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::CallSite(body.value.hir_id.local_id);
311 self.call_site_scope = Some(call_site);
314 let fn_hir_id = self.tcx.hir.node_to_hir_id(id);
315 match self.tables.borrow().liberated_fn_sigs().get(fn_hir_id) {
316 Some(f) => f.clone(),
318 bug!("No fn-sig entry for id={}", id);
323 // Collect the types from which we create inferred bounds.
324 // For the return type, if diverging, substitute `bool` just
325 // because it will have no effect.
327 // FIXME(#27579) return types should not be implied bounds
328 let fn_sig_tys: Vec<_> =
329 fn_sig.inputs().iter().cloned().chain(Some(fn_sig.output())).collect();
331 self.outlives_environment.add_implied_bounds(
336 self.link_fn_args(region::Scope::Node(body.value.hir_id.local_id), &body.arguments);
337 self.visit_body(body);
338 self.visit_region_obligations(body_id.node_id);
340 let call_site_scope = self.call_site_scope.unwrap();
341 debug!("visit_fn_body body.id {:?} call_site_scope: {:?}",
342 body.id(), call_site_scope);
343 let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope));
345 let body_hir_id = self.tcx.hir.node_to_hir_id(body_id.node_id);
346 self.type_of_node_must_outlive(infer::CallReturn(span),
350 self.constrain_anon_types(
351 &self.fcx.anon_types.borrow(),
352 self.outlives_environment.free_region_map(),
356 fn visit_region_obligations(&mut self, node_id: ast::NodeId)
358 debug!("visit_region_obligations: node_id={}", node_id);
360 // region checking can introduce new pending obligations
361 // which, when processed, might generate new region
362 // obligations. So make sure we process those.
363 self.select_all_obligations_or_error();
365 self.infcx.process_registered_region_obligations(
366 self.outlives_environment.region_bound_pairs(),
367 self.implicit_region_bound,
372 fn resolve_regions_and_report_errors(&self) {
373 self.fcx.resolve_regions_and_report_errors(self.subject_def_id,
374 &self.region_scope_tree,
375 &self.outlives_environment);
378 fn resolve_regions_and_report_errors_unless_nll(&self) {
379 self.fcx.resolve_regions_and_report_errors_unless_nll(self.subject_def_id,
380 &self.region_scope_tree,
381 &self.outlives_environment);
384 fn constrain_bindings_in_pat(&mut self, pat: &hir::Pat) {
385 debug!("regionck::visit_pat(pat={:?})", pat);
386 pat.each_binding(|_, hir_id, span, _| {
387 // If we have a variable that contains region'd data, that
388 // data will be accessible from anywhere that the variable is
389 // accessed. We must be wary of loops like this:
391 // // from src/test/compile-fail/borrowck-lend-flow.rs
392 // let mut v = box 3, w = box 4;
393 // let mut x = &mut w;
396 // borrow(v); //~ ERROR cannot borrow
397 // x = &mut v; // (1)
400 // Typically, we try to determine the region of a borrow from
401 // those points where it is dereferenced. In this case, one
402 // might imagine that the lifetime of `x` need only be the
403 // body of the loop. But of course this is incorrect because
404 // the pointer that is created at point (1) is consumed at
405 // point (2), meaning that it must be live across the loop
406 // iteration. The easiest way to guarantee this is to require
407 // that the lifetime of any regions that appear in a
408 // variable's type enclose at least the variable's scope.
409 let var_scope = self.region_scope_tree.var_scope(hir_id.local_id);
410 let var_region = self.tcx.mk_region(ty::ReScope(var_scope));
412 let origin = infer::BindingTypeIsNotValidAtDecl(span);
413 self.type_of_node_must_outlive(origin, hir_id, var_region);
415 let typ = self.resolve_node_type(hir_id);
416 let body_id = self.body_id;
417 let _ = dropck::check_safety_of_destructor_if_necessary(
418 self, typ, span, body_id, var_scope);
423 impl<'a, 'gcx, 'tcx> Visitor<'gcx> for RegionCtxt<'a, 'gcx, 'tcx> {
424 // (..) FIXME(#3238) should use visit_pat, not visit_arm/visit_local,
425 // However, right now we run into an issue whereby some free
426 // regions are not properly related if they appear within the
427 // types of arguments that must be inferred. This could be
428 // addressed by deferring the construction of the region
429 // hierarchy, and in particular the relationships between free
430 // regions, until regionck, as described in #3238.
