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
88 use middle::free_region::FreeRegionMap;
89 use middle::mem_categorization as mc;
90 use middle::mem_categorization::Categorization;
91 use middle::region::{self, CodeExtent};
92 use middle::subst::Substs;
94 use middle::ty::{self, Ty, TyCtxt, MethodCall, TypeFoldable};
95 use middle::infer::{self, GenericKind, InferCtxt, SubregionOrigin, TypeOrigin, VerifyBound};
97 use middle::ty::adjustment;
98 use middle::ty::wf::ImpliedBound;
102 use syntax::codemap::Span;
103 use rustc_front::intravisit::{self, Visitor};
104 use rustc_front::hir::{self, PatKind};
105 use rustc_front::util as hir_util;
107 use self::SubjectNode::Subject;
109 // a variation on try that just returns unit
110 macro_rules! ignore_err {
111 ($e:expr) => (match $e { Ok(e) => e, Err(_) => return () })
114 ///////////////////////////////////////////////////////////////////////////
115 // PUBLIC ENTRY POINTS
117 pub fn regionck_expr(fcx: &FnCtxt, e: &hir::Expr) {
118 let mut rcx = Rcx::new(fcx, RepeatingScope(e.id), e.id, Subject(e.id));
119 if fcx.err_count_since_creation() == 0 {
120 // regionck assumes typeck succeeded
122 rcx.visit_region_obligations(e.id);
124 rcx.resolve_regions_and_report_errors();
127 /// Region checking during the WF phase for items. `wf_tys` are the
128 /// types from which we should derive implied bounds, if any.
129 pub fn regionck_item<'a,'tcx>(fcx: &FnCtxt<'a,'tcx>,
130 item_id: ast::NodeId,
132 wf_tys: &[Ty<'tcx>]) {
133 debug!("regionck_item(item.id={:?}, wf_tys={:?}", item_id, wf_tys);
134 let mut rcx = Rcx::new(fcx, RepeatingScope(item_id), item_id, Subject(item_id));
137 .relate_free_regions_from_predicates(tcx, &fcx.infcx().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(fcx: &FnCtxt,
148 debug!("regionck_fn(id={})", fn_id);
149 let mut rcx = Rcx::new(fcx, RepeatingScope(blk.id), blk.id, Subject(fn_id));
151 if fcx.err_count_since_creation() == 0 {
152 // regionck assumes typeck succeeded
153 rcx.visit_fn_body(fn_id, decl, blk, fn_span);
158 .relate_free_regions_from_predicates(tcx, &fcx.infcx().parameter_environment.caller_bounds);
160 rcx.resolve_regions_and_report_errors();
162 // For the top-level fn, store the free-region-map. We don't store
163 // any map for closures; they just share the same map as the
164 // function that created them.
165 fcx.tcx().store_free_region_map(fn_id, rcx.free_region_map);
168 ///////////////////////////////////////////////////////////////////////////
171 pub struct Rcx<'a, 'tcx: 'a> {
172 pub fcx: &'a FnCtxt<'a, 'tcx>,
174 region_bound_pairs: Vec<(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: SubjectNode,
192 pub struct RepeatingScope(ast::NodeId);
193 pub enum SubjectNode { Subject(ast::NodeId), None }
195 impl<'a, 'tcx> Rcx<'a, 'tcx> {
196 pub fn new(fcx: &'a FnCtxt<'a, 'tcx>,
197 initial_repeating_scope: RepeatingScope,
198 initial_body_id: ast::NodeId,
199 subject: SubjectNode) -> Rcx<'a, 'tcx> {
200 let RepeatingScope(initial_repeating_scope) = initial_repeating_scope;
202 repeating_scope: initial_repeating_scope,
203 body_id: initial_body_id,
204 call_site_scope: None,
206 region_bound_pairs: Vec::new(),
207 free_region_map: FreeRegionMap::new(),
211 pub fn tcx(&self) -> &'a TyCtxt<'tcx> {
215 pub fn infcx(&self) -> &InferCtxt<'a,'tcx> {
219 fn set_call_site_scope(&mut self, call_site_scope: Option<CodeExtent>) -> Option<CodeExtent> {
220 mem::replace(&mut self.call_site_scope, call_site_scope)
223 fn set_body_id(&mut self, body_id: ast::NodeId) -> ast::NodeId {
224 mem::replace(&mut self.body_id, body_id)
227 fn set_repeating_scope(&mut self, scope: ast::NodeId) -> ast::NodeId {
228 mem::replace(&mut self.repeating_scope, scope)
231 /// Try to resolve the type for the given node, returning t_err if an error results. Note that
232 /// we never care about the details of the error, the same error will be detected and reported
233 /// in the writeback phase.
235 /// Note one important point: we do not attempt to resolve *region variables* here. This is
236 /// because regionck is essentially adding constraints to those region variables and so may yet
237 /// influence how they are resolved.
239 /// Consider this silly example:
242 /// fn borrow(x: &i32) -> &i32 {x}
243 /// fn foo(x: @i32) -> i32 { // block: B
244 /// let b = borrow(x); // region: <R0>
249 /// Here, the region of `b` will be `<R0>`. `<R0>` is constrained to be some subregion of the
250 /// block B and some superregion of the call. If we forced it now, we'd choose the smaller
251 /// region (the call). But that would make the *b illegal. Since we don't resolve, the type
252 /// of b will be `&<R0>.i32` and then `*b` will require that `<R0>` be bigger than the let and
253 /// the `*b` expression, so we will effectively resolve `<R0>` to be the block B.
254 pub fn resolve_type(&self, unresolved_ty: Ty<'tcx>) -> Ty<'tcx> {
255 self.fcx.infcx().resolve_type_vars_if_possible(&unresolved_ty)
258 /// Try to resolve the type for the given node.
259 fn resolve_node_type(&self, id: ast::NodeId) -> Ty<'tcx> {
260 let t = self.fcx.node_ty(id);
264 fn resolve_method_type(&self, method_call: MethodCall) -> Option<Ty<'tcx>> {
265 let method_ty = self.fcx.inh.tables.borrow().method_map
266 .get(&method_call).map(|method| method.ty);
267 method_ty.map(|method_ty| self.resolve_type(method_ty))
270 /// Try to resolve the type for the given node.
271 pub fn resolve_expr_type_adjusted(&mut self, expr: &hir::Expr) -> Ty<'tcx> {
272 let ty_unadjusted = self.resolve_node_type(expr.id);
273 if ty_unadjusted.references_error() {
276 ty_unadjusted.adjust(
277 self.fcx.tcx(), expr.span, expr.id,
278 self.fcx.inh.tables.borrow().adjustments.get(&expr.id),
279 |method_call| self.resolve_method_type(method_call))
283 fn visit_fn_body(&mut self,
284 id: ast::NodeId, // the id of the fn itself
285 fn_decl: &hir::FnDecl,
289 // When we enter a function, we can derive
290 debug!("visit_fn_body(id={})", id);
292 let call_site = self.fcx.tcx().region_maps.lookup_code_extent(
293 region::CodeExtentData::CallSiteScope { fn_id: id, body_id: body.id });
294 let old_call_site_scope = self.set_call_site_scope(Some(call_site));
297 let fn_sig_map = &self.infcx().tables.borrow().liberated_fn_sigs;
298 match fn_sig_map.get(&id) {
299 Some(f) => f.clone(),
302 &format!("No fn-sig entry for id={}", id));
307 let old_region_bounds_pairs_len = self.region_bound_pairs.len();
309 // Collect the types from which we create inferred bounds.
310 // For the return type, if diverging, substitute `bool` just
311 // because it will have no effect.
