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(_) => return () })
111 ///////////////////////////////////////////////////////////////////////////
112 // PUBLIC ENTRY POINTS
114 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
115 pub fn regionck_expr(&self, body: &'gcx hir::Body) {
116 let subject = self.tcx.hir.body_owner_def_id(body.id());
117 let id = body.value.id;
118 let mut rcx = RegionCtxt::new(self,
123 if self.err_count_since_creation() == 0 {
124 // regionck assumes typeck succeeded
125 rcx.visit_body(body);
126 rcx.visit_region_obligations(id);
128 rcx.resolve_regions_and_report_errors_unless_nll();
130 assert!(self.tables.borrow().free_region_map.is_empty());
131 self.tables.borrow_mut().free_region_map = rcx.outlives_environment.into_free_region_map();
134 /// Region checking during the WF phase for items. `wf_tys` are the
135 /// types from which we should derive implied bounds, if any.
136 pub fn regionck_item(&self,
137 item_id: ast::NodeId,
139 wf_tys: &[Ty<'tcx>]) {
140 debug!("regionck_item(item.id={:?}, wf_tys={:?})", item_id, wf_tys);
141 let subject = self.tcx.hir.local_def_id(item_id);
142 let mut rcx = RegionCtxt::new(self,
143 RepeatingScope(item_id),
147 rcx.outlives_environment.add_implied_bounds(self, wf_tys, item_id, span);
148 rcx.visit_region_obligations(item_id);
149 rcx.resolve_regions_and_report_errors();
152 /// Region check a function body. Not invoked on closures, but
153 /// only on the "root" fn item (in which closures may be
154 /// embedded). Walks the function body and adds various add'l
155 /// constraints that are needed for region inference. This is
156 /// separated both to isolate "pure" region constraints from the
157 /// rest of type check and because sometimes we need type
158 /// inference to have completed before we can determine which
159 /// constraints to add.
160 pub fn regionck_fn(&self,
162 body: &'gcx hir::Body) {
163 debug!("regionck_fn(id={})", fn_id);
164 let subject = self.tcx.hir.body_owner_def_id(body.id());
165 let node_id = body.value.id;
166 let mut rcx = RegionCtxt::new(self,
167 RepeatingScope(node_id),
172 if self.err_count_since_creation() == 0 {
173 // regionck assumes typeck succeeded
174 rcx.visit_fn_body(fn_id, body, self.tcx.hir.span(fn_id));
177 rcx.resolve_regions_and_report_errors_unless_nll();
179 // In this mode, we also copy the free-region-map into the
180 // tables of the enclosing fcx. In the other regionck modes
181 // (e.g., `regionck_item`), we don't have an enclosing tables.
182 assert!(self.tables.borrow().free_region_map.is_empty());
183 self.tables.borrow_mut().free_region_map = rcx.outlives_environment.into_free_region_map();
187 ///////////////////////////////////////////////////////////////////////////
190 pub struct RegionCtxt<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
191 pub fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
193 pub region_scope_tree: Lrc<region::ScopeTree>,
195 outlives_environment: OutlivesEnvironment<'tcx>,
197 // id of innermost fn body id
198 body_id: ast::NodeId,
200 // call_site scope of innermost fn
201 call_site_scope: Option<region::Scope>,
203 // id of innermost fn or loop
204 repeating_scope: ast::NodeId,
206 // id of AST node being analyzed (the subject of the analysis).
207 subject_def_id: DefId,
211 impl<'a, 'gcx, 'tcx> Deref for RegionCtxt<'a, 'gcx, 'tcx> {
212 type Target = FnCtxt<'a, 'gcx, 'tcx>;
213 fn deref(&self) -> &Self::Target {
218 pub struct RepeatingScope(ast::NodeId);
219 pub struct Subject(DefId);
221 impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
222 pub fn new(fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
223 RepeatingScope(initial_repeating_scope): RepeatingScope,
224 initial_body_id: ast::NodeId,
225 Subject(subject): Subject,
226 param_env: ty::ParamEnv<'tcx>)
227 -> RegionCtxt<'a, 'gcx, 'tcx> {
228 let region_scope_tree = fcx.tcx.region_scope_tree(subject);
229 let outlives_environment = OutlivesEnvironment::new(param_env);
233 repeating_scope: initial_repeating_scope,
234 body_id: initial_body_id,
235 call_site_scope: None,
236 subject_def_id: subject,
237 outlives_environment,
241 fn set_repeating_scope(&mut self, scope: ast::NodeId) -> ast::NodeId {
242 mem::replace(&mut self.repeating_scope, scope)
245 /// Try to resolve the type for the given node, returning t_err if an error results. Note that
246 /// we never care about the details of the error, the same error will be detected and reported
247 /// in the writeback phase.
249 /// Note one important point: we do not attempt to resolve *region variables* here. This is
250 /// because regionck is essentially adding constraints to those region variables and so may yet
251 /// influence how they are resolved.
