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::mem_categorization as mc;
88 use middle::mem_categorization::Categorization;
90 use rustc::hir::def_id::DefId;
91 use rustc::ty::subst::Substs;
92 use rustc::ty::{self, Ty};
94 use rustc::infer::outlives::env::OutlivesEnvironment;
95 use rustc::ty::adjustment;
100 use rustc_data_structures::sync::Lrc;
102 use syntax_pos::Span;
103 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
104 use rustc::hir::{self, PatKind};
106 // a variation on try that just returns unit
107 macro_rules! ignore_err {
108 ($e:expr) => (match $e { Ok(e) => e, Err(_) => {
109 debug!("ignoring mem-categorization error!");
114 ///////////////////////////////////////////////////////////////////////////
115 // PUBLIC ENTRY POINTS
117 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
118 pub fn regionck_expr(&self, body: &'gcx hir::Body) {
119 let subject = self.tcx.hir.body_owner_def_id(body.id());
120 let id = body.value.id;
121 let mut rcx = RegionCtxt::new(self,
126 if self.err_count_since_creation() == 0 {
127 // regionck assumes typeck succeeded
128 rcx.visit_body(body);
129 rcx.visit_region_obligations(id);
131 rcx.resolve_regions_and_report_errors_unless_nll();
133 assert!(self.tables.borrow().free_region_map.is_empty());
134 self.tables.borrow_mut().free_region_map = rcx.outlives_environment.into_free_region_map();
137 /// Region checking during the WF phase for items. `wf_tys` are the
138 /// types from which we should derive implied bounds, if any.
139 pub fn regionck_item(&self,
140 item_id: ast::NodeId,
142 wf_tys: &[Ty<'tcx>]) {
143 debug!("regionck_item(item.id={:?}, wf_tys={:?})", item_id, wf_tys);
144 let subject = self.tcx.hir.local_def_id(item_id);
145 let mut rcx = RegionCtxt::new(self,
146 RepeatingScope(item_id),
150 rcx.outlives_environment.add_implied_bounds(self, wf_tys, item_id, span);
151 rcx.visit_region_obligations(item_id);
152 rcx.resolve_regions_and_report_errors();
155 /// Region check a function body. Not invoked on closures, but
156 /// only on the "root" fn item (in which closures may be
157 /// embedded). Walks the function body and adds various add'l
158 /// constraints that are needed for region inference. This is
159 /// separated both to isolate "pure" region constraints from the
160 /// rest of type check and because sometimes we need type
161 /// inference to have completed before we can determine which
162 /// constraints to add.
163 pub fn regionck_fn(&self,
165 body: &'gcx hir::Body) {
166 debug!("regionck_fn(id={})", fn_id);
167 let subject = self.tcx.hir.body_owner_def_id(body.id());
168 let node_id = body.value.id;
169 let mut rcx = RegionCtxt::new(self,
170 RepeatingScope(node_id),
175 if self.err_count_since_creation() == 0 {
176 // regionck assumes typeck succeeded
177 rcx.visit_fn_body(fn_id, body, self.tcx.hir.span(fn_id));
180 rcx.resolve_regions_and_report_errors_unless_nll();
182 // In this mode, we also copy the free-region-map into the
183 // tables of the enclosing fcx. In the other regionck modes
184 // (e.g., `regionck_item`), we don't have an enclosing tables.
185 assert!(self.tables.borrow().free_region_map.is_empty());
186 self.tables.borrow_mut().free_region_map = rcx.outlives_environment.into_free_region_map();
190 ///////////////////////////////////////////////////////////////////////////
193 pub struct RegionCtxt<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
194 pub fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
196 pub region_scope_tree: Lrc<region::ScopeTree>,
198 outlives_environment: OutlivesEnvironment<'tcx>,
200 // id of innermost fn body id
201 body_id: ast::NodeId,
203 // call_site scope of innermost fn
204 call_site_scope: Option<region::Scope>,
206 // id of innermost fn or loop
207 repeating_scope: ast::NodeId,
209 // id of AST node being analyzed (the subject of the analysis).
210 subject_def_id: DefId,
214 impl<'a, 'gcx, 'tcx> Deref for RegionCtxt<'a, 'gcx, 'tcx> {
215 type Target = FnCtxt<'a, 'gcx, 'tcx>;
216 fn deref(&self) -> &Self::Target {
221 pub struct RepeatingScope(ast::NodeId);
222 pub struct Subject(DefId);
224 impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
225 pub fn new(fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
226 RepeatingScope(initial_repeating_scope): RepeatingScope,
227 initial_body_id: ast::NodeId,
228 Subject(subject): Subject,
229 param_env: ty::ParamEnv<'tcx>)
230 -> RegionCtxt<'a, 'gcx, 'tcx> {
231 let region_scope_tree = fcx.tcx.region_scope_tree(subject);
232 let outlives_environment = OutlivesEnvironment::new(param_env);
236 repeating_scope: initial_repeating_scope,
237 body_id: initial_body_id,
238 call_site_scope: None,
239 subject_def_id: subject,
240 outlives_environment,
244 fn set_repeating_scope(&mut self, scope: ast::NodeId) -> ast::NodeId {
245 mem::replace(&mut self.repeating_scope, scope)
248 /// Try to resolve the type for the given node, returning t_err if an error results. Note that
249 /// we never care about the details of the error, the same error will be detected and reported
250 /// in the writeback phase.
252 /// Note one important point: we do not attempt to resolve *region variables* here. This is
253 /// because regionck is essentially adding constraints to those region variables and so may yet
254 /// influence how they are resolved.
