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::{CodeExtent, RegionMaps};
91 use rustc::hir::def_id::DefId;
92 use rustc::ty::subst::Substs;
94 use rustc::ty::{self, Ty, 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.param_env.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.param_env.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>,
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>,
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>)
228 -> Option<CodeExtent> {
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 = CodeExtent::CallSiteScope(body_id);
290 let old_call_site_scope = self.set_call_site_scope(Some(call_site));
293 let fn_sig_map = &self.tables.borrow().liberated_fn_sigs;
294 match fn_sig_map.get(&id) {
295 Some(f) => f.clone(),
297 bug!("No fn-sig entry for id={}", id);
302 let old_region_bounds_pairs_len = self.region_bound_pairs.len();
304 // Collect the types from which we create inferred bounds.
305 // For the return type, if diverging, substitute `bool` just
306 // because it will have no effect.
308 // FIXME(#27579) return types should not be implied bounds
309 let fn_sig_tys: Vec<_> =
310 fn_sig.inputs().iter().cloned().chain(Some(fn_sig.output())).collect();
312 let old_body_id = self.set_body_id(body_id.node_id);
313 self.relate_free_regions(&fn_sig_tys[..], body_id.node_id, span);
314 self.link_fn_args(CodeExtent::Misc(body_id.node_id), &body.arguments);
315 self.visit_body(body);
316 self.visit_region_obligations(body_id.node_id);
318 let call_site_scope = self.call_site_scope.unwrap();
319 debug!("visit_fn_body body.id {:?} call_site_scope: {:?}",
320 body.id(), call_site_scope);
321 let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope));
322 self.type_of_node_must_outlive(infer::CallReturn(span),
326 self.region_bound_pairs.truncate(old_region_bounds_pairs_len);
328 self.set_body_id(old_body_id);
329 self.set_call_site_scope(old_call_site_scope);
332 fn visit_region_obligations(&mut self, node_id: ast::NodeId)
334 debug!("visit_region_obligations: node_id={}", node_id);
336 // region checking can introduce new pending obligations
337 // which, when processed, might generate new region
338 // obligations. So make sure we process those.
339 self.select_all_obligations_or_error();
341 // Make a copy of the region obligations vec because we'll need
342 // to be able to borrow the fulfillment-cx below when projecting.
343 let region_obligations =
346 .region_obligations(node_id)
349 for r_o in ®ion_obligations {
350 debug!("visit_region_obligations: r_o={:?} cause={:?}",
352 let sup_type = self.resolve_type(r_o.sup_type);
353 let origin = self.code_to_origin(&r_o.cause, sup_type);
354 self.type_must_outlive(origin, sup_type, r_o.sub_region);
357 // Processing the region obligations should not cause the list to grow further:
358 assert_eq!(region_obligations.len(),
359 self.fulfillment_cx.borrow().region_obligations(node_id).len());
362 fn code_to_origin(&self,
363 cause: &traits::ObligationCause<'tcx>,
365 -> SubregionOrigin<'tcx> {
366 SubregionOrigin::from_obligation_cause(cause,
367 || infer::RelateParamBound(cause.span, sup_type))
370 /// This method populates the region map's `free_region_map`. It walks over the transformed
371 /// argument and return types for each function just before we check the body of that function,
372 /// looking for types where you have a borrowed pointer to other borrowed data (e.g., `&'a &'b
373 /// [usize]`. We do not allow references to outlive the things they point at, so we can assume
374 /// that `'a <= 'b`. This holds for both the argument and return types, basically because, on
375 /// the caller side, the caller is responsible for checking that the type of every expression
376 /// (including the actual values for the arguments, as well as the return type of the fn call)
379 /// Tests: `src/test/compile-fail/regions-free-region-ordering-*.rs`
380 fn relate_free_regions(&mut self,
381 fn_sig_tys: &[Ty<'tcx>],
382 body_id: ast::NodeId,
384 debug!("relate_free_regions >>");
386 for &ty in fn_sig_tys {
387 let ty = self.resolve_type(ty);
388 debug!("relate_free_regions(t={:?})", ty);
389 let implied_bounds = ty::wf::implied_bounds(self, body_id, ty, span);
391 // Record any relations between free regions that we observe into the free-region-map.
392 self.free_region_map.relate_free_regions_from_implied_bounds(&implied_bounds);
394 // But also record other relationships, such as `T:'x`,
395 // that don't go into the free-region-map but which we use
397 for implication in implied_bounds {
398 debug!("implication: {:?}", implication);
400 ImpliedBound::RegionSubRegion(r_a @ &ty::ReEarlyBound(_),
402 ImpliedBound::RegionSubRegion(r_a @ &ty::ReFree(_),
403 &ty::ReVar(vid_b)) => {
404 self.add_given(r_a, vid_b);
406 ImpliedBound::RegionSubParam(r_a, param_b) => {
407 self.region_bound_pairs.push((r_a, GenericKind::Param(param_b)));
409 ImpliedBound::RegionSubProjection(r_a, projection_b) => {
410 self.region_bound_pairs.push((r_a, GenericKind::Projection(projection_b)));
412 ImpliedBound::RegionSubRegion(..) => {
413 // In principle, we could record (and take
414 // advantage of) every relationship here, but
415 // we are also free not to -- it simply means
416 // strictly less that we can successfully type
417 // check. (It may also be that we should
418 // revise our inference system to be more
419 // general and to make use of *every*
420 // relationship that arises here, but
421 // presently we do not.)
427 debug!("<< relate_free_regions");
430 fn resolve_regions_and_report_errors(&self) {
431 self.fcx.resolve_regions_and_report_errors(self.subject_def_id,
433 &self.free_region_map);
436 fn constrain_bindings_in_pat(&mut self, pat: &hir::Pat) {
437 debug!("regionck::visit_pat(pat={:?})", pat);
438 pat.each_binding(|_, id, span, _| {
439 // If we have a variable that contains region'd data, that
440 // data will be accessible from anywhere that the variable is
441 // accessed. We must be wary of loops like this:
443 // // from src/test/compile-fail/borrowck-lend-flow.rs
444 // let mut v = box 3, w = box 4;
445 // let mut x = &mut w;
448 // borrow(v); //~ ERROR cannot borrow
449 // x = &mut v; // (1)
452 // Typically, we try to determine the region of a borrow from
453 // those points where it is dereferenced. In this case, one
454 // might imagine that the lifetime of `x` need only be the
455 // body of the loop. But of course this is incorrect because
456 // the pointer that is created at point (1) is consumed at
457 // point (2), meaning that it must be live across the loop
458 // iteration. The easiest way to guarantee this is to require
459 // that the lifetime of any regions that appear in a
460 // variable's type enclose at least the variable's scope.
