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};
91 use rustc::ty::subst::Substs;
93 use rustc::ty::{self, Ty, MethodCall, TypeFoldable};
94 use rustc::infer::{self, GenericKind, SubregionOrigin, VerifyBound};
95 use rustc::ty::adjustment;
96 use rustc::ty::wf::ImpliedBound;
101 use syntax_pos::Span;
102 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
103 use rustc::hir::{self, PatKind};
105 // a variation on try that just returns unit
106 macro_rules! ignore_err {
107 ($e:expr) => (match $e { Ok(e) => e, Err(_) => return () })
110 ///////////////////////////////////////////////////////////////////////////
111 // PUBLIC ENTRY POINTS
113 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
114 pub fn regionck_expr(&self, body: &'gcx hir::Body) {
115 let id = body.value.id;
116 let mut rcx = RegionCtxt::new(self, RepeatingScope(id), id, Subject(id));
117 if self.err_count_since_creation() == 0 {
118 // regionck assumes typeck succeeded
119 rcx.visit_body(body);
120 rcx.visit_region_obligations(id);
122 rcx.resolve_regions_and_report_errors();
124 assert!(self.tables.borrow().free_region_map.is_empty());
125 self.tables.borrow_mut().free_region_map = rcx.free_region_map;
128 /// Region checking during the WF phase for items. `wf_tys` are the
129 /// types from which we should derive implied bounds, if any.
130 pub fn regionck_item(&self,
131 item_id: ast::NodeId,
133 wf_tys: &[Ty<'tcx>]) {
134 debug!("regionck_item(item.id={:?}, wf_tys={:?}", item_id, wf_tys);
135 let mut rcx = RegionCtxt::new(self, RepeatingScope(item_id), item_id, Subject(item_id));
136 rcx.free_region_map.relate_free_regions_from_predicates(
137 &self.parameter_environment.caller_bounds);
138 rcx.relate_free_regions(wf_tys, item_id, span);
139 rcx.visit_region_obligations(item_id);
140 rcx.resolve_regions_and_report_errors();
143 pub fn regionck_fn(&self,
145 body: &'gcx hir::Body) {
146 debug!("regionck_fn(id={})", fn_id);
147 let node_id = body.value.id;
148 let mut rcx = RegionCtxt::new(self, RepeatingScope(node_id), node_id, Subject(fn_id));
150 if self.err_count_since_creation() == 0 {
151 // regionck assumes typeck succeeded
152 rcx.visit_fn_body(fn_id, body, self.tcx.hir.span(fn_id));
155 rcx.free_region_map.relate_free_regions_from_predicates(
156 &self.parameter_environment.caller_bounds);
158 rcx.resolve_regions_and_report_errors();
160 // In this mode, we also copy the free-region-map into the
161 // tables of the enclosing fcx. In the other regionck modes
162 // (e.g., `regionck_item`), we don't have an enclosing tables.
163 assert!(self.tables.borrow().free_region_map.is_empty());
164 self.tables.borrow_mut().free_region_map = rcx.free_region_map;
168 ///////////////////////////////////////////////////////////////////////////
171 pub struct RegionCtxt<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
172 pub fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
174 region_bound_pairs: Vec<(&'tcx ty::Region, GenericKind<'tcx>)>,
176 free_region_map: FreeRegionMap,
178 // id of innermost fn body id
179 body_id: ast::NodeId,
181 // call_site scope of innermost fn
182 call_site_scope: Option<CodeExtent>,
184 // id of innermost fn or loop
185 repeating_scope: ast::NodeId,
187 // id of AST node being analyzed (the subject of the analysis).
188 subject: ast::NodeId,
192 impl<'a, 'gcx, 'tcx> Deref for RegionCtxt<'a, 'gcx, 'tcx> {
193 type Target = FnCtxt<'a, 'gcx, 'tcx>;
194 fn deref(&self) -> &Self::Target {
199 pub struct RepeatingScope(ast::NodeId);
200 pub struct Subject(ast::NodeId);
202 impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
203 pub fn new(fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
204 RepeatingScope(initial_repeating_scope): RepeatingScope,
205 initial_body_id: ast::NodeId,
206 Subject(subject): Subject) -> RegionCtxt<'a, 'gcx, 'tcx> {
209 repeating_scope: initial_repeating_scope,
210 body_id: initial_body_id,
211 call_site_scope: None,
213 region_bound_pairs: Vec::new(),
214 free_region_map: FreeRegionMap::new(),
218 fn set_call_site_scope(&mut self, call_site_scope: Option<CodeExtent>) -> Option<CodeExtent> {
219 mem::replace(&mut self.call_site_scope, call_site_scope)
222 fn set_body_id(&mut self, body_id: ast::NodeId) -> ast::NodeId {
223 mem::replace(&mut self.body_id, body_id)
226 fn set_repeating_scope(&mut self, scope: ast::NodeId) -> ast::NodeId {
227 mem::replace(&mut self.repeating_scope, scope)
230 /// Try to resolve the type for the given node, returning t_err if an error results. Note that
231 /// we never care about the details of the error, the same error will be detected and reported
232 /// in the writeback phase.
234 /// Note one important point: we do not attempt to resolve *region variables* here. This is
235 /// because regionck is essentially adding constraints to those region variables and so may yet
236 /// influence how they are resolved.
238 /// Consider this silly example:
241 /// fn borrow(x: &i32) -> &i32 {x}
242 /// fn foo(x: @i32) -> i32 { // block: B
243 /// let b = borrow(x); // region: <R0>
248 /// Here, the region of `b` will be `<R0>`. `<R0>` is constrained to be some subregion of the
249 /// block B and some superregion of the call. If we forced it now, we'd choose the smaller
250 /// region (the call). But that would make the *b illegal. Since we don't resolve, the type
251 /// of b will be `&<R0>.i32` and then `*b` will require that `<R0>` be bigger than the let and
252 /// the `*b` expression, so we will effectively resolve `<R0>` to be the block B.
253 pub fn resolve_type(&self, unresolved_ty: Ty<'tcx>) -> Ty<'tcx> {
254 self.resolve_type_vars_if_possible(&unresolved_ty)
257 /// Try to resolve the type for the given node.
258 fn resolve_node_type(&self, id: ast::NodeId) -> Ty<'tcx> {
259 let t = self.node_ty(id);
263 /// Try to resolve the type for the given node.
264 pub fn resolve_expr_type_adjusted(&mut self, expr: &hir::Expr) -> Ty<'tcx> {
265 let ty = self.tables.borrow().expr_ty_adjusted(expr);
266 self.resolve_type(ty)
269 fn visit_fn_body(&mut self,
270 id: ast::NodeId, // the id of the fn itself
271 body: &'gcx hir::Body,
274 // When we enter a function, we can derive
275 debug!("visit_fn_body(id={})", id);
277 let body_id = body.id();
279 let call_site = self.tcx.region_maps().lookup_code_extent(
280 region::CodeExtentData::CallSiteScope { fn_id: id, body_id: body_id.node_id });
281 let old_call_site_scope = self.set_call_site_scope(Some(call_site));
284 let fn_sig_map = &self.tables.borrow().liberated_fn_sigs;
285 match fn_sig_map.get(&id) {
286 Some(f) => f.clone(),
288 bug!("No fn-sig entry for id={}", id);
293 let old_region_bounds_pairs_len = self.region_bound_pairs.len();
295 // Collect the types from which we create inferred bounds.
296 // For the return type, if diverging, substitute `bool` just
297 // because it will have no effect.