256 /// Consider this silly example:
259 /// fn borrow(x: &i32) -> &i32 {x}
260 /// fn foo(x: @i32) -> i32 { // block: B
261 /// let b = borrow(x); // region: <R0>
266 /// Here, the region of `b` will be `<R0>`. `<R0>` is constrained to be some subregion of the
267 /// block B and some superregion of the call. If we forced it now, we'd choose the smaller
268 /// region (the call). But that would make the *b illegal. Since we don't resolve, the type
269 /// of b will be `&<R0>.i32` and then `*b` will require that `<R0>` be bigger than the let and
270 /// the `*b` expression, so we will effectively resolve `<R0>` to be the block B.
271 pub fn resolve_type(&self, unresolved_ty: Ty<'tcx>) -> Ty<'tcx> {
272 self.resolve_type_vars_if_possible(&unresolved_ty)
275 /// Try to resolve the type for the given node.
276 fn resolve_node_type(&self, id: hir::HirId) -> Ty<'tcx> {
277 let t = self.node_ty(id);
281 /// Try to resolve the type for the given node.
282 pub fn resolve_expr_type_adjusted(&mut self, expr: &hir::Expr) -> Ty<'tcx> {
283 let ty = self.tables.borrow().expr_ty_adjusted(expr);
284 self.resolve_type(ty)
287 /// This is the "main" function when region-checking a function item or a closure
288 /// within a function item. It begins by updating various fields (e.g., `call_site_scope`
289 /// and `outlives_environment`) to be appropriate to the function and then adds constraints
290 /// derived from the function body.
292 /// Note that it does **not** restore the state of the fields that
293 /// it updates! This is intentional, since -- for the main
294 /// function -- we wish to be able to read the final
295 /// `outlives_environment` and other fields from the caller. For
296 /// closures, however, we save and restore any "scoped state"
297 /// before we invoke this function. (See `visit_fn` in the
298 /// `intravisit::Visitor` impl below.)
299 fn visit_fn_body(&mut self,
300 id: ast::NodeId, // the id of the fn itself
301 body: &'gcx hir::Body,
304 // When we enter a function, we can derive
305 debug!("visit_fn_body(id={})", id);
307 let body_id = body.id();
308 self.body_id = body_id.node_id;
310 let call_site = region::Scope {
311 id: body.value.hir_id.local_id,
312 data: region::ScopeData::CallSite
314 self.call_site_scope = Some(call_site);
317 let fn_hir_id = self.tcx.hir.node_to_hir_id(id);
318 match self.tables.borrow().liberated_fn_sigs().get(fn_hir_id) {
319 Some(f) => f.clone(),
321 bug!("No fn-sig entry for id={}", id);
326 // Collect the types from which we create inferred bounds.
327 // For the return type, if diverging, substitute `bool` just
328 // because it will have no effect.
330 // FIXME(#27579) return types should not be implied bounds
331 let fn_sig_tys: Vec<_> =
332 fn_sig.inputs().iter().cloned().chain(Some(fn_sig.output())).collect();
334 self.outlives_environment.add_implied_bounds(
341 id: body.value.hir_id.local_id,
342 data: region::ScopeData::Node
345 self.visit_body(body);
346 self.visit_region_obligations(body_id.node_id);
348 let call_site_scope = self.call_site_scope.unwrap();
349 debug!("visit_fn_body body.id {:?} call_site_scope: {:?}",
350 body.id(), call_site_scope);
351 let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope));
353 let body_hir_id = self.tcx.hir.node_to_hir_id(body_id.node_id);
354 self.type_of_node_must_outlive(infer::CallReturn(span),
358 self.constrain_opaque_types(
359 &self.fcx.opaque_types.borrow(),
360 self.outlives_environment.free_region_map(),
364 fn visit_region_obligations(&mut self, node_id: ast::NodeId)
366 debug!("visit_region_obligations: node_id={}", node_id);
368 // region checking can introduce new pending obligations
369 // which, when processed, might generate new region
370 // obligations. So make sure we process those.
371 self.select_all_obligations_or_error();
373 self.infcx.process_registered_region_obligations(
374 self.outlives_environment.region_bound_pairs(),
375 self.implicit_region_bound,
380 fn resolve_regions_and_report_errors(&self) {
381 self.fcx.resolve_regions_and_report_errors(self.subject_def_id,
382 &self.region_scope_tree,
383 &self.outlives_environment);
386 fn resolve_regions_and_report_errors_unless_nll(&self) {
387 self.fcx.resolve_regions_and_report_errors_unless_nll(self.subject_def_id,
388 &self.region_scope_tree,
389 &self.outlives_environment);
392 fn constrain_bindings_in_pat(&mut self, pat: &hir::Pat) {
393 debug!("regionck::visit_pat(pat={:?})", pat);
394 pat.each_binding(|_, hir_id, span, _| {
395 // If we have a variable that contains region'd data, that
396 // data will be accessible from anywhere that the variable is
397 // accessed. We must be wary of loops like this:
399 // // from src/test/compile-fail/borrowck-lend-flow.rs
400 // let mut v = box 3, w = box 4;
401 // let mut x = &mut w;
404 // borrow(v); //~ ERROR cannot borrow
405 // x = &mut v; // (1)
408 // Typically, we try to determine the region of a borrow from
409 // those points where it is dereferenced. In this case, one
410 // might imagine that the lifetime of `x` need only be the
411 // body of the loop. But of course this is incorrect because
412 // the pointer that is created at point (1) is consumed at
413 // point (2), meaning that it must be live across the loop
414 // iteration. The easiest way to guarantee this is to require
415 // that the lifetime of any regions that appear in a
416 // variable's type enclose at least the variable's scope.