432 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'gcx> {
433 NestedVisitorMap::None
436 fn visit_fn(&mut self,
437 fk: intravisit::FnKind<'gcx>,
438 _: &'gcx hir::FnDecl,
439 body_id: hir::BodyId,
442 assert!(match fk { intravisit::FnKind::Closure(..) => true, _ => false },
443 "visit_fn invoked for something other than a closure");
445 // Save state of current function before invoking
446 // `visit_fn_body`. We will restore afterwards.
447 let old_body_id = self.body_id;
448 let old_call_site_scope = self.call_site_scope;
449 let env_snapshot = self.outlives_environment.push_snapshot_pre_closure();
451 let body = self.tcx.hir.body(body_id);
452 self.visit_fn_body(id, body, span);
454 // Restore state from previous function.
455 self.outlives_environment.pop_snapshot_post_closure(env_snapshot);
456 self.call_site_scope = old_call_site_scope;
457 self.body_id = old_body_id;
460 //visit_pat: visit_pat, // (..) see above
462 fn visit_arm(&mut self, arm: &'gcx hir::Arm) {
465 self.constrain_bindings_in_pat(p);
467 intravisit::walk_arm(self, arm);
470 fn visit_local(&mut self, l: &'gcx hir::Local) {
472 self.constrain_bindings_in_pat(&l.pat);
474 intravisit::walk_local(self, l);
477 fn visit_expr(&mut self, expr: &'gcx hir::Expr) {
478 debug!("regionck::visit_expr(e={:?}, repeating_scope={})",
479 expr, self.repeating_scope);
481 // No matter what, the type of each expression must outlive the
482 // scope of that expression. This also guarantees basic WF.
483 let expr_ty = self.resolve_node_type(expr.hir_id);
484 // the region corresponding to this expression
485 let expr_region = self.tcx.mk_region(ty::ReScope(
486 region::Scope::Node(expr.hir_id.local_id)));
487 self.type_must_outlive(infer::ExprTypeIsNotInScope(expr_ty, expr.span),
488 expr_ty, expr_region);
490 let is_method_call = self.tables.borrow().is_method_call(expr);
492 // If we are calling a method (either explicitly or via an
493 // overloaded operator), check that all of the types provided as
494 // arguments for its type parameters are well-formed, and all the regions
495 // provided as arguments outlive the call.
497 let origin = match expr.node {
498 hir::ExprKind::MethodCall(..) =>
499 infer::ParameterOrigin::MethodCall,
500 hir::ExprKind::Unary(op, _) if op == hir::UnDeref =>
501 infer::ParameterOrigin::OverloadedDeref,
503 infer::ParameterOrigin::OverloadedOperator
506 let substs = self.tables.borrow().node_substs(expr.hir_id);
507 self.substs_wf_in_scope(origin, substs, expr.span, expr_region);
508 // Arguments (sub-expressions) are checked via `constrain_call`, below.
511 // Check any autoderefs or autorefs that appear.
512 let cmt_result = self.constrain_adjustments(expr);
514 // If necessary, constrain destructors in this expression. This will be
515 // the adjusted form if there is an adjustment.
518 self.check_safety_of_rvalue_destructor_if_necessary(&head_cmt, expr.span);
521 self.tcx.sess.delay_span_bug(expr.span, "cat_expr Errd");
525 debug!("regionck::visit_expr(e={:?}, repeating_scope={}) - visiting subexprs",
526 expr, self.repeating_scope);
528 hir::ExprKind::Path(_) => {
529 let substs = self.tables.borrow().node_substs(expr.hir_id);
530 let origin = infer::ParameterOrigin::Path;
531 self.substs_wf_in_scope(origin, substs, expr.span, expr_region);
534 hir::ExprKind::Call(ref callee, ref args) => {
536 self.constrain_call(expr, Some(&callee), args.iter().map(|e| &*e));
538 self.constrain_callee(&callee);
539 self.constrain_call(expr, None, args.iter().map(|e| &*e));
542 intravisit::walk_expr(self, expr);
545 hir::ExprKind::MethodCall(.., ref args) => {
546 self.constrain_call(expr, Some(&args[0]), args[1..].iter().map(|e| &*e));
548 intravisit::walk_expr(self, expr);
551 hir::ExprKind::AssignOp(_, ref lhs, ref rhs) => {
553 self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter());
556 intravisit::walk_expr(self, expr);
559 hir::ExprKind::Index(ref lhs, ref rhs) if is_method_call => {
560 self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter());
562 intravisit::walk_expr(self, expr);
565 hir::ExprKind::Binary(_, ref lhs, ref rhs) if is_method_call => {
566 // As `ExprKind::MethodCall`, but the call is via an overloaded op.