313 // FIXME(#27579) return types should not be implied bounds
314 let fn_sig_tys: Vec<_> =
317 .chain(Some(fn_sig.output.unwrap_or(self.tcx().types.bool)))
320 let old_body_id = self.set_body_id(body.id);
321 self.relate_free_regions(&fn_sig_tys[..], body.id, span);
323 self.tcx().region_maps.node_extent(body.id),
324 &fn_decl.inputs[..]);
325 self.visit_block(body);
326 self.visit_region_obligations(body.id);
328 let call_site_scope = self.call_site_scope.unwrap();
329 debug!("visit_fn_body body.id {} call_site_scope: {:?}",
330 body.id, call_site_scope);
331 type_of_node_must_outlive(self,
332 infer::CallReturn(span),
334 ty::ReScope(call_site_scope));
336 self.region_bound_pairs.truncate(old_region_bounds_pairs_len);
338 self.set_body_id(old_body_id);
339 self.set_call_site_scope(old_call_site_scope);
342 fn visit_region_obligations(&mut self, node_id: ast::NodeId)
344 debug!("visit_region_obligations: node_id={}", node_id);
346 // region checking can introduce new pending obligations
347 // which, when processed, might generate new region
348 // obligations. So make sure we process those.
349 self.fcx.select_all_obligations_or_error();
351 // Make a copy of the region obligations vec because we'll need
352 // to be able to borrow the fulfillment-cx below when projecting.
353 let region_obligations =
358 .region_obligations(node_id)
361 for r_o in ®ion_obligations {
362 debug!("visit_region_obligations: r_o={:?} cause={:?}",
364 let sup_type = self.resolve_type(r_o.sup_type);
365 let origin = self.code_to_origin(r_o.cause.span, sup_type, &r_o.cause.code);
366 type_must_outlive(self, origin, sup_type, r_o.sub_region);
369 // Processing the region obligations should not cause the list to grow further:
370 assert_eq!(region_obligations.len(),
371 self.fcx.inh.fulfillment_cx.borrow().region_obligations(node_id).len());
374 fn code_to_origin(&self,
377 code: &traits::ObligationCauseCode<'tcx>)
378 -> SubregionOrigin<'tcx> {
380 traits::ObligationCauseCode::ReferenceOutlivesReferent(ref_type) =>
381 infer::ReferenceOutlivesReferent(ref_type, span),
383 infer::RelateParamBound(span, sup_type),
387 /// This method populates the region map's `free_region_map`. It walks over the transformed
388 /// argument and return types for each function just before we check the body of that function,
389 /// looking for types where you have a borrowed pointer to other borrowed data (e.g., `&'a &'b
390 /// [usize]`. We do not allow references to outlive the things they point at, so we can assume
391 /// that `'a <= 'b`. This holds for both the argument and return types, basically because, on
392 /// the caller side, the caller is responsible for checking that the type of every expression
393 /// (including the actual values for the arguments, as well as the return type of the fn call)
396 /// Tests: `src/test/compile-fail/regions-free-region-ordering-*.rs`
397 fn relate_free_regions(&mut self,
398 fn_sig_tys: &[Ty<'tcx>],
399 body_id: ast::NodeId,
401 debug!("relate_free_regions >>");
403 for &ty in fn_sig_tys {
404 let ty = self.resolve_type(ty);
405 debug!("relate_free_regions(t={:?})", ty);
406 let implied_bounds = ty::wf::implied_bounds(self.fcx.infcx(), body_id, ty, span);
408 // Record any relations between free regions that we observe into the free-region-map.
409 self.free_region_map.relate_free_regions_from_implied_bounds(&implied_bounds);
411 // But also record other relationships, such as `T:'x`,
412 // that don't go into the free-region-map but which we use
414 for implication in implied_bounds {
415 debug!("implication: {:?}", implication);
417 ImpliedBound::RegionSubRegion(ty::ReFree(free_a),
418 ty::ReVar(vid_b)) => {
419 self.fcx.inh.infcx.add_given(free_a, vid_b);
421 ImpliedBound::RegionSubParam(r_a, param_b) => {
422 self.region_bound_pairs.push((r_a, GenericKind::Param(param_b)));
424 ImpliedBound::RegionSubProjection(r_a, projection_b) => {
425 self.region_bound_pairs.push((r_a, GenericKind::Projection(projection_b)));
427 ImpliedBound::RegionSubRegion(..) => {
428 // In principle, we could record (and take
429 // advantage of) every relationship here, but
430 // we are also free not to -- it simply means
431 // strictly less that we can successfully type
432 // check. (It may also be that we should
433 // revise our inference system to be more
434 // general and to make use of *every*
435 // relationship that arises here, but
436 // presently we do not.)
442 debug!("<< relate_free_regions");
445 fn resolve_regions_and_report_errors(&self) {
446 let subject_node_id = match self.subject {
448 SubjectNode::None => {
449 self.tcx().sess.bug("cannot resolve_regions_and_report_errors \
450 without subject node");
454 self.fcx.infcx().resolve_regions_and_report_errors(&self.free_region_map,
459 impl<'a, 'tcx, 'v> Visitor<'v> for Rcx<'a, 'tcx> {
460 // (..) FIXME(#3238) should use visit_pat, not visit_arm/visit_local,
461 // However, right now we run into an issue whereby some free
462 // regions are not properly related if they appear within the
463 // types of arguments that must be inferred. This could be
464 // addressed by deferring the construction of the region
465 // hierarchy, and in particular the relationships between free
466 // regions, until regionck, as described in #3238.
468 fn visit_fn(&mut self, _fk: intravisit::FnKind<'v>, fd: &'v hir::FnDecl,
469 b: &'v hir::Block, span: Span, id: ast::NodeId) {
470 self.visit_fn_body(id, fd, b, span)
473 fn visit_expr(&mut self, ex: &hir::Expr) { visit_expr(self, ex); }
475 //visit_pat: visit_pat, // (..) see above
477 fn visit_arm(&mut self, a: &hir::Arm) { visit_arm(self, a); }
479 fn visit_local(&mut self, l: &hir::Local) { visit_local(self, l); }
481 fn visit_block(&mut self, b: &hir::Block) { visit_block(self, b); }
484 fn visit_block(rcx: &mut Rcx, b: &hir::Block) {
485 intravisit::walk_block(rcx, b);
488 fn visit_arm(rcx: &mut Rcx, arm: &hir::Arm) {
491 constrain_bindings_in_pat(&p, rcx);
494 intravisit::walk_arm(rcx, arm);
497 fn visit_local(rcx: &mut Rcx, l: &hir::Local) {
499 constrain_bindings_in_pat(&l.pat, rcx);
501 intravisit::walk_local(rcx, l);
504 fn constrain_bindings_in_pat(pat: &hir::Pat, rcx: &mut Rcx) {
505 let tcx = rcx.fcx.tcx();
506 debug!("regionck::visit_pat(pat={:?})", pat);
507 pat_util::pat_bindings(&tcx.def_map, pat, |_, id, span, _| {
508 // If we have a variable that contains region'd data, that
509 // data will be accessible from anywhere that the variable is
510 // accessed. We must be wary of loops like this:
512 // // from src/test/compile-fail/borrowck-lend-flow.rs
513 // let mut v = box 3, w = box 4;
514 // let mut x = &mut w;
517 // borrow(v); //~ ERROR cannot borrow
518 // x = &mut v; // (1)
521 // Typically, we try to determine the region of a borrow from
522 // those points where it is dereferenced. In this case, one
523 // might imagine that the lifetime of `x` need only be the
524 // body of the loop. But of course this is incorrect because
525 // the pointer that is created at point (1) is consumed at
526 // point (2), meaning that it must be live across the loop
527 // iteration. The easiest way to guarantee this is to require
528 // that the lifetime of any regions that appear in a
529 // variable's type enclose at least the variable's scope.