417 let var_scope = self.region_scope_tree.var_scope(hir_id.local_id);
418 let var_region = self.tcx.mk_region(ty::ReScope(var_scope));
420 let origin = infer::BindingTypeIsNotValidAtDecl(span);
421 self.type_of_node_must_outlive(origin, hir_id, var_region);
423 let typ = self.resolve_node_type(hir_id);
424 let body_id = self.body_id;
425 let _ = dropck::check_safety_of_destructor_if_necessary(
426 self, typ, span, body_id, var_scope);
431 impl<'a, 'gcx, 'tcx> Visitor<'gcx> for RegionCtxt<'a, 'gcx, 'tcx> {
432 // (..) FIXME(#3238) should use visit_pat, not visit_arm/visit_local,
433 // However, right now we run into an issue whereby some free
434 // regions are not properly related if they appear within the
435 // types of arguments that must be inferred. This could be
436 // addressed by deferring the construction of the region
437 // hierarchy, and in particular the relationships between free
438 // regions, until regionck, as described in #3238.
440 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'gcx> {
441 NestedVisitorMap::None
444 fn visit_fn(&mut self,
445 fk: intravisit::FnKind<'gcx>,
446 _: &'gcx hir::FnDecl,
447 body_id: hir::BodyId,
450 assert!(match fk { intravisit::FnKind::Closure(..) => true, _ => false },
451 "visit_fn invoked for something other than a closure");
453 // Save state of current function before invoking
454 // `visit_fn_body`. We will restore afterwards.
455 let old_body_id = self.body_id;
456 let old_call_site_scope = self.call_site_scope;
457 let env_snapshot = self.outlives_environment.push_snapshot_pre_closure();
459 let body = self.tcx.hir.body(body_id);
460 self.visit_fn_body(id, body, span);
462 // Restore state from previous function.
463 self.outlives_environment.pop_snapshot_post_closure(env_snapshot);
464 self.call_site_scope = old_call_site_scope;
465 self.body_id = old_body_id;
468 //visit_pat: visit_pat, // (..) see above
470 fn visit_arm(&mut self, arm: &'gcx hir::Arm) {
473 self.constrain_bindings_in_pat(p);
475 intravisit::walk_arm(self, arm);
478 fn visit_local(&mut self, l: &'gcx hir::Local) {
480 self.constrain_bindings_in_pat(&l.pat);
482 intravisit::walk_local(self, l);
485 fn visit_expr(&mut self, expr: &'gcx hir::Expr) {
486 debug!("regionck::visit_expr(e={:?}, repeating_scope={})",
487 expr, self.repeating_scope);
489 // No matter what, the type of each expression must outlive the
490 // scope of that expression. This also guarantees basic WF.
491 let expr_ty = self.resolve_node_type(expr.hir_id);
492 // the region corresponding to this expression
493 let expr_region = self.tcx.mk_region(ty::ReScope(
495 id: expr.hir_id.local_id,
496 data: region::ScopeData::Node
498 self.type_must_outlive(infer::ExprTypeIsNotInScope(expr_ty, expr.span),
499 expr_ty, expr_region);
501 let is_method_call = self.tables.borrow().is_method_call(expr);
503 // If we are calling a method (either explicitly or via an
504 // overloaded operator), check that all of the types provided as
505 // arguments for its type parameters are well-formed, and all the regions
506 // provided as arguments outlive the call.
508 let origin = match expr.node {
509 hir::ExprKind::MethodCall(..) =>
510 infer::ParameterOrigin::MethodCall,
511 hir::ExprKind::Unary(op, _) if op == hir::UnDeref =>
512 infer::ParameterOrigin::OverloadedDeref,
514 infer::ParameterOrigin::OverloadedOperator
517 let substs = self.tables.borrow().node_substs(expr.hir_id);
518 self.substs_wf_in_scope(origin, substs, expr.span, expr_region);
519 // Arguments (sub-expressions) are checked via `constrain_call`, below.
522 // Check any autoderefs or autorefs that appear.
523 let cmt_result = self.constrain_adjustments(expr);
525 // If necessary, constrain destructors in this expression. This will be
526 // the adjusted form if there is an adjustment.
529 self.check_safety_of_rvalue_destructor_if_necessary(&head_cmt, expr.span);
532 self.tcx.sess.delay_span_bug(expr.span, "cat_expr Errd");
536 debug!("regionck::visit_expr(e={:?}, repeating_scope={}) - visiting subexprs",
537 expr, self.repeating_scope);
539 hir::ExprKind::Path(_) => {
540 let substs = self.tables.borrow().node_substs(expr.hir_id);
541 let origin = infer::ParameterOrigin::Path;
542 self.substs_wf_in_scope(origin, substs, expr.span, expr_region);
545 hir::ExprKind::Call(ref callee, ref args) => {
547 self.constrain_call(expr, Some(&callee), args.iter().map(|e| &*e));
549 self.constrain_callee(&callee);
550 self.constrain_call(expr, None, args.iter().map(|e| &*e));
553 intravisit::walk_expr(self, expr);
556 hir::ExprKind::MethodCall(.., ref args) => {
557 self.constrain_call(expr, Some(&args[0]), args[1..].iter().map(|e| &*e));
559 intravisit::walk_expr(self, expr);
562 hir::ExprKind::AssignOp(_, ref lhs, ref rhs) => {
564 self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter());
567 intravisit::walk_expr(self, expr);
570 hir::ExprKind::Index(ref lhs, ref rhs) if is_method_call => {
571 self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter());
573 intravisit::walk_expr(self, expr);
576 hir::ExprKind::Binary(_, ref lhs, ref rhs) if is_method_call => {
577 // As `ExprKind::MethodCall`, but the call is via an overloaded op.
