closure(_, substs) = ty.kind() { 885 match self.infcx.closure_kind(substs) { 886 Some(ty::ClosureKind::Fn | ty::ClosureKind::FnMut) => { 887 // Region of environment pointer 888 let env_region = self.tcx.mk_region(ty::ReFree(ty::FreeRegion { 889 scope: upvar_id.closure_expr_id.to_def_id(), 890 bound_region: ty::BrEnv, 891 })); 892 self.sub_regions( 893 infer::ReborrowUpvar(span, upvar_id), 894 borrow_region, 895 env_region, 896 ); 897 } 898 Some(ty::ClosureKind::FnOnce) => {} 899 None => { 900 span_bug!(span, "Have not inferred closure kind before regionck"); 901 } 902 } 903 } 904 } 905 } 906