567 self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter());
569 intravisit::walk_expr(self, expr);
572 hir::ExprKind::Binary(_, ref lhs, ref rhs) => {
573 // If you do `x OP y`, then the types of `x` and `y` must
574 // outlive the operation you are performing.
575 let lhs_ty = self.resolve_expr_type_adjusted(&lhs);
576 let rhs_ty = self.resolve_expr_type_adjusted(&rhs);
577 for &ty in &[lhs_ty, rhs_ty] {
578 self.type_must_outlive(infer::Operand(expr.span),
581 intravisit::walk_expr(self, expr);
584 hir::ExprKind::Unary(hir::UnDeref, ref base) => {
585 // For *a, the lifetime of a must enclose the deref
587 self.constrain_call(expr, Some(base), None::<hir::Expr>.iter());
589 // For overloaded derefs, base_ty is the input to `Deref::deref`,
590 // but it's a reference type uing the same region as the output.
591 let base_ty = self.resolve_expr_type_adjusted(base);
592 if let ty::Ref(r_ptr, _, _) = base_ty.sty {
593 self.mk_subregion_due_to_dereference(expr.span, expr_region, r_ptr);
596 intravisit::walk_expr(self, expr);
599 hir::ExprKind::Unary(_, ref lhs) if is_method_call => {
601 self.constrain_call(expr, Some(&lhs), None::<hir::Expr>.iter());
603 intravisit::walk_expr(self, expr);
606 hir::ExprKind::Index(ref vec_expr, _) => {
607 // For a[b], the lifetime of a must enclose the deref
608 let vec_type = self.resolve_expr_type_adjusted(&vec_expr);
609 self.constrain_index(expr, vec_type);
611 intravisit::walk_expr(self, expr);
614 hir::ExprKind::Cast(ref source, _) => {
615 // Determine if we are casting `source` to a trait
616 // instance. If so, we have to be sure that the type of
617 // the source obeys the trait's region bound.
618 self.constrain_cast(expr, &source);
619 intravisit::walk_expr(self, expr);
622 hir::ExprKind::AddrOf(m, ref base) => {
623 self.link_addr_of(expr, m, &base);
625 // Require that when you write a `&expr` expression, the
626 // resulting pointer has a lifetime that encompasses the
627 // `&expr` expression itself. Note that we constraining
628 // the type of the node expr.id here *before applying
631 // FIXME(https://github.com/rust-lang/rfcs/issues/811)
632 // nested method calls requires that this rule change
633 let ty0 = self.resolve_node_type(expr.hir_id);
634 self.type_must_outlive(infer::AddrOf(expr.span), ty0, expr_region);
635 intravisit::walk_expr(self, expr);
638 hir::ExprKind::Match(ref discr, ref arms, _) => {
639 self.link_match(&discr, &arms[..]);
641 intravisit::walk_expr(self, expr);
644 hir::ExprKind::Closure(.., body_id, _, _) => {
645 self.check_expr_fn_block(expr, body_id);
648 hir::ExprKind::Loop(ref body, _, _) => {
649 let repeating_scope = self.set_repeating_scope(body.id);
650 intravisit::walk_expr(self, expr);
651 self.set_repeating_scope(repeating_scope);
654 hir::ExprKind::While(ref cond, ref body, _) => {
655 let repeating_scope = self.set_repeating_scope(cond.id);
656 self.visit_expr(&cond);
658 self.set_repeating_scope(body.id);
659 self.visit_block(&body);
661 self.set_repeating_scope(repeating_scope);
664 hir::ExprKind::Ret(Some(ref ret_expr)) => {
665 let call_site_scope = self.call_site_scope;
666 debug!("visit_expr ExprKind::Ret ret_expr.id {} call_site_scope: {:?}",
667 ret_expr.id, call_site_scope);
668 let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope.unwrap()));
669 self.type_of_node_must_outlive(infer::CallReturn(ret_expr.span),
672 intravisit::walk_expr(self, expr);
676 intravisit::walk_expr(self, expr);
682 impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
683 fn constrain_cast(&mut self,
684 cast_expr: &hir::Expr,
685 source_expr: &hir::Expr)
687 debug!("constrain_cast(cast_expr={:?}, source_expr={:?})",
691 let source_ty = self.resolve_node_type(source_expr.hir_id);
692 let target_ty = self.resolve_node_type(cast_expr.hir_id);
694 self.walk_cast(cast_expr, source_ty, target_ty);
697 fn walk_cast(&mut self,
698 cast_expr: &hir::Expr,
701 debug!("walk_cast(from_ty={:?}, to_ty={:?})",
704 match (&from_ty.sty, &to_ty.sty) {
705 /*From:*/ (&ty::Ref(from_r, from_ty, _),
706 /*To: */ &ty::Ref(to_r, to_ty, _)) => {
707 // Target cannot outlive source, naturally.