578 self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter());
580 intravisit::walk_expr(self, expr);
583 hir::ExprKind::Binary(_, ref lhs, ref rhs) => {
584 // If you do `x OP y`, then the types of `x` and `y` must
585 // outlive the operation you are performing.
586 let lhs_ty = self.resolve_expr_type_adjusted(&lhs);
587 let rhs_ty = self.resolve_expr_type_adjusted(&rhs);
588 for &ty in &[lhs_ty, rhs_ty] {
589 self.type_must_outlive(infer::Operand(expr.span),
592 intravisit::walk_expr(self, expr);
595 hir::ExprKind::Unary(hir::UnDeref, ref base) => {
596 // For *a, the lifetime of a must enclose the deref
598 self.constrain_call(expr, Some(base), None::<hir::Expr>.iter());
600 // For overloaded derefs, base_ty is the input to `Deref::deref`,
601 // but it's a reference type uing the same region as the output.
602 let base_ty = self.resolve_expr_type_adjusted(base);
603 if let ty::Ref(r_ptr, _, _) = base_ty.sty {
604 self.mk_subregion_due_to_dereference(expr.span, expr_region, r_ptr);
607 intravisit::walk_expr(self, expr);
610 hir::ExprKind::Unary(_, ref lhs) if is_method_call => {
612 self.constrain_call(expr, Some(&lhs), None::<hir::Expr>.iter());
614 intravisit::walk_expr(self, expr);
617 hir::ExprKind::Index(ref vec_expr, _) => {
618 // For a[b], the lifetime of a must enclose the deref
619 let vec_type = self.resolve_expr_type_adjusted(&vec_expr);
620 self.constrain_index(expr, vec_type);
622 intravisit::walk_expr(self, expr);
625 hir::ExprKind::Cast(ref source, _) => {
626 // Determine if we are casting `source` to a trait
627 // instance. If so, we have to be sure that the type of
628 // the source obeys the trait's region bound.
629 self.constrain_cast(expr, &source);
630 intravisit::walk_expr(self, expr);
633 hir::ExprKind::AddrOf(m, ref base) => {
634 self.link_addr_of(expr, m, &base);
636 // Require that when you write a `&expr` expression, the
637 // resulting pointer has a lifetime that encompasses the
638 // `&expr` expression itself. Note that we constraining
639 // the type of the node expr.id here *before applying
642 // FIXME(https://github.com/rust-lang/rfcs/issues/811)
643 // nested method calls requires that this rule change
644 let ty0 = self.resolve_node_type(expr.hir_id);
645 self.type_must_outlive(infer::AddrOf(expr.span), ty0, expr_region);
646 intravisit::walk_expr(self, expr);
649 hir::ExprKind::Match(ref discr, ref arms, _) => {
650 self.link_match(&discr, &arms[..]);
652 intravisit::walk_expr(self, expr);
655 hir::ExprKind::Closure(.., body_id, _, _) => {
656 self.check_expr_fn_block(expr, body_id);
659 hir::ExprKind::Loop(ref body, _, _) => {
660 let repeating_scope = self.set_repeating_scope(body.id);
661 intravisit::walk_expr(self, expr);
662 self.set_repeating_scope(repeating_scope);
665 hir::ExprKind::While(ref cond, ref body, _) => {
666 let repeating_scope = self.set_repeating_scope(cond.id);
667 self.visit_expr(&cond);
669 self.set_repeating_scope(body.id);
670 self.visit_block(&body);
672 self.set_repeating_scope(repeating_scope);
675 hir::ExprKind::Ret(Some(ref ret_expr)) => {
676 let call_site_scope = self.call_site_scope;
677 debug!("visit_expr ExprKind::Ret ret_expr.id {} call_site_scope: {:?}",
678 ret_expr.id, call_site_scope);
679 let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope.unwrap()));
680 self.type_of_node_must_outlive(infer::CallReturn(ret_expr.span),
683 intravisit::walk_expr(self, expr);
687 intravisit::walk_expr(self, expr);
693 impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
694 fn constrain_cast(&mut self,
695 cast_expr: &hir::Expr,
696 source_expr: &hir::Expr)
698 debug!("constrain_cast(cast_expr={:?}, source_expr={:?})",
702 let source_ty = self.resolve_node_type(source_expr.hir_id);
703 let target_ty = self.resolve_node_type(cast_expr.hir_id);
705 self.walk_cast(cast_expr, source_ty, target_ty);
708 fn walk_cast(&mut self,
709 cast_expr: &hir::Expr,
712 debug!("walk_cast(from_ty={:?}, to_ty={:?})",
715 match (&from_ty.sty, &to_ty.sty) {
716 /*From:*/ (&ty::Ref(from_r, from_ty, _),
717 /*To: */ &ty::Ref(to_r, to_ty, _)) => {
718 // Target cannot outlive source, naturally.
719 self.sub_regions(infer::Reborrow(cast_expr.span), to_r, from_r);
720 self.walk_cast(cast_expr, from_ty, to_ty);
724 /*To: */ &ty::Dynamic(.., r)) => {
725 // When T is existentially quantified as a trait
726 // `Foo+'to`, it must outlive the region bound `'to`.
