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.
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.
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
19 //! ### Interaction with the borrow checker
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.
35 //! ### Inferring the duration of borrows, automatic and otherwise
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).
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).
59 //! There are a number of troublesome scenarios in the tests
60 //! `region-dependent-*.rs`, but here is one example:
62 //! struct Foo { i: i32 }
63 //! struct Bar { foo: Foo }
64 //! fn get_i<'a>(x: &'a Bar) -> &'a i32 {
65 //! let foo = &x.foo; // Lifetime L1
66 //! &foo.i // Lifetime L2
69 //! Note that this comes up either with `&` expressions, `ref`
70 //! bindings, and `autorefs`, which are the three ways to introduce
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
79 //! interior offsets or boxes. We say that the guarantor
80 //! of such data is the region of the borrowed pointer that was
81 //! traversed. This is essentially the same as the ownership
82 //! relation, except that a borrowed pointer never owns its
87 use middle::free_region::FreeRegionMap;
88 use middle::mem_categorization as mc;
89 use middle::mem_categorization::Categorization;
90 use middle::region::{self, CodeExtent, RegionMaps};
91 use rustc::hir::def_id::DefId;
92 use rustc::ty::subst::Substs;
94 use rustc::ty::{self, Ty, MethodCall, TypeFoldable};
95 use rustc::infer::{self, GenericKind, SubregionOrigin, VerifyBound};
96 use rustc::ty::adjustment;
97 use rustc::ty::wf::ImpliedBound;
103 use syntax_pos::Span;
104 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
105 use rustc::hir::{self, PatKind};
107 // a variation on try that just returns unit
108 macro_rules! ignore_err {
109 ($e:expr) => (match $e { Ok(e) => e, Err(_) => return () })
112 ///////////////////////////////////////////////////////////////////////////
113 // PUBLIC ENTRY POINTS
115 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
116 pub fn regionck_expr(&self, body: &'gcx hir::Body) {
117 let subject = self.tcx.hir.body_owner_def_id(body.id());
118 let id = body.value.id;
119 let mut rcx = RegionCtxt::new(self, RepeatingScope(id), id, Subject(subject));
120 if self.err_count_since_creation() == 0 {
121 // regionck assumes typeck succeeded
122 rcx.visit_body(body);
123 rcx.visit_region_obligations(id);
125 rcx.resolve_regions_and_report_errors();
127 assert!(self.tables.borrow().free_region_map.is_empty());
128 self.tables.borrow_mut().free_region_map = rcx.free_region_map;
131 /// Region checking during the WF phase for items. `wf_tys` are the
132 /// types from which we should derive implied bounds, if any.
133 pub fn regionck_item(&self,
134 item_id: ast::NodeId,
136 wf_tys: &[Ty<'tcx>]) {
137 debug!("regionck_item(item.id={:?}, wf_tys={:?}", item_id, wf_tys);
138 let subject = self.tcx.hir.local_def_id(item_id);
139 let mut rcx = RegionCtxt::new(self, RepeatingScope(item_id), item_id, Subject(subject));
140 rcx.free_region_map.relate_free_regions_from_predicates(
141 &self.parameter_environment.caller_bounds);
142 rcx.relate_free_regions(wf_tys, item_id, span);
143 rcx.visit_region_obligations(item_id);
144 rcx.resolve_regions_and_report_errors();
147 pub fn regionck_fn(&self,
149 body: &'gcx hir::Body) {
150 debug!("regionck_fn(id={})", fn_id);
151 let subject = self.tcx.hir.body_owner_def_id(body.id());
152 let node_id = body.value.id;
153 let mut rcx = RegionCtxt::new(self, RepeatingScope(node_id), node_id, Subject(subject));
155 if self.err_count_since_creation() == 0 {
156 // regionck assumes typeck succeeded
157 rcx.visit_fn_body(fn_id, body, self.tcx.hir.span(fn_id));
160 rcx.free_region_map.relate_free_regions_from_predicates(
161 &self.parameter_environment.caller_bounds);
163 rcx.resolve_regions_and_report_errors();
165 // In this mode, we also copy the free-region-map into the
166 // tables of the enclosing fcx. In the other regionck modes
167 // (e.g., `regionck_item`), we don't have an enclosing tables.
168 assert!(self.tables.borrow().free_region_map.is_empty());
169 self.tables.borrow_mut().free_region_map = rcx.free_region_map;
173 ///////////////////////////////////////////////////////////////////////////
176 pub struct RegionCtxt<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
177 pub fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
179 region_bound_pairs: Vec<(ty::Region<'tcx>, GenericKind<'tcx>)>,
181 pub region_maps: Rc<RegionMaps<'tcx>>,
183 free_region_map: FreeRegionMap<'tcx>,
185 // id of innermost fn body id
186 body_id: ast::NodeId,
188 // call_site scope of innermost fn
189 call_site_scope: Option<CodeExtent<'tcx>>,
191 // id of innermost fn or loop
192 repeating_scope: ast::NodeId,
194 // id of AST node being analyzed (the subject of the analysis).
195 subject_def_id: DefId,
199 impl<'a, 'gcx, 'tcx> Deref for RegionCtxt<'a, 'gcx, 'tcx> {
200 type Target = FnCtxt<'a, 'gcx, 'tcx>;
201 fn deref(&self) -> &Self::Target {
206 pub struct RepeatingScope(ast::NodeId);
207 pub struct Subject(DefId);
209 impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
210 pub fn new(fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
211 RepeatingScope(initial_repeating_scope): RepeatingScope,
212 initial_body_id: ast::NodeId,
213 Subject(subject): Subject) -> RegionCtxt<'a, 'gcx, 'tcx> {
214 let region_maps = fcx.tcx.region_maps(subject);
217 region_maps: region_maps,
218 repeating_scope: initial_repeating_scope,
219 body_id: initial_body_id,
220 call_site_scope: None,
221 subject_def_id: subject,
222 region_bound_pairs: Vec::new(),
223 free_region_map: FreeRegionMap::new(),
227 fn set_call_site_scope(&mut self, call_site_scope: Option<CodeExtent<'tcx>>)
228 -> Option<CodeExtent<'tcx>> {
229 mem::replace(&mut self.call_site_scope, call_site_scope)
232 fn set_body_id(&mut self, body_id: ast::NodeId) -> ast::NodeId {
233 mem::replace(&mut self.body_id, body_id)
236 fn set_repeating_scope(&mut self, scope: ast::NodeId) -> ast::NodeId {
237 mem::replace(&mut self.repeating_scope, scope)
240 /// Try to resolve the type for the given node, returning t_err if an error results. Note that
241 /// we never care about the details of the error, the same error will be detected and reported
242 /// in the writeback phase.
244 /// Note one important point: we do not attempt to resolve *region variables* here. This is
245 /// because regionck is essentially adding constraints to those region variables and so may yet
246 /// influence how they are resolved.
248 /// Consider this silly example:
251 /// fn borrow(x: &i32) -> &i32 {x}
252 /// fn foo(x: @i32) -> i32 { // block: B
253 /// let b = borrow(x); // region: <R0>
258 /// Here, the region of `b` will be `<R0>`. `<R0>` is constrained to be some subregion of the
259 /// block B and some superregion of the call. If we forced it now, we'd choose the smaller
260 /// region (the call). But that would make the *b illegal. Since we don't resolve, the type
261 /// of b will be `&<R0>.i32` and then `*b` will require that `<R0>` be bigger than the let and
262 /// the `*b` expression, so we will effectively resolve `<R0>` to be the block B.
263 pub fn resolve_type(&self, unresolved_ty: Ty<'tcx>) -> Ty<'tcx> {
264 self.resolve_type_vars_if_possible(&unresolved_ty)
267 /// Try to resolve the type for the given node.