299 // FIXME(#27579) return types should not be implied bounds
300 let fn_sig_tys: Vec<_> =
301 fn_sig.inputs().iter().cloned().chain(Some(fn_sig.output())).collect();
303 let old_body_id = self.set_body_id(body_id.node_id);
304 self.relate_free_regions(&fn_sig_tys[..], body_id.node_id, span);
305 self.link_fn_args(self.tcx.region_maps().node_extent(body_id.node_id), &body.arguments);
306 self.visit_body(body);
307 self.visit_region_obligations(body_id.node_id);
309 let call_site_scope = self.call_site_scope.unwrap();
310 debug!("visit_fn_body body.id {:?} call_site_scope: {:?}",
311 body.id(), call_site_scope);
312 let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope));
313 self.type_of_node_must_outlive(infer::CallReturn(span),
317 self.region_bound_pairs.truncate(old_region_bounds_pairs_len);
319 self.set_body_id(old_body_id);
320 self.set_call_site_scope(old_call_site_scope);
323 fn visit_region_obligations(&mut self, node_id: ast::NodeId)
325 debug!("visit_region_obligations: node_id={}", node_id);
327 // region checking can introduce new pending obligations
328 // which, when processed, might generate new region
329 // obligations. So make sure we process those.
330 self.select_all_obligations_or_error();
332 // Make a copy of the region obligations vec because we'll need
333 // to be able to borrow the fulfillment-cx below when projecting.
334 let region_obligations =
337 .region_obligations(node_id)
340 for r_o in ®ion_obligations {
341 debug!("visit_region_obligations: r_o={:?} cause={:?}",
343 let sup_type = self.resolve_type(r_o.sup_type);
344 let origin = self.code_to_origin(&r_o.cause, sup_type);
345 self.type_must_outlive(origin, sup_type, r_o.sub_region);
348 // Processing the region obligations should not cause the list to grow further:
349 assert_eq!(region_obligations.len(),
350 self.fulfillment_cx.borrow().region_obligations(node_id).len());
353 fn code_to_origin(&self,
354 cause: &traits::ObligationCause<'tcx>,
356 -> SubregionOrigin<'tcx> {
357 SubregionOrigin::from_obligation_cause(cause,
358 || infer::RelateParamBound(cause.span, sup_type))
361 /// This method populates the region map's `free_region_map`. It walks over the transformed
362 /// argument and return types for each function just before we check the body of that function,
363 /// looking for types where you have a borrowed pointer to other borrowed data (e.g., `&'a &'b
364 /// [usize]`. We do not allow references to outlive the things they point at, so we can assume
365 /// that `'a <= 'b`. This holds for both the argument and return types, basically because, on
366 /// the caller side, the caller is responsible for checking that the type of every expression
367 /// (including the actual values for the arguments, as well as the return type of the fn call)
370 /// Tests: `src/test/compile-fail/regions-free-region-ordering-*.rs`
371 fn relate_free_regions(&mut self,
372 fn_sig_tys: &[Ty<'tcx>],
373 body_id: ast::NodeId,
375 debug!("relate_free_regions >>");
377 for &ty in fn_sig_tys {
378 let ty = self.resolve_type(ty);
379 debug!("relate_free_regions(t={:?})", ty);
380 let implied_bounds = ty::wf::implied_bounds(self, body_id, ty, span);
382 // Record any relations between free regions that we observe into the free-region-map.
383 self.free_region_map.relate_free_regions_from_implied_bounds(&implied_bounds);
385 // But also record other relationships, such as `T:'x`,
386 // that don't go into the free-region-map but which we use
388 for implication in implied_bounds {
389 debug!("implication: {:?}", implication);
391 ImpliedBound::RegionSubRegion(&ty::ReFree(free_a),
392 &ty::ReVar(vid_b)) => {
393 self.add_given(free_a, vid_b);
395 ImpliedBound::RegionSubParam(r_a, param_b) => {
396 self.region_bound_pairs.push((r_a, GenericKind::Param(param_b)));
398 ImpliedBound::RegionSubProjection(r_a, projection_b) => {
399 self.region_bound_pairs.push((r_a, GenericKind::Projection(projection_b)));
401 ImpliedBound::RegionSubRegion(..) => {
402 // In principle, we could record (and take
403 // advantage of) every relationship here, but
404 // we are also free not to -- it simply means
405 // strictly less that we can successfully type
406 // check. (It may also be that we should
407 // revise our inference system to be more
408 // general and to make use of *every*
409 // relationship that arises here, but
410 // presently we do not.)
416 debug!("<< relate_free_regions");
419 fn resolve_regions_and_report_errors(&self) {
420 let subject_node_id = self.subject;
422 self.fcx.resolve_regions_and_report_errors(&self.free_region_map,
426 fn constrain_bindings_in_pat(&mut self, pat: &hir::Pat) {
428 debug!("regionck::visit_pat(pat={:?})", pat);
429 pat.each_binding(|_, id, span, _| {
430 // If we have a variable that contains region'd data, that
431 // data will be accessible from anywhere that the variable is
432 // accessed. We must be wary of loops like this:
434 // // from src/test/compile-fail/borrowck-lend-flow.rs
435 // let mut v = box 3, w = box 4;
436 // let mut x = &mut w;
439 // borrow(v); //~ ERROR cannot borrow
440 // x = &mut v; // (1)
443 // Typically, we try to determine the region of a borrow from
444 // those points where it is dereferenced. In this case, one
445 // might imagine that the lifetime of `x` need only be the
446 // body of the loop. But of course this is incorrect because
447 // the pointer that is created at point (1) is consumed at
448 // point (2), meaning that it must be live across the loop
449 // iteration. The easiest way to guarantee this is to require
450 // that the lifetime of any regions that appear in a
451 // variable's type enclose at least the variable's scope.
453 let var_scope = tcx.region_maps().var_scope(id);
454 let var_region = self.tcx.mk_region(ty::ReScope(var_scope));
456 let origin = infer::BindingTypeIsNotValidAtDecl(span);
457 self.type_of_node_must_outlive(origin, id, var_region);
459 let typ = self.resolve_node_type(id);
460 let _ = dropck::check_safety_of_destructor_if_necessary(
461 self, typ, span, var_scope);
466 impl<'a, 'gcx, 'tcx> Visitor<'gcx> for RegionCtxt<'a, 'gcx, 'tcx> {
467 // (..) FIXME(#3238) should use visit_pat, not visit_arm/visit_local,
468 // However, right now we run into an issue whereby some free
469 // regions are not properly related if they appear within the
470 // types of arguments that must be inferred. This could be
471 // addressed by deferring the construction of the region
472 // hierarchy, and in particular the relationships between free
473 // regions, until regionck, as described in #3238.
475 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'gcx> {
476 NestedVisitorMap::None
479 fn visit_fn(&mut self, _fk: intravisit::FnKind<'gcx>, _: &'gcx hir::FnDecl,
480 b: hir::BodyId, span: Span, id: ast::NodeId) {
481 let body = self.tcx.hir.body(b);
482 self.visit_fn_body(id, body, span)
485 //visit_pat: visit_pat, // (..) see above
487 fn visit_arm(&mut self, arm: &'gcx hir::Arm) {
490 self.constrain_bindings_in_pat(p);
492 intravisit::walk_arm(self, arm);
495 fn visit_local(&mut self, l: &'gcx hir::Local) {
497 self.constrain_bindings_in_pat(&l.pat);
499 intravisit::walk_local(self, l);
502 fn visit_expr(&mut self, expr: &'gcx hir::Expr) {
503 debug!("regionck::visit_expr(e={:?}, repeating_scope={})",
504 expr, self.repeating_scope);
506 // No matter what, the type of each expression must outlive the
507 // scope of that expression. This also guarantees basic WF.