708 self.sub_regions(infer::Reborrow(cast_expr.span), to_r, from_r);
709 self.walk_cast(cast_expr, from_ty, to_ty);
713 /*To: */ &ty::Dynamic(.., r)) => {
714 // When T is existentially quantified as a trait
715 // `Foo+'to`, it must outlive the region bound `'to`.
716 self.type_must_outlive(infer::RelateObjectBound(cast_expr.span), from_ty, r);
719 /*From:*/ (&ty::Adt(from_def, _),
720 /*To: */ &ty::Adt(to_def, _)) if from_def.is_box() && to_def.is_box() => {
721 self.walk_cast(cast_expr, from_ty.boxed_ty(), to_ty.boxed_ty());
728 fn check_expr_fn_block(&mut self,
729 expr: &'gcx hir::Expr,
730 body_id: hir::BodyId) {
731 let repeating_scope = self.set_repeating_scope(body_id.node_id);
732 intravisit::walk_expr(self, expr);
733 self.set_repeating_scope(repeating_scope);
736 fn constrain_callee(&mut self, callee_expr: &hir::Expr) {
737 let callee_ty = self.resolve_node_type(callee_expr.hir_id);
738 match callee_ty.sty {
739 ty::FnDef(..) | ty::FnPtr(_) => { }
741 // this should not happen, but it does if the program is
746 // "Calling non-function: {}",
752 fn constrain_call<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
753 call_expr: &hir::Expr,
754 receiver: Option<&hir::Expr>,
756 //! Invoked on every call site (i.e., normal calls, method calls,
757 //! and overloaded operators). Constrains the regions which appear
758 //! in the type of the function. Also constrains the regions that
759 //! appear in the arguments appropriately.
761 debug!("constrain_call(call_expr={:?}, receiver={:?})",
765 // `callee_region` is the scope representing the time in which the
768 // FIXME(#6268) to support nested method calls, should be callee_id
769 let callee_scope = region::Scope::Node(call_expr.hir_id.local_id);
770 let callee_region = self.tcx.mk_region(ty::ReScope(callee_scope));
772 debug!("callee_region={:?}", callee_region);
774 for arg_expr in arg_exprs {
775 debug!("Argument: {:?}", arg_expr);
777 // ensure that any regions appearing in the argument type are
778 // valid for at least the lifetime of the function:
779 self.type_of_node_must_outlive(infer::CallArg(arg_expr.span),
784 // as loop above, but for receiver
785 if let Some(r) = receiver {
786 debug!("receiver: {:?}", r);
787 self.type_of_node_must_outlive(infer::CallRcvr(r.span),
793 /// Create a temporary `MemCategorizationContext` and pass it to the closure.
794 fn with_mc<F, R>(&self, f: F) -> R
795 where F: for<'b> FnOnce(mc::MemCategorizationContext<'b, 'gcx, 'tcx>) -> R
797 f(mc::MemCategorizationContext::with_infer(&self.infcx,
798 &self.region_scope_tree,
799 &self.tables.borrow()))
802 /// Invoked on any adjustments that occur. Checks that if this is a region pointer being
803 /// dereferenced, the lifetime of the pointer includes the deref expr.
804 fn constrain_adjustments(&mut self, expr: &hir::Expr) -> mc::McResult<mc::cmt_<'tcx>> {
805 debug!("constrain_adjustments(expr={:?})", expr);
807 let mut cmt = self.with_mc(|mc| mc.cat_expr_unadjusted(expr))?;
809 let tables = self.tables.borrow();
810 let adjustments = tables.expr_adjustments(&expr);
811 if adjustments.is_empty() {
815 debug!("constrain_adjustments: adjustments={:?}", adjustments);
817 // If necessary, constrain destructors in the unadjusted form of this
819 self.check_safety_of_rvalue_destructor_if_necessary(&cmt, expr.span);
821 let expr_region = self.tcx.mk_region(ty::ReScope(
822 region::Scope::Node(expr.hir_id.local_id)));
823 for adjustment in adjustments {
824 debug!("constrain_adjustments: adjustment={:?}, cmt={:?}",
827 if let adjustment::Adjust::Deref(Some(deref)) = adjustment.kind {
828 debug!("constrain_adjustments: overloaded deref: {:?}", deref);
830 // Treat overloaded autoderefs as if an AutoBorrow adjustment
831 // was applied on the base type, as that is always the case.