727 self.type_must_outlive(infer::RelateObjectBound(cast_expr.span), from_ty, r);
730 /*From:*/ (&ty::Adt(from_def, _),
731 /*To: */ &ty::Adt(to_def, _)) if from_def.is_box() && to_def.is_box() => {
732 self.walk_cast(cast_expr, from_ty.boxed_ty(), to_ty.boxed_ty());
739 fn check_expr_fn_block(&mut self,
740 expr: &'gcx hir::Expr,
741 body_id: hir::BodyId) {
742 let repeating_scope = self.set_repeating_scope(body_id.node_id);
743 intravisit::walk_expr(self, expr);
744 self.set_repeating_scope(repeating_scope);
747 fn constrain_callee(&mut self, callee_expr: &hir::Expr) {
748 let callee_ty = self.resolve_node_type(callee_expr.hir_id);
749 match callee_ty.sty {
750 ty::FnDef(..) | ty::FnPtr(_) => { }
752 // this should not happen, but it does if the program is
757 // "Calling non-function: {}",
763 fn constrain_call<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
764 call_expr: &hir::Expr,
765 receiver: Option<&hir::Expr>,
767 //! Invoked on every call site (i.e., normal calls, method calls,
768 //! and overloaded operators). Constrains the regions which appear
769 //! in the type of the function. Also constrains the regions that
770 //! appear in the arguments appropriately.
772 debug!("constrain_call(call_expr={:?}, receiver={:?})",
776 // `callee_region` is the scope representing the time in which the
779 // FIXME(#6268) to support nested method calls, should be callee_id
780 let callee_scope = region::Scope {
781 id: call_expr.hir_id.local_id,
782 data: region::ScopeData::Node
784 let callee_region = self.tcx.mk_region(ty::ReScope(callee_scope));
786 debug!("callee_region={:?}", callee_region);
788 for arg_expr in arg_exprs {
789 debug!("Argument: {:?}", arg_expr);
791 // ensure that any regions appearing in the argument type are
792 // valid for at least the lifetime of the function:
793 self.type_of_node_must_outlive(infer::CallArg(arg_expr.span),
798 // as loop above, but for receiver
799 if let Some(r) = receiver {
800 debug!("receiver: {:?}", r);
801 self.type_of_node_must_outlive(infer::CallRcvr(r.span),
807 /// Create a temporary `MemCategorizationContext` and pass it to the closure.
808 fn with_mc<F, R>(&self, f: F) -> R
809 where F: for<'b> FnOnce(mc::MemCategorizationContext<'b, 'gcx, 'tcx>) -> R
811 f(mc::MemCategorizationContext::with_infer(&self.infcx,
812 &self.region_scope_tree,
813 &self.tables.borrow()))
816 /// Invoked on any adjustments that occur. Checks that if this is a region pointer being
817 /// dereferenced, the lifetime of the pointer includes the deref expr.
818 fn constrain_adjustments(&mut self, expr: &hir::Expr) -> mc::McResult<mc::cmt_<'tcx>> {
819 debug!("constrain_adjustments(expr={:?})", expr);
821 let mut cmt = self.with_mc(|mc| mc.cat_expr_unadjusted(expr))?;
823 let tables = self.tables.borrow();
824 let adjustments = tables.expr_adjustments(&expr);
825 if adjustments.is_empty() {
829 debug!("constrain_adjustments: adjustments={:?}", adjustments);
831 // If necessary, constrain destructors in the unadjusted form of this
833 self.check_safety_of_rvalue_destructor_if_necessary(&cmt, expr.span);
835 let expr_region = self.tcx.mk_region(ty::ReScope(
837 id: expr.hir_id.local_id,
838 data: region::ScopeData::Node
840 for adjustment in adjustments {
841 debug!("constrain_adjustments: adjustment={:?}, cmt={:?}",
844 if let adjustment::Adjust::Deref(Some(deref)) = adjustment.kind {
845 debug!("constrain_adjustments: overloaded deref: {:?}", deref);
847 // Treat overloaded autoderefs as if an AutoBorrow adjustment
848 // was applied on the base type, as that is always the case.
849 let input = self.tcx.mk_ref(deref.region, ty::TypeAndMut {
853 let output = self.tcx.mk_ref(deref.region, ty::TypeAndMut {
854 ty: adjustment.target,
858 self.link_region(expr.span, deref.region,
859 ty::BorrowKind::from_mutbl(deref.mutbl), &cmt);
861 // Specialized version of constrain_call.
862 self.type_must_outlive(infer::CallRcvr(expr.span),
864 self.type_must_outlive(infer::CallReturn(expr.span),
865 output, expr_region);
868 if let adjustment::Adjust::Borrow(ref autoref) = adjustment.kind {
869 self.link_autoref(expr, &cmt, autoref);
871 // Require that the resulting region encompasses
874 // FIXME(#6268) remove to support nested method calls
875 self.type_of_node_must_outlive(infer::AutoBorrow(expr.span),
880 cmt = self.with_mc(|mc| mc.cat_expr_adjusted(expr, cmt, &adjustment))?;
882 if let Categorization::Deref(_, mc::BorrowedPtr(_, r_ptr)) = cmt.cat {
883 self.mk_subregion_due_to_dereference(expr.span,
891 pub fn mk_subregion_due_to_dereference(&mut self,
893 minimum_lifetime: ty::Region<'tcx>,
894 maximum_lifetime: ty::Region<'tcx>) {
895 self.sub_regions(infer::DerefPointer(deref_span),
896 minimum_lifetime, maximum_lifetime)
899 fn check_safety_of_rvalue_destructor_if_necessary(&mut self,
900 cmt: &mc::cmt_<'tcx>,
903 Categorization::Rvalue(region) => {
905 ty::ReScope(rvalue_scope) => {
906 let typ = self.resolve_type(cmt.ty);
907 let body_id = self.body_id;
908 let _ = dropck::check_safety_of_destructor_if_necessary(
909 self, typ, span, body_id, rvalue_scope);
914 "unexpected rvalue region in rvalue \
915 destructor safety checking: `{:?}`",
924 /// Invoked on any index expression that occurs. Checks that if this is a slice
925 /// being indexed, the lifetime of the pointer includes the deref expr.