531 let var_scope = tcx.region_maps.var_scope(id);
533 let origin = infer::BindingTypeIsNotValidAtDecl(span);
534 type_of_node_must_outlive(rcx, origin, id, ty::ReScope(var_scope));
536 let typ = rcx.resolve_node_type(id);
537 dropck::check_safety_of_destructor_if_necessary(rcx, typ, span, var_scope);
541 fn visit_expr(rcx: &mut Rcx, expr: &hir::Expr) {
542 debug!("regionck::visit_expr(e={:?}, repeating_scope={})",
543 expr, rcx.repeating_scope);
545 // No matter what, the type of each expression must outlive the
546 // scope of that expression. This also guarantees basic WF.
547 let expr_ty = rcx.resolve_node_type(expr.id);
548 // the region corresponding to this expression
549 let expr_region = ty::ReScope(rcx.tcx().region_maps.node_extent(expr.id));
550 type_must_outlive(rcx, infer::ExprTypeIsNotInScope(expr_ty, expr.span),
551 expr_ty, expr_region);
553 let method_call = MethodCall::expr(expr.id);
554 let opt_method_callee = rcx.fcx.inh.tables.borrow().method_map.get(&method_call).cloned();
555 let has_method_map = opt_method_callee.is_some();
557 // If we are calling a method (either explicitly or via an
558 // overloaded operator), check that all of the types provided as
559 // arguments for its type parameters are well-formed, and all the regions
560 // provided as arguments outlive the call.
561 if let Some(callee) = opt_method_callee {
562 let origin = match expr.node {
563 hir::ExprMethodCall(..) =>
564 infer::ParameterOrigin::MethodCall,
565 hir::ExprUnary(op, _) if op == hir::UnDeref =>
566 infer::ParameterOrigin::OverloadedDeref,
568 infer::ParameterOrigin::OverloadedOperator
571 substs_wf_in_scope(rcx, origin, &callee.substs, expr.span, expr_region);
572 type_must_outlive(rcx, infer::ExprTypeIsNotInScope(callee.ty, expr.span),
573 callee.ty, expr_region);
576 // Check any autoderefs or autorefs that appear.
577 let adjustment = rcx.fcx.inh.tables.borrow().adjustments.get(&expr.id).map(|a| a.clone());
578 if let Some(adjustment) = adjustment {
579 debug!("adjustment={:?}", adjustment);
581 adjustment::AdjustDerefRef(adjustment::AutoDerefRef {
582 autoderefs, ref autoref, ..
584 let expr_ty = rcx.resolve_node_type(expr.id);
585 constrain_autoderefs(rcx, expr, autoderefs, expr_ty);
586 if let Some(ref autoref) = *autoref {
587 link_autoref(rcx, expr, autoderefs, autoref);
589 // Require that the resulting region encompasses
592 // FIXME(#6268) remove to support nested method calls
593 type_of_node_must_outlive(
594 rcx, infer::AutoBorrow(expr.span),
595 expr.id, expr_region);
599 adjustment::AutoObject(_, ref bounds, _, _) => {
600 // Determine if we are casting `expr` to a trait
601 // instance. If so, we have to be sure that the type
602 // of the source obeys the new region bound.
603 let source_ty = rcx.resolve_node_type(expr.id);
604 type_must_outlive(rcx, infer::RelateObjectBound(expr.span),
605 source_ty, bounds.region_bound);
611 // If necessary, constrain destructors in the unadjusted form of this
614 let mc = mc::MemCategorizationContext::new(rcx.fcx.infcx());
615 mc.cat_expr_unadjusted(expr)
619 check_safety_of_rvalue_destructor_if_necessary(rcx,
624 let tcx = rcx.fcx.tcx();
625 tcx.sess.delay_span_bug(expr.span, "cat_expr_unadjusted Errd");
630 // If necessary, constrain destructors in this expression. This will be
631 // the adjusted form if there is an adjustment.
633 let mc = mc::MemCategorizationContext::new(rcx.fcx.infcx());
638 check_safety_of_rvalue_destructor_if_necessary(rcx, head_cmt, expr.span);
641 let tcx = rcx.fcx.tcx();
642 tcx.sess.delay_span_bug(expr.span, "cat_expr Errd");
646 debug!("regionck::visit_expr(e={:?}, repeating_scope={}) - visiting subexprs",
647 expr, rcx.repeating_scope);
649 hir::ExprPath(..) => {
650 rcx.fcx.opt_node_ty_substs(expr.id, |item_substs| {
651 let origin = infer::ParameterOrigin::Path;
652 substs_wf_in_scope(rcx, origin, &item_substs.substs, expr.span, expr_region);
656 hir::ExprCall(ref callee, ref args) => {
658 constrain_call(rcx, expr, Some(&callee),
659 args.iter().map(|e| &**e), false);
661 constrain_callee(rcx, callee.id, expr, &callee);
662 constrain_call(rcx, expr, None,
663 args.iter().map(|e| &**e), false);
666 intravisit::walk_expr(rcx, expr);
669 hir::ExprMethodCall(_, _, ref args) => {
670 constrain_call(rcx, expr, Some(&args[0]),
671 args[1..].iter().map(|e| &**e), false);
673 intravisit::walk_expr(rcx, expr);
676 hir::ExprAssignOp(_, ref lhs, ref rhs) => {
678 constrain_call(rcx, expr, Some(&lhs),
679 Some(&**rhs).into_iter(), false);
682 intravisit::walk_expr(rcx, expr);
685 hir::ExprIndex(ref lhs, ref rhs) if has_method_map => {
686 constrain_call(rcx, expr, Some(&lhs),
687 Some(&**rhs).into_iter(), true);
689 intravisit::walk_expr(rcx, expr);
692 hir::ExprBinary(op, ref lhs, ref rhs) if has_method_map => {
693 let implicitly_ref_args = !hir_util::is_by_value_binop(op.node);
695 // As `expr_method_call`, but the call is via an
696 // overloaded op. Note that we (sadly) currently use an
697 // implicit "by ref" sort of passing style here. This
698 // should be converted to an adjustment!
699 constrain_call(rcx, expr, Some(&lhs),
700 Some(&**rhs).into_iter(), implicitly_ref_args);
702 intravisit::walk_expr(rcx, expr);
705 hir::ExprBinary(_, ref lhs, ref rhs) => {
706 // If you do `x OP y`, then the types of `x` and `y` must
707 // outlive the operation you are performing.
708 let lhs_ty = rcx.resolve_expr_type_adjusted(&lhs);
709 let rhs_ty = rcx.resolve_expr_type_adjusted(&rhs);
710 for &ty in &[lhs_ty, rhs_ty] {
711 type_must_outlive(rcx,
712 infer::Operand(expr.span),
716 intravisit::walk_expr(rcx, expr);
719 hir::ExprUnary(op, ref lhs) if has_method_map => {
720 let implicitly_ref_args = !hir_util::is_by_value_unop(op);
723 constrain_call(rcx, expr, Some(&lhs),
724 None::<hir::Expr>.iter(), implicitly_ref_args);
726 intravisit::walk_expr(rcx, expr);
729 hir::ExprUnary(hir::UnDeref, ref base) => {
730 // For *a, the lifetime of a must enclose the deref
731 let method_call = MethodCall::expr(expr.id);
732 let base_ty = match rcx.fcx.inh.tables.borrow().method_map.get(&method_call) {
734 constrain_call(rcx, expr, Some(&base),
735 None::<hir::Expr>.iter(), true);
736 let fn_ret = // late-bound regions in overloaded method calls are instantiated
737 rcx.tcx().no_late_bound_regions(&method.ty.fn_ret()).unwrap();
740 None => rcx.resolve_node_type(base.id)
742 if let ty::TyRef(r_ptr, _) = base_ty.sty {
743 mk_subregion_due_to_dereference(
744 rcx, expr.span, expr_region, *r_ptr);
747 intravisit::walk_expr(rcx, expr);
750 hir::ExprIndex(ref vec_expr, _) => {
751 // For a[b], the lifetime of a must enclose the deref
752 let vec_type = rcx.resolve_expr_type_adjusted(&vec_expr);
753 constrain_index(rcx, expr, vec_type);
755 intravisit::walk_expr(rcx, expr);
758 hir::ExprCast(ref source, _) => {
759 // Determine if we are casting `source` to a trait
760 // instance. If so, we have to be sure that the type of
761 // the source obeys the trait's region bound.