832 let input = self.tcx.mk_ref(deref.region, ty::TypeAndMut {
836 let output = self.tcx.mk_ref(deref.region, ty::TypeAndMut {
837 ty: adjustment.target,
841 self.link_region(expr.span, deref.region,
842 ty::BorrowKind::from_mutbl(deref.mutbl), &cmt);
844 // Specialized version of constrain_call.
845 self.type_must_outlive(infer::CallRcvr(expr.span),
847 self.type_must_outlive(infer::CallReturn(expr.span),
848 output, expr_region);
851 if let adjustment::Adjust::Borrow(ref autoref) = adjustment.kind {
852 self.link_autoref(expr, &cmt, autoref);
854 // Require that the resulting region encompasses
857 // FIXME(#6268) remove to support nested method calls
858 self.type_of_node_must_outlive(infer::AutoBorrow(expr.span),
863 cmt = self.with_mc(|mc| mc.cat_expr_adjusted(expr, cmt, &adjustment))?;
865 if let Categorization::Deref(_, mc::BorrowedPtr(_, r_ptr)) = cmt.cat {
866 self.mk_subregion_due_to_dereference(expr.span,
874 pub fn mk_subregion_due_to_dereference(&mut self,
876 minimum_lifetime: ty::Region<'tcx>,
877 maximum_lifetime: ty::Region<'tcx>) {
878 self.sub_regions(infer::DerefPointer(deref_span),
879 minimum_lifetime, maximum_lifetime)
882 fn check_safety_of_rvalue_destructor_if_necessary(&mut self,
883 cmt: &mc::cmt_<'tcx>,
886 Categorization::Rvalue(region) => {
888 ty::ReScope(rvalue_scope) => {
889 let typ = self.resolve_type(cmt.ty);
890 let body_id = self.body_id;
891 let _ = dropck::check_safety_of_destructor_if_necessary(
892 self, typ, span, body_id, rvalue_scope);
897 "unexpected rvalue region in rvalue \
898 destructor safety checking: `{:?}`",
907 /// Invoked on any index expression that occurs. Checks that if this is a slice
908 /// being indexed, the lifetime of the pointer includes the deref expr.
909 fn constrain_index(&mut self,
910 index_expr: &hir::Expr,
911 indexed_ty: Ty<'tcx>)
913 debug!("constrain_index(index_expr=?, indexed_ty={}",
914 self.ty_to_string(indexed_ty));
916 let r_index_expr = ty::ReScope(region::Scope::Node(index_expr.hir_id.local_id));
917 if let ty::Ref(r_ptr, r_ty, _) = indexed_ty.sty {
919 ty::Slice(_) | ty::TyStr => {
920 self.sub_regions(infer::IndexSlice(index_expr.span),
921 self.tcx.mk_region(r_index_expr), r_ptr);
928 /// Guarantees that any lifetimes which appear in the type of the node `id` (after applying
929 /// adjustments) are valid for at least `minimum_lifetime`
930 fn type_of_node_must_outlive(&mut self,
931 origin: infer::SubregionOrigin<'tcx>,
933 minimum_lifetime: ty::Region<'tcx>)
935 // Try to resolve the type. If we encounter an error, then typeck
936 // is going to fail anyway, so just stop here and let typeck
937 // report errors later on in the writeback phase.
938 let ty0 = self.resolve_node_type(hir_id);
944 .and_then(|adj| adj.last())
945 .map_or(ty0, |adj| adj.target);
946 let ty = self.resolve_type(ty);
947 debug!("constrain_regions_in_type_of_node(\
948 ty={}, ty0={}, id={:?}, minimum_lifetime={:?})",
950 hir_id, minimum_lifetime);
951 self.type_must_outlive(origin, ty, minimum_lifetime);
954 /// Adds constraints to inference such that `T: 'a` holds (or
955 /// reports an error if it cannot).
959 /// - `origin`, the reason we need this constraint
960 /// - `ty`, the type `T`
961 /// - `region`, the region `'a`
962 pub fn type_must_outlive(&self,
963 origin: infer::SubregionOrigin<'tcx>,
965 region: ty::Region<'tcx>)
967 self.infcx.type_must_outlive(self.outlives_environment.region_bound_pairs(),
968 self.implicit_region_bound,
975 /// Computes the guarantor for an expression `&base` and then ensures that the lifetime of the
976 /// resulting pointer is linked to the lifetime of its guarantor (if any).