508 let expr_ty = self.resolve_node_type(expr.id);
509 // the region corresponding to this expression
510 let expr_region = self.tcx.node_scope_region(expr.id);
511 self.type_must_outlive(infer::ExprTypeIsNotInScope(expr_ty, expr.span),
512 expr_ty, expr_region);
514 let method_call = MethodCall::expr(expr.id);
515 let opt_method_callee = self.tables.borrow().method_map.get(&method_call).cloned();
516 let has_method_map = opt_method_callee.is_some();
518 // If we are calling a method (either explicitly or via an
519 // overloaded operator), check that all of the types provided as
520 // arguments for its type parameters are well-formed, and all the regions
521 // provided as arguments outlive the call.
522 if let Some(callee) = opt_method_callee {
523 let origin = match expr.node {
524 hir::ExprMethodCall(..) =>
525 infer::ParameterOrigin::MethodCall,
526 hir::ExprUnary(op, _) if op == hir::UnDeref =>
527 infer::ParameterOrigin::OverloadedDeref,
529 infer::ParameterOrigin::OverloadedOperator
532 self.substs_wf_in_scope(origin, &callee.substs, expr.span, expr_region);
533 self.type_must_outlive(infer::ExprTypeIsNotInScope(callee.ty, expr.span),
534 callee.ty, expr_region);
537 // Check any autoderefs or autorefs that appear.
538 let adjustment = self.tables.borrow().adjustments.get(&expr.id).map(|a| a.clone());
539 if let Some(adjustment) = adjustment {
540 debug!("adjustment={:?}", adjustment);
541 match adjustment.kind {
542 adjustment::Adjust::DerefRef { autoderefs, ref autoref, .. } => {
543 let expr_ty = self.resolve_node_type(expr.id);
544 self.constrain_autoderefs(expr, autoderefs, expr_ty);
545 if let Some(ref autoref) = *autoref {
546 self.link_autoref(expr, autoderefs, autoref);
548 // Require that the resulting region encompasses
551 // FIXME(#6268) remove to support nested method calls
552 self.type_of_node_must_outlive(infer::AutoBorrow(expr.span),
553 expr.id, expr_region);
557 adjustment::AutoObject(_, ref bounds, ..) => {
558 // Determine if we are casting `expr` to a trait
559 // instance. If so, we have to be sure that the type
560 // of the source obeys the new region bound.
561 let source_ty = self.resolve_node_type(expr.id);
562 self.type_must_outlive(infer::RelateObjectBound(expr.span),
563 source_ty, bounds.region_bound);
569 // If necessary, constrain destructors in the unadjusted form of this
572 let mc = mc::MemCategorizationContext::new(self);
573 mc.cat_expr_unadjusted(expr)
577 self.check_safety_of_rvalue_destructor_if_necessary(head_cmt,
581 self.tcx.sess.delay_span_bug(expr.span, "cat_expr_unadjusted Errd");
586 // If necessary, constrain destructors in this expression. This will be
587 // the adjusted form if there is an adjustment.
589 let mc = mc::MemCategorizationContext::new(self);
594 self.check_safety_of_rvalue_destructor_if_necessary(head_cmt, expr.span);
597 self.tcx.sess.delay_span_bug(expr.span, "cat_expr Errd");
601 debug!("regionck::visit_expr(e={:?}, repeating_scope={}) - visiting subexprs",
602 expr, self.repeating_scope);
604 hir::ExprPath(_) => {
605 self.fcx.opt_node_ty_substs(expr.id, |item_substs| {
606 let origin = infer::ParameterOrigin::Path;
607 self.substs_wf_in_scope(origin, &item_substs.substs, expr.span, expr_region);
611 hir::ExprCall(ref callee, ref args) => {
613 self.constrain_call(expr, Some(&callee),
614 args.iter().map(|e| &*e), false);
616 self.constrain_callee(callee.id, expr, &callee);
617 self.constrain_call(expr, None,
618 args.iter().map(|e| &*e), false);
621 intravisit::walk_expr(self, expr);
624 hir::ExprMethodCall(.., ref args) => {
625 self.constrain_call(expr, Some(&args[0]),
626 args[1..].iter().map(|e| &*e), false);
628 intravisit::walk_expr(self, expr);
631 hir::ExprAssignOp(_, ref lhs, ref rhs) => {
633 self.constrain_call(expr, Some(&lhs),
634 Some(&**rhs).into_iter(), false);
637 intravisit::walk_expr(self, expr);
640 hir::ExprIndex(ref lhs, ref rhs) if has_method_map => {
641 self.constrain_call(expr, Some(&lhs),
642 Some(&**rhs).into_iter(), true);
644 intravisit::walk_expr(self, expr);
647 hir::ExprBinary(op, ref lhs, ref rhs) if has_method_map => {
648 let implicitly_ref_args = !op.node.is_by_value();
650 // As `expr_method_call`, but the call is via an
651 // overloaded op. Note that we (sadly) currently use an
652 // implicit "by ref" sort of passing style here. This
653 // should be converted to an adjustment!
654 self.constrain_call(expr, Some(&lhs),
655 Some(&**rhs).into_iter(), implicitly_ref_args);
657 intravisit::walk_expr(self, expr);
660 hir::ExprBinary(_, ref lhs, ref rhs) => {
661 // If you do `x OP y`, then the types of `x` and `y` must
662 // outlive the operation you are performing.
663 let lhs_ty = self.resolve_expr_type_adjusted(&lhs);
664 let rhs_ty = self.resolve_expr_type_adjusted(&rhs);
665 for &ty in &[lhs_ty, rhs_ty] {
666 self.type_must_outlive(infer::Operand(expr.span),
669 intravisit::walk_expr(self, expr);
672 hir::ExprUnary(op, ref lhs) if has_method_map => {
673 let implicitly_ref_args = !op.is_by_value();
676 self.constrain_call(expr, Some(&lhs),
677 None::<hir::Expr>.iter(), implicitly_ref_args);
679 intravisit::walk_expr(self, expr);
682 hir::ExprUnary(hir::UnDeref, ref base) => {
683 // For *a, the lifetime of a must enclose the deref
684 let method_call = MethodCall::expr(expr.id);
685 let base_ty = match self.tables.borrow().method_map.get(&method_call) {
687 self.constrain_call(expr, Some(&base),
688 None::<hir::Expr>.iter(), true);
689 // late-bound regions in overloaded method calls are instantiated
690 let fn_ret = self.tcx.no_late_bound_regions(&method.ty.fn_ret());
693 None => self.resolve_node_type(base.id)
695 if let ty::TyRef(r_ptr, _) = base_ty.sty {
696 self.mk_subregion_due_to_dereference(expr.span, expr_region, r_ptr);
699 intravisit::walk_expr(self, expr);
702 hir::ExprIndex(ref vec_expr, _) => {
703 // For a[b], the lifetime of a must enclose the deref
704 let vec_type = self.resolve_expr_type_adjusted(&vec_expr);
705 self.constrain_index(expr, vec_type);
707 intravisit::walk_expr(self, expr);
710 hir::ExprCast(ref source, _) => {
711 // Determine if we are casting `source` to a trait
712 // instance. If so, we have to be sure that the type of
713 // the source obeys the trait's region bound.