462 let var_scope = self.region_maps.var_scope(id);
463 let var_region = self.tcx.mk_region(ty::ReScope(var_scope));
465 let origin = infer::BindingTypeIsNotValidAtDecl(span);
466 self.type_of_node_must_outlive(origin, id, var_region);
468 let typ = self.resolve_node_type(id);
469 let _ = dropck::check_safety_of_destructor_if_necessary(
470 self, typ, span, var_scope);
475 impl<'a, 'gcx, 'tcx> Visitor<'gcx> for RegionCtxt<'a, 'gcx, 'tcx> {
476 // (..) FIXME(#3238) should use visit_pat, not visit_arm/visit_local,
477 // However, right now we run into an issue whereby some free
478 // regions are not properly related if they appear within the
479 // types of arguments that must be inferred. This could be
480 // addressed by deferring the construction of the region
481 // hierarchy, and in particular the relationships between free
482 // regions, until regionck, as described in #3238.
484 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'gcx> {
485 NestedVisitorMap::None
488 fn visit_fn(&mut self, _fk: intravisit::FnKind<'gcx>, _: &'gcx hir::FnDecl,
489 b: hir::BodyId, span: Span, id: ast::NodeId) {
490 let body = self.tcx.hir.body(b);
491 self.visit_fn_body(id, body, span)
494 //visit_pat: visit_pat, // (..) see above
496 fn visit_arm(&mut self, arm: &'gcx hir::Arm) {
499 self.constrain_bindings_in_pat(p);
501 intravisit::walk_arm(self, arm);
504 fn visit_local(&mut self, l: &'gcx hir::Local) {
506 self.constrain_bindings_in_pat(&l.pat);
508 intravisit::walk_local(self, l);
511 fn visit_expr(&mut self, expr: &'gcx hir::Expr) {
512 debug!("regionck::visit_expr(e={:?}, repeating_scope={})",
513 expr, self.repeating_scope);
515 // No matter what, the type of each expression must outlive the
516 // scope of that expression. This also guarantees basic WF.
517 let expr_ty = self.resolve_node_type(expr.id);
518 // the region corresponding to this expression
519 let expr_region = self.tcx.node_scope_region(expr.id);
520 self.type_must_outlive(infer::ExprTypeIsNotInScope(expr_ty, expr.span),
521 expr_ty, expr_region);
523 let is_method_call = self.tables.borrow().is_method_call(expr);
525 // If we are calling a method (either explicitly or via an
526 // overloaded operator), check that all of the types provided as
527 // arguments for its type parameters are well-formed, and all the regions
528 // provided as arguments outlive the call.
530 let origin = match expr.node {
531 hir::ExprMethodCall(..) =>
532 infer::ParameterOrigin::MethodCall,
533 hir::ExprUnary(op, _) if op == hir::UnDeref =>
534 infer::ParameterOrigin::OverloadedDeref,
536 infer::ParameterOrigin::OverloadedOperator
539 let substs = self.tables.borrow().node_substs(expr.id);
540 self.substs_wf_in_scope(origin, substs, expr.span, expr_region);
541 // Arguments (sub-expressions) are checked via `constrain_call`, below.
544 // Check any autoderefs or autorefs that appear.
545 let cmt_result = self.constrain_adjustments(expr);
547 // If necessary, constrain destructors in this expression. This will be
548 // the adjusted form if there is an adjustment.
551 self.check_safety_of_rvalue_destructor_if_necessary(head_cmt, expr.span);
554 self.tcx.sess.delay_span_bug(expr.span, "cat_expr Errd");
558 debug!("regionck::visit_expr(e={:?}, repeating_scope={}) - visiting subexprs",
559 expr, self.repeating_scope);
561 hir::ExprPath(_) => {
562 let substs = self.tables.borrow().node_substs(expr.id);
563 let origin = infer::ParameterOrigin::Path;
564 self.substs_wf_in_scope(origin, substs, expr.span, expr_region);
567 hir::ExprCall(ref callee, ref args) => {
569 self.constrain_call(expr, Some(&callee), args.iter().map(|e| &*e));
571 self.constrain_callee(callee.id, expr, &callee);
572 self.constrain_call(expr, None, args.iter().map(|e| &*e));
575 intravisit::walk_expr(self, expr);
578 hir::ExprMethodCall(.., ref args) => {
579 self.constrain_call(expr, Some(&args[0]), args[1..].iter().map(|e| &*e));
581 intravisit::walk_expr(self, expr);
584 hir::ExprAssignOp(_, ref lhs, ref rhs) => {
586 self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter());
589 intravisit::walk_expr(self, expr);
592 hir::ExprIndex(ref lhs, ref rhs) if is_method_call => {
593 self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter());
595 intravisit::walk_expr(self, expr);
598 hir::ExprBinary(_, ref lhs, ref rhs) if is_method_call => {
599 // As `ExprMethodCall`, but the call is via an overloaded op.
600 self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter());
602 intravisit::walk_expr(self, expr);
605 hir::ExprBinary(_, ref lhs, ref rhs) => {
606 // If you do `x OP y`, then the types of `x` and `y` must
607 // outlive the operation you are performing.
608 let lhs_ty = self.resolve_expr_type_adjusted(&lhs);
609 let rhs_ty = self.resolve_expr_type_adjusted(&rhs);
610 for &ty in &[lhs_ty, rhs_ty] {
611 self.type_must_outlive(infer::Operand(expr.span),
614 intravisit::walk_expr(self, expr);
617 hir::ExprUnary(hir::UnDeref, ref base) => {
618 // For *a, the lifetime of a must enclose the deref
620 self.constrain_call(expr, Some(base), None::<hir::Expr>.iter());
622 // For overloaded derefs, base_ty is the input to `Deref::deref`,
623 // but it's a reference type uing the same region as the output.