268 fn resolve_node_type(&self, id: ast::NodeId) -> Ty<'tcx> {
269 let t = self.node_ty(id);
273 /// Try to resolve the type for the given node.
274 pub fn resolve_expr_type_adjusted(&mut self, expr: &hir::Expr) -> Ty<'tcx> {
275 let ty = self.tables.borrow().expr_ty_adjusted(expr);
276 self.resolve_type(ty)
279 fn visit_fn_body(&mut self,
280 id: ast::NodeId, // the id of the fn itself
281 body: &'gcx hir::Body,
284 // When we enter a function, we can derive
285 debug!("visit_fn_body(id={})", id);
287 let body_id = body.id();
289 let call_site = self.tcx.intern_code_extent(
290 region::CodeExtentData::CallSiteScope { fn_id: id, body_id: body_id.node_id });
291 let old_call_site_scope = self.set_call_site_scope(Some(call_site));
294 let fn_sig_map = &self.tables.borrow().liberated_fn_sigs;
295 match fn_sig_map.get(&id) {
296 Some(f) => f.clone(),
298 bug!("No fn-sig entry for id={}", id);
303 let old_region_bounds_pairs_len = self.region_bound_pairs.len();
305 // Collect the types from which we create inferred bounds.
306 // For the return type, if diverging, substitute `bool` just
307 // because it will have no effect.
309 // FIXME(#27579) return types should not be implied bounds
310 let fn_sig_tys: Vec<_> =
311 fn_sig.inputs().iter().cloned().chain(Some(fn_sig.output())).collect();
313 let old_body_id = self.set_body_id(body_id.node_id);
314 self.relate_free_regions(&fn_sig_tys[..], body_id.node_id, span);
315 self.link_fn_args(self.tcx.node_extent(body_id.node_id), &body.arguments);
316 self.visit_body(body);
317 self.visit_region_obligations(body_id.node_id);
319 let call_site_scope = self.call_site_scope.unwrap();
320 debug!("visit_fn_body body.id {:?} call_site_scope: {:?}",
321 body.id(), call_site_scope);
322 let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope));
323 self.type_of_node_must_outlive(infer::CallReturn(span),
327 self.region_bound_pairs.truncate(old_region_bounds_pairs_len);
329 self.set_body_id(old_body_id);
330 self.set_call_site_scope(old_call_site_scope);
333 fn visit_region_obligations(&mut self, node_id: ast::NodeId)
335 debug!("visit_region_obligations: node_id={}", node_id);
337 // region checking can introduce new pending obligations
338 // which, when processed, might generate new region
339 // obligations. So make sure we process those.
340 self.select_all_obligations_or_error();
342 // Make a copy of the region obligations vec because we'll need
343 // to be able to borrow the fulfillment-cx below when projecting.
344 let region_obligations =
347 .region_obligations(node_id)
350 for r_o in ®ion_obligations {
351 debug!("visit_region_obligations: r_o={:?} cause={:?}",
353 let sup_type = self.resolve_type(r_o.sup_type);
354 let origin = self.code_to_origin(&r_o.cause, sup_type);
355 self.type_must_outlive(origin, sup_type, r_o.sub_region);
358 // Processing the region obligations should not cause the list to grow further:
359 assert_eq!(region_obligations.len(),
360 self.fulfillment_cx.borrow().region_obligations(node_id).len());
363 fn code_to_origin(&self,
364 cause: &traits::ObligationCause<'tcx>,
366 -> SubregionOrigin<'tcx> {
367 SubregionOrigin::from_obligation_cause(cause,
368 || infer::RelateParamBound(cause.span, sup_type))
371 /// This method populates the region map's `free_region_map`. It walks over the transformed
372 /// argument and return types for each function just before we check the body of that function,
373 /// looking for types where you have a borrowed pointer to other borrowed data (e.g., `&'a &'b
374 /// [usize]`. We do not allow references to outlive the things they point at, so we can assume
375 /// that `'a <= 'b`. This holds for both the argument and return types, basically because, on
376 /// the caller side, the caller is responsible for checking that the type of every expression
377 /// (including the actual values for the arguments, as well as the return type of the fn call)
380 /// Tests: `src/test/compile-fail/regions-free-region-ordering-*.rs`
381 fn relate_free_regions(&mut self,
382 fn_sig_tys: &[Ty<'tcx>],
383 body_id: ast::NodeId,
385 debug!("relate_free_regions >>");
387 for &ty in fn_sig_tys {
388 let ty = self.resolve_type(ty);
389 debug!("relate_free_regions(t={:?})", ty);
390 let implied_bounds = ty::wf::implied_bounds(self, body_id, ty, span);
392 // Record any relations between free regions that we observe into the free-region-map.
393 self.free_region_map.relate_free_regions_from_implied_bounds(&implied_bounds);
395 // But also record other relationships, such as `T:'x`,
396 // that don't go into the free-region-map but which we use
398 for implication in implied_bounds {
399 debug!("implication: {:?}", implication);
401 ImpliedBound::RegionSubRegion(&ty::ReFree(free_a),
402 &ty::ReVar(vid_b)) => {
403 self.add_given(free_a, vid_b);
405 ImpliedBound::RegionSubParam(r_a, param_b) => {
406 self.region_bound_pairs.push((r_a, GenericKind::Param(param_b)));
408 ImpliedBound::RegionSubProjection(r_a, projection_b) => {
409 self.region_bound_pairs.push((r_a, GenericKind::Projection(projection_b)));
411 ImpliedBound::RegionSubRegion(..) => {
412 // In principle, we could record (and take
413 // advantage of) every relationship here, but
414 // we are also free not to -- it simply means
415 // strictly less that we can successfully type
416 // check. (It may also be that we should
417 // revise our inference system to be more
418 // general and to make use of *every*
419 // relationship that arises here, but
420 // presently we do not.)
426 debug!("<< relate_free_regions");
429 fn resolve_regions_and_report_errors(&self) {
430 self.fcx.resolve_regions_and_report_errors(self.subject_def_id,
432 &self.free_region_map);
435 fn constrain_bindings_in_pat(&mut self, pat: &hir::Pat) {
436 debug!("regionck::visit_pat(pat={:?})", pat);
437 pat.each_binding(|_, id, span, _| {
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:
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;
447 // borrow(v); //~ ERROR cannot borrow
448 // x = &mut v; // (1)
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.
461 let var_scope = self.region_maps.var_scope(id);
462 let var_region = self.tcx.mk_region(ty::ReScope(var_scope));
464 let origin = infer::BindingTypeIsNotValidAtDecl(span);
465 self.type_of_node_must_outlive(origin, id, var_region);
467 let typ = self.resolve_node_type(id);
468 let _ = dropck::check_safety_of_destructor_if_necessary(
469 self, typ, span, var_scope);
474 impl<'a, 'gcx, 'tcx> Visitor<'gcx> for RegionCtxt<'a, 'gcx, 'tcx> {
475 // (..) FIXME(#3238) should use visit_pat, not visit_arm/visit_local,
476 // However, right now we run into an issue whereby some free
477 // regions are not properly related if they appear within the
478 // types of arguments that must be inferred. This could be
479 // addressed by deferring the construction of the region
480 // hierarchy, and in particular the relationships between free
481 // regions, until regionck, as described in #3238.