714 self.constrain_cast(expr, &source);
715 intravisit::walk_expr(self, expr);
718 hir::ExprAddrOf(m, ref base) => {
719 self.link_addr_of(expr, m, &base);
721 // Require that when you write a `&expr` expression, the
722 // resulting pointer has a lifetime that encompasses the
723 // `&expr` expression itself. Note that we constraining
724 // the type of the node expr.id here *before applying
727 // FIXME(#6268) nested method calls requires that this rule change
728 let ty0 = self.resolve_node_type(expr.id);
729 self.type_must_outlive(infer::AddrOf(expr.span), ty0, expr_region);
730 intravisit::walk_expr(self, expr);
733 hir::ExprMatch(ref discr, ref arms, _) => {
734 self.link_match(&discr, &arms[..]);
736 intravisit::walk_expr(self, expr);
739 hir::ExprClosure(.., body_id, _) => {
740 self.check_expr_fn_block(expr, body_id);
743 hir::ExprLoop(ref body, _, _) => {
744 let repeating_scope = self.set_repeating_scope(body.id);
745 intravisit::walk_expr(self, expr);
746 self.set_repeating_scope(repeating_scope);
749 hir::ExprWhile(ref cond, ref body, _) => {
750 let repeating_scope = self.set_repeating_scope(cond.id);
751 self.visit_expr(&cond);
753 self.set_repeating_scope(body.id);
754 self.visit_block(&body);
756 self.set_repeating_scope(repeating_scope);
759 hir::ExprRet(Some(ref ret_expr)) => {
760 let call_site_scope = self.call_site_scope;
761 debug!("visit_expr ExprRet ret_expr.id {} call_site_scope: {:?}",
762 ret_expr.id, call_site_scope);
763 let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope.unwrap()));
764 self.type_of_node_must_outlive(infer::CallReturn(ret_expr.span),
767 intravisit::walk_expr(self, expr);
771 intravisit::walk_expr(self, expr);
777 impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
778 fn constrain_cast(&mut self,
779 cast_expr: &hir::Expr,
780 source_expr: &hir::Expr)
782 debug!("constrain_cast(cast_expr={:?}, source_expr={:?})",
786 let source_ty = self.resolve_node_type(source_expr.id);
787 let target_ty = self.resolve_node_type(cast_expr.id);
789 self.walk_cast(cast_expr, source_ty, target_ty);
792 fn walk_cast(&mut self,
793 cast_expr: &hir::Expr,
796 debug!("walk_cast(from_ty={:?}, to_ty={:?})",
799 match (&from_ty.sty, &to_ty.sty) {
800 /*From:*/ (&ty::TyRef(from_r, ref from_mt),
801 /*To: */ &ty::TyRef(to_r, ref to_mt)) => {
802 // Target cannot outlive source, naturally.
803 self.sub_regions(infer::Reborrow(cast_expr.span), to_r, from_r);
804 self.walk_cast(cast_expr, from_mt.ty, to_mt.ty);
808 /*To: */ &ty::TyDynamic(.., r)) => {
809 // When T is existentially quantified as a trait
810 // `Foo+'to`, it must outlive the region bound `'to`.
811 self.type_must_outlive(infer::RelateObjectBound(cast_expr.span), from_ty, r);
814 /*From:*/ (&ty::TyAdt(from_def, _),
815 /*To: */ &ty::TyAdt(to_def, _)) if from_def.is_box() && to_def.is_box() => {
816 self.walk_cast(cast_expr, from_ty.boxed_ty(), to_ty.boxed_ty());
823 fn check_expr_fn_block(&mut self,
824 expr: &'gcx hir::Expr,
825 body_id: hir::BodyId) {
826 let repeating_scope = self.set_repeating_scope(body_id.node_id);
827 intravisit::walk_expr(self, expr);
828 self.set_repeating_scope(repeating_scope);
831 fn constrain_callee(&mut self,
832 callee_id: ast::NodeId,
833 _call_expr: &hir::Expr,
834 _callee_expr: &hir::Expr) {
835 let callee_ty = self.resolve_node_type(callee_id);
836 match callee_ty.sty {
837 ty::TyFnDef(..) | ty::TyFnPtr(_) => { }
839 // this should not happen, but it does if the program is
844 // "Calling non-function: {}",
850 fn constrain_call<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
851 call_expr: &hir::Expr,
852 receiver: Option<&hir::Expr>,
854 implicitly_ref_args: bool) {
855 //! Invoked on every call site (i.e., normal calls, method calls,
856 //! and overloaded operators). Constrains the regions which appear
857 //! in the type of the function. Also constrains the regions that
858 //! appear in the arguments appropriately.
860 debug!("constrain_call(call_expr={:?}, \
862 implicitly_ref_args={})",
865 implicitly_ref_args);
867 // `callee_region` is the scope representing the time in which the
870 // FIXME(#6268) to support nested method calls, should be callee_id
871 let callee_scope = self.tcx.region_maps().node_extent(call_expr.id);
872 let callee_region = self.tcx.mk_region(ty::ReScope(callee_scope));
874 debug!("callee_region={:?}", callee_region);
876 for arg_expr in arg_exprs {
877 debug!("Argument: {:?}", arg_expr);
879 // ensure that any regions appearing in the argument type are
880 // valid for at least the lifetime of the function:
881 self.type_of_node_must_outlive(infer::CallArg(arg_expr.span),
882 arg_expr.id, callee_region);
884 // unfortunately, there are two means of taking implicit
885 // references, and we need to propagate constraints as a
886 // result. modes are going away and the "DerefArgs" code
887 // should be ported to use adjustments
888 if implicitly_ref_args {
889 self.link_by_ref(arg_expr, callee_scope);
893 // as loop above, but for receiver
894 if let Some(r) = receiver {
895 debug!("receiver: {:?}", r);
896 self.type_of_node_must_outlive(infer::CallRcvr(r.span),
897 r.id, callee_region);
898 if implicitly_ref_args {
899 self.link_by_ref(&r, callee_scope);
904 /// Invoked on any auto-dereference that occurs. Checks that if this is a region pointer being
905 /// dereferenced, the lifetime of the pointer includes the deref expr.
906 fn constrain_autoderefs(&mut self,
907 deref_expr: &hir::Expr,
909 mut derefd_ty: Ty<'tcx>)
911 debug!("constrain_autoderefs(deref_expr={:?}, derefs={}, derefd_ty={:?})",
916 let r_deref_expr = self.tcx.node_scope_region(deref_expr.id);
918 let method_call = MethodCall::autoderef(deref_expr.id, i as u32);
919 debug!("constrain_autoderefs: method_call={:?} (of {:?} total)", method_call, derefs);
921 let method = self.tables.borrow().method_map.get(&method_call).map(|m| m.clone());
923 derefd_ty = match method {
925 debug!("constrain_autoderefs: #{} is overloaded, method={:?}",
928 let origin = infer::ParameterOrigin::OverloadedDeref;
929 self.substs_wf_in_scope(origin, method.substs, deref_expr.span, r_deref_expr);
931 // Treat overloaded autoderefs as if an AutoBorrow adjustment
932 // was applied on the base type, as that is always the case.
933 let fn_sig = method.ty.fn_sig();
934 let fn_sig = // late-bound regions should have been instantiated
935 self.tcx.no_late_bound_regions(&fn_sig).unwrap();
936 let self_ty = fn_sig.inputs()[0];
937 let (m, r) = match self_ty.sty {
938 ty::TyRef(r, ref m) => (m.mutbl, r),
942 "bad overloaded deref type {:?}",
947 debug!("constrain_autoderefs: receiver r={:?} m={:?}",
951 let mc = mc::MemCategorizationContext::new(self);
952 let self_cmt = ignore_err!(mc.cat_expr_autoderefd(deref_expr, i));
953 debug!("constrain_autoderefs: self_cmt={:?}",
955 self.link_region(deref_expr.span, r,
956 ty::BorrowKind::from_mutbl(m), self_cmt);
959 // Specialized version of constrain_call.