624 let base_ty = self.resolve_expr_type_adjusted(base);
625 if let ty::TyRef(r_ptr, _) = base_ty.sty {
626 self.mk_subregion_due_to_dereference(expr.span, expr_region, r_ptr);
629 intravisit::walk_expr(self, expr);
632 hir::ExprUnary(_, ref lhs) if is_method_call => {
634 self.constrain_call(expr, Some(&lhs), None::<hir::Expr>.iter());
636 intravisit::walk_expr(self, expr);
639 hir::ExprIndex(ref vec_expr, _) => {
640 // For a[b], the lifetime of a must enclose the deref
641 let vec_type = self.resolve_expr_type_adjusted(&vec_expr);
642 self.constrain_index(expr, vec_type);
644 intravisit::walk_expr(self, expr);
647 hir::ExprCast(ref source, _) => {
648 // Determine if we are casting `source` to a trait
649 // instance. If so, we have to be sure that the type of
650 // the source obeys the trait's region bound.
651 self.constrain_cast(expr, &source);
652 intravisit::walk_expr(self, expr);
655 hir::ExprAddrOf(m, ref base) => {
656 self.link_addr_of(expr, m, &base);
658 // Require that when you write a `&expr` expression, the
659 // resulting pointer has a lifetime that encompasses the
660 // `&expr` expression itself. Note that we constraining
661 // the type of the node expr.id here *before applying
664 // FIXME(#6268) nested method calls requires that this rule change
665 let ty0 = self.resolve_node_type(expr.id);
666 self.type_must_outlive(infer::AddrOf(expr.span), ty0, expr_region);
667 intravisit::walk_expr(self, expr);
670 hir::ExprMatch(ref discr, ref arms, _) => {
671 self.link_match(&discr, &arms[..]);
673 intravisit::walk_expr(self, expr);
676 hir::ExprClosure(.., body_id, _) => {
677 self.check_expr_fn_block(expr, body_id);
680 hir::ExprLoop(ref body, _, _) => {
681 let repeating_scope = self.set_repeating_scope(body.id);
682 intravisit::walk_expr(self, expr);
683 self.set_repeating_scope(repeating_scope);
686 hir::ExprWhile(ref cond, ref body, _) => {
687 let repeating_scope = self.set_repeating_scope(cond.id);
688 self.visit_expr(&cond);
690 self.set_repeating_scope(body.id);
691 self.visit_block(&body);
693 self.set_repeating_scope(repeating_scope);
696 hir::ExprRet(Some(ref ret_expr)) => {
697 let call_site_scope = self.call_site_scope;
698 debug!("visit_expr ExprRet ret_expr.id {} call_site_scope: {:?}",
699 ret_expr.id, call_site_scope);
700 let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope.unwrap()));
701 self.type_of_node_must_outlive(infer::CallReturn(ret_expr.span),
704 intravisit::walk_expr(self, expr);
708 intravisit::walk_expr(self, expr);
714 impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
715 fn constrain_cast(&mut self,
716 cast_expr: &hir::Expr,
717 source_expr: &hir::Expr)
719 debug!("constrain_cast(cast_expr={:?}, source_expr={:?})",
723 let source_ty = self.resolve_node_type(source_expr.id);
724 let target_ty = self.resolve_node_type(cast_expr.id);
726 self.walk_cast(cast_expr, source_ty, target_ty);
729 fn walk_cast(&mut self,
730 cast_expr: &hir::Expr,
733 debug!("walk_cast(from_ty={:?}, to_ty={:?})",
736 match (&from_ty.sty, &to_ty.sty) {
737 /*From:*/ (&ty::TyRef(from_r, ref from_mt),
738 /*To: */ &ty::TyRef(to_r, ref to_mt)) => {
739 // Target cannot outlive source, naturally.
740 self.sub_regions(infer::Reborrow(cast_expr.span), to_r, from_r);
741 self.walk_cast(cast_expr, from_mt.ty, to_mt.ty);
745 /*To: */ &ty::TyDynamic(.., r)) => {
746 // When T is existentially quantified as a trait
747 // `Foo+'to`, it must outlive the region bound `'to`.
748 self.type_must_outlive(infer::RelateObjectBound(cast_expr.span), from_ty, r);
751 /*From:*/ (&ty::TyAdt(from_def, _),
752 /*To: */ &ty::TyAdt(to_def, _)) if from_def.is_box() && to_def.is_box() => {
753 self.walk_cast(cast_expr, from_ty.boxed_ty(), to_ty.boxed_ty());
760 fn check_expr_fn_block(&mut self,
761 expr: &'gcx hir::Expr,
762 body_id: hir::BodyId) {
763 let repeating_scope = self.set_repeating_scope(body_id.node_id);
764 intravisit::walk_expr(self, expr);
765 self.set_repeating_scope(repeating_scope);
768 fn constrain_callee(&mut self,
769 callee_id: ast::NodeId,
770 _call_expr: &hir::Expr,
771 _callee_expr: &hir::Expr) {
772 let callee_ty = self.resolve_node_type(callee_id);
773 match callee_ty.sty {
774 ty::TyFnDef(..) | ty::TyFnPtr(_) => { }
776 // this should not happen, but it does if the program is
781 // "Calling non-function: {}",
787 fn constrain_call<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
788 call_expr: &hir::Expr,
789 receiver: Option<&hir::Expr>,
791 //! Invoked on every call site (i.e., normal calls, method calls,
792 //! and overloaded operators). Constrains the regions which appear
793 //! in the type of the function. Also constrains the regions that
794 //! appear in the arguments appropriately.
796 debug!("constrain_call(call_expr={:?}, receiver={:?})",
800 // `callee_region` is the scope representing the time in which the
803 // FIXME(#6268) to support nested method calls, should be callee_id
804 let callee_scope = CodeExtent::Misc(call_expr.id);
805 let callee_region = self.tcx.mk_region(ty::ReScope(callee_scope));
807 debug!("callee_region={:?}", callee_region);
809 for arg_expr in arg_exprs {
810 debug!("Argument: {:?}", arg_expr);
812 // ensure that any regions appearing in the argument type are
813 // valid for at least the lifetime of the function:
814 self.type_of_node_must_outlive(infer::CallArg(arg_expr.span),
815 arg_expr.id, callee_region);
818 // as loop above, but for receiver
819 if let Some(r) = receiver {
820 debug!("receiver: {:?}", r);
821 self.type_of_node_must_outlive(infer::CallRcvr(r.span),
822 r.id, callee_region);
826 /// Invoked on any adjustments that occur. Checks that if this is a region pointer being
827 /// dereferenced, the lifetime of the pointer includes the deref expr.