977 fn link_addr_of(&mut self, expr: &hir::Expr,
978 mutability: hir::Mutability, base: &hir::Expr) {
979 debug!("link_addr_of(expr={:?}, base={:?})", expr, base);
981 let cmt = ignore_err!(self.with_mc(|mc| mc.cat_expr(base)));
983 debug!("link_addr_of: cmt={:?}", cmt);
985 self.link_region_from_node_type(expr.span, expr.hir_id, mutability, &cmt);
988 /// Computes the guarantors for any ref bindings in a `let` and
989 /// then ensures that the lifetime of the resulting pointer is
990 /// linked to the lifetime of the initialization expression.
991 fn link_local(&self, local: &hir::Local) {
992 debug!("regionck::for_local()");
993 let init_expr = match local.init {
995 Some(ref expr) => &**expr,
997 let discr_cmt = Rc::new(ignore_err!(self.with_mc(|mc| mc.cat_expr(init_expr))));
998 self.link_pattern(discr_cmt, &local.pat);
1001 /// Computes the guarantors for any ref bindings in a match and
1002 /// then ensures that the lifetime of the resulting pointer is
1003 /// linked to the lifetime of its guarantor (if any).
1004 fn link_match(&self, discr: &hir::Expr, arms: &[hir::Arm]) {
1005 debug!("regionck::for_match()");
1006 let discr_cmt = Rc::new(ignore_err!(self.with_mc(|mc| mc.cat_expr(discr))));
1007 debug!("discr_cmt={:?}", discr_cmt);
1009 for root_pat in &arm.pats {
1010 self.link_pattern(discr_cmt.clone(), &root_pat);
1015 /// Computes the guarantors for any ref bindings in a match and
1016 /// then ensures that the lifetime of the resulting pointer is
1017 /// linked to the lifetime of its guarantor (if any).
1018 fn link_fn_args(&self, body_scope: region::Scope, args: &[hir::Arg]) {
1019 debug!("regionck::link_fn_args(body_scope={:?})", body_scope);
1021 let arg_ty = self.node_ty(arg.hir_id);
1022 let re_scope = self.tcx.mk_region(ty::ReScope(body_scope));
1023 let arg_cmt = self.with_mc(|mc| {
1024 Rc::new(mc.cat_rvalue(arg.hir_id, arg.pat.span, re_scope, arg_ty))
1026 debug!("arg_ty={:?} arg_cmt={:?} arg={:?}",
1030 self.link_pattern(arg_cmt, &arg.pat);
1034 /// Link lifetimes of any ref bindings in `root_pat` to the pointers found
1035 /// in the discriminant, if needed.
1036 fn link_pattern(&self, discr_cmt: mc::cmt<'tcx>, root_pat: &hir::Pat) {
1037 debug!("link_pattern(discr_cmt={:?}, root_pat={:?})",
1040 ignore_err!(self.with_mc(|mc| {
1041 mc.cat_pattern(discr_cmt, root_pat, |sub_cmt, sub_pat| {
1042 match sub_pat.node {
1044 PatKind::Binding(..) => {
1045 if let Some(&bm) = mc.tables.pat_binding_modes().get(sub_pat.hir_id) {
1046 if let ty::BindByReference(mutbl) = bm {
1047 self.link_region_from_node_type(sub_pat.span, sub_pat.hir_id,
1051 self.tcx.sess.delay_span_bug(sub_pat.span, "missing binding mode");
1060 /// Link lifetime of borrowed pointer resulting from autoref to lifetimes in the value being
1062 fn link_autoref(&self,
1064 expr_cmt: &mc::cmt_<'tcx>,
1065 autoref: &adjustment::AutoBorrow<'tcx>)
1067 debug!("link_autoref(autoref={:?}, expr_cmt={:?})", autoref, expr_cmt);
1070 adjustment::AutoBorrow::Ref(r, m) => {
1071 self.link_region(expr.span, r, ty::BorrowKind::from_mutbl(m.into()), expr_cmt);
1074 adjustment::AutoBorrow::RawPtr(m) => {
1075 let r = self.tcx.mk_region(ty::ReScope(region::Scope::Node(expr.hir_id.local_id)));
1076 self.link_region(expr.span, r, ty::BorrowKind::from_mutbl(m), expr_cmt);
1081 /// Like `link_region()`, except that the region is extracted from the type of `id`,
1082 /// which must be some reference (`&T`, `&str`, etc).