960 self.type_must_outlive(infer::CallRcvr(deref_expr.span),
961 self_ty, r_deref_expr);
962 self.type_must_outlive(infer::CallReturn(deref_expr.span),
963 fn_sig.output(), r_deref_expr);
969 if let ty::TyRef(r_ptr, _) = derefd_ty.sty {
970 self.mk_subregion_due_to_dereference(deref_expr.span,
971 r_deref_expr, r_ptr);
974 match derefd_ty.builtin_deref(true, ty::NoPreference) {
975 Some(mt) => derefd_ty = mt.ty,
976 /* if this type can't be dereferenced, then there's already an error
977 in the session saying so. Just bail out for now */
983 pub fn mk_subregion_due_to_dereference(&mut self,
985 minimum_lifetime: &'tcx ty::Region,
986 maximum_lifetime: &'tcx ty::Region) {
987 self.sub_regions(infer::DerefPointer(deref_span),
988 minimum_lifetime, maximum_lifetime)
991 fn check_safety_of_rvalue_destructor_if_necessary(&mut self,
995 Categorization::Rvalue(region, _) => {
997 ty::ReScope(rvalue_scope) => {
998 let typ = self.resolve_type(cmt.ty);
999 let _ = dropck::check_safety_of_destructor_if_necessary(
1000 self, typ, span, rvalue_scope);
1005 "unexpected rvalue region in rvalue \
1006 destructor safety checking: `{:?}`",
1015 /// Invoked on any index expression that occurs. Checks that if this is a slice
1016 /// being indexed, the lifetime of the pointer includes the deref expr.
1017 fn constrain_index(&mut self,
1018 index_expr: &hir::Expr,
1019 indexed_ty: Ty<'tcx>)
1021 debug!("constrain_index(index_expr=?, indexed_ty={}",
1022 self.ty_to_string(indexed_ty));
1024 let r_index_expr = ty::ReScope(self.tcx.region_maps().node_extent(index_expr.id));
1025 if let ty::TyRef(r_ptr, mt) = indexed_ty.sty {
1027 ty::TySlice(_) | ty::TyStr => {
1028 self.sub_regions(infer::IndexSlice(index_expr.span),
1029 self.tcx.mk_region(r_index_expr), r_ptr);
1036 /// Guarantees that any lifetimes which appear in the type of the node `id` (after applying
1037 /// adjustments) are valid for at least `minimum_lifetime`
1038 fn type_of_node_must_outlive(&mut self,
1039 origin: infer::SubregionOrigin<'tcx>,
1041 minimum_lifetime: &'tcx ty::Region)
1043 // Try to resolve the type. If we encounter an error, then typeck
1044 // is going to fail anyway, so just stop here and let typeck
1045 // report errors later on in the writeback phase.
1046 let ty0 = self.resolve_node_type(id);
1047 let ty = self.tables.borrow().adjustments.get(&id).map_or(ty0, |adj| adj.target);
1048 let ty = self.resolve_type(ty);
1049 debug!("constrain_regions_in_type_of_node(\
1050 ty={}, ty0={}, id={}, minimum_lifetime={:?})",
1052 id, minimum_lifetime);
1053 self.type_must_outlive(origin, ty, minimum_lifetime);
1056 /// Computes the guarantor for an expression `&base` and then ensures that the lifetime of the
1057 /// resulting pointer is linked to the lifetime of its guarantor (if any).
1058 fn link_addr_of(&mut self, expr: &hir::Expr,
1059 mutability: hir::Mutability, base: &hir::Expr) {
1060 debug!("link_addr_of(expr={:?}, base={:?})", expr, base);
1063 let mc = mc::MemCategorizationContext::new(self);
1064 ignore_err!(mc.cat_expr(base))
1067 debug!("link_addr_of: cmt={:?}", cmt);
1069 self.link_region_from_node_type(expr.span, expr.id, mutability, cmt);
1072 /// Computes the guarantors for any ref bindings in a `let` and
1073 /// then ensures that the lifetime of the resulting pointer is
1074 /// linked to the lifetime of the initialization expression.
1075 fn link_local(&self, local: &hir::Local) {
1076 debug!("regionck::for_local()");
1077 let init_expr = match local.init {
1079 Some(ref expr) => &**expr,
1081 let mc = mc::MemCategorizationContext::new(self);
1082 let discr_cmt = ignore_err!(mc.cat_expr(init_expr));
1083 self.link_pattern(mc, discr_cmt, &local.pat);
1086 /// Computes the guarantors for any ref bindings in a match and
1087 /// then ensures that the lifetime of the resulting pointer is
1088 /// linked to the lifetime of its guarantor (if any).
1089 fn link_match(&self, discr: &hir::Expr, arms: &[hir::Arm]) {
1090 debug!("regionck::for_match()");
1091 let mc = mc::MemCategorizationContext::new(self);
1092 let discr_cmt = ignore_err!(mc.cat_expr(discr));
1093 debug!("discr_cmt={:?}", discr_cmt);
1095 for root_pat in &arm.pats {
1096 self.link_pattern(mc, discr_cmt.clone(), &root_pat);
1101 /// Computes the guarantors for any ref bindings in a match and
1102 /// then ensures that the lifetime of the resulting pointer is
1103 /// linked to the lifetime of its guarantor (if any).
1104 fn link_fn_args(&self, body_scope: CodeExtent, args: &[hir::Arg]) {
1105 debug!("regionck::link_fn_args(body_scope={:?})", body_scope);
1106 let mc = mc::MemCategorizationContext::new(self);
1108 let arg_ty = self.node_ty(arg.id);
1109 let re_scope = self.tcx.mk_region(ty::ReScope(body_scope));
1110 let arg_cmt = mc.cat_rvalue(
1111 arg.id, arg.pat.span, re_scope, re_scope, arg_ty);
1112 debug!("arg_ty={:?} arg_cmt={:?} arg={:?}",
1116 self.link_pattern(mc, arg_cmt, &arg.pat);
1120 /// Link lifetimes of any ref bindings in `root_pat` to the pointers found
1121 /// in the discriminant, if needed.
1122 fn link_pattern<'t>(&self,
1123 mc: mc::MemCategorizationContext<'a, 'gcx, 'tcx>,
1124 discr_cmt: mc::cmt<'tcx>,
1125 root_pat: &hir::Pat) {
1126 debug!("link_pattern(discr_cmt={:?}, root_pat={:?})",
1129 let _ = mc.cat_pattern(discr_cmt, root_pat, |_, sub_cmt, sub_pat| {
1130 match sub_pat.node {
1132 PatKind::Binding(hir::BindByRef(mutbl), ..) => {
1133 self.link_region_from_node_type(sub_pat.span, sub_pat.id,
1141 /// Link lifetime of borrowed pointer resulting from autoref to lifetimes in the value being
1143 fn link_autoref(&self,
1146 autoref: &adjustment::AutoBorrow<'tcx>)
1148 debug!("link_autoref(autoderefs={}, autoref={:?})", autoderefs, autoref);
1149 let mc = mc::MemCategorizationContext::new(self);
1150 let expr_cmt = ignore_err!(mc.cat_expr_autoderefd(expr, autoderefs));
1151 debug!("expr_cmt={:?}", expr_cmt);
1154 adjustment::AutoBorrow::Ref(r, m) => {
1155 self.link_region(expr.span, r,
1156 ty::BorrowKind::from_mutbl(m), expr_cmt);
1159 adjustment::AutoBorrow::RawPtr(m) => {
1160 let r = self.tcx.node_scope_region(expr.id);
1161 self.link_region(expr.span, r, ty::BorrowKind::from_mutbl(m), expr_cmt);
1166 /// Computes the guarantor for cases where the `expr` is being passed by implicit reference and
1167 /// must outlive `callee_scope`.