483 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'gcx> {
484 NestedVisitorMap::None
487 fn visit_fn(&mut self, _fk: intravisit::FnKind<'gcx>, _: &'gcx hir::FnDecl,
488 b: hir::BodyId, span: Span, id: ast::NodeId) {
489 let body = self.tcx.hir.body(b);
490 self.visit_fn_body(id, body, span)
493 //visit_pat: visit_pat, // (..) see above
495 fn visit_arm(&mut self, arm: &'gcx hir::Arm) {
498 self.constrain_bindings_in_pat(p);
500 intravisit::walk_arm(self, arm);
503 fn visit_local(&mut self, l: &'gcx hir::Local) {
505 self.constrain_bindings_in_pat(&l.pat);
507 intravisit::walk_local(self, l);
510 fn visit_expr(&mut self, expr: &'gcx hir::Expr) {
511 debug!("regionck::visit_expr(e={:?}, repeating_scope={})",
512 expr, self.repeating_scope);
514 // No matter what, the type of each expression must outlive the
515 // scope of that expression. This also guarantees basic WF.
516 let expr_ty = self.resolve_node_type(expr.id);
517 // the region corresponding to this expression
518 let expr_region = self.tcx.node_scope_region(expr.id);
519 self.type_must_outlive(infer::ExprTypeIsNotInScope(expr_ty, expr.span),
520 expr_ty, expr_region);
522 let method_call = MethodCall::expr(expr.id);
523 let opt_method_callee = self.tables.borrow().method_map.get(&method_call).cloned();
524 let has_method_map = opt_method_callee.is_some();
526 // If we are calling a method (either explicitly or via an
527 // overloaded operator), check that all of the types provided as
528 // arguments for its type parameters are well-formed, and all the regions
529 // provided as arguments outlive the call.
530 if let Some(callee) = opt_method_callee {
531 let origin = match expr.node {
532 hir::ExprMethodCall(..) =>
533 infer::ParameterOrigin::MethodCall,
534 hir::ExprUnary(op, _) if op == hir::UnDeref =>
535 infer::ParameterOrigin::OverloadedDeref,
537 infer::ParameterOrigin::OverloadedOperator
540 self.substs_wf_in_scope(origin, &callee.substs, expr.span, expr_region);
541 self.type_must_outlive(infer::ExprTypeIsNotInScope(callee.ty, expr.span),
542 callee.ty, expr_region);
545 // Check any autoderefs or autorefs that appear.
546 let adjustment = self.tables.borrow().adjustments.get(&expr.id).map(|a| a.clone());
547 if let Some(adjustment) = adjustment {
548 debug!("adjustment={:?}", adjustment);
549 match adjustment.kind {
550 adjustment::Adjust::DerefRef { autoderefs, ref autoref, .. } => {
551 let expr_ty = self.resolve_node_type(expr.id);
552 self.constrain_autoderefs(expr, autoderefs, expr_ty);
553 if let Some(ref autoref) = *autoref {
554 self.link_autoref(expr, autoderefs, autoref);
556 // Require that the resulting region encompasses
559 // FIXME(#6268) remove to support nested method calls
560 self.type_of_node_must_outlive(infer::AutoBorrow(expr.span),
561 expr.id, expr_region);
565 adjustment::AutoObject(_, ref bounds, ..) => {
566 // Determine if we are casting `expr` to a trait
567 // instance. If so, we have to be sure that the type
568 // of the source obeys the new region bound.
569 let source_ty = self.resolve_node_type(expr.id);
570 self.type_must_outlive(infer::RelateObjectBound(expr.span),
571 source_ty, bounds.region_bound);
577 // If necessary, constrain destructors in the unadjusted form of this
580 let mc = mc::MemCategorizationContext::new(self, self.subject_def_id);
581 mc.cat_expr_unadjusted(expr)
585 self.check_safety_of_rvalue_destructor_if_necessary(head_cmt,
589 self.tcx.sess.delay_span_bug(expr.span, "cat_expr_unadjusted Errd");
594 // If necessary, constrain destructors in this expression. This will be
595 // the adjusted form if there is an adjustment.
597 let mc = mc::MemCategorizationContext::new(self, self.subject_def_id);
602 self.check_safety_of_rvalue_destructor_if_necessary(head_cmt, expr.span);
605 self.tcx.sess.delay_span_bug(expr.span, "cat_expr Errd");
609 debug!("regionck::visit_expr(e={:?}, repeating_scope={}) - visiting subexprs",
610 expr, self.repeating_scope);
612 hir::ExprPath(_) => {
613 self.fcx.opt_node_ty_substs(expr.id, |item_substs| {
614 let origin = infer::ParameterOrigin::Path;
615 self.substs_wf_in_scope(origin, &item_substs.substs, expr.span, expr_region);
619 hir::ExprCall(ref callee, ref args) => {
621 self.constrain_call(expr, Some(&callee),
622 args.iter().map(|e| &*e), false);
624 self.constrain_callee(callee.id, expr, &callee);
625 self.constrain_call(expr, None,
626 args.iter().map(|e| &*e), false);
629 intravisit::walk_expr(self, expr);
632 hir::ExprMethodCall(.., ref args) => {
633 self.constrain_call(expr, Some(&args[0]),
634 args[1..].iter().map(|e| &*e), false);
636 intravisit::walk_expr(self, expr);
639 hir::ExprAssignOp(_, ref lhs, ref rhs) => {
641 self.constrain_call(expr, Some(&lhs),
642 Some(&**rhs).into_iter(), false);
645 intravisit::walk_expr(self, expr);
648 hir::ExprIndex(ref lhs, ref rhs) if has_method_map => {
649 self.constrain_call(expr, Some(&lhs),
650 Some(&**rhs).into_iter(), true);
652 intravisit::walk_expr(self, expr);
655 hir::ExprBinary(op, ref lhs, ref rhs) if has_method_map => {
656 let implicitly_ref_args = !op.node.is_by_value();
658 // As `expr_method_call`, but the call is via an
659 // overloaded op. Note that we (sadly) currently use an
660 // implicit "by ref" sort of passing style here. This
661 // should be converted to an adjustment!
662 self.constrain_call(expr, Some(&lhs),
663 Some(&**rhs).into_iter(), implicitly_ref_args);
665 intravisit::walk_expr(self, expr);
668 hir::ExprBinary(_, ref lhs, ref rhs) => {
669 // If you do `x OP y`, then the types of `x` and `y` must
670 // outlive the operation you are performing.
671 let lhs_ty = self.resolve_expr_type_adjusted(&lhs);
672 let rhs_ty = self.resolve_expr_type_adjusted(&rhs);
673 for &ty in &[lhs_ty, rhs_ty] {
674 self.type_must_outlive(infer::Operand(expr.span),
677 intravisit::walk_expr(self, expr);
680 hir::ExprUnary(op, ref lhs) if has_method_map => {
681 let implicitly_ref_args = !op.is_by_value();
684 self.constrain_call(expr, Some(&lhs),
685 None::<hir::Expr>.iter(), implicitly_ref_args);
687 intravisit::walk_expr(self, expr);
690 hir::ExprUnary(hir::UnDeref, ref base) => {
691 // For *a, the lifetime of a must enclose the deref
692 let method_call = MethodCall::expr(expr.id);
693 let base_ty = match self.tables.borrow().method_map.get(&method_call) {
695 self.constrain_call(expr, Some(&base),
696 None::<hir::Expr>.iter(), true);
697 // late-bound regions in overloaded method calls are instantiated
698 let fn_ret = self.tcx.no_late_bound_regions(&method.ty.fn_ret());
701 None => self.resolve_node_type(base.id)
703 if let ty::TyRef(r_ptr, _) = base_ty.sty {
704 self.mk_subregion_due_to_dereference(expr.span, expr_region, r_ptr);
707 intravisit::walk_expr(self, expr);
710 hir::ExprIndex(ref vec_expr, _) => {
711 // For a[b], the lifetime of a must enclose the deref
712 let vec_type = self.resolve_expr_type_adjusted(&vec_expr);
713 self.constrain_index(expr, vec_type);
715 intravisit::walk_expr(self, expr);
718 hir::ExprCast(ref source, _) => {
719 // Determine if we are casting `source` to a trait
720 // instance. If so, we have to be sure that the type of
721 // the source obeys the trait's region bound.