828 fn constrain_adjustments(&mut self, expr: &hir::Expr) -> mc::McResult<mc::cmt<'tcx>> {
829 debug!("constrain_adjustments(expr={:?})", expr);
832 let mc = mc::MemCategorizationContext::new(self, &self.region_maps);
833 mc.cat_expr_unadjusted(expr)?
836 //NOTE(@jroesch): mixed RefCell borrow causes crash
837 let adjustments = self.tables.borrow().expr_adjustments(&expr).to_vec();
838 if adjustments.is_empty() {
842 debug!("constrain_adjustments: adjustments={:?}", adjustments);
844 // If necessary, constrain destructors in the unadjusted form of this
846 self.check_safety_of_rvalue_destructor_if_necessary(cmt.clone(), expr.span);
848 let expr_region = self.tcx.node_scope_region(expr.id);
849 for adjustment in adjustments {
850 debug!("constrain_adjustments: adjustment={:?}, cmt={:?}",
853 if let adjustment::Adjust::Deref(Some(deref)) = adjustment.kind {
854 debug!("constrain_adjustments: overloaded deref: {:?}", deref);
856 // Treat overloaded autoderefs as if an AutoBorrow adjustment
857 // was applied on the base type, as that is always the case.
858 let input = self.tcx.mk_ref(deref.region, ty::TypeAndMut {
862 let output = self.tcx.mk_ref(deref.region, ty::TypeAndMut {
863 ty: adjustment.target,
867 self.link_region(expr.span, deref.region,
868 ty::BorrowKind::from_mutbl(deref.mutbl), cmt.clone());
870 // Specialized version of constrain_call.
871 self.type_must_outlive(infer::CallRcvr(expr.span),
873 self.type_must_outlive(infer::CallReturn(expr.span),
874 output, expr_region);
877 if let adjustment::Adjust::Borrow(ref autoref) = adjustment.kind {
878 self.link_autoref(expr, cmt.clone(), autoref);
880 // Require that the resulting region encompasses
883 // FIXME(#6268) remove to support nested method calls
884 self.type_of_node_must_outlive(infer::AutoBorrow(expr.span),
885 expr.id, expr_region);
889 let mc = mc::MemCategorizationContext::new(self, &self.region_maps);
890 cmt = mc.cat_expr_adjusted(expr, cmt, &adjustment)?;
893 if let Categorization::Deref(_, mc::BorrowedPtr(_, r_ptr)) = cmt.cat {
894 self.mk_subregion_due_to_dereference(expr.span,
902 pub fn mk_subregion_due_to_dereference(&mut self,
904 minimum_lifetime: ty::Region<'tcx>,
905 maximum_lifetime: ty::Region<'tcx>) {
906 self.sub_regions(infer::DerefPointer(deref_span),
907 minimum_lifetime, maximum_lifetime)
910 fn check_safety_of_rvalue_destructor_if_necessary(&mut self,
914 Categorization::Rvalue(region, _) => {
916 ty::ReScope(rvalue_scope) => {
917 let typ = self.resolve_type(cmt.ty);
918 let _ = dropck::check_safety_of_destructor_if_necessary(
919 self, typ, span, rvalue_scope);
924 "unexpected rvalue region in rvalue \
925 destructor safety checking: `{:?}`",
934 /// Invoked on any index expression that occurs. Checks that if this is a slice
935 /// being indexed, the lifetime of the pointer includes the deref expr.
936 fn constrain_index(&mut self,
937 index_expr: &hir::Expr,
938 indexed_ty: Ty<'tcx>)
940 debug!("constrain_index(index_expr=?, indexed_ty={}",
941 self.ty_to_string(indexed_ty));
943 let r_index_expr = ty::ReScope(CodeExtent::Misc(index_expr.id));
944 if let ty::TyRef(r_ptr, mt) = indexed_ty.sty {
946 ty::TySlice(_) | ty::TyStr => {
947 self.sub_regions(infer::IndexSlice(index_expr.span),
948 self.tcx.mk_region(r_index_expr), r_ptr);
955 /// Guarantees that any lifetimes which appear in the type of the node `id` (after applying
956 /// adjustments) are valid for at least `minimum_lifetime`
957 fn type_of_node_must_outlive(&mut self,
958 origin: infer::SubregionOrigin<'tcx>,
960 minimum_lifetime: ty::Region<'tcx>)
962 // Try to resolve the type. If we encounter an error, then typeck
963 // is going to fail anyway, so just stop here and let typeck
964 // report errors later on in the writeback phase.
965 let ty0 = self.resolve_node_type(id);
966 let ty = self.tables.borrow().adjustments.get(&id)
967 .and_then(|adj| adj.last())
968 .map_or(ty0, |adj| adj.target);
969 let ty = self.resolve_type(ty);
970 debug!("constrain_regions_in_type_of_node(\
971 ty={}, ty0={}, id={}, minimum_lifetime={:?})",
973 id, minimum_lifetime);
974 self.type_must_outlive(origin, ty, minimum_lifetime);
977 /// Computes the guarantor for an expression `&base` and then ensures that the lifetime of the
978 /// resulting pointer is linked to the lifetime of its guarantor (if any).
979 fn link_addr_of(&mut self, expr: &hir::Expr,
980 mutability: hir::Mutability, base: &hir::Expr) {
981 debug!("link_addr_of(expr={:?}, base={:?})", expr, base);
984 let mc = mc::MemCategorizationContext::new(self, &self.region_maps);
985 ignore_err!(mc.cat_expr(base))
988 debug!("link_addr_of: cmt={:?}", cmt);
990 self.link_region_from_node_type(expr.span, expr.id, mutability, cmt);
993 /// Computes the guarantors for any ref bindings in a `let` and
994 /// then ensures that the lifetime of the resulting pointer is
995 /// linked to the lifetime of the initialization expression.