1168 fn link_by_ref(&self,
1170 callee_scope: CodeExtent) {
1171 debug!("link_by_ref(expr={:?}, callee_scope={:?})",
1172 expr, callee_scope);
1173 let mc = mc::MemCategorizationContext::new(self);
1174 let expr_cmt = ignore_err!(mc.cat_expr(expr));
1175 let borrow_region = self.tcx.mk_region(ty::ReScope(callee_scope));
1176 self.link_region(expr.span, borrow_region, ty::ImmBorrow, expr_cmt);
1179 /// Like `link_region()`, except that the region is extracted from the type of `id`,
1180 /// which must be some reference (`&T`, `&str`, etc).
1181 fn link_region_from_node_type(&self,
1184 mutbl: hir::Mutability,
1185 cmt_borrowed: mc::cmt<'tcx>) {
1186 debug!("link_region_from_node_type(id={:?}, mutbl={:?}, cmt_borrowed={:?})",
1187 id, mutbl, cmt_borrowed);
1189 let rptr_ty = self.resolve_node_type(id);
1190 if let ty::TyRef(r, _) = rptr_ty.sty {
1191 debug!("rptr_ty={}", rptr_ty);
1192 self.link_region(span, r, ty::BorrowKind::from_mutbl(mutbl),
1197 /// Informs the inference engine that `borrow_cmt` is being borrowed with
1198 /// kind `borrow_kind` and lifetime `borrow_region`.
1199 /// In order to ensure borrowck is satisfied, this may create constraints
1200 /// between regions, as explained in `link_reborrowed_region()`.
1201 fn link_region(&self,
1203 borrow_region: &'tcx ty::Region,
1204 borrow_kind: ty::BorrowKind,
1205 borrow_cmt: mc::cmt<'tcx>) {
1206 let mut borrow_cmt = borrow_cmt;
1207 let mut borrow_kind = borrow_kind;
1209 let origin = infer::DataBorrowed(borrow_cmt.ty, span);
1210 self.type_must_outlive(origin, borrow_cmt.ty, borrow_region);
1213 debug!("link_region(borrow_region={:?}, borrow_kind={:?}, borrow_cmt={:?})",
1217 match borrow_cmt.cat.clone() {
1218 Categorization::Deref(ref_cmt, _,
1219 mc::Implicit(ref_kind, ref_region)) |
1220 Categorization::Deref(ref_cmt, _,
1221 mc::BorrowedPtr(ref_kind, ref_region)) => {
1222 match self.link_reborrowed_region(span,
1223 borrow_region, borrow_kind,
1224 ref_cmt, ref_region, ref_kind,
1236 Categorization::Downcast(cmt_base, _) |
1237 Categorization::Deref(cmt_base, _, mc::Unique) |
1238 Categorization::Interior(cmt_base, _) => {
1239 // Borrowing interior or owned data requires the base
1240 // to be valid and borrowable in the same fashion.
1241 borrow_cmt = cmt_base;
1242 borrow_kind = borrow_kind;
1245 Categorization::Deref(.., mc::UnsafePtr(..)) |
1246 Categorization::StaticItem |
1247 Categorization::Upvar(..) |
1248 Categorization::Local(..) |
1249 Categorization::Rvalue(..) => {
1250 // These are all "base cases" with independent lifetimes
1251 // that are not subject to inference
1258 /// This is the most complicated case: the path being borrowed is
1259 /// itself the referent of a borrowed pointer. Let me give an
1260 /// example fragment of code to make clear(er) the situation:
1262 /// let r: &'a mut T = ...; // the original reference "r" has lifetime 'a
1264 /// &'z *r // the reborrow has lifetime 'z
1266 /// Now, in this case, our primary job is to add the inference
1267 /// constraint that `'z <= 'a`. Given this setup, let's clarify the
1268 /// parameters in (roughly) terms of the example:
1270 /// A borrow of: `& 'z bk * r` where `r` has type `& 'a bk T`
1271 /// borrow_region ^~ ref_region ^~
1272 /// borrow_kind ^~ ref_kind ^~
1275 /// Here `bk` stands for some borrow-kind (e.g., `mut`, `uniq`, etc).
1277 /// Unfortunately, there are some complications beyond the simple
1278 /// scenario I just painted:
1280 /// 1. The reference `r` might in fact be a "by-ref" upvar. In that
1281 /// case, we have two jobs. First, we are inferring whether this reference
1282 /// should be an `&T`, `&mut T`, or `&uniq T` reference, and we must
1283 /// adjust that based on this borrow (e.g., if this is an `&mut` borrow,
1284 /// then `r` must be an `&mut` reference). Second, whenever we link
1285 /// two regions (here, `'z <= 'a`), we supply a *cause*, and in this
1286 /// case we adjust the cause to indicate that the reference being
1287 /// "reborrowed" is itself an upvar. This provides a nicer error message
1288 /// should something go wrong.
1290 /// 2. There may in fact be more levels of reborrowing. In the
1291 /// example, I said the borrow was like `&'z *r`, but it might
1292 /// in fact be a borrow like `&'z **q` where `q` has type `&'a
1293 /// &'b mut T`. In that case, we want to ensure that `'z <= 'a`
1294 /// and `'z <= 'b`. This is explained more below.
1296 /// The return value of this function indicates whether we need to
1297 /// recurse and process `ref_cmt` (see case 2 above).
1298 fn link_reborrowed_region(&self,
1300 borrow_region: &'tcx ty::Region,
1301 borrow_kind: ty::BorrowKind,
1302 ref_cmt: mc::cmt<'tcx>,
1303 ref_region: &'tcx ty::Region,
1304 mut ref_kind: ty::BorrowKind,
1306 -> Option<(mc::cmt<'tcx>, ty::BorrowKind)>
1308 // Possible upvar ID we may need later to create an entry in the
1311 // Detect by-ref upvar `x`:
1312 let cause = match note {
1313 mc::NoteUpvarRef(ref upvar_id) => {
1314 let upvar_capture_map = &self.tables.borrow_mut().upvar_capture_map;
1315 match upvar_capture_map.get(upvar_id) {
1316 Some(&ty::UpvarCapture::ByRef(ref upvar_borrow)) => {
1317 // The mutability of the upvar may have been modified
1318 // by the above adjustment, so update our local variable.
1319 ref_kind = upvar_borrow.kind;
1321 infer::ReborrowUpvar(span, *upvar_id)
1324 span_bug!( span, "Illegal upvar id: {:?}", upvar_id);
1328 mc::NoteClosureEnv(ref upvar_id) => {
1329 // We don't have any mutability changes to propagate, but
1330 // we do want to note that an upvar reborrow caused this
1332 infer::ReborrowUpvar(span, *upvar_id)
1335 infer::Reborrow(span)
1339 debug!("link_reborrowed_region: {:?} <= {:?}",
1342 self.sub_regions(cause, borrow_region, ref_region);
1344 // If we end up needing to recurse and establish a region link
1345 // with `ref_cmt`, calculate what borrow kind we will end up
1346 // needing. This will be used below.