762 constrain_cast(rcx, expr, &source);
763 intravisit::walk_expr(rcx, expr);
766 hir::ExprAddrOf(m, ref base) => {
767 link_addr_of(rcx, expr, m, &base);
769 // Require that when you write a `&expr` expression, the
770 // resulting pointer has a lifetime that encompasses the
771 // `&expr` expression itself. Note that we constraining
772 // the type of the node expr.id here *before applying
775 // FIXME(#6268) nested method calls requires that this rule change
776 let ty0 = rcx.resolve_node_type(expr.id);
777 type_must_outlive(rcx, infer::AddrOf(expr.span), ty0, expr_region);
778 intravisit::walk_expr(rcx, expr);
781 hir::ExprMatch(ref discr, ref arms, _) => {
782 link_match(rcx, &discr, &arms[..]);
784 intravisit::walk_expr(rcx, expr);
787 hir::ExprClosure(_, _, ref body) => {
788 check_expr_fn_block(rcx, expr, &body);
791 hir::ExprLoop(ref body, _) => {
792 let repeating_scope = rcx.set_repeating_scope(body.id);
793 intravisit::walk_expr(rcx, expr);
794 rcx.set_repeating_scope(repeating_scope);
797 hir::ExprWhile(ref cond, ref body, _) => {
798 let repeating_scope = rcx.set_repeating_scope(cond.id);
799 rcx.visit_expr(&cond);
801 rcx.set_repeating_scope(body.id);
802 rcx.visit_block(&body);
804 rcx.set_repeating_scope(repeating_scope);
807 hir::ExprRet(Some(ref ret_expr)) => {
808 let call_site_scope = rcx.call_site_scope;
809 debug!("visit_expr ExprRet ret_expr.id {} call_site_scope: {:?}",
810 ret_expr.id, call_site_scope);
811 type_of_node_must_outlive(rcx,
812 infer::CallReturn(ret_expr.span),
814 ty::ReScope(call_site_scope.unwrap()));
815 intravisit::walk_expr(rcx, expr);
819 intravisit::walk_expr(rcx, expr);
824 fn constrain_cast(rcx: &mut Rcx,
825 cast_expr: &hir::Expr,
826 source_expr: &hir::Expr)
828 debug!("constrain_cast(cast_expr={:?}, source_expr={:?})",
832 let source_ty = rcx.resolve_node_type(source_expr.id);
833 let target_ty = rcx.resolve_node_type(cast_expr.id);
835 walk_cast(rcx, cast_expr, source_ty, target_ty);
837 fn walk_cast<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>,
838 cast_expr: &hir::Expr,
841 debug!("walk_cast(from_ty={:?}, to_ty={:?})",
844 match (&from_ty.sty, &to_ty.sty) {
845 /*From:*/ (&ty::TyRef(from_r, ref from_mt),
846 /*To: */ &ty::TyRef(to_r, ref to_mt)) => {
847 // Target cannot outlive source, naturally.
848 rcx.fcx.mk_subr(infer::Reborrow(cast_expr.span), *to_r, *from_r);
849 walk_cast(rcx, cast_expr, from_mt.ty, to_mt.ty);
853 /*To: */ &ty::TyTrait(box ty::TraitTy { ref bounds, .. })) => {
854 // When T is existentially quantified as a trait
855 // `Foo+'to`, it must outlive the region bound `'to`.
856 type_must_outlive(rcx, infer::RelateObjectBound(cast_expr.span),
857 from_ty, bounds.region_bound);
860 /*From:*/ (&ty::TyBox(from_referent_ty),
861 /*To: */ &ty::TyBox(to_referent_ty)) => {
862 walk_cast(rcx, cast_expr, from_referent_ty, to_referent_ty);
870 fn check_expr_fn_block(rcx: &mut Rcx,
873 let repeating_scope = rcx.set_repeating_scope(body.id);
874 intravisit::walk_expr(rcx, expr);
875 rcx.set_repeating_scope(repeating_scope);
878 fn constrain_callee(rcx: &mut Rcx,
879 callee_id: ast::NodeId,
880 _call_expr: &hir::Expr,
881 _callee_expr: &hir::Expr) {
882 let callee_ty = rcx.resolve_node_type(callee_id);
883 match callee_ty.sty {
884 ty::TyFnDef(..) | ty::TyFnPtr(_) => { }
886 // this should not happen, but it does if the program is
889 // tcx.sess.span_bug(
891 // format!("Calling non-function: {}", callee_ty));
896 fn constrain_call<'a, I: Iterator<Item=&'a hir::Expr>>(rcx: &mut Rcx,
897 call_expr: &hir::Expr,
898 receiver: Option<&hir::Expr>,
900 implicitly_ref_args: bool) {
901 //! Invoked on every call site (i.e., normal calls, method calls,
902 //! and overloaded operators). Constrains the regions which appear
903 //! in the type of the function. Also constrains the regions that
904 //! appear in the arguments appropriately.
906 debug!("constrain_call(call_expr={:?}, \
908 implicitly_ref_args={})",
911 implicitly_ref_args);
913 // `callee_region` is the scope representing the time in which the
916 // FIXME(#6268) to support nested method calls, should be callee_id
917 let callee_scope = rcx.tcx().region_maps.node_extent(call_expr.id);
918 let callee_region = ty::ReScope(callee_scope);
920 debug!("callee_region={:?}", callee_region);
922 for arg_expr in arg_exprs {
923 debug!("Argument: {:?}", arg_expr);
925 // ensure that any regions appearing in the argument type are
926 // valid for at least the lifetime of the function:
927 type_of_node_must_outlive(
928 rcx, infer::CallArg(arg_expr.span),
929 arg_expr.id, callee_region);
931 // unfortunately, there are two means of taking implicit
932 // references, and we need to propagate constraints as a
933 // result. modes are going away and the "DerefArgs" code
934 // should be ported to use adjustments
935 if implicitly_ref_args {
936 link_by_ref(rcx, arg_expr, callee_scope);
940 // as loop above, but for receiver
941 if let Some(r) = receiver {
942 debug!("receiver: {:?}", r);
943 type_of_node_must_outlive(
944 rcx, infer::CallRcvr(r.span),
945 r.id, callee_region);
946 if implicitly_ref_args {
947 link_by_ref(rcx, &r, callee_scope);
952 /// Invoked on any auto-dereference that occurs. Checks that if this is a region pointer being
953 /// dereferenced, the lifetime of the pointer includes the deref expr.
954 fn constrain_autoderefs<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>,
955 deref_expr: &hir::Expr,
957 mut derefd_ty: Ty<'tcx>)
959 debug!("constrain_autoderefs(deref_expr={:?}, derefs={}, derefd_ty={:?})",
964 let s_deref_expr = rcx.tcx().region_maps.node_extent(deref_expr.id);
965 let r_deref_expr = ty::ReScope(s_deref_expr);
967 let method_call = MethodCall::autoderef(deref_expr.id, i as u32);
968 debug!("constrain_autoderefs: method_call={:?} (of {:?} total)", method_call, derefs);
970 let method = rcx.fcx.inh.tables.borrow().method_map.get(&method_call).map(|m| m.clone());
972 derefd_ty = match method {
974 debug!("constrain_autoderefs: #{} is overloaded, method={:?}",
977 let origin = infer::ParameterOrigin::OverloadedDeref;
978 substs_wf_in_scope(rcx, origin, method.substs, deref_expr.span, r_deref_expr);
980 // Treat overloaded autoderefs as if an AutoRef adjustment
981 // was applied on the base type, as that is always the case.