996 fn link_local(&self, local: &hir::Local) {
997 debug!("regionck::for_local()");
998 let init_expr = match local.init {
1000 Some(ref expr) => &**expr,
1002 let mc = &mc::MemCategorizationContext::new(self, &self.region_maps);
1003 let discr_cmt = ignore_err!(mc.cat_expr(init_expr));
1004 self.link_pattern(mc, discr_cmt, &local.pat);
1007 /// Computes the guarantors for any ref bindings in a match and
1008 /// then ensures that the lifetime of the resulting pointer is
1009 /// linked to the lifetime of its guarantor (if any).
1010 fn link_match(&self, discr: &hir::Expr, arms: &[hir::Arm]) {
1011 debug!("regionck::for_match()");
1012 let mc = &mc::MemCategorizationContext::new(self, &self.region_maps);
1013 let discr_cmt = ignore_err!(mc.cat_expr(discr));
1014 debug!("discr_cmt={:?}", discr_cmt);
1016 for root_pat in &arm.pats {
1017 self.link_pattern(mc, discr_cmt.clone(), &root_pat);
1022 /// Computes the guarantors for any ref bindings in a match and
1023 /// then ensures that the lifetime of the resulting pointer is
1024 /// linked to the lifetime of its guarantor (if any).
1025 fn link_fn_args(&self, body_scope: CodeExtent, args: &[hir::Arg]) {
1026 debug!("regionck::link_fn_args(body_scope={:?})", body_scope);
1027 let mc = &mc::MemCategorizationContext::new(self, &self.region_maps);
1029 let arg_ty = self.node_ty(arg.id);
1030 let re_scope = self.tcx.mk_region(ty::ReScope(body_scope));
1031 let arg_cmt = mc.cat_rvalue(
1032 arg.id, arg.pat.span, re_scope, re_scope, arg_ty);
1033 debug!("arg_ty={:?} arg_cmt={:?} arg={:?}",
1037 self.link_pattern(mc, arg_cmt, &arg.pat);
1041 /// Link lifetimes of any ref bindings in `root_pat` to the pointers found
1042 /// in the discriminant, if needed.
1043 fn link_pattern<'t>(&self,
1044 mc: &mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
1045 discr_cmt: mc::cmt<'tcx>,
1046 root_pat: &hir::Pat) {
1047 debug!("link_pattern(discr_cmt={:?}, root_pat={:?})",
1050 let _ = mc.cat_pattern(discr_cmt, root_pat, |_, sub_cmt, sub_pat| {
1051 match sub_pat.node {
1053 PatKind::Binding(hir::BindByRef(mutbl), ..) => {
1054 self.link_region_from_node_type(sub_pat.span, sub_pat.id,
1062 /// Link lifetime of borrowed pointer resulting from autoref to lifetimes in the value being
1064 fn link_autoref(&self,
1066 expr_cmt: mc::cmt<'tcx>,
1067 autoref: &adjustment::AutoBorrow<'tcx>)
1069 debug!("link_autoref(autoref={:?}, expr_cmt={:?})", autoref, expr_cmt);
1072 adjustment::AutoBorrow::Ref(r, m) => {
1073 self.link_region(expr.span, r,
1074 ty::BorrowKind::from_mutbl(m), expr_cmt);
1077 adjustment::AutoBorrow::RawPtr(m) => {
1078 let r = self.tcx.node_scope_region(expr.id);
1079 self.link_region(expr.span, r, ty::BorrowKind::from_mutbl(m), expr_cmt);
1084 /// Like `link_region()`, except that the region is extracted from the type of `id`,
1085 /// which must be some reference (`&T`, `&str`, etc).
1086 fn link_region_from_node_type(&self,
1089 mutbl: hir::Mutability,
1090 cmt_borrowed: mc::cmt<'tcx>) {
1091 debug!("link_region_from_node_type(id={:?}, mutbl={:?}, cmt_borrowed={:?})",
1092 id, mutbl, cmt_borrowed);
1094 let rptr_ty = self.resolve_node_type(id);
1095 if let ty::TyRef(r, _) = rptr_ty.sty {
1096 debug!("rptr_ty={}", rptr_ty);
1097 self.link_region(span, r, ty::BorrowKind::from_mutbl(mutbl),
1102 /// Informs the inference engine that `borrow_cmt` is being borrowed with
1103 /// kind `borrow_kind` and lifetime `borrow_region`.
1104 /// In order to ensure borrowck is satisfied, this may create constraints
1105 /// between regions, as explained in `link_reborrowed_region()`.
1106 fn link_region(&self,
1108 borrow_region: ty::Region<'tcx>,
1109 borrow_kind: ty::BorrowKind,
1110 borrow_cmt: mc::cmt<'tcx>) {
1111 let mut borrow_cmt = borrow_cmt;
1112 let mut borrow_kind = borrow_kind;
1114 let origin = infer::DataBorrowed(borrow_cmt.ty, span);
1115 self.type_must_outlive(origin, borrow_cmt.ty, borrow_region);
1118 debug!("link_region(borrow_region={:?}, borrow_kind={:?}, borrow_cmt={:?})",
1122 match borrow_cmt.cat.clone() {
1123 Categorization::Deref(ref_cmt, mc::Implicit(ref_kind, ref_region)) |
1124 Categorization::Deref(ref_cmt, mc::BorrowedPtr(ref_kind, ref_region)) => {
1125 match self.link_reborrowed_region(span,
1126 borrow_region, borrow_kind,
1127 ref_cmt, ref_region, ref_kind,
1139 Categorization::Downcast(cmt_base, _) |
1140 Categorization::Deref(cmt_base, mc::Unique) |
1141 Categorization::Interior(cmt_base, _) => {
1142 // Borrowing interior or owned data requires the base
1143 // to be valid and borrowable in the same fashion.