1348 // One interesting twist is that we can weaken the borrow kind
1349 // when we recurse: to reborrow an `&mut` referent as mutable,
1350 // borrowck requires a unique path to the `&mut` reference but not
1351 // necessarily a *mutable* path.
1352 let new_borrow_kind = match borrow_kind {
1355 ty::MutBorrow | ty::UniqueImmBorrow =>
1359 // Decide whether we need to recurse and link any regions within
1360 // the `ref_cmt`. This is concerned for the case where the value
1361 // being reborrowed is in fact a borrowed pointer found within
1362 // another borrowed pointer. For example:
1364 // let p: &'b &'a mut T = ...;
1368 // What makes this case particularly tricky is that, if the data
1369 // being borrowed is a `&mut` or `&uniq` borrow, borrowck requires
1370 // not only that `'z <= 'a`, (as before) but also `'z <= 'b`
1371 // (otherwise the user might mutate through the `&mut T` reference
1372 // after `'b` expires and invalidate the borrow we are looking at
1375 // So let's re-examine our parameters in light of this more
1376 // complicated (possible) scenario:
1378 // A borrow of: `& 'z bk * * p` where `p` has type `&'b bk & 'a bk T`
1379 // borrow_region ^~ ref_region ^~
1380 // borrow_kind ^~ ref_kind ^~
1383 // (Note that since we have not examined `ref_cmt.cat`, we don't
1384 // know whether this scenario has occurred; but I wanted to show
1385 // how all the types get adjusted.)
1388 // The reference being reborrowed is a sharable ref of
1389 // type `&'a T`. In this case, it doesn't matter where we
1390 // *found* the `&T` pointer, the memory it references will
1391 // be valid and immutable for `'a`. So we can stop here.
1393 // (Note that the `borrow_kind` must also be ImmBorrow or
1394 // else the user is borrowed imm memory as mut memory,
1395 // which means they'll get an error downstream in borrowck
1400 ty::MutBorrow | ty::UniqueImmBorrow => {
1401 // The reference being reborrowed is either an `&mut T` or
1402 // `&uniq T`. This is the case where recursion is needed.
1403 return Some((ref_cmt, new_borrow_kind));
1408 /// Checks that the values provided for type/region arguments in a given
1409 /// expression are well-formed and in-scope.
1410 fn substs_wf_in_scope(&mut self,
1411 origin: infer::ParameterOrigin,
1412 substs: &Substs<'tcx>,
1414 expr_region: &'tcx ty::Region) {
1415 debug!("substs_wf_in_scope(substs={:?}, \
1419 substs, expr_region, origin, expr_span);
1421 let origin = infer::ParameterInScope(origin, expr_span);
1423 for region in substs.regions() {
1424 self.sub_regions(origin.clone(), expr_region, region);
1427 for ty in substs.types() {
1428 let ty = self.resolve_type(ty);
1429 self.type_must_outlive(origin.clone(), ty, expr_region);
1433 /// Ensures that type is well-formed in `region`, which implies (among
1434 /// other things) that all borrowed data reachable via `ty` outlives
1436 pub fn type_must_outlive(&self,
1437 origin: infer::SubregionOrigin<'tcx>,
1439 region: &'tcx ty::Region)
1441 let ty = self.resolve_type(ty);
1443 debug!("type_must_outlive(ty={:?}, region={:?}, origin={:?})",
1448 assert!(!ty.has_escaping_regions());
1450 let components = self.tcx.outlives_components(ty);
1451 self.components_must_outlive(origin, components, region);
1454 fn components_must_outlive(&self,
1455 origin: infer::SubregionOrigin<'tcx>,
1456 components: Vec<ty::outlives::Component<'tcx>>,
1457 region: &'tcx ty::Region)
1459 for component in components {
1460 let origin = origin.clone();
1462 ty::outlives::Component::Region(region1) => {
1463 self.sub_regions(origin, region, region1);
1465 ty::outlives::Component::Param(param_ty) => {
1466 self.param_ty_must_outlive(origin, region, param_ty);
1468 ty::outlives::Component::Projection(projection_ty) => {
1469 self.projection_must_outlive(origin, region, projection_ty);
1471 ty::outlives::Component::EscapingProjection(subcomponents) => {
1472 self.components_must_outlive(origin, subcomponents, region);
1474 ty::outlives::Component::UnresolvedInferenceVariable(v) => {
1475 // ignore this, we presume it will yield an error
1476 // later, since if a type variable is not resolved by
1477 // this point it never will be
1478 self.tcx.sess.delay_span_bug(
1480 &format!("unresolved inference variable in outlives: {:?}", v));
1486 fn param_ty_must_outlive(&self,
1487 origin: infer::SubregionOrigin<'tcx>,
1488 region: &'tcx ty::Region,
1489 param_ty: ty::ParamTy) {
1490 debug!("param_ty_must_outlive(region={:?}, param_ty={:?}, origin={:?})",
1491 region, param_ty, origin);
1493 let verify_bound = self.param_bound(param_ty);
1494 let generic = GenericKind::Param(param_ty);
1495 self.verify_generic_bound(origin, generic, region, verify_bound);
1498 fn projection_must_outlive(&self,
1499 origin: infer::SubregionOrigin<'tcx>,
1500 region: &'tcx ty::Region,
1501 projection_ty: ty::ProjectionTy<'tcx>)
1503 debug!("projection_must_outlive(region={:?}, projection_ty={:?}, origin={:?})",
1504 region, projection_ty, origin);
1506 // This case is thorny for inference. The fundamental problem is
1507 // that there are many cases where we have choice, and inference
1508 // doesn't like choice (the current region inference in
1509 // particular). :) First off, we have to choose between using the
1510 // OutlivesProjectionEnv, OutlivesProjectionTraitDef, and
1511 // OutlivesProjectionComponent rules, any one of which is
1512 // sufficient. If there are no inference variables involved, it's
1513 // not hard to pick the right rule, but if there are, we're in a
1514 // bit of a catch 22: if we picked which rule we were going to
1515 // use, we could add constraints to the region inference graph
1516 // that make it apply, but if we don't add those constraints, the
1517 // rule might not apply (but another rule might). For now, we err
1518 // on the side of adding too few edges into the graph.
1520 // Compute the bounds we can derive from the environment or trait
1521 // definition. We know that the projection outlives all the
1522 // regions in this list.
1523 let env_bounds = self.projection_declared_bounds(origin.span(), projection_ty);
1525 debug!("projection_must_outlive: env_bounds={:?}",
1528 // If we know that the projection outlives 'static, then we're
1530 if env_bounds.contains(&&ty::ReStatic) {
1531 debug!("projection_must_outlive: 'static as declared bound");
1535 // If declared bounds list is empty, the only applicable rule is
1536 // OutlivesProjectionComponent. If there are inference variables,
1537 // then, we can break down the outlives into more primitive
1538 // components without adding unnecessary edges.
1540 // If there are *no* inference variables, however, we COULD do
1541 // this, but we choose not to, because the error messages are less
1542 // good. For example, a requirement like `T::Item: 'r` would be
1543 // translated to a requirement that `T: 'r`; when this is reported
1544 // to the user, it will thus say "T: 'r must hold so that T::Item:
1545 // 'r holds". But that makes it sound like the only way to fix
1546 // the problem is to add `T: 'r`, which isn't true. So, if there are no
1547 // inference variables, we use a verify constraint instead of adding
1548 // edges, which winds up enforcing the same condition.