722 self.constrain_cast(expr, &source);
723 intravisit::walk_expr(self, expr);
726 hir::ExprAddrOf(m, ref base) => {
727 self.link_addr_of(expr, m, &base);
729 // Require that when you write a `&expr` expression, the
730 // resulting pointer has a lifetime that encompasses the
731 // `&expr` expression itself. Note that we constraining
732 // the type of the node expr.id here *before applying
735 // FIXME(#6268) nested method calls requires that this rule change
736 let ty0 = self.resolve_node_type(expr.id);
737 self.type_must_outlive(infer::AddrOf(expr.span), ty0, expr_region);
738 intravisit::walk_expr(self, expr);
741 hir::ExprMatch(ref discr, ref arms, _) => {
742 self.link_match(&discr, &arms[..]);
744 intravisit::walk_expr(self, expr);
747 hir::ExprClosure(.., body_id, _) => {
748 self.check_expr_fn_block(expr, body_id);
751 hir::ExprLoop(ref body, _, _) => {
752 let repeating_scope = self.set_repeating_scope(body.id);
753 intravisit::walk_expr(self, expr);
754 self.set_repeating_scope(repeating_scope);
757 hir::ExprWhile(ref cond, ref body, _) => {
758 let repeating_scope = self.set_repeating_scope(cond.id);
759 self.visit_expr(&cond);
761 self.set_repeating_scope(body.id);
762 self.visit_block(&body);
764 self.set_repeating_scope(repeating_scope);
767 hir::ExprRet(Some(ref ret_expr)) => {
768 let call_site_scope = self.call_site_scope;
769 debug!("visit_expr ExprRet ret_expr.id {} call_site_scope: {:?}",
770 ret_expr.id, call_site_scope);
771 let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope.unwrap()));
772 self.type_of_node_must_outlive(infer::CallReturn(ret_expr.span),
775 intravisit::walk_expr(self, expr);
779 intravisit::walk_expr(self, expr);
785 impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
786 fn constrain_cast(&mut self,
787 cast_expr: &hir::Expr,
788 source_expr: &hir::Expr)
790 debug!("constrain_cast(cast_expr={:?}, source_expr={:?})",
794 let source_ty = self.resolve_node_type(source_expr.id);
795 let target_ty = self.resolve_node_type(cast_expr.id);
797 self.walk_cast(cast_expr, source_ty, target_ty);
800 fn walk_cast(&mut self,
801 cast_expr: &hir::Expr,
804 debug!("walk_cast(from_ty={:?}, to_ty={:?})",
807 match (&from_ty.sty, &to_ty.sty) {
808 /*From:*/ (&ty::TyRef(from_r, ref from_mt),
809 /*To: */ &ty::TyRef(to_r, ref to_mt)) => {
810 // Target cannot outlive source, naturally.
811 self.sub_regions(infer::Reborrow(cast_expr.span), to_r, from_r);
812 self.walk_cast(cast_expr, from_mt.ty, to_mt.ty);
816 /*To: */ &ty::TyDynamic(.., r)) => {
817 // When T is existentially quantified as a trait
818 // `Foo+'to`, it must outlive the region bound `'to`.
819 self.type_must_outlive(infer::RelateObjectBound(cast_expr.span), from_ty, r);
822 /*From:*/ (&ty::TyAdt(from_def, _),
823 /*To: */ &ty::TyAdt(to_def, _)) if from_def.is_box() && to_def.is_box() => {
824 self.walk_cast(cast_expr, from_ty.boxed_ty(), to_ty.boxed_ty());
831 fn check_expr_fn_block(&mut self,
832 expr: &'gcx hir::Expr,
833 body_id: hir::BodyId) {
834 let repeating_scope = self.set_repeating_scope(body_id.node_id);
835 intravisit::walk_expr(self, expr);
836 self.set_repeating_scope(repeating_scope);
839 fn constrain_callee(&mut self,
840 callee_id: ast::NodeId,
841 _call_expr: &hir::Expr,
842 _callee_expr: &hir::Expr) {
843 let callee_ty = self.resolve_node_type(callee_id);
844 match callee_ty.sty {
845 ty::TyFnDef(..) | ty::TyFnPtr(_) => { }
847 // this should not happen, but it does if the program is
852 // "Calling non-function: {}",
858 fn constrain_call<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
859 call_expr: &hir::Expr,
860 receiver: Option<&hir::Expr>,
862 implicitly_ref_args: bool) {
863 //! Invoked on every call site (i.e., normal calls, method calls,
864 //! and overloaded operators). Constrains the regions which appear
865 //! in the type of the function. Also constrains the regions that
866 //! appear in the arguments appropriately.
868 debug!("constrain_call(call_expr={:?}, \
870 implicitly_ref_args={})",
873 implicitly_ref_args);
875 // `callee_region` is the scope representing the time in which the
878 // FIXME(#6268) to support nested method calls, should be callee_id
879 let callee_scope = self.tcx.node_extent(call_expr.id);
880 let callee_region = self.tcx.mk_region(ty::ReScope(callee_scope));
882 debug!("callee_region={:?}", callee_region);
884 for arg_expr in arg_exprs {
885 debug!("Argument: {:?}", arg_expr);
887 // ensure that any regions appearing in the argument type are
888 // valid for at least the lifetime of the function:
889 self.type_of_node_must_outlive(infer::CallArg(arg_expr.span),
890 arg_expr.id, callee_region);
892 // unfortunately, there are two means of taking implicit
893 // references, and we need to propagate constraints as a
894 // result. modes are going away and the "DerefArgs" code
895 // should be ported to use adjustments
896 if implicitly_ref_args {
897 self.link_by_ref(arg_expr, callee_scope);
901 // as loop above, but for receiver
902 if let Some(r) = receiver {
903 debug!("receiver: {:?}", r);
904 self.type_of_node_must_outlive(infer::CallRcvr(r.span),
905 r.id, callee_region);
906 if implicitly_ref_args {
907 self.link_by_ref(&r, callee_scope);
912 /// Invoked on any auto-dereference that occurs. Checks that if this is a region pointer being
913 /// dereferenced, the lifetime of the pointer includes the deref expr.
914 fn constrain_autoderefs(&mut self,
915 deref_expr: &hir::Expr,
917 mut derefd_ty: Ty<'tcx>)
919 debug!("constrain_autoderefs(deref_expr={:?}, derefs={}, derefd_ty={:?})",
924 let r_deref_expr = self.tcx.node_scope_region(deref_expr.id);
926 let method_call = MethodCall::autoderef(deref_expr.id, i as u32);
927 debug!("constrain_autoderefs: method_call={:?} (of {:?} total)", method_call, derefs);
929 let method = self.tables.borrow().method_map.get(&method_call).map(|m| m.clone());
931 derefd_ty = match method {
933 debug!("constrain_autoderefs: #{} is overloaded, method={:?}",
936 let origin = infer::ParameterOrigin::OverloadedDeref;
937 self.substs_wf_in_scope(origin, method.substs, deref_expr.span, r_deref_expr);
939 // Treat overloaded autoderefs as if an AutoBorrow adjustment
940 // was applied on the base type, as that is always the case.