926 fn constrain_index(&mut self,
927 index_expr: &hir::Expr,
928 indexed_ty: Ty<'tcx>)
930 debug!("constrain_index(index_expr=?, indexed_ty={}",
931 self.ty_to_string(indexed_ty));
933 let r_index_expr = ty::ReScope(region::Scope {
934 id: index_expr.hir_id.local_id,
935 data: region::ScopeData::Node
937 if let ty::Ref(r_ptr, r_ty, _) = indexed_ty.sty {
939 ty::Slice(_) | ty::Str => {
940 self.sub_regions(infer::IndexSlice(index_expr.span),
941 self.tcx.mk_region(r_index_expr), r_ptr);
948 /// Guarantees that any lifetimes which appear in the type of the node `id` (after applying
949 /// adjustments) are valid for at least `minimum_lifetime`
950 fn type_of_node_must_outlive(&mut self,
951 origin: infer::SubregionOrigin<'tcx>,
953 minimum_lifetime: ty::Region<'tcx>)
955 // Try to resolve the type. If we encounter an error, then typeck
956 // is going to fail anyway, so just stop here and let typeck
957 // report errors later on in the writeback phase.
958 let ty0 = self.resolve_node_type(hir_id);
964 .and_then(|adj| adj.last())
965 .map_or(ty0, |adj| adj.target);
966 let ty = self.resolve_type(ty);
967 debug!("constrain_regions_in_type_of_node(\
968 ty={}, ty0={}, id={:?}, minimum_lifetime={:?})",
970 hir_id, minimum_lifetime);
971 self.type_must_outlive(origin, ty, minimum_lifetime);
974 /// Adds constraints to inference such that `T: 'a` holds (or
975 /// reports an error if it cannot).
979 /// - `origin`, the reason we need this constraint
980 /// - `ty`, the type `T`
981 /// - `region`, the region `'a`
982 pub fn type_must_outlive(&self,
983 origin: infer::SubregionOrigin<'tcx>,
985 region: ty::Region<'tcx>)
987 self.infcx.type_must_outlive(self.outlives_environment.region_bound_pairs(),
988 self.implicit_region_bound,
995 /// Computes the guarantor for an expression `&base` and then ensures that the lifetime of the
996 /// resulting pointer is linked to the lifetime of its guarantor (if any).
997 fn link_addr_of(&mut self, expr: &hir::Expr,
998 mutability: hir::Mutability, base: &hir::Expr) {
999 debug!("link_addr_of(expr={:?}, base={:?})", expr, base);
1001 let cmt = ignore_err!(self.with_mc(|mc| mc.cat_expr(base)));
1003 debug!("link_addr_of: cmt={:?}", cmt);
1005 self.link_region_from_node_type(expr.span, expr.hir_id, mutability, &cmt);
1008 /// Computes the guarantors for any ref bindings in a `let` and
1009 /// then ensures that the lifetime of the resulting pointer is
1010 /// linked to the lifetime of the initialization expression.
1011 fn link_local(&self, local: &hir::Local) {
1012 debug!("regionck::for_local()");
1013 let init_expr = match local.init {
1015 Some(ref expr) => &**expr,
1017 let discr_cmt = Rc::new(ignore_err!(self.with_mc(|mc| mc.cat_expr(init_expr))));
1018 self.link_pattern(discr_cmt, &local.pat);
1021 /// Computes the guarantors for any ref bindings in a match and
1022 /// then ensures that the lifetime of the resulting pointer is
1023 /// linked to the lifetime of its guarantor (if any).
1024 fn link_match(&self, discr: &hir::Expr, arms: &[hir::Arm]) {
1025 debug!("regionck::for_match()");
1026 let discr_cmt = Rc::new(ignore_err!(self.with_mc(|mc| mc.cat_expr(discr))));
1027 debug!("discr_cmt={:?}", discr_cmt);
1029 for root_pat in &arm.pats {
1030 self.link_pattern(discr_cmt.clone(), &root_pat);
1035 /// Computes the guarantors for any ref bindings in a match and
1036 /// then ensures that the lifetime of the resulting pointer is
1037 /// linked to the lifetime of its guarantor (if any).
1038 fn link_fn_args(&self, body_scope: region::Scope, args: &[hir::Arg]) {
1039 debug!("regionck::link_fn_args(body_scope={:?})", body_scope);
1041 let arg_ty = self.node_ty(arg.hir_id);
1042 let re_scope = self.tcx.mk_region(ty::ReScope(body_scope));
1043 let arg_cmt = self.with_mc(|mc| {
1044 Rc::new(mc.cat_rvalue(arg.hir_id, arg.pat.span, re_scope, arg_ty))
1046 debug!("arg_ty={:?} arg_cmt={:?} arg={:?}",
1050 self.link_pattern(arg_cmt, &arg.pat);
1054 /// Link lifetimes of any ref bindings in `root_pat` to the pointers found
1055 /// in the discriminant, if needed.