982 let fn_sig = method.ty.fn_sig();
983 let fn_sig = // late-bound regions should have been instantiated
984 rcx.tcx().no_late_bound_regions(fn_sig).unwrap();
985 let self_ty = fn_sig.inputs[0];
986 let (m, r) = match self_ty.sty {
987 ty::TyRef(r, ref m) => (m.mutbl, r),
989 rcx.tcx().sess.span_bug(
991 &format!("bad overloaded deref type {:?}",
996 debug!("constrain_autoderefs: receiver r={:?} m={:?}",
1000 let mc = mc::MemCategorizationContext::new(rcx.fcx.infcx());
1001 let self_cmt = ignore_err!(mc.cat_expr_autoderefd(deref_expr, i));
1002 debug!("constrain_autoderefs: self_cmt={:?}",
1004 link_region(rcx, deref_expr.span, r,
1005 ty::BorrowKind::from_mutbl(m), self_cmt);
1008 // Specialized version of constrain_call.
1009 type_must_outlive(rcx, infer::CallRcvr(deref_expr.span),
1010 self_ty, r_deref_expr);
1011 match fn_sig.output {
1012 ty::FnConverging(return_type) => {
1013 type_must_outlive(rcx, infer::CallReturn(deref_expr.span),
1014 return_type, r_deref_expr);
1017 ty::FnDiverging => unreachable!()
1023 if let ty::TyRef(r_ptr, _) = derefd_ty.sty {
1024 mk_subregion_due_to_dereference(rcx, deref_expr.span,
1025 r_deref_expr, *r_ptr);
1028 match derefd_ty.builtin_deref(true, ty::NoPreference) {
1029 Some(mt) => derefd_ty = mt.ty,
1030 /* if this type can't be dereferenced, then there's already an error
1031 in the session saying so. Just bail out for now */
1037 pub fn mk_subregion_due_to_dereference(rcx: &mut Rcx,
1039 minimum_lifetime: ty::Region,
1040 maximum_lifetime: ty::Region) {
1041 rcx.fcx.mk_subr(infer::DerefPointer(deref_span),
1042 minimum_lifetime, maximum_lifetime)
1045 fn check_safety_of_rvalue_destructor_if_necessary<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>,
1049 Categorization::Rvalue(region) => {
1051 ty::ReScope(rvalue_scope) => {
1052 let typ = rcx.resolve_type(cmt.ty);
1053 dropck::check_safety_of_destructor_if_necessary(rcx,
1063 &format!("unexpected rvalue region in rvalue \
1064 destructor safety checking: `{:?}`",
1073 /// Invoked on any index expression that occurs. Checks that if this is a slice being indexed, the
1074 /// lifetime of the pointer includes the deref expr.
1075 fn constrain_index<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>,
1076 index_expr: &hir::Expr,
1077 indexed_ty: Ty<'tcx>)
1079 debug!("constrain_index(index_expr=?, indexed_ty={}",
1080 rcx.fcx.infcx().ty_to_string(indexed_ty));
1082 let r_index_expr = ty::ReScope(rcx.tcx().region_maps.node_extent(index_expr.id));
1083 if let ty::TyRef(r_ptr, mt) = indexed_ty.sty {
1085 ty::TySlice(_) | ty::TyStr => {
1086 rcx.fcx.mk_subr(infer::IndexSlice(index_expr.span),
1087 r_index_expr, *r_ptr);
1094 /// Guarantees that any lifetimes which appear in the type of the node `id` (after applying
1095 /// adjustments) are valid for at least `minimum_lifetime`
1096 fn type_of_node_must_outlive<'a, 'tcx>(
1097 rcx: &mut Rcx<'a, 'tcx>,
1098 origin: infer::SubregionOrigin<'tcx>,
1100 minimum_lifetime: ty::Region)
1102 let tcx = rcx.fcx.tcx();
1104 // Try to resolve the type. If we encounter an error, then typeck
1105 // is going to fail anyway, so just stop here and let typeck
1106 // report errors later on in the writeback phase.
1107 let ty0 = rcx.resolve_node_type(id);
1108 let ty = ty0.adjust(tcx, origin.span(), id,
1109 rcx.fcx.inh.tables.borrow().adjustments.get(&id),
1110 |method_call| rcx.resolve_method_type(method_call));
1111 debug!("constrain_regions_in_type_of_node(\
1112 ty={}, ty0={}, id={}, minimum_lifetime={:?})",
1114 id, minimum_lifetime);
1115 type_must_outlive(rcx, origin, ty, minimum_lifetime);
1118 /// Computes the guarantor for an expression `&base` and then ensures that the lifetime of the
1119 /// resulting pointer is linked to the lifetime of its guarantor (if any).
1120 fn link_addr_of(rcx: &mut Rcx, expr: &hir::Expr,
1121 mutability: hir::Mutability, base: &hir::Expr) {
1122 debug!("link_addr_of(expr={:?}, base={:?})", expr, base);
1125 let mc = mc::MemCategorizationContext::new(rcx.fcx.infcx());
1126 ignore_err!(mc.cat_expr(base))
1129 debug!("link_addr_of: cmt={:?}", cmt);
1131 link_region_from_node_type(rcx, expr.span, expr.id, mutability, cmt);
1134 /// Computes the guarantors for any ref bindings in a `let` and
1135 /// then ensures that the lifetime of the resulting pointer is
1136 /// linked to the lifetime of the initialization expression.
1137 fn link_local(rcx: &Rcx, local: &hir::Local) {
1138 debug!("regionck::for_local()");
1139 let init_expr = match local.init {
1141 Some(ref expr) => &**expr,
1143 let mc = mc::MemCategorizationContext::new(rcx.fcx.infcx());
1144 let discr_cmt = ignore_err!(mc.cat_expr(init_expr));
1145 link_pattern(rcx, mc, discr_cmt, &local.pat);
1148 /// Computes the guarantors for any ref bindings in a match and
1149 /// then ensures that the lifetime of the resulting pointer is
1150 /// linked to the lifetime of its guarantor (if any).
1151 fn link_match(rcx: &Rcx, discr: &hir::Expr, arms: &[hir::Arm]) {
1152 debug!("regionck::for_match()");
1153 let mc = mc::MemCategorizationContext::new(rcx.fcx.infcx());
1154 let discr_cmt = ignore_err!(mc.cat_expr(discr));
1155 debug!("discr_cmt={:?}", discr_cmt);
1157 for root_pat in &arm.pats {
1158 link_pattern(rcx, mc, discr_cmt.clone(), &root_pat);
1163 /// Computes the guarantors for any ref bindings in a match and
1164 /// then ensures that the lifetime of the resulting pointer is
1165 /// linked to the lifetime of its guarantor (if any).