941 let fn_sig = method.ty.fn_sig();
942 let fn_sig = // late-bound regions should have been instantiated
943 self.tcx.no_late_bound_regions(&fn_sig).unwrap();
944 let self_ty = fn_sig.inputs()[0];
945 let (m, r) = match self_ty.sty {
946 ty::TyRef(r, ref m) => (m.mutbl, r),
950 "bad overloaded deref type {:?}",
955 debug!("constrain_autoderefs: receiver r={:?} m={:?}",
959 let mc = mc::MemCategorizationContext::new(self, self.subject_def_id);
960 let self_cmt = ignore_err!(mc.cat_expr_autoderefd(deref_expr, i));
961 debug!("constrain_autoderefs: self_cmt={:?}",
963 self.link_region(deref_expr.span, r,
964 ty::BorrowKind::from_mutbl(m), self_cmt);
967 // Specialized version of constrain_call.
968 self.type_must_outlive(infer::CallRcvr(deref_expr.span),
969 self_ty, r_deref_expr);
970 self.type_must_outlive(infer::CallReturn(deref_expr.span),
971 fn_sig.output(), r_deref_expr);
977 if let ty::TyRef(r_ptr, _) = derefd_ty.sty {
978 self.mk_subregion_due_to_dereference(deref_expr.span,
979 r_deref_expr, r_ptr);
982 match derefd_ty.builtin_deref(true, ty::NoPreference) {
983 Some(mt) => derefd_ty = mt.ty,
984 /* if this type can't be dereferenced, then there's already an error
985 in the session saying so. Just bail out for now */
991 pub fn mk_subregion_due_to_dereference(&mut self,
993 minimum_lifetime: ty::Region<'tcx>,
994 maximum_lifetime: ty::Region<'tcx>) {
995 self.sub_regions(infer::DerefPointer(deref_span),
996 minimum_lifetime, maximum_lifetime)
999 fn check_safety_of_rvalue_destructor_if_necessary(&mut self,
1003 Categorization::Rvalue(region, _) => {
1005 ty::ReScope(rvalue_scope) => {
1006 let typ = self.resolve_type(cmt.ty);
1007 let _ = dropck::check_safety_of_destructor_if_necessary(
1008 self, typ, span, rvalue_scope);
1013 "unexpected rvalue region in rvalue \
1014 destructor safety checking: `{:?}`",
1023 /// Invoked on any index expression that occurs. Checks that if this is a slice
1024 /// being indexed, the lifetime of the pointer includes the deref expr.
1025 fn constrain_index(&mut self,
1026 index_expr: &hir::Expr,
1027 indexed_ty: Ty<'tcx>)
1029 debug!("constrain_index(index_expr=?, indexed_ty={}",
1030 self.ty_to_string(indexed_ty));
1032 let r_index_expr = ty::ReScope(self.tcx.node_extent(index_expr.id));
1033 if let ty::TyRef(r_ptr, mt) = indexed_ty.sty {
1035 ty::TySlice(_) | ty::TyStr => {
1036 self.sub_regions(infer::IndexSlice(index_expr.span),
1037 self.tcx.mk_region(r_index_expr), r_ptr);
1044 /// Guarantees that any lifetimes which appear in the type of the node `id` (after applying
1045 /// adjustments) are valid for at least `minimum_lifetime`
1046 fn type_of_node_must_outlive(&mut self,
1047 origin: infer::SubregionOrigin<'tcx>,
1049 minimum_lifetime: ty::Region<'tcx>)
1051 // Try to resolve the type. If we encounter an error, then typeck
1052 // is going to fail anyway, so just stop here and let typeck
1053 // report errors later on in the writeback phase.
1054 let ty0 = self.resolve_node_type(id);
1055 let ty = self.tables.borrow().adjustments.get(&id).map_or(ty0, |adj| adj.target);
1056 let ty = self.resolve_type(ty);
1057 debug!("constrain_regions_in_type_of_node(\
1058 ty={}, ty0={}, id={}, minimum_lifetime={:?})",
1060 id, minimum_lifetime);
1061 self.type_must_outlive(origin, ty, minimum_lifetime);
1064 /// Computes the guarantor for an expression `&base` and then ensures that the lifetime of the
1065 /// resulting pointer is linked to the lifetime of its guarantor (if any).
1066 fn link_addr_of(&mut self, expr: &hir::Expr,
1067 mutability: hir::Mutability, base: &hir::Expr) {
1068 debug!("link_addr_of(expr={:?}, base={:?})", expr, base);
1071 let mc = mc::MemCategorizationContext::new(self, self.subject_def_id);
1072 ignore_err!(mc.cat_expr(base))
1075 debug!("link_addr_of: cmt={:?}", cmt);
1077 self.link_region_from_node_type(expr.span, expr.id, mutability, cmt);
1080 /// Computes the guarantors for any ref bindings in a `let` and
1081 /// then ensures that the lifetime of the resulting pointer is
1082 /// linked to the lifetime of the initialization expression.
1083 fn link_local(&self, local: &hir::Local) {
1084 debug!("regionck::for_local()");
1085 let init_expr = match local.init {
1087 Some(ref expr) => &**expr,
1089 let mc = &mc::MemCategorizationContext::new(self, self.subject_def_id);
1090 let discr_cmt = ignore_err!(mc.cat_expr(init_expr));
1091 self.link_pattern(mc, discr_cmt, &local.pat);
1094 /// Computes the guarantors for any ref bindings in a match and
1095 /// then ensures that the lifetime of the resulting pointer is
1096 /// linked to the lifetime of its guarantor (if any).
1097 fn link_match(&self, discr: &hir::Expr, arms: &[hir::Arm]) {
1098 debug!("regionck::for_match()");
1099 let mc = &mc::MemCategorizationContext::new(self, self.subject_def_id);
1100 let discr_cmt = ignore_err!(mc.cat_expr(discr));
1101 debug!("discr_cmt={:?}", discr_cmt);
1103 for root_pat in &arm.pats {
1104 self.link_pattern(mc, discr_cmt.clone(), &root_pat);
1109 /// Computes the guarantors for any ref bindings in a match and
1110 /// then ensures that the lifetime of the resulting pointer is
1111 /// linked to the lifetime of its guarantor (if any).
1112 fn link_fn_args(&self, body_scope: CodeExtent<'tcx>, args: &[hir::Arg]) {
1113 debug!("regionck::link_fn_args(body_scope={:?})", body_scope);
1114 let mc = &mc::MemCategorizationContext::new(self, self.subject_def_id);
1116 let arg_ty = self.node_ty(arg.id);
1117 let re_scope = self.tcx.mk_region(ty::ReScope(body_scope));
1118 let arg_cmt = mc.cat_rvalue(
1119 arg.id, arg.pat.span, re_scope, re_scope, arg_ty);
1120 debug!("arg_ty={:?} arg_cmt={:?} arg={:?}",
1124 self.link_pattern(mc, arg_cmt, &arg.pat);
1128 /// Link lifetimes of any ref bindings in `root_pat` to the pointers found
1129 /// in the discriminant, if needed.