1056 fn link_pattern(&self, discr_cmt: mc::cmt<'tcx>, root_pat: &hir::Pat) {
1057 debug!("link_pattern(discr_cmt={:?}, root_pat={:?})",
1060 ignore_err!(self.with_mc(|mc| {
1061 mc.cat_pattern(discr_cmt, root_pat, |sub_cmt, sub_pat| {
1062 match sub_pat.node {
1064 PatKind::Binding(..) => {
1065 if let Some(&bm) = mc.tables.pat_binding_modes().get(sub_pat.hir_id) {
1066 if let ty::BindByReference(mutbl) = bm {
1067 self.link_region_from_node_type(sub_pat.span, sub_pat.hir_id,
1071 self.tcx.sess.delay_span_bug(sub_pat.span, "missing binding mode");
1080 /// Link lifetime of borrowed pointer resulting from autoref to lifetimes in the value being
1082 fn link_autoref(&self,
1084 expr_cmt: &mc::cmt_<'tcx>,
1085 autoref: &adjustment::AutoBorrow<'tcx>)
1087 debug!("link_autoref(autoref={:?}, expr_cmt={:?})", autoref, expr_cmt);
1090 adjustment::AutoBorrow::Ref(r, m) => {
1091 self.link_region(expr.span, r, ty::BorrowKind::from_mutbl(m.into()), expr_cmt);
1094 adjustment::AutoBorrow::RawPtr(m) => {
1095 let r = self.tcx.mk_region(ty::ReScope(region::Scope {
1096 id: expr.hir_id.local_id,
1097 data: region::ScopeData::Node
1099 self.link_region(expr.span, r, ty::BorrowKind::from_mutbl(m), expr_cmt);
1104 /// Like `link_region()`, except that the region is extracted from the type of `id`,
1105 /// which must be some reference (`&T`, `&str`, etc).
1106 fn link_region_from_node_type(&self,
1109 mutbl: hir::Mutability,
1110 cmt_borrowed: &mc::cmt_<'tcx>) {
1111 debug!("link_region_from_node_type(id={:?}, mutbl={:?}, cmt_borrowed={:?})",
1112 id, mutbl, cmt_borrowed);
1114 let rptr_ty = self.resolve_node_type(id);
1115 if let ty::Ref(r, _, _) = rptr_ty.sty {
1116 debug!("rptr_ty={}", rptr_ty);
1117 self.link_region(span, r, ty::BorrowKind::from_mutbl(mutbl), cmt_borrowed);
1121 /// Informs the inference engine that `borrow_cmt` is being borrowed with
1122 /// kind `borrow_kind` and lifetime `borrow_region`.
1123 /// In order to ensure borrowck is satisfied, this may create constraints
1124 /// between regions, as explained in `link_reborrowed_region()`.
1125 fn link_region(&self,
1127 borrow_region: ty::Region<'tcx>,
1128 borrow_kind: ty::BorrowKind,
1129 borrow_cmt: &mc::cmt_<'tcx>) {
1130 let origin = infer::DataBorrowed(borrow_cmt.ty, span);
1131 self.type_must_outlive(origin, borrow_cmt.ty, borrow_region);
1133 let mut borrow_kind = borrow_kind;
1134 let mut borrow_cmt_cat = borrow_cmt.cat.clone();
1137 debug!("link_region(borrow_region={:?}, borrow_kind={:?}, borrow_cmt={:?})",
1141 match borrow_cmt_cat {
1142 Categorization::Deref(ref_cmt, mc::BorrowedPtr(ref_kind, ref_region)) => {
1143 match self.link_reborrowed_region(span,
1144 borrow_region, borrow_kind,
1145 ref_cmt, ref_region, ref_kind,
1148 borrow_cmt_cat = c.cat.clone();
1157 Categorization::Downcast(cmt_base, _) |
1158 Categorization::Deref(cmt_base, mc::Unique) |
1159 Categorization::Interior(cmt_base, _) => {
1160 // Borrowing interior or owned data requires the base
1161 // to be valid and borrowable in the same fashion.
1162 borrow_cmt_cat = cmt_base.cat.clone();
1163 borrow_kind = borrow_kind;
1166 Categorization::Deref(_, mc::UnsafePtr(..)) |
1167 Categorization::StaticItem |
1168 Categorization::Upvar(..) |
1169 Categorization::Local(..) |
1170 Categorization::Rvalue(..) => {
1171 // These are all "base cases" with independent lifetimes
1172 // that are not subject to inference
1179 /// This is the most complicated case: the path being borrowed is
1180 /// itself the referent of a borrowed pointer. Let me give an
1181 /// example fragment of code to make clear(er) the situation:
1183 /// let r: &'a mut T = ...; // the original reference "r" has lifetime 'a
1185 /// &'z *r // the reborrow has lifetime 'z
1187 /// Now, in this case, our primary job is to add the inference
1188 /// constraint that `'z <= 'a`. Given this setup, let's clarify the
1189 /// parameters in (roughly) terms of the example:
1191 /// ```plain,ignore (pseudo-Rust)
1192 /// A borrow of: `& 'z bk * r` where `r` has type `& 'a bk T`
1193 /// borrow_region ^~ ref_region ^~
1194 /// borrow_kind ^~ ref_kind ^~
1198 /// Here `bk` stands for some borrow-kind (e.g., `mut`, `uniq`, etc).