253 /// Consider this silly example:
256 /// fn borrow(x: &i32) -> &i32 {x}
257 /// fn foo(x: @i32) -> i32 { // block: B
258 /// let b = borrow(x); // region: <R0>
263 /// Here, the region of `b` will be `<R0>`. `<R0>` is constrained to be some subregion of the
264 /// block B and some superregion of the call. If we forced it now, we'd choose the smaller
265 /// region (the call). But that would make the *b illegal. Since we don't resolve, the type
266 /// of b will be `&<R0>.i32` and then `*b` will require that `<R0>` be bigger than the let and
267 /// the `*b` expression, so we will effectively resolve `<R0>` to be the block B.
268 pub fn resolve_type(&self, unresolved_ty: Ty<'tcx>) -> Ty<'tcx> {
269 self.resolve_type_vars_if_possible(&unresolved_ty)
272 /// Try to resolve the type for the given node.
273 fn resolve_node_type(&self, id: hir::HirId) -> Ty<'tcx> {
274 let t = self.node_ty(id);
278 /// Try to resolve the type for the given node.
279 pub fn resolve_expr_type_adjusted(&mut self, expr: &hir::Expr) -> Ty<'tcx> {
280 let ty = self.tables.borrow().expr_ty_adjusted(expr);
281 self.resolve_type(ty)
284 /// This is the "main" function when region-checking a function item or a closure
285 /// within a function item. It begins by updating various fields (e.g., `call_site_scope`
286 /// and `outlives_environment`) to be appropriate to the function and then adds constraints
287 /// derived from the function body.
289 /// Note that it does **not** restore the state of the fields that
290 /// it updates! This is intentional, since -- for the main
291 /// function -- we wish to be able to read the final
292 /// `outlives_environment` and other fields from the caller. For
293 /// closures, however, we save and restore any "scoped state"
294 /// before we invoke this function. (See `visit_fn` in the
295 /// `intravisit::Visitor` impl below.)
296 fn visit_fn_body(&mut self,
297 id: ast::NodeId, // the id of the fn itself
298 body: &'gcx hir::Body,
301 // When we enter a function, we can derive
302 debug!("visit_fn_body(id={})", id);
304 let body_id = body.id();
305 self.body_id = body_id.node_id;
307 let call_site = region::Scope::CallSite(body.value.hir_id.local_id);
308 self.call_site_scope = Some(call_site);
311 let fn_hir_id = self.tcx.hir.node_to_hir_id(id);
312 match self.tables.borrow().liberated_fn_sigs().get(fn_hir_id) {
313 Some(f) => f.clone(),
315 bug!("No fn-sig entry for id={}", id);
320 // Collect the types from which we create inferred bounds.
321 // For the return type, if diverging, substitute `bool` just
322 // because it will have no effect.
324 // FIXME(#27579) return types should not be implied bounds
325 let fn_sig_tys: Vec<_> =
326 fn_sig.inputs().iter().cloned().chain(Some(fn_sig.output())).collect();
328 self.outlives_environment.add_implied_bounds(
333 self.link_fn_args(region::Scope::Node(body.value.hir_id.local_id), &body.arguments);
334 self.visit_body(body);
335 self.visit_region_obligations(body_id.node_id);
337 let call_site_scope = self.call_site_scope.unwrap();
338 debug!("visit_fn_body body.id {:?} call_site_scope: {:?}",
339 body.id(), call_site_scope);
340 let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope));
342 let body_hir_id = self.tcx.hir.node_to_hir_id(body_id.node_id);
343 self.type_of_node_must_outlive(infer::CallReturn(span),
347 self.constrain_anon_types(
348 &self.fcx.anon_types.borrow(),
349 self.outlives_environment.free_region_map(),
353 fn visit_region_obligations(&mut self, node_id: ast::NodeId)
355 debug!("visit_region_obligations: node_id={}", node_id);
357 // region checking can introduce new pending obligations
358 // which, when processed, might generate new region
359 // obligations. So make sure we process those.
360 self.select_all_obligations_or_error();
362 self.infcx.process_registered_region_obligations(
363 self.outlives_environment.region_bound_pairs(),
364 self.implicit_region_bound,
369 fn resolve_regions_and_report_errors(&self) {
370 self.fcx.resolve_regions_and_report_errors(self.subject_def_id,
371 &self.region_scope_tree,
372 &self.outlives_environment);
375 fn resolve_regions_and_report_errors_unless_nll(&self) {
376 self.fcx.resolve_regions_and_report_errors_unless_nll(self.subject_def_id,
377 &self.region_scope_tree,
378 &self.outlives_environment);
381 fn constrain_bindings_in_pat(&mut self, pat: &hir::Pat) {
382 debug!("regionck::visit_pat(pat={:?})", pat);
383 pat.each_binding(|_, hir_id, span, _| {
384 // If we have a variable that contains region'd data, that
385 // data will be accessible from anywhere that the variable is
386 // accessed. We must be wary of loops like this:
388 // // from src/test/compile-fail/borrowck-lend-flow.rs
389 // let mut v = box 3, w = box 4;
390 // let mut x = &mut w;
393 // borrow(v); //~ ERROR cannot borrow
394 // x = &mut v; // (1)
397 // Typically, we try to determine the region of a borrow from
398 // those points where it is dereferenced. In this case, one
399 // might imagine that the lifetime of `x` need only be the
400 // body of the loop. But of course this is incorrect because
401 // the pointer that is created at point