1144 borrow_cmt = cmt_base;
1145 borrow_kind = borrow_kind;
1148 Categorization::Deref(_, mc::UnsafePtr(..)) |
1149 Categorization::StaticItem |
1150 Categorization::Upvar(..) |
1151 Categorization::Local(..) |
1152 Categorization::Rvalue(..) => {
1153 // These are all "base cases" with independent lifetimes
1154 // that are not subject to inference
1161 /// This is the most complicated case: the path being borrowed is
1162 /// itself the referent of a borrowed pointer. Let me give an
1163 /// example fragment of code to make clear(er) the situation:
1165 /// let r: &'a mut T = ...; // the original reference "r" has lifetime 'a
1167 /// &'z *r // the reborrow has lifetime 'z
1169 /// Now, in this case, our primary job is to add the inference
1170 /// constraint that `'z <= 'a`. Given this setup, let's clarify the
1171 /// parameters in (roughly) terms of the example:
1173 /// A borrow of: `& 'z bk * r` where `r` has type `& 'a bk T`
1174 /// borrow_region ^~ ref_region ^~
1175 /// borrow_kind ^~ ref_kind ^~
1178 /// Here `bk` stands for some borrow-kind (e.g., `mut`, `uniq`, etc).
1180 /// Unfortunately, there are some complications beyond the simple
1181 /// scenario I just painted:
1183 /// 1. The reference `r` might in fact be a "by-ref" upvar. In that
1184 /// case, we have two jobs. First, we are inferring whether this reference
1185 /// should be an `&T`, `&mut T`, or `&uniq T` reference, and we must
1186 /// adjust that based on this borrow (e.g., if this is an `&mut` borrow,
1187 /// then `r` must be an `&mut` reference). Second, whenever we link
1188 /// two regions (here, `'z <= 'a`), we supply a *cause*, and in this
1189 /// case we adjust the cause to indicate that the reference being
1190 /// "reborrowed" is itself an upvar. This provides a nicer error message
1191 /// should something go wrong.
1193 /// 2. There may in fact be more levels of reborrowing. In the
1194 /// example, I said the borrow was like `&'z *r`, but it might
1195 /// in fact be a borrow like `&'z **q` where `q` has type `&'a
1196 /// &'b mut T`. In that case, we want to ensure that `'z <= 'a`
1197 /// and `'z <= 'b`. This is explained more below.
1199 /// The return value of this function indicates whether we need to
1200 /// recurse and process `ref_cmt` (see case 2 above).
1201 fn link_reborrowed_region(&self,
1203 borrow_region: ty::Region<'tcx>,
1204 borrow_kind: ty::BorrowKind,
1205 ref_cmt: mc::cmt<'tcx>,
1206 ref_region: ty::Region<'tcx>,
1207 mut ref_kind: ty::BorrowKind,
1209 -> Option<(mc::cmt<'tcx>, ty::BorrowKind)>
1211 // Possible upvar ID we may need later to create an entry in the
1214 // Detect by-ref upvar `x`:
1215 let cause = match note {
1216 mc::NoteUpvarRef(ref upvar_id) => {
1217 let upvar_capture_map = &self.tables.borrow_mut().upvar_capture_map;
1218 match upvar_capture_map.get(upvar_id) {
1219 Some(&ty::UpvarCapture::ByRef(ref upvar_borrow)) => {
1220 // The mutability of the upvar may have been modified
1221 // by the above adjustment, so update our local variable.
1222 ref_kind = upvar_borrow.kind;
1224 infer::ReborrowUpvar(span, *upvar_id)
1227 span_bug!( span, "Illegal upvar id: {:?}", upvar_id);
1231 mc::NoteClosureEnv(ref upvar_id) => {
1232 // We don't have any mutability changes to propagate, but
1233 // we do want to note that an upvar reborrow caused this
1235 infer::ReborrowUpvar(span, *upvar_id)
1238 infer::Reborrow(span)
1242 debug!("link_reborrowed_region: {:?} <= {:?}",
1245 self.sub_regions(cause, borrow_region, ref_region);
1247 // If we end up needing to recurse and establish a region link
1248 // with `ref_cmt`, calculate what borrow kind we will end up
1249 // needing. This will be used below.
1251 // One interesting twist is that we can weaken the borrow kind
1252 // when we recurse: to reborrow an `&mut` referent as mutable,
1253 // borrowck requires a unique path to the `&mut` reference but not
1254 // necessarily a *mutable* path.
1255 let new_borrow_kind = match borrow_kind {
1258 ty::MutBorrow | ty::UniqueImmBorrow =>
1262 // Decide whether we need to recurse and link any regions within
1263 // the `ref_cmt`. This is concerned for the case where the value
1264 // being reborrowed is in fact a borrowed pointer found within
1265 // another borrowed pointer. For example:
1267 // let p: &'b &'a mut T = ...;
1271 // What makes this case particularly tricky is that, if the data
1272 // being borrowed is a `&mut` or `&uniq` borrow, borrowck requires
1273 // not only that `'z <= 'a`, (as before) but also `'z <= 'b`
1274 // (otherwise the user might mutate through the `&mut T` reference
1275 // after `'b` expires and invalidate the borrow we are looking at
1278 // So let's re-examine our parameters in light of this more
1279 // complicated (possible) scenario:
1281 // A borrow of: `& 'z bk * * p` where `p` has type `&'b bk & 'a bk T`
1282 // borrow_region ^~ ref_region ^~
1283 // borrow_kind ^~ ref_kind ^~
1286 // (Note that since we have not examined `ref_cmt.cat`, we don't
1287 // know whether this scenario has occurred; but I wanted to show
1288 // how all the types get adjusted.)
1291 // The reference being reborrowed is a sharable ref of
1292 // type `&'a T`. In this case, it doesn't matter where we
1293 // *found* the `&T` pointer, the memory it references will
1294 // be valid and immutable for `'a`. So we can stop here.
1296 // (Note that the `borrow_kind` must also be ImmBorrow or
1297 // else the user is borrowed imm memory as mut memory,
1298 // which means they'll get an error downstream in borrowck
1303 ty::MutBorrow | ty::UniqueImmBorrow => {
1304 // The reference being reborrowed is either an `&mut T` or
1305 // `&uniq T`. This is the case where recursion is needed.
1306 return Some((ref_cmt, new_borrow_kind));
1311 /// Checks that the values provided for type/region arguments in a given
1312 /// expression are well-formed and in-scope.