1083 fn link_region_from_node_type(&self,
1086 mutbl: hir::Mutability,
1087 cmt_borrowed: &mc::cmt_<'tcx>) {
1088 debug!("link_region_from_node_type(id={:?}, mutbl={:?}, cmt_borrowed={:?})",
1089 id, mutbl, cmt_borrowed);
1091 let rptr_ty = self.resolve_node_type(id);
1092 if let ty::Ref(r, _, _) = rptr_ty.sty {
1093 debug!("rptr_ty={}", rptr_ty);
1094 self.link_region(span, r, ty::BorrowKind::from_mutbl(mutbl), cmt_borrowed);
1098 /// Informs the inference engine that `borrow_cmt` is being borrowed with
1099 /// kind `borrow_kind` and lifetime `borrow_region`.
1100 /// In order to ensure borrowck is satisfied, this may create constraints
1101 /// between regions, as explained in `link_reborrowed_region()`.
1102 fn link_region(&self,
1104 borrow_region: ty::Region<'tcx>,
1105 borrow_kind: ty::BorrowKind,
1106 borrow_cmt: &mc::cmt_<'tcx>) {
1107 let origin = infer::DataBorrowed(borrow_cmt.ty, span);
1108 self.type_must_outlive(origin, borrow_cmt.ty, borrow_region);
1110 let mut borrow_kind = borrow_kind;
1111 let mut borrow_cmt_cat = borrow_cmt.cat.clone();
1114 debug!("link_region(borrow_region={:?}, borrow_kind={:?}, borrow_cmt={:?})",
1118 match borrow_cmt_cat {
1119 Categorization::Deref(ref_cmt, mc::BorrowedPtr(ref_kind, ref_region)) => {
1120 match self.link_reborrowed_region(span,
1121 borrow_region, borrow_kind,
1122 ref_cmt, ref_region, ref_kind,
1125 borrow_cmt_cat = c.cat.clone();
1134 Categorization::Downcast(cmt_base, _) |
1135 Categorization::Deref(cmt_base, mc::Unique) |
1136 Categorization::Interior(cmt_base, _) => {
1137 // Borrowing interior or owned data requires the base
1138 // to be valid and borrowable in the same fashion.
1139 borrow_cmt_cat = cmt_base.cat.clone();
1140 borrow_kind = borrow_kind;
1143 Categorization::Deref(_, mc::UnsafePtr(..)) |
1144 Categorization::StaticItem |
1145 Categorization::Upvar(..) |
1146 Categorization::Local(..) |
1147 Categorization::Rvalue(..) => {
1148 // These are all "base cases" with independent lifetimes
1149 // that are not subject to inference
1156 /// This is the most complicated case: the path being borrowed is
1157 /// itself the referent of a borrowed pointer. Let me give an
1158 /// example fragment of code to make clear(er) the situation:
1160 /// let r: &'a mut T = ...; // the original reference "r" has lifetime 'a
1162 /// &'z *r // the reborrow has lifetime 'z
1164 /// Now, in this case, our primary job is to add the inference
1165 /// constraint that `'z <= 'a`. Given this setup, let's clarify the
1166 /// parameters in (roughly) terms of the example:
1168 /// ```plain,ignore (pseudo-Rust)
1169 /// A borrow of: `& 'z bk * r` where `r` has type `& 'a bk T`
1170 /// borrow_region ^~ ref_region ^~
1171 /// borrow_kind ^~ ref_kind ^~
1175 /// Here `bk` stands for some borrow-kind (e.g., `mut`, `uniq`, etc).
1177 /// Unfortunately, there are some complications beyond the simple
1178 /// scenario I just painted:
1180 /// 1. The reference `r` might in fact be a "by-ref" upvar. In that
1181 /// case, we have two jobs. First, we are inferring whether this reference
1182 /// should be an `&T`, `&mut T`, or `&uniq T` reference, and we must
1183 /// adjust that based on this borrow (e.g., if this is an `&mut` borrow,
1184 /// then `r` must be an `&mut` reference). Second, whenever we link
1185 /// two regions (here, `'z <= 'a`), we supply a *cause*, and in this
1186 /// case we adjust the cause to indicate that the reference being
1187 /// "reborrowed" is itself an upvar. This provides a nicer error message
1188 /// should something go wrong.
1190 /// 2. There may in fact be more levels of reborrowing. In the
1191 /// example, I said the borrow was like `&'z *r`, but it might
1192 /// in fact be a borrow like `&'z **q` where `q` has type `&'a
1193 /// &'b mut T`. In that case, we want to ensure that `'z <= 'a`
1194 /// and `'z <= 'b`. This is explained more below.
1196 /// The return value of this function indicates whether we need to
1197 /// recurse and process `ref_cmt` (see case 2 above).