1549 let needs_infer = projection_ty.trait_ref.needs_infer();
1550 if env_bounds.is_empty() && needs_infer {
1551 debug!("projection_must_outlive: no declared bounds");
1553 for component_ty in projection_ty.trait_ref.substs.types() {
1554 self.type_must_outlive(origin.clone(), component_ty, region);
1557 for r in projection_ty.trait_ref.substs.regions() {
1558 self.sub_regions(origin.clone(), region, r);
1564 // If we find that there is a unique declared bound `'b`, and this bound
1565 // appears in the trait reference, then the best action is to require that `'b:'r`,
1566 // so do that. This is best no matter what rule we use:
1568 // - OutlivesProjectionEnv or OutlivesProjectionTraitDef: these would translate to
1569 // the requirement that `'b:'r`
1570 // - OutlivesProjectionComponent: this would require `'b:'r` in addition to
1572 if !env_bounds.is_empty() && env_bounds[1..].iter().all(|b| *b == env_bounds[0]) {
1573 let unique_bound = env_bounds[0];
1574 debug!("projection_must_outlive: unique declared bound = {:?}", unique_bound);
1575 if projection_ty.trait_ref.substs.regions().any(|r| env_bounds.contains(&r)) {
1576 debug!("projection_must_outlive: unique declared bound appears in trait ref");
1577 self.sub_regions(origin.clone(), region, unique_bound);
1582 // Fallback to verifying after the fact that there exists a
1583 // declared bound, or that all the components appearing in the
1584 // projection outlive; in some cases, this may add insufficient
1585 // edges into the inference graph, leading to inference failures
1586 // even though a satisfactory solution exists.
1587 let verify_bound = self.projection_bound(origin.span(), env_bounds, projection_ty);
1588 let generic = GenericKind::Projection(projection_ty);
1589 self.verify_generic_bound(origin, generic.clone(), region, verify_bound);
1592 fn type_bound(&self, span: Span, ty: Ty<'tcx>) -> VerifyBound<'tcx> {
1597 ty::TyProjection(data) => {
1598 let declared_bounds = self.projection_declared_bounds(span, data);
1599 self.projection_bound(span, declared_bounds, data)
1602 self.recursive_type_bound(span, ty)
1607 fn param_bound(&self, param_ty: ty::ParamTy) -> VerifyBound<'tcx> {
1608 let param_env = &self.parameter_environment;
1610 debug!("param_bound(param_ty={:?})",
1613 let mut param_bounds = self.declared_generic_bounds_from_env(GenericKind::Param(param_ty));
1615 // Add in the default bound of fn body that applies to all in
1616 // scope type parameters:
1617 param_bounds.push(param_env.implicit_region_bound);
1619 VerifyBound::AnyRegion(param_bounds)
1622 fn projection_declared_bounds(&self,
1624 projection_ty: ty::ProjectionTy<'tcx>)
1625 -> Vec<&'tcx ty::Region>
1627 // First assemble bounds from where clauses and traits.
1629 let mut declared_bounds =
1630 self.declared_generic_bounds_from_env(GenericKind::Projection(projection_ty));
1632 declared_bounds.extend_from_slice(
1633 &self.declared_projection_bounds_from_trait(span, projection_ty));
1638 fn projection_bound(&self,
1640 declared_bounds: Vec<&'tcx ty::Region>,
1641 projection_ty: ty::ProjectionTy<'tcx>)
1642 -> VerifyBound<'tcx> {
1643 debug!("projection_bound(declared_bounds={:?}, projection_ty={:?})",
1644 declared_bounds, projection_ty);
1646 // see the extensive comment in projection_must_outlive
1648 let ty = self.tcx.mk_projection(projection_ty.trait_ref, projection_ty.item_name);
1649 let recursive_bound = self.recursive_type_bound(span, ty);
1651 VerifyBound::AnyRegion(declared_bounds).or(recursive_bound)
1654 fn recursive_type_bound(&self, span: Span, ty: Ty<'tcx>) -> VerifyBound<'tcx> {
1655 let mut bounds = vec![];
1657 for subty in ty.walk_shallow() {
1658 bounds.push(self.type_bound(span, subty));
1661 let mut regions = ty.regions();
1662 regions.retain(|r| !r.is_bound()); // ignore late-bound regions
1663 bounds.push(VerifyBound::AllRegions(regions));
1665 // remove bounds that must hold, since they are not interesting
1666 bounds.retain(|b| !b.must_hold());
1668 if bounds.len() == 1 {
1669 bounds.pop().unwrap()
1671 VerifyBound::AllBounds(bounds)
1675 fn declared_generic_bounds_from_env(&self, generic: GenericKind<'tcx>)
1676 -> Vec<&'tcx ty::Region>
1678 let param_env = &self.parameter_environment;
1680 // To start, collect bounds from user:
1681 let mut param_bounds = self.tcx.required_region_bounds(generic.to_ty(self.tcx),
1682 param_env.caller_bounds.clone());
1684 // Next, collect regions we scraped from the well-formedness
1685 // constraints in the fn signature. To do that, we walk the list
1686 // of known relations from the fn ctxt.
1688 // This is crucial because otherwise code like this fails:
1690 // fn foo<'a, A>(x: &'a A) { x.bar() }
1692 // The problem is that the type of `x` is `&'a A`. To be
1693 // well-formed, then, A must be lower-generic by `'a`, but we
1694 // don't know that this holds from first principles.
1695 for &(r, p) in &self.region_bound_pairs {
1696 debug!("generic={:?} p={:?}",
1700 param_bounds.push(r);
1707 fn declared_projection_bounds_from_trait(&self,
1709 projection_ty: ty::ProjectionTy<'tcx>)
1710 -> Vec<&'tcx ty::Region>
1712 debug!("projection_bounds(projection_ty={:?})",
1715 let ty = self.tcx.mk_projection(projection_ty.trait_ref.clone(),
1716 projection_ty.item_name);
1718 // Say we have a projection `<T as SomeTrait<'a>>::SomeType`. We are interested
1719 // in looking for a trait definition like:
1722 // trait SomeTrait<'a> {
1723 // type SomeType : 'a;
1727 // we can thus deduce that `<T as SomeTrait<'a>>::SomeType : 'a`.
1728 let trait_predicates = self.tcx.predicates_of(projection_ty.trait_ref.def_id);
1729 assert_eq!(trait_predicates.parent, None);
1730 let predicates = trait_predicates.predicates.as_slice().to_vec();
1731 traits::elaborate_predicates(self.tcx, predicates)
1732 .filter_map(|predicate| {
1733 // we're only interesting in `T : 'a` style predicates:
1734 let outlives = match predicate {
1735 ty::Predicate::TypeOutlives(data) => data,
1736 _ => { return None; }
1739 debug!("projection_bounds: outlives={:?} (1)",
1742 // apply the substitutions (and normalize any projected types)
1743 let outlives = self.instantiate_type_scheme(span,
1744 projection_ty.trait_ref.substs,
1747 debug!("projection_bounds: outlives={:?} (2)",
1750 let region_result = self.commit_if_ok(|_| {
1752 self.replace_late_bound_regions_with_fresh_var(
1754 infer::AssocTypeProjection(projection_ty.item_name),
1757 debug!("projection_bounds: outlives={:?} (3)",
1760 // check whether this predicate applies to our current projection
1761 let cause = self.fcx.misc(span);
1762 match self.eq_types(false, &cause, ty, outlives.0) {
1764 self.register_infer_ok_obligations(ok);
1767 Err(_) => { Err(()) }
1771 debug!("projection_bounds: region_result={:?}",