1166 fn link_fn_args(rcx: &Rcx, body_scope: CodeExtent, args: &[hir::Arg]) {
1167 debug!("regionck::link_fn_args(body_scope={:?})", body_scope);
1168 let mc = mc::MemCategorizationContext::new(rcx.fcx.infcx());
1170 let arg_ty = rcx.fcx.node_ty(arg.id);
1171 let re_scope = ty::ReScope(body_scope);
1172 let arg_cmt = mc.cat_rvalue(arg.id, arg.ty.span, re_scope, arg_ty);
1173 debug!("arg_ty={:?} arg_cmt={:?} arg={:?}",
1177 link_pattern(rcx, mc, arg_cmt, &arg.pat);
1181 /// Link lifetimes of any ref bindings in `root_pat` to the pointers found in the discriminant, if
1183 fn link_pattern<'t, 'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1184 mc: mc::MemCategorizationContext<'t, 'a, 'tcx>,
1185 discr_cmt: mc::cmt<'tcx>,
1186 root_pat: &hir::Pat) {
1187 debug!("link_pattern(discr_cmt={:?}, root_pat={:?})",
1190 let _ = mc.cat_pattern(discr_cmt, root_pat, |mc, sub_cmt, sub_pat| {
1191 match sub_pat.node {
1193 PatKind::Ident(hir::BindByRef(mutbl), _, _) => {
1194 link_region_from_node_type(
1195 rcx, sub_pat.span, sub_pat.id,
1199 // `[_, ..slice, _]` pattern
1200 PatKind::Vec(_, Some(ref slice_pat), _) => {
1201 match mc.cat_slice_pattern(sub_cmt, &slice_pat) {
1202 Ok((slice_cmt, slice_mutbl, slice_r)) => {
1203 link_region(rcx, sub_pat.span, &slice_r,
1204 ty::BorrowKind::from_mutbl(slice_mutbl),
1215 /// Link lifetime of borrowed pointer resulting from autoref to lifetimes in the value being
1217 fn link_autoref(rcx: &Rcx,
1220 autoref: &adjustment::AutoRef)
1222 debug!("link_autoref(autoref={:?})", autoref);
1223 let mc = mc::MemCategorizationContext::new(rcx.fcx.infcx());
1224 let expr_cmt = ignore_err!(mc.cat_expr_autoderefd(expr, autoderefs));
1225 debug!("expr_cmt={:?}", expr_cmt);
1228 adjustment::AutoPtr(r, m) => {
1229 link_region(rcx, expr.span, r,
1230 ty::BorrowKind::from_mutbl(m), expr_cmt);
1233 adjustment::AutoUnsafe(m) => {
1234 let r = ty::ReScope(rcx.tcx().region_maps.node_extent(expr.id));
1235 link_region(rcx, expr.span, &r, ty::BorrowKind::from_mutbl(m), expr_cmt);
1240 /// Computes the guarantor for cases where the `expr` is being passed by implicit reference and
1241 /// must outlive `callee_scope`.
1242 fn link_by_ref(rcx: &Rcx,
1244 callee_scope: CodeExtent) {
1245 debug!("link_by_ref(expr={:?}, callee_scope={:?})",
1246 expr, callee_scope);
1247 let mc = mc::MemCategorizationContext::new(rcx.fcx.infcx());
1248 let expr_cmt = ignore_err!(mc.cat_expr(expr));
1249 let borrow_region = ty::ReScope(callee_scope);
1250 link_region(rcx, expr.span, &borrow_region, ty::ImmBorrow, expr_cmt);
1253 /// Like `link_region()`, except that the region is extracted from the type of `id`, which must be
1254 /// some reference (`&T`, `&str`, etc).
1255 fn link_region_from_node_type<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1258 mutbl: hir::Mutability,
1259 cmt_borrowed: mc::cmt<'tcx>) {
1260 debug!("link_region_from_node_type(id={:?}, mutbl={:?}, cmt_borrowed={:?})",
1261 id, mutbl, cmt_borrowed);
1263 let rptr_ty = rcx.resolve_node_type(id);
1264 if let ty::TyRef(&r, _) = rptr_ty.sty {
1265 debug!("rptr_ty={}", rptr_ty);
1266 link_region(rcx, span, &r, ty::BorrowKind::from_mutbl(mutbl),
1271 /// Informs the inference engine that `borrow_cmt` is being borrowed with kind `borrow_kind` and
1272 /// lifetime `borrow_region`. In order to ensure borrowck is satisfied, this may create constraints
1273 /// between regions, as explained in `link_reborrowed_region()`.
1274 fn link_region<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1276 borrow_region: &ty::Region,
1277 borrow_kind: ty::BorrowKind,
1278 borrow_cmt: mc::cmt<'tcx>) {
1279 let mut borrow_cmt = borrow_cmt;
1280 let mut borrow_kind = borrow_kind;
1282 let origin = infer::DataBorrowed(borrow_cmt.ty, span);
1283 type_must_outlive(rcx, origin, borrow_cmt.ty, *borrow_region);
1286 debug!("link_region(borrow_region={:?}, borrow_kind={:?}, borrow_cmt={:?})",
1290 match borrow_cmt.cat.clone() {
1291 Categorization::Deref(ref_cmt, _,
1292 mc::Implicit(ref_kind, ref_region)) |
1293 Categorization::Deref(ref_cmt, _,
1294 mc::BorrowedPtr(ref_kind, ref_region)) => {
1295 match link_reborrowed_region(rcx, span,
1296 borrow_region, borrow_kind,
1297 ref_cmt, ref_region, ref_kind,
1309 Categorization::Downcast(cmt_base, _) |
1310 Categorization::Deref(cmt_base, _, mc::Unique) |
1311 Categorization::Interior(cmt_base, _) => {
1312 // Borrowing interior or owned data requires the base
1313 // to be valid and borrowable in the same fashion.
1314 borrow_cmt = cmt_base;
1315 borrow_kind = borrow_kind;
1318 Categorization::Deref(_, _, mc::UnsafePtr(..)) |
1319 Categorization::StaticItem |
1320 Categorization::Upvar(..) |
1321 Categorization::Local(..) |
1322 Categorization::Rvalue(..) => {
1323 // These are all "base cases" with independent lifetimes
1324 // that are not subject to inference
1331 /// This is the most complicated case: the path being borrowed is
1332 /// itself the referent of a borrowed pointer. Let me give an
1333 /// example fragment of code to make clear(er) the situation:
1335 /// let r: &'a mut T = ...; // the original reference "r" has lifetime 'a
1337 /// &'z *r // the reborrow has lifetime 'z
1339 /// Now, in this case, our primary job is to add the inference
1340 /// constraint that `'z <= 'a`. Given this setup, let's clarify the
1341 /// parameters in (roughly) terms of the example:
1343 /// A borrow of: `& 'z bk * r` where `r` has type `& 'a bk T`
1344 /// borrow_region ^~ ref_region ^~
1345 /// borrow_kind ^~ ref_kind ^~
1348 /// Here `bk` stands for some borrow-kind (e.g., `mut`, `uniq`, etc).
1350 /// Unfortunately, there are some complications beyond the simple
1351 /// scenario I just painted:
1353 /// 1. The reference `r` might in fact be a "by-ref" upvar. In that
1354 /// case, we have two jobs. First, we are inferring whether this reference
1355 /// should be an `&T`, `&mut T`, or `&uniq T` reference, and we must
1356 /// adjust that based on this borrow (e.g., if this is an `&mut` borrow,
1357 /// then `r` must be an `&mut` reference). Second, whenever we link
1358 /// two regions (here, `'z <= 'a`), we supply a *cause*, and in this
1359 /// case we adjust the cause to indicate that the reference being
1360 /// "reborrowed" is itself an upvar. This provides a nicer error message
1361 /// should something go wrong.
1363 /// 2. There may in fact be more levels of reborrowing. In the
1364 /// example, I said the borrow was like `&'z *r`, but it might
1365 /// in fact be a borrow like `&'z **q` where `q` has type `&'a
1366 /// &'b mut T`. In that case, we want to ensure that `'z <= 'a`
1367 /// and `'z <= 'b`. This is explained more below.
1369 /// The return value of this function indicates whether we need to
1370 /// recurse and process `ref_cmt` (see case 2 above).
1371 fn link_reborrowed_region<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1373 borrow_region: &ty::Region,
1374 borrow_kind: ty::BorrowKind,
1375 ref_cmt: mc::cmt<'tcx>,
1376 ref_region: ty::Region,
1377 mut ref_kind: ty::BorrowKind,
1379 -> Option<(mc::cmt<'tcx>, ty::BorrowKind)>
1381 // Possible upvar ID we may need later to create an entry in the
1384 // Detect by-ref upvar `x`:
1385 let cause = match note {
1386 mc::NoteUpvarRef(ref upvar_id) => {
1387 let upvar_capture_map = &rcx.fcx.inh.tables.borrow_mut().upvar_capture_map;
1388 match upvar_capture_map.get(upvar_id) {
1389 Some(&ty::UpvarCapture::ByRef(ref upvar_borrow)) => {
1390 // The mutability of the upvar may have been modified
1391 // by the above adjustment, so update our local variable.