1313 fn substs_wf_in_scope(&mut self,
1314 origin: infer::ParameterOrigin,
1315 substs: &Substs<'tcx>,
1317 expr_region: ty::Region<'tcx>) {
1318 debug!("substs_wf_in_scope(substs={:?}, \
1322 substs, expr_region, origin, expr_span);
1324 let origin = infer::ParameterInScope(origin, expr_span);
1326 for region in substs.regions() {
1327 self.sub_regions(origin.clone(), expr_region, region);
1330 for ty in substs.types() {
1331 let ty = self.resolve_type(ty);
1332 self.type_must_outlive(origin.clone(), ty, expr_region);
1336 /// Ensures that type is well-formed in `region`, which implies (among
1337 /// other things) that all borrowed data reachable via `ty` outlives
1339 pub fn type_must_outlive(&self,
1340 origin: infer::SubregionOrigin<'tcx>,
1342 region: ty::Region<'tcx>)
1344 let ty = self.resolve_type(ty);
1346 debug!("type_must_outlive(ty={:?}, region={:?}, origin={:?})",
1351 assert!(!ty.has_escaping_regions());
1353 let components = self.tcx.outlives_components(ty);
1354 self.components_must_outlive(origin, components, region);
1357 fn components_must_outlive(&self,
1358 origin: infer::SubregionOrigin<'tcx>,
1359 components: Vec<ty::outlives::Component<'tcx>>,
1360 region: ty::Region<'tcx>)
1362 for component in components {
1363 let origin = origin.clone();
1365 ty::outlives::Component::Region(region1) => {
1366 self.sub_regions(origin, region, region1);
1368 ty::outlives::Component::Param(param_ty) => {
1369 self.param_ty_must_outlive(origin, region, param_ty);
1371 ty::outlives::Component::Projection(projection_ty) => {
1372 self.projection_must_outlive(origin, region, projection_ty);
1374 ty::outlives::Component::EscapingProjection(subcomponents) => {
1375 self.components_must_outlive(origin, subcomponents, region);
1377 ty::outlives::Component::UnresolvedInferenceVariable(v) => {
1378 // ignore this, we presume it will yield an error
1379 // later, since if a type variable is not resolved by
1380 // this point it never will be
1381 self.tcx.sess.delay_span_bug(
1383 &format!("unresolved inference variable in outlives: {:?}", v));
1389 fn param_ty_must_outlive(&self,
1390 origin: infer::SubregionOrigin<'tcx>,
1391 region: ty::Region<'tcx>,
1392 param_ty: ty::ParamTy) {
1393 debug!("param_ty_must_outlive(region={:?}, param_ty={:?}, origin={:?})",
1394 region, param_ty, origin);
1396 let verify_bound = self.param_bound(param_ty);
1397 let generic = GenericKind::Param(param_ty);
1398 self.verify_generic_bound(origin, generic, region, verify_bound);
1401 fn projection_must_outlive(&self,
1402 origin: infer::SubregionOrigin<'tcx>,
1403 region: ty::Region<'tcx>,
1404 projection_ty: ty::ProjectionTy<'tcx>)
1406 debug!("projection_must_outlive(region={:?}, projection_ty={:?}, origin={:?})",
1407 region, projection_ty, origin);
1409 // This case is thorny for inference. The fundamental problem is
1410 // that there are many cases where we have choice, and inference
1411 // doesn't like choice (the current region inference in
1412 // particular). :) First off, we have to choose between using the
1413 // OutlivesProjectionEnv, OutlivesProjectionTraitDef, and
1414 // OutlivesProjectionComponent rules, any one of which is
1415 // sufficient. If there are no inference variables involved, it's
1416 // not hard to pick the right rule, but if there are, we're in a
1417 // bit of a catch 22: if we picked which rule we were going to
1418 // use, we could add constraints to the region inference graph
1419 // that make it apply, but if we don't add those constraints, the
1420 // rule might not apply (but another rule might). For now, we err
1421 // on the side of adding too few edges into the graph.
1423 // Compute the bounds we can derive from the environment or trait
1424 // definition. We know that the projection outlives all the
1425 // regions in this list.
1426 let env_bounds = self.projection_declared_bounds(origin.span(), projection_ty);
1428 debug!("projection_must_outlive: env_bounds={:?}",
1431 // If we know that the projection outlives 'static, then we're
1433 if env_bounds.contains(&&ty::ReStatic) {
1434 debug!("projection_must_outlive: 'static as declared bound");
1438 // If declared bounds list is empty, the only applicable rule is
1439 // OutlivesProjectionComponent. If there are inference variables,
1440 // then, we can break down the outlives into more primitive
1441 // components without adding unnecessary edges.
1443 // If there are *no* inference variables, however, we COULD do
1444 // this, but we choose not to, because the error messages are less
1445 // good. For example, a requirement like `T::Item: 'r` would be
1446 // translated to a requirement that `T: 'r`; when this is reported
1447 // to the user, it will thus say "T: 'r must hold so that T::Item:
1448 // 'r holds". But that makes it sound like the only way to fix
1449 // the problem is to add `T: 'r`, which isn't true. So, if there are no
1450 // inference variables, we use a verify constraint instead of adding
1451 // edges, which winds up enforcing the same condition.
1452 let needs_infer = projection_ty.trait_ref.needs_infer();
1453 if env_bounds.is_empty() && needs_infer {
1454 debug!("projection_must_outlive: no declared bounds");
1456 for component_ty in projection_ty.trait_ref.substs.types() {
1457 self.type_must_outlive(origin.clone(), component_ty, region);
1460 for r in projection_ty.trait_ref.substs.regions() {
1461 self.sub_regions(origin.clone(), region, r);
1467 // If we find that there is a unique declared bound `'b`, and this bound
1468 // appears in the trait reference, then the best action is to require that `'b:'r`,
1469 // so do that. This is best no matter what rule we use:
1471 // - OutlivesProjectionEnv or OutlivesProjectionTraitDef: these would translate to
1472 // the requirement that `'b:'r`
1473 // - OutlivesProjectionComponent: this would require `'b:'r` in addition to
1475 if !env_bounds.is_empty() && env_bounds[1..].iter().all(|b| *b == env_bounds[0]) {
1476 let unique_bound = env_bounds[0];
1477 debug!("projection_must_outlive: unique declared bound = {:?}", unique_bound);
1478 if projection_ty.trait_ref.substs.regions().any(|r| env_bounds.contains(&r)) {
1479 debug!("projection_must_outlive: unique declared bound appears in trait ref");
1480 self.sub_regions(origin.clone(), region, unique_bound);
1485 // Fallback to verifying after the fact that there exists a
1486 // declared bound, or that all the components appearing in the
1487 // projection outlive; in some cases, this may add insufficient
1488 // edges into the inference graph, leading to inference failures
1489 // even though a satisfactory solution exists.