1198 fn link_reborrowed_region(&self,
1200 borrow_region: ty::Region<'tcx>,
1201 borrow_kind: ty::BorrowKind,
1202 ref_cmt: mc::cmt<'tcx>,
1203 ref_region: ty::Region<'tcx>,
1204 mut ref_kind: ty::BorrowKind,
1206 -> Option<(mc::cmt<'tcx>, ty::BorrowKind)>
1208 // Possible upvar ID we may need later to create an entry in the
1211 // Detect by-ref upvar `x`:
1212 let cause = match note {
1213 mc::NoteUpvarRef(ref upvar_id) => {
1214 match self.tables.borrow().upvar_capture_map.get(upvar_id) {
1215 Some(&ty::UpvarCapture::ByRef(ref upvar_borrow)) => {
1216 // The mutability of the upvar may have been modified
1217 // by the above adjustment, so update our local variable.
1218 ref_kind = upvar_borrow.kind;
1220 infer::ReborrowUpvar(span, *upvar_id)
1223 span_bug!( span, "Illegal upvar id: {:?}", upvar_id);
1227 mc::NoteClosureEnv(ref upvar_id) => {
1228 // We don't have any mutability changes to propagate, but
1229 // we do want to note that an upvar reborrow caused this
1231 infer::ReborrowUpvar(span, *upvar_id)
1234 infer::Reborrow(span)
1238 debug!("link_reborrowed_region: {:?} <= {:?}",
1241 self.sub_regions(cause, borrow_region, ref_region);
1243 // If we end up needing to recurse and establish a region link
1244 // with `ref_cmt`, calculate what borrow kind we will end up
1245 // needing. This will be used below.
1247 // One interesting twist is that we can weaken the borrow kind
1248 // when we recurse: to reborrow an `&mut` referent as mutable,
1249 // borrowck requires a unique path to the `&mut` reference but not
1250 // necessarily a *mutable* path.
1251 let new_borrow_kind = match borrow_kind {
1254 ty::MutBorrow | ty::UniqueImmBorrow =>
1258 // Decide whether we need to recurse and link any regions within
1259 // the `ref_cmt`. This is concerned for the case where the value
1260 // being reborrowed is in fact a borrowed pointer found within
1261 // another borrowed pointer. For example:
1263 // let p: &'b &'a mut T = ...;
1267 // What makes this case particularly tricky is that, if the data
1268 // being borrowed is a `&mut` or `&uniq` borrow, borrowck requires
1269 // not only that `'z <= 'a`, (as before) but also `'z <= 'b`
1270 // (otherwise the user might mutate through the `&mut T` reference
1271 // after `'b` expires and invalidate the borrow we are looking at
1274 // So let's re-examine our parameters in light of this more
1275 // complicated (possible) scenario:
1277 // A borrow of: `& 'z bk * * p` where `p` has type `&'b bk & 'a bk T`
1278 // borrow_region ^~ ref_region ^~
1279 // borrow_kind ^~ ref_kind ^~
1282 // (Note that since we have not examined `ref_cmt.cat`, we don't
1283 // know whether this scenario has occurred; but I wanted to show
1284 // how all the types get adjusted.)
1287 // The reference being reborrowed is a shareable ref of
1288 // type `&'a T`. In this case, it doesn't matter where we
1289 // *found* the `&T` pointer, the memory it references will
1290 // be valid and immutable for `'a`. So we can stop here.
1292 // (Note that the `borrow_kind` must also be ImmBorrow or
1293 // else the user is borrowed imm memory as mut memory,
1294 // which means they'll get an error downstream in borrowck
1299 ty::MutBorrow | ty::UniqueImmBorrow => {
1300 // The reference being reborrowed is either an `&mut T` or
1301 // `&uniq T`. This is the case where recursion is needed.
1302 return Some((ref_cmt, new_borrow_kind));
1307 /// Checks that the values provided for type/region arguments in a given
1308 /// expression are well-formed and in-scope.
1309 fn substs_wf_in_scope(&mut self,
1310 origin: infer::ParameterOrigin,
1311 substs: &Substs<'tcx>,
1313 expr_region: ty::Region<'tcx>) {
1314 debug!("substs_wf_in_scope(substs={:?}, \
1318 substs, expr_region, origin, expr_span);
1320 let origin = infer::ParameterInScope(origin, expr_span);
1322 for region in substs.regions() {
1323 self.sub_regions(origin.clone(), expr_region, region);
1326 for ty in substs.types() {
1327 let ty = self.resolve_type(ty);
1328 self.type_must_outlive(origin.clone(), ty, expr_region);