1392 ref_kind = upvar_borrow.kind;
1394 infer::ReborrowUpvar(span, *upvar_id)
1397 rcx.tcx().sess.span_bug(
1399 &format!("Illegal upvar id: {:?}",
1404 mc::NoteClosureEnv(ref upvar_id) => {
1405 // We don't have any mutability changes to propagate, but
1406 // we do want to note that an upvar reborrow caused this
1408 infer::ReborrowUpvar(span, *upvar_id)
1411 infer::Reborrow(span)
1415 debug!("link_reborrowed_region: {:?} <= {:?}",
1418 rcx.fcx.mk_subr(cause, *borrow_region, ref_region);
1420 // If we end up needing to recurse and establish a region link
1421 // with `ref_cmt`, calculate what borrow kind we will end up
1422 // needing. This will be used below.
1424 // One interesting twist is that we can weaken the borrow kind
1425 // when we recurse: to reborrow an `&mut` referent as mutable,
1426 // borrowck requires a unique path to the `&mut` reference but not
1427 // necessarily a *mutable* path.
1428 let new_borrow_kind = match borrow_kind {
1431 ty::MutBorrow | ty::UniqueImmBorrow =>
1435 // Decide whether we need to recurse and link any regions within
1436 // the `ref_cmt`. This is concerned for the case where the value
1437 // being reborrowed is in fact a borrowed pointer found within
1438 // another borrowed pointer. For example:
1440 // let p: &'b &'a mut T = ...;
1444 // What makes this case particularly tricky is that, if the data
1445 // being borrowed is a `&mut` or `&uniq` borrow, borrowck requires
1446 // not only that `'z <= 'a`, (as before) but also `'z <= 'b`
1447 // (otherwise the user might mutate through the `&mut T` reference
1448 // after `'b` expires and invalidate the borrow we are looking at
1451 // So let's re-examine our parameters in light of this more
1452 // complicated (possible) scenario:
1454 // A borrow of: `& 'z bk * * p` where `p` has type `&'b bk & 'a bk T`
1455 // borrow_region ^~ ref_region ^~
1456 // borrow_kind ^~ ref_kind ^~
1459 // (Note that since we have not examined `ref_cmt.cat`, we don't
1460 // know whether this scenario has occurred; but I wanted to show
1461 // how all the types get adjusted.)
1464 // The reference being reborrowed is a sharable ref of
1465 // type `&'a T`. In this case, it doesn't matter where we
1466 // *found* the `&T` pointer, the memory it references will
1467 // be valid and immutable for `'a`. So we can stop here.
1469 // (Note that the `borrow_kind` must also be ImmBorrow or
1470 // else the user is borrowed imm memory as mut memory,
1471 // which means they'll get an error downstream in borrowck
1476 ty::MutBorrow | ty::UniqueImmBorrow => {
1477 // The reference being reborrowed is either an `&mut T` or
1478 // `&uniq T`. This is the case where recursion is needed.
1479 return Some((ref_cmt, new_borrow_kind));
1484 /// Checks that the values provided for type/region arguments in a given
1485 /// expression are well-formed and in-scope.
1486 pub fn substs_wf_in_scope<'a,'tcx>(rcx: &mut Rcx<'a,'tcx>,
1487 origin: infer::ParameterOrigin,
1488 substs: &Substs<'tcx>,
1490 expr_region: ty::Region) {
1491 debug!("substs_wf_in_scope(substs={:?}, \
1495 substs, expr_region, origin, expr_span);
1497 let origin = infer::ParameterInScope(origin, expr_span);
1499 for ®ion in substs.regions() {
1500 rcx.fcx.mk_subr(origin.clone(), expr_region, region);
1503 for &ty in &substs.types {
1504 let ty = rcx.resolve_type(ty);
1505 type_must_outlive(rcx, origin.clone(), ty, expr_region);
1509 /// Ensures that type is well-formed in `region`, which implies (among
1510 /// other things) that all borrowed data reachable via `ty` outlives
1512 pub fn type_must_outlive<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1513 origin: infer::SubregionOrigin<'tcx>,
1517 let ty = rcx.resolve_type(ty);
1519 debug!("type_must_outlive(ty={:?}, region={:?}, origin={:?})",
1524 assert!(!ty.has_escaping_regions());
1526 let components = ty::outlives::components(rcx.infcx(), ty);
1527 components_must_outlive(rcx, origin, components, region);
1530 fn components_must_outlive<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1531 origin: infer::SubregionOrigin<'tcx>,
1532 components: Vec<ty::outlives::Component<'tcx>>,
1535 for component in components {
1536 let origin = origin.clone();
1538 ty::outlives::Component::Region(region1) => {
1539 rcx.fcx.mk_subr(origin, region, region1);
1541 ty::outlives::Component::Param(param_ty) => {
1542 param_ty_must_outlive(rcx, origin, region, param_ty);
1544 ty::outlives::Component::Projection(projection_ty) => {
1545 projection_must_outlive(rcx, origin, region, projection_ty);
1547 ty::outlives::Component::EscapingProjection(subcomponents) => {
1548 components_must_outlive(rcx, origin, subcomponents, region);
1550 ty::outlives::Component::UnresolvedInferenceVariable(v) => {
1551 // ignore this, we presume it will yield an error
1552 // later, since if a type variable is not resolved by
1553 // this point it never will be
1554 rcx.tcx().sess.delay_span_bug(
1556 &format!("unresolved inference variable in outlives: {:?}", v));
1562 fn param_ty_must_outlive<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1563 origin: infer::SubregionOrigin<'tcx>,
1565 param_ty: ty::ParamTy) {
1566 debug!("param_ty_must_outlive(region={:?}, param_ty={:?}, origin={:?})",
1567 region, param_ty, origin);
1569 let verify_bound = param_bound(rcx, param_ty);
1570 let generic = GenericKind::Param(param_ty);
1571 rcx.fcx.infcx().verify_generic_bound(origin, generic, region, verify_bound);
1574 fn projection_must_outlive<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1575 origin: infer::SubregionOrigin<'tcx>,
1577 projection_ty: ty::ProjectionTy<'tcx>)
1579 debug!("projection_must_outlive(region={:?}, projection_ty={:?}, origin={:?})",
1580 region, projection_ty, origin);
1582 // This case is thorny for inference. The fundamental problem is
1583 // that there are many cases where we have choice, and inference
1584 // doesn't like choice (the current region inference in
1585 // particular). :) First off, we have to choose between using the
1586 // OutlivesProjectionEnv, OutlivesProjectionTraitDef, and
1587 // OutlivesProjectionComponent rules, any one of which is
1588 // sufficient. If there are no inference variables involved, it's
1589 // not hard to pick the right rule, but if there are, we're in a
1590 // bit of a catch 22: if we picked which rule we were going to
1591 // use, we could add constraints to the region inference graph
1592 // that make it apply, but if we don't add those constraints, the
1593 // rule might not apply (but another rule might). For now, we err
1594 // on the side of adding too few edges into the graph.
1596 // Compute the bounds we can derive from the environment or trait
1597 // definition. We know that the projection outlives all the
1598 // regions in this list.
1599 let env_bounds = projection_declared_bounds(rcx, origin.span(), projection_ty);
1601 debug!("projection_must_outlive: env_bounds={:?}",
1604 // If we know that the projection outlives 'static, then we're
1606 if env_bounds.contains(&ty::ReStatic) {
1607 debug!("projection_must_outlive: 'static as declared bound");
1611 // If declared bounds list is empty, the only applicable rule is
1612 // OutlivesProjectionComponent. If there are inference variables,
1613 // then, we can break down the outlives into more primitive
1614 // components without adding unnecessary edges.
1616 // If there are *no* inference variables, however, we COULD do
1617 // this, but we choose not to, because the error messages are less
1618 // good. For example, a requirement like `T::Item: 'r` would be
1619 // translated to a requirement that `T: 'r`; when this is reported
1620 // to the user, it will thus say "T: 'r must hold so that T::Item:
1621 // 'r holds". But that makes it sound like the only way to fix
1622 // the problem is to add `T: 'r`, which isn't true. So, if there are no
1623 // inference variables, we use a verify constraint instead of adding
1624 // edges, which winds up enforcing the same condition.