1490 let verify_bound = self.projection_bound(origin.span(), env_bounds, projection_ty);
1491 let generic = GenericKind::Projection(projection_ty);
1492 self.verify_generic_bound(origin, generic.clone(), region, verify_bound);
1495 fn type_bound(&self, span: Span, ty: Ty<'tcx>) -> VerifyBound<'tcx> {
1500 ty::TyProjection(data) => {
1501 let declared_bounds = self.projection_declared_bounds(span, data);
1502 self.projection_bound(span, declared_bounds, data)
1505 self.recursive_type_bound(span, ty)
1510 fn param_bound(&self, param_ty: ty::ParamTy) -> VerifyBound<'tcx> {
1511 debug!("param_bound(param_ty={:?})",
1514 let mut param_bounds = self.declared_generic_bounds_from_env(GenericKind::Param(param_ty));
1516 // Add in the default bound of fn body that applies to all in
1517 // scope type parameters:
1518 param_bounds.extend(self.implicit_region_bound);
1520 VerifyBound::AnyRegion(param_bounds)
1523 fn projection_declared_bounds(&self,
1525 projection_ty: ty::ProjectionTy<'tcx>)
1526 -> Vec<ty::Region<'tcx>>
1528 // First assemble bounds from where clauses and traits.
1530 let mut declared_bounds =
1531 self.declared_generic_bounds_from_env(GenericKind::Projection(projection_ty));
1533 declared_bounds.extend_from_slice(
1534 &self.declared_projection_bounds_from_trait(span, projection_ty));
1539 fn projection_bound(&self,
1541 declared_bounds: Vec<ty::Region<'tcx>>,
1542 projection_ty: ty::ProjectionTy<'tcx>)
1543 -> VerifyBound<'tcx> {
1544 debug!("projection_bound(declared_bounds={:?}, projection_ty={:?})",
1545 declared_bounds, projection_ty);
1547 // see the extensive comment in projection_must_outlive
1549 let ty = self.tcx.mk_projection(projection_ty.trait_ref, projection_ty.item_name);
1550 let recursive_bound = self.recursive_type_bound(span, ty);
1552 VerifyBound::AnyRegion(declared_bounds).or(recursive_bound)
1555 fn recursive_type_bound(&self, span: Span, ty: Ty<'tcx>) -> VerifyBound<'tcx> {
1556 let mut bounds = vec![];
1558 for subty in ty.walk_shallow() {
1559 bounds.push(self.type_bound(span, subty));
1562 let mut regions = ty.regions();
1563 regions.retain(|r| !r.is_late_bound()); // ignore late-bound regions
1564 bounds.push(VerifyBound::AllRegions(regions));
1566 // remove bounds that must hold, since they are not interesting
1567 bounds.retain(|b| !b.must_hold());
1569 if bounds.len() == 1 {
1570 bounds.pop().unwrap()
1572 VerifyBound::AllBounds(bounds)
1576 fn declared_generic_bounds_from_env(&self, generic: GenericKind<'tcx>)
1577 -> Vec<ty::Region<'tcx>>
1579 let param_env = &self.param_env;
1581 // To start, collect bounds from user:
1582 let mut param_bounds = self.tcx.required_region_bounds(generic.to_ty(self.tcx),
1583 param_env.caller_bounds.to_vec());
1585 // Next, collect regions we scraped from the well-formedness
1586 // constraints in the fn signature. To do that, we walk the list
1587 // of known relations from the fn ctxt.
1589 // This is crucial because otherwise code like this fails:
1591 // fn foo<'a, A>(x: &'a A) { x.bar() }
1593 // The problem is that the type of `x` is `&'a A`. To be
1594 // well-formed, then, A must be lower-generic by `'a`, but we
1595 // don't know that this holds from first principles.
1596 for &(r, p) in &self.region_bound_pairs {
1597 debug!("generic={:?} p={:?}",
1601 param_bounds.push(r);
1608 fn declared_projection_bounds_from_trait(&self,
1610 projection_ty: ty::ProjectionTy<'tcx>)
1611 -> Vec<ty::Region<'tcx>>
1613 debug!("projection_bounds(projection_ty={:?})",
1616 let ty = self.tcx.mk_projection(projection_ty.trait_ref.clone(),
1617 projection_ty.item_name);
1619 // Say we have a projection `<T as SomeTrait<'a>>::SomeType`. We are interested
1620 // in looking for a trait definition like:
1623 // trait SomeTrait<'a> {
1624 // type SomeType : 'a;
1628 // we can thus deduce that `<T as SomeTrait<'a>>::SomeType : 'a`.
1629 let trait_predicates = self.tcx.predicates_of(projection_ty.trait_ref.def_id);
1630 assert_eq!(trait_predicates.parent, None);
1631 let predicates = trait_predicates.predicates.as_slice().to_vec();
1632 traits::elaborate_predicates(self.tcx, predicates)
1633 .filter_map(|predicate| {
1634 // we're only interesting in `T : 'a` style predicates:
1635 let outlives = match predicate {
1636 ty::Predicate::TypeOutlives(data) => data,
1637 _ => { return None; }
1640 debug!("projection_bounds: outlives={:?} (1)",
1643 // apply the substitutions (and normalize any projected types)
1644 let outlives = self.instantiate_type_scheme(span,
1645 projection_ty.trait_ref.substs,
1648 debug!("projection_bounds: outlives={:?} (2)",
1651 let region_result = self.commit_if_ok(|_| {
1653 self.replace_late_bound_regions_with_fresh_var(
1655 infer::AssocTypeProjection(projection_ty.item_name),
1658 debug!("projection_bounds: outlives={:?} (3)",
1661 // check whether this predicate applies to our current projection
1662 let cause = self.fcx.misc(span);
1663 match self.eq_types(false, &cause, ty, outlives.0) {
1665 self.register_infer_ok_obligations(ok);
1668 Err(_) => { Err(()) }
1672 debug!("projection_bounds: region_result={:?}",