1130 fn link_pattern<'t>(&self,
1131 mc: &mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
1132 discr_cmt: mc::cmt<'tcx>,
1133 root_pat: &hir::Pat) {
1134 debug!("link_pattern(discr_cmt={:?}, root_pat={:?})",
1137 let _ = mc.cat_pattern(discr_cmt, root_pat, |_, sub_cmt, sub_pat| {
1138 match sub_pat.node {
1140 PatKind::Binding(hir::BindByRef(mutbl), ..) => {
1141 self.link_region_from_node_type(sub_pat.span, sub_pat.id,
1149 /// Link lifetime of borrowed pointer resulting from autoref to lifetimes in the value being
1151 fn link_autoref(&self,
1154 autoref: &adjustment::AutoBorrow<'tcx>)
1156 debug!("link_autoref(autoderefs={}, autoref={:?})", autoderefs, autoref);
1157 let mc = mc::MemCategorizationContext::new(self, self.subject_def_id);
1158 let expr_cmt = ignore_err!(mc.cat_expr_autoderefd(expr, autoderefs));
1159 debug!("expr_cmt={:?}", expr_cmt);
1162 adjustment::AutoBorrow::Ref(r, m) => {
1163 self.link_region(expr.span, r,
1164 ty::BorrowKind::from_mutbl(m), expr_cmt);
1167 adjustment::AutoBorrow::RawPtr(m) => {
1168 let r = self.tcx.node_scope_region(expr.id);
1169 self.link_region(expr.span, r, ty::BorrowKind::from_mutbl(m), expr_cmt);
1174 /// Computes the guarantor for cases where the `expr` is being passed by implicit reference and
1175 /// must outlive `callee_scope`.
1176 fn link_by_ref(&self,
1178 callee_scope: CodeExtent<'tcx>) {
1179 debug!("link_by_ref(expr={:?}, callee_scope={:?})",
1180 expr, callee_scope);
1181 let mc = mc::MemCategorizationContext::new(self, self.subject_def_id);
1182 let expr_cmt = ignore_err!(mc.cat_expr(expr));
1183 let borrow_region = self.tcx.mk_region(ty::ReScope(callee_scope));
1184 self.link_region(expr.span, borrow_region, ty::ImmBorrow, expr_cmt);
1187 /// Like `link_region()`, except that the region is extracted from the type of `id`,
1188 /// which must be some reference (`&T`, `&str`, etc).
1189 fn link_region_from_node_type(&self,
1192 mutbl: hir::Mutability,
1193 cmt_borrowed: mc::cmt<'tcx>) {
1194 debug!("link_region_from_node_type(id={:?}, mutbl={:?}, cmt_borrowed={:?})",
1195 id, mutbl, cmt_borrowed);
1197 let rptr_ty = self.resolve_node_type(id);
1198 if let ty::TyRef(r, _) = rptr_ty.sty {
1199 debug!("rptr_ty={}", rptr_ty);
1200 self.link_region(span, r, ty::BorrowKind::from_mutbl(mutbl),
1205 /// Informs the inference engine that `borrow_cmt` is being borrowed with
1206 /// kind `borrow_kind` and lifetime `borrow_region`.
1207 /// In order to ensure borrowck is satisfied, this may create constraints
1208 /// between regions, as explained in `link_reborrowed_region()`.
1209 fn link_region(&self,
1211 borrow_region: ty::Region<'tcx>,
1212 borrow_kind: ty::BorrowKind,
1213 borrow_cmt: mc::cmt<'tcx>) {
1214 let mut borrow_cmt = borrow_cmt;
1215 let mut borrow_kind = borrow_kind;
1217 let origin = infer::DataBorrowed(borrow_cmt.ty, span);
1218 self.type_must_outlive(origin, borrow_cmt.ty, borrow_region);
1221 debug!("link_region(borrow_region={:?}, borrow_kind={:?}, borrow_cmt={:?})",
1225 match borrow_cmt.cat.clone() {
1226 Categorization::Deref(ref_cmt, _,
1227 mc::Implicit(ref_kind, ref_region)) |
1228 Categorization::Deref(ref_cmt, _,
1229 mc::BorrowedPtr(ref_kind, ref_region)) => {
1230 match self.link_reborrowed_region(span,
1231 borrow_region, borrow_kind,
1232 ref_cmt, ref_region, ref_kind,
1244 Categorization::Downcast(cmt_base, _) |
1245 Categorization::Deref(cmt_base, _, mc::Unique) |
1246 Categorization::Interior(cmt_base, _) => {
1247 // Borrowing interior or owned data requires the base
1248 // to be valid and borrowable in the same fashion.
1249 borrow_cmt = cmt_base;
1250 borrow_kind = borrow_kind;
1253 Categorization::Deref(.., mc::UnsafePtr(..)) |
1254 Categorization::StaticItem |
1255 Categorization::Upvar(..) |
1256 Categorization::Local(..) |
1257 Categorization::Rvalue(..) => {
1258 // These are all "base cases" with independent lifetimes
1259 // that are not subject to inference
1266 /// This is the most complicated case: the path being borrowed is
1267 /// itself the referent of a borrowed pointer. Let me give an
1268 /// example fragment of code to make clear(er) the situation:
1270 /// let r: &'a mut T = ...; // the original reference "r" has lifetime 'a
1272 /// &'z *r // the reborrow has lifetime 'z
1274 /// Now, in this case, our primary job is to add the inference
1275 /// constraint that `'z <= 'a`. Given this setup, let's clarify the
1276 /// parameters in (roughly) terms of the example:
1278 /// A borrow of: `& 'z bk * r` where `r` has type `& 'a bk T`
1279 /// borrow_region ^~ ref_region ^~
1280 /// borrow_kind ^~ ref_kind ^~
1283 /// Here `bk` stands for some borrow-kind (e.g., `mut`, `uniq`, etc).
1285 /// Unfortunately, there are some complications beyond the simple
1286 /// scenario I just painted:
1288 /// 1. The reference `r` might in fact be a "by-ref" upvar. In that
1289 /// case, we have two jobs. First, we are inferring whether this reference
1290 /// should be an `&T`, `&mut T`, or `&uniq T` reference, and we must
1291 /// adjust that based on this borrow (e.g., if this is an `&mut` borrow,
1292 /// then `r` must be an `&mut` reference). Second, whenever we link
1293 /// two regions (here, `'z <= 'a`), we supply a *cause*, and in this
1294 /// case we adjust the cause to indicate that the reference being
1295 /// "reborrowed" is itself an upvar. This provides a nicer error message
1296 /// should something go wrong.
1298 /// 2. There may in fact be more levels of reborrowing. In the
1299 /// example, I said the borrow was like `&'z *r`, but it might
1300 /// in fact be a borrow like `&'z **q` where `q` has type `&'a
1301 /// &'b mut T`. In that case, we want to ensure that `'z <= 'a`
1302 /// and `'z <= 'b`. This is explained more below.
1304 /// The return value of this function indicates whether we need to
1305 /// recurse and process `ref_cmt` (see case 2 above).
1306 fn link_reborrowed_region(&self,
1308 borrow_region: ty::Region<'tcx>,
1309 borrow_kind: ty::BorrowKind,
1310 ref_cmt: mc::cmt<'tcx>,
1311 ref_region: ty::Region<'tcx>,
1312 mut ref_kind: ty::BorrowKind,
1314 -> Option<(mc::cmt<'tcx>, ty::BorrowKind)>
1316 // Possible upvar ID we may need later to create an entry in the
1319 // Detect by-ref upvar `x`:
1320 let cause = match note {
1321 mc::NoteUpvarRef(ref upvar_id) => {
1322 let upvar_capture_map = &self.tables.borrow_mut().upvar_capture_map;
1323 match upvar_capture_map.get(upvar_id) {
1324 Some(&ty::UpvarCapture::ByRef(ref upvar_borrow)) => {
1325 // The mutability of the upvar may have been modified
1326 // by the above adjustment, so update our local variable.
1327 ref_kind = upvar_borrow.kind;
1329 infer::ReborrowUpvar(span, *upvar_id)
1332 span_bug!( span, "Illegal upvar id: {:?}", upvar_id);
1336 mc::NoteClosureEnv(ref upvar_id) => {
1337 // We don't have any mutability changes to propagate, but
1338 // we do want to note that an upvar reborrow caused this
1340 infer::ReborrowUpvar(span, *upvar_id)
1343 infer::Reborrow(span)
1347 debug!("link_reborrowed_region: {:?} <= {:?}",
1350 self.sub_regions(cause, borrow_region, ref_region);
1352 // If we end up needing to recurse and establish a region link
1353 // with `ref_cmt`, calculate what borrow kind we will end up
1354 // needing. This will be used below.