1626 projection_ty.trait_ref.substs.types.iter().any(|t| t.needs_infer()) ||
1627 projection_ty.trait_ref.substs.regions().iter().any(|r| r.needs_infer())
1629 if env_bounds.is_empty() && needs_infer {
1630 debug!("projection_must_outlive: no declared bounds");
1632 for &component_ty in &projection_ty.trait_ref.substs.types {
1633 type_must_outlive(rcx, origin.clone(), component_ty, region);
1636 for &r in projection_ty.trait_ref.substs.regions() {
1637 rcx.fcx.mk_subr(origin.clone(), region, r);
1643 // If we find that there is a unique declared bound `'b`, and this bound
1644 // appears in the trait reference, then the best action is to require that `'b:'r`,
1645 // so do that. This is best no matter what rule we use:
1647 // - OutlivesProjectionEnv or OutlivesProjectionTraitDef: these would translate to
1648 // the requirement that `'b:'r`
1649 // - OutlivesProjectionComponent: this would require `'b:'r` in addition to other conditions
1650 if !env_bounds.is_empty() && env_bounds[1..].iter().all(|b| *b == env_bounds[0]) {
1651 let unique_bound = env_bounds[0];
1652 debug!("projection_must_outlive: unique declared bound = {:?}", unique_bound);
1653 if projection_ty.trait_ref.substs.regions()
1655 .any(|r| env_bounds.contains(r))
1657 debug!("projection_must_outlive: unique declared bound appears in trait ref");
1658 rcx.fcx.mk_subr(origin.clone(), region, unique_bound);
1663 // Fallback to verifying after the fact that there exists a
1664 // declared bound, or that all the components appearing in the
1665 // projection outlive; in some cases, this may add insufficient
1666 // edges into the inference graph, leading to inference failures
1667 // even though a satisfactory solution exists.
1668 let verify_bound = projection_bound(rcx, origin.span(), env_bounds, projection_ty);
1669 let generic = GenericKind::Projection(projection_ty);
1670 rcx.fcx.infcx().verify_generic_bound(origin, generic.clone(), region, verify_bound);
1673 fn type_bound<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, span: Span, ty: Ty<'tcx>) -> VerifyBound {
1678 ty::TyProjection(data) => {
1679 let declared_bounds = projection_declared_bounds(rcx, span, data);
1680 projection_bound(rcx, span, declared_bounds, data)
1683 recursive_type_bound(rcx, span, ty)
1688 fn param_bound<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>, param_ty: ty::ParamTy) -> VerifyBound {
1689 let param_env = &rcx.infcx().parameter_environment;
1691 debug!("param_bound(param_ty={:?})",
1694 let mut param_bounds = declared_generic_bounds_from_env(rcx, GenericKind::Param(param_ty));
1696 // Add in the default bound of fn body that applies to all in
1697 // scope type parameters:
1698 param_bounds.push(param_env.implicit_region_bound);
1700 VerifyBound::AnyRegion(param_bounds)
1703 fn projection_declared_bounds<'a, 'tcx>(rcx: &Rcx<'a,'tcx>,
1705 projection_ty: ty::ProjectionTy<'tcx>)
1708 // First assemble bounds from where clauses and traits.
1710 let mut declared_bounds =
1711 declared_generic_bounds_from_env(rcx, GenericKind::Projection(projection_ty));
1713 declared_bounds.extend_from_slice(
1714 &declared_projection_bounds_from_trait(rcx, span, projection_ty));
1719 fn projection_bound<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1721 declared_bounds: Vec<ty::Region>,
1722 projection_ty: ty::ProjectionTy<'tcx>)
1724 debug!("projection_bound(declared_bounds={:?}, projection_ty={:?})",
1725 declared_bounds, projection_ty);
1727 // see the extensive comment in projection_must_outlive
1729 let ty = rcx.tcx().mk_projection(projection_ty.trait_ref, projection_ty.item_name);
1730 let recursive_bound = recursive_type_bound(rcx, span, ty);
1732 VerifyBound::AnyRegion(declared_bounds).or(recursive_bound)
1735 fn recursive_type_bound<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1739 let mut bounds = vec![];
1741 for subty in ty.walk_shallow() {
1742 bounds.push(type_bound(rcx, span, subty));
1745 let mut regions = ty.regions();
1746 regions.retain(|r| !r.is_bound()); // ignore late-bound regions
1747 bounds.push(VerifyBound::AllRegions(regions));
1749 // remove bounds that must hold, since they are not interesting
1750 bounds.retain(|b| !b.must_hold());
1752 if bounds.len() == 1 {
1753 bounds.pop().unwrap()
1755 VerifyBound::AllBounds(bounds)
1759 fn declared_generic_bounds_from_env<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1760 generic: GenericKind<'tcx>)
1763 let param_env = &rcx.infcx().parameter_environment;
1765 // To start, collect bounds from user:
1766 let mut param_bounds = rcx.tcx().required_region_bounds(generic.to_ty(rcx.tcx()),
1767 param_env.caller_bounds.clone());
1769 // Next, collect regions we scraped from the well-formedness
1770 // constraints in the fn signature. To do that, we walk the list
1771 // of known relations from the fn ctxt.
1773 // This is crucial because otherwise code like this fails:
1775 // fn foo<'a, A>(x: &'a A) { x.bar() }
1777 // The problem is that the type of `x` is `&'a A`. To be
1778 // well-formed, then, A must be lower-generic by `'a`, but we
1779 // don't know that this holds from first principles.
1780 for &(r, p) in &rcx.region_bound_pairs {
1781 debug!("generic={:?} p={:?}",
1785 param_bounds.push(r);
1792 fn declared_projection_bounds_from_trait<'a,'tcx>(rcx: &Rcx<'a, 'tcx>,
1794 projection_ty: ty::ProjectionTy<'tcx>)
1798 let tcx = fcx.tcx();
1799 let infcx = fcx.infcx();
1801 debug!("projection_bounds(projection_ty={:?})",
1804 let ty = tcx.mk_projection(projection_ty.trait_ref.clone(), projection_ty.item_name);
1806 // Say we have a projection `<T as SomeTrait<'a>>::SomeType`. We are interested
1807 // in looking for a trait definition like:
1810 // trait SomeTrait<'a> {
1811 // type SomeType : 'a;
1815 // we can thus deduce that `<T as SomeTrait<'a>>::SomeType : 'a`.
1816 let trait_predicates = tcx.lookup_predicates(projection_ty.trait_ref.def_id);
1817 let predicates = trait_predicates.predicates.as_slice().to_vec();
1818 traits::elaborate_predicates(tcx, predicates)
1819 .filter_map(|predicate| {
1820 // we're only interesting in `T : 'a` style predicates:
1821 let outlives = match predicate {
1822 ty::Predicate::TypeOutlives(data) => data,
1823 _ => { return None; }
1826 debug!("projection_bounds: outlives={:?} (1)",
1829 // apply the substitutions (and normalize any projected types)
1830 let outlives = fcx.instantiate_type_scheme(span,
1831 projection_ty.trait_ref.substs,
1834 debug!("projection_bounds: outlives={:?} (2)",
1837 let region_result = infcx.commit_if_ok(|_| {
1839 infcx.replace_late_bound_regions_with_fresh_var(
1841 infer::AssocTypeProjection(projection_ty.item_name),
1844 debug!("projection_bounds: outlives={:?} (3)",
1847 // check whether this predicate applies to our current projection
1848 match infer::mk_eqty(infcx, false, TypeOrigin::Misc(span), ty, outlives.0) {
1849 Ok(()) => { Ok(outlives.1) }
1850 Err(_) => { Err(()) }
1854 debug!("projection_bounds: region_result={:?}",