1200 /// Unfortunately, there are some complications beyond the simple
1201 /// scenario I just painted:
1203 /// 1. The reference `r` might in fact be a "by-ref" upvar. In that
1204 /// case, we have two jobs. First, we are inferring whether this reference
1205 /// should be an `&T`, `&mut T`, or `&uniq T` reference, and we must
1206 /// adjust that based on this borrow (e.g., if this is an `&mut` borrow,
1207 /// then `r` must be an `&mut` reference). Second, whenever we link
1208 /// two regions (here, `'z <= 'a`), we supply a *cause*, and in this
1209 /// case we adjust the cause to indicate that the reference being
1210 /// "reborrowed" is itself an upvar. This provides a nicer error message
1211 /// should something go wrong.
1213 /// 2. There may in fact be more levels of reborrowing. In the
1214 /// example, I said the borrow was like `&'z *r`, but it might
1215 /// in fact be a borrow like `&'z **q` where `q` has type `&'a
1216 /// &'b mut T`. In that case, we want to ensure that `'z <= 'a`
1217 /// and `'z <= 'b`. This is explained more below.
1219 /// The return value of this function indicates whether we need to
1220 /// recurse and process `ref_cmt` (see case 2 above).
1221 fn link_reborrowed_region(&self,
1223 borrow_region: ty::Region<'tcx>,
1224 borrow_kind: ty::BorrowKind,
1225 ref_cmt: mc::cmt<'tcx>,
1226 ref_region: ty::Region<'tcx>,
1227 mut ref_kind: ty::BorrowKind,
1229 -> Option<(mc::cmt<'tcx>, ty::BorrowKind)>
1231 // Possible upvar ID we may need later to create an entry in the
1234 // Detect by-ref upvar `x`:
1235 let cause = match note {
1236 mc::NoteUpvarRef(ref upvar_id) => {
1237 match self.tables.borrow().upvar_capture_map.get(upvar_id) {
1238 Some(&ty::UpvarCapture::ByRef(ref upvar_borrow)) => {
1239 // The mutability of the upvar may have been modified
1240 // by the above adjustment, so update our local variable.
1241 ref_kind = upvar_borrow.kind;
1243 infer::ReborrowUpvar(span, *upvar_id)
1246 span_bug!( span, "Illegal upvar id: {:?}", upvar_id);
1250 mc::NoteClosureEnv(ref upvar_id) => {
1251 // We don't have any mutability changes to propagate, but
1252 // we do want to note that an upvar reborrow caused this
1254 infer::ReborrowUpvar(span, *upvar_id)
1257 infer::Reborrow(span)
1261 debug!("link_reborrowed_region: {:?} <= {:?}",
1264 self.sub_regions(cause, borrow_region, ref_region);
1266 // If we end up needing to recurse and establish a region link
1267 // with `ref_cmt`, calculate what borrow kind we will end up
1268 // needing. This will be used below.
1270 // One interesting twist is that we can weaken the borrow kind
1271 // when we recurse: to reborrow an `&mut` referent as mutable,
1272 // borrowck requires a unique path to the `&mut` reference but not
1273 // necessarily a *mutable* path.
1274 let new_borrow_kind = match borrow_kind {
1277 ty::MutBorrow | ty::UniqueImmBorrow =>
1281 // Decide whether we need to recurse and link any regions within
1282 // the `ref_cmt`. This is concerned for the case where the value
1283 // being reborrowed is in fact a borrowed pointer found within
1284 // another borrowed pointer. For example:
1286 // let p: &'b &'a mut T = ...;
1290 // What makes this case particularly tricky is that, if the data
1291 // being borrowed is a `&mut` or `&uniq` borrow, borrowck requires
1292 // not only that `'z <= 'a`, (as before) but also `'z <= 'b`
1293 // (otherwise the user might mutate through the `&mut T` reference
1294 // after `'b` expires and invalidate the borrow we are looking at
1297 // So let's re-examine our parameters in light of this more
1298 // complicated (possible) scenario:
1300 // A borrow of: `& 'z bk * * p` where `p` has type `&'b bk & 'a bk T`
1301 // borrow_region ^~ ref_region ^~
1302 // borrow_kind ^~ ref_kind ^~
1305 // (Note that since we have not examined `ref_cmt.cat`, we don't
1306 // know whether this scenario has occurred; but I wanted to show
1307 // how all the types get adjusted.)
1310 // The reference being reborrowed is a shareable ref of
1311 // type `&'a T`. In this case, it doesn't matter where we
1312 // *found* the `&T` pointer, the memory it references will
1313 // be valid and immutable for `'a`. So we can stop here.
1315 // (Note that the `borrow_kind` must also be ImmBorrow or
1316 // else the user is borrowed imm memory as mut memory,
1317 // which means they'll get an error downstream in borrowck
1322 ty::MutBorrow | ty::UniqueImmBorrow => {
1323 // The reference being reborrowed is either an `&mut T` or
1324 // `&uniq T`. This is the case where recursion is needed.
1325 return Some((ref_cmt, new_borrow_kind));
1330 /// Checks that the values provided for type/region arguments in a given
1331 /// expression are well-formed and in-scope.
1332 fn substs_wf_in_scope(&mut self,
1333 origin: infer::ParameterOrigin,
1334 substs: &Substs<'tcx>,
1336 expr_region: ty::Region<'tcx>) {
1337 debug!("substs_wf_in_scope(substs={:?}, \
1341 substs, expr_region, origin, expr_span);
1343 let origin = infer::ParameterInScope(origin, expr_span);
1345 for region in substs.regions() {
1346 self.sub_regions(origin.clone(), expr_region, region);
1349 for ty in substs.types() {
1350 let ty = self.resolve_type(ty);
1351 self.type_must_outlive(origin.clone(), ty, expr_region);