1356 // One interesting twist is that we can weaken the borrow kind
1357 // when we recurse: to reborrow an `&mut` referent as mutable,
1358 // borrowck requires a unique path to the `&mut` reference but not
1359 // necessarily a *mutable* path.
1360 let new_borrow_kind = match borrow_kind {
1363 ty::MutBorrow | ty::UniqueImmBorrow =>
1367 // Decide whether we need to recurse and link any regions within
1368 // the `ref_cmt`. This is concerned for the case where the value
1369 // being reborrowed is in fact a borrowed pointer found within
1370 // another borrowed pointer. For example:
1372 // let p: &'b &'a mut T = ...;
1376 // What makes this case particularly tricky is that, if the data
1377 // being borrowed is a `&mut` or `&uniq` borrow, borrowck requires
1378 // not only that `'z <= 'a`, (as before) but also `'z <= 'b`
1379 // (otherwise the user might mutate through the `&mut T` reference
1380 // after `'b` expires and invalidate the borrow we are looking at
1383 // So let's re-examine our parameters in light of this more
1384 // complicated (possible) scenario:
1386 // A borrow of: `& 'z bk * * p` where `p` has type `&'b bk & 'a bk T`
1387 // borrow_region ^~ ref_region ^~
1388 // borrow_kind ^~ ref_kind ^~
1391 // (Note that since we have not examined `ref_cmt.cat`, we don't
1392 // know whether this scenario has occurred; but I wanted to show
1393 // how all the types get adjusted.)
1396 // The reference being reborrowed is a sharable ref of
1397 // type `&'a T`. In this case, it doesn't matter where we
1398 // *found* the `&T` pointer, the memory it references will
1399 // be valid and immutable for `'a`. So we can stop here.
1401 // (Note that the `borrow_kind` must also be ImmBorrow or
1402 // else the user is borrowed imm memory as mut memory,
1403 // which means they'll get an error downstream in borrowck
1408 ty::MutBorrow | ty::UniqueImmBorrow => {
1409 // The reference being reborrowed is either an `&mut T` or
1410 // `&uniq T`. This is the case where recursion is needed.
1411 return Some((ref_cmt, new_borrow_kind));
1416 /// Checks that the values provided for type/region arguments in a given
1417 /// expression are well-formed and in-scope.
1418 fn substs_wf_in_scope(&mut self,
1419 origin: infer::ParameterOrigin,
1420 substs: &Substs<'tcx>,
1422 expr_region: ty::Region<'tcx>) {
1423 debug!("substs_wf_in_scope(substs={:?}, \
1427 substs, expr_region, origin, expr_span);
1429 let origin = infer::ParameterInScope(origin, expr_span);
1431 for region in substs.regions() {
1432 self.sub_regions(origin.clone(), expr_region, region);
1435 for ty in substs.types() {
1436 let ty = self.resolve_type(ty);
1437 self.type_must_outlive(origin.clone(), ty, expr_region);
1441 /// Ensures that type is well-formed in `region`, which implies (among
1442 /// other things) that all borrowed data reachable via `ty` outlives
1444 pub fn type_must_outlive(&self,
1445 origin: infer::SubregionOrigin<'tcx>,
1447 region: ty::Region<'tcx>)
1449 let ty = self.resolve_type(ty);
1451 debug!("type_must_outlive(ty={:?}, region={:?}, origin={:?})",
1456 assert!(!ty.has_escaping_regions());
1458 let components = self.tcx.outlives_components(ty);
1459 self.components_must_outlive(origin, components, region);
1462 fn components_must_outlive(&self,
1463 origin: infer::SubregionOrigin<'tcx>,
1464 components: Vec<ty::outlives::Component<'tcx>>,
1465 region: ty::Region<'tcx>)
1467 for component in components {
1468 let origin = origin.clone();
1470 ty::outlives::Component::Region(region1) => {
1471 self.sub_regions(origin, region, region1);
1473 ty::outlives::Component::Param(param_ty) => {
1474 self.param_ty_must_outlive(origin, region, param_ty);
1476 ty::outlives::Component::Projection(projection_ty) => {
1477 self.projection_must_outlive(origin, region, projection_ty);
1479 ty::outlives::Component::EscapingProjection(subcomponents) => {
1480 self.components_must_outlive(origin, subcomponents, region);
1482 ty::outlives::Component::UnresolvedInferenceVariable(v) => {
1483 // ignore this, we presume it will yield an error
1484 // later, since if a type variable is not resolved by
1485 // this point it never will be
1486 self.tcx.sess.delay_span_bug(
1488 &format!("unresolved inference variable in outlives: {:?}", v));
1494 fn param_ty_must_outlive(&self,
1495 origin: infer::SubregionOrigin<'tcx>,
1496 region: ty::Region<'tcx>,
1497 param_ty: ty::ParamTy) {
1498 debug!("param_ty_must_outlive(region={:?}, param_ty={:?}, origin={:?})",
1499 region, param_ty, origin);
1501 let verify_bound = self.param_bound(param_ty);
1502 let generic = GenericKind::Param(param_ty);
1503 self.verify_generic_bound(origin, generic, region, verify_bound);
1506 fn projection_must_outlive(&self,
1507 origin: infer::SubregionOrigin<'tcx>,
1508 region: ty::Region<'tcx>,
1509 projection_ty: ty::ProjectionTy<'tcx>)
1511 debug!("projection_must_outlive(region={:?}, projection_ty={:?}, origin={:?})",
1512 region, projection_ty, origin);
1514 // This case is thorny for inference. The fundamental problem is
1515 // that there are many cases where we have choice, and inference
1516 // doesn't like choice (the current region inference in
1517 // particular). :) First off, we have to choose between using the
1518 // OutlivesProjectionEnv, OutlivesProjectionTraitDef, and
1519 // OutlivesProjectionComponent rules, any one of which is
1520 // sufficient. If there are no inference variables involved, it's
1521 // not hard to pick the right rule, but if there are, we're in a
1522 // bit of a catch 22: if we picked which rule we were going to
1523 // use, we could add constraints to the region inference graph
1524 // that make it apply, but if we don't add those constraints, the
1525 // rule might not apply (but another rule might). For now, we err
1526 // on the side of adding too few edges into the graph.
1528 // Compute the bounds we can derive from the environment or trait
1529 // definition. We know that the projection outlives all the
1530 // regions in this list.
1531 let env_bounds = self.projection_declared_bounds(origin.span(), projection_ty);
1533 debug!("projection_must_outlive: env_bounds={:?}",
1536 // If we know that the projection outlives 'static, then we're
1538 if env_bounds.contains(&&ty::ReStatic) {
1539 debug!("projection_must_outlive: 'static as declared bound");
1543 // If declared bounds list is empty, the only applicable rule is
1544 // OutlivesProjectionComponent. If there are inference variables,
1545 // then, we can break down the outlives into more primitive
1546 // components without adding unnecessary edges.
1548 // If there are *no* inference variables, however, we COULD do
1549 // this, but we choose not to, because the error messages are less
1550 // good. For example, a requirement like `T::Item: 'r` would be
1551 // translated to a requirement that `T: 'r`; when this is reported
1552 // to the user, it will thus say "T: 'r must hold so that T::Item:
1553 // 'r holds". But that makes it sound like the only way to fix
1554 // the problem is to add `T: 'r`, which isn't true. So, if there are no
1555 // inference variables, we use a verify constraint instead of adding
1556 // edges, which winds up enforcing the same condition.
1557 let needs_infer = projection_ty.trait_ref.needs_infer();
1558 if env_bounds.is_empty() && needs_infer {
1559 debug!("projection_must_outlive: no declared bounds");
1561 for component_ty in projection_ty.trait_ref.substs.types() {
1562 self.type_must_outlive(origin.clone(), component_ty, region);
1565 for r in projection_ty.trait_ref.substs.regions() {
1566 self.sub_regions(origin.clone(), region, r);
1572 // If we find that there is a unique declared bound `'b`, and this bound
1573 // appears in the trait reference, then the best action is to require that `'b:'r`,
1574 // so do that. This is best no matter what rule we use:
1576 // - OutlivesProjectionEnv or OutlivesProjectionTraitDef: these would translate to
1577 // the requirement that `'b:'r`
1578 // - OutlivesProjectionComponent: this would require `'b:'r` in addition to
1580 if !env_bounds.is_empty() && env_bounds[1..].iter().all(|b| *b == env_bounds[0]) {
1581 let unique_bound = env_bounds[0];
1582 debug!("projection_must_outlive: unique declared bound = {:?}", unique_bound);
1583 if projection_ty.trait_ref.substs.regions().any(|r| env_bounds.contains(&r)) {
1584 debug!("projection_must_outlive: unique declared bound appears in trait ref");
1585 self.sub_regions(origin.clone(), region, unique_bound);
1590 // Fallback to verifying after the fact that there exists a
1591 // declared bound, or that all the components appearing in the
1592 // projection outlive; in some cases, this may add insufficient
1593 // edges into the inference graph, leading to inference failures
1594 // even though a satisfactory solution exists.
1595 let verify_bound = self.projection_bound(origin.span(), env_bounds, projection_ty);
1596 let generic = GenericKind::Projection(projection_ty);
1597 self.verify_generic_bound(origin, generic.clone(), region, verify_bound);
1600 fn type_bound(&self, span: Span, ty: Ty<'tcx>) -> VerifyBound<'tcx> {
1605 ty::TyProjection(data) => {
1606 let declared_bounds = self.projection_declared_bounds(span, data);
1607 self.projection_bound(span, declared_bounds, data)
1610 self.recursive_type_bound(span, ty)
1615 fn param_bound(&self, param_ty: ty::ParamTy) -> VerifyBound<'tcx> {
1616 let param_env = &self.parameter_environment;
1618 debug!("param_bound(param_ty={:?})",
1621 let mut param_bounds = self.declared_generic_bounds_from_env(GenericKind::Param(param_ty));
1623 // Add in the default bound of fn body that applies to all in
1624 // scope type parameters:
1625 param_bounds.extend(param_env.implicit_region_bound);
1627 VerifyBound::AnyRegion(param_bounds)
1630 fn projection_declared_bounds(&self,
1632 projection_ty: ty::ProjectionTy<'tcx>)
1633 -> Vec<ty::Region<'tcx>>
1635 // First assemble bounds from where clauses and traits.
1637 let mut declared_bounds =
1638 self.declared_generic_bounds_from_env(GenericKind::Projection(projection_ty));
1640 declared_bounds.extend_from_slice(
1641 &self.declared_projection_bounds_from_trait(span, projection_ty));
1646 fn projection_bound(&self,
1648 declared_bounds: Vec<ty::Region<'tcx>>,
1649 projection_ty: ty::ProjectionTy<'tcx>)
1650 -> VerifyBound<'tcx> {
1651 debug!("projection_bound(declared_bounds={:?}, projection_ty={:?})",
1652 declared_bounds, projection_ty);
1654 // see the extensive comment in projection_must_outlive
1656 let ty = self.tcx.mk_projection(projection_ty.trait_ref, projection_ty.item_name);
1657 let recursive_bound = self.recursive_type_bound(span, ty);
1659 VerifyBound::AnyRegion(declared_bounds).or(recursive_bound)
1662 fn recursive_type_bound(&self, span: Span, ty: Ty<'tcx>) -> VerifyBound<'tcx> {
1663 let mut bounds = vec![];
1665 for subty in ty.walk_shallow() {
1666 bounds.push(self.type_bound(span, subty));
1669 let mut regions = ty.regions();
1670 regions.retain(|r| !r.is_bound()); // ignore late-bound regions
1671 bounds.push(VerifyBound::AllRegions(regions));
1673 // remove bounds that must hold, since they are not interesting
1674 bounds.retain(|b| !b.must_hold());
1676 if bounds.len() == 1 {
1677 bounds.pop().unwrap()
1679 VerifyBound::AllBounds(bounds)
1683 fn declared_generic_bounds_from_env(&self, generic: GenericKind<'tcx>)
1684 -> Vec<ty::Region<'tcx>>
1686 let param_env = &self.parameter_environment;
1688 // To start, collect bounds from user:
1689 let mut param_bounds = self.tcx.required_region_bounds(generic.to_ty(self.tcx),
1690 param_env.caller_bounds.clone());
1692 // Next, collect regions we scraped from the well-formedness
1693 // constraints in the fn signature. To do that, we walk the list
1694 // of known relations from the fn ctxt.
1696 // This is crucial because otherwise code like this fails:
1698 // fn foo<'a, A>(x: &'a A) { x.bar() }
1700 // The problem is that the type of `x` is `&'a A`. To be
1701 // well-formed, then, A must be lower-generic by `'a`, but we
1702 // don't know that this holds from first principles.
1703 for &(r, p) in &self.region_bound_pairs {
1704 debug!("generic={:?} p={:?}",
1708 param_bounds.push(r);
1715 fn declared_projection_bounds_from_trait(&self,
1717 projection_ty: ty::ProjectionTy<'tcx>)
1718 -> Vec<ty::Region<'tcx>>
1720 debug!("projection_bounds(projection_ty={:?})",
1723 let ty = self.tcx.mk_projection(projection_ty.trait_ref.clone(),
1724 projection_ty.item_name);
1726 // Say we have a projection `<T as SomeTrait<'a>>::SomeType`. We are interested
1727 // in looking for a trait definition like:
1730 // trait SomeTrait<'a> {
1731 // type SomeType : 'a;
1735 // we can thus deduce that `<T as SomeTrait<'a>>::SomeType : 'a`.
1736 let trait_predicates = self.tcx.predicates_of(projection_ty.trait_ref.def_id);
1737 assert_eq!(trait_predicates.parent, None);
1738 let predicates = trait_predicates.predicates.as_slice().to_vec();
1739 traits::elaborate_predicates(self.tcx, predicates)
1740 .filter_map(|predicate| {
1741 // we're only interesting in `T : 'a` style predicates:
1742 let outlives = match predicate {
1743 ty::Predicate::TypeOutlives(data) => data,
1744 _ => { return None; }
1747 debug!("projection_bounds: outlives={:?} (1)",
1750 // apply the substitutions (and normalize any projected types)
1751 let outlives = self.instantiate_type_scheme(span,
1752 projection_ty.trait_ref.substs,
1755 debug!("projection_bounds: outlives={:?} (2)",
1758 let region_result = self.commit_if_ok(|_| {
1760 self.replace_late_bound_regions_with_fresh_var(
1762 infer::AssocTypeProjection(projection_ty.item_name),
1765 debug!("projection_bounds: outlives={:?} (3)",
1768 // check whether this predicate applies to our current projection
1769 let cause = self.fcx.misc(span);
1770 match self.eq_types(false, &cause, ty, outlives.0) {
1772 self.register_infer_ok_obligations(ok);
1775 Err(_) => { Err(()) }
1779 debug!("projection_bounds: region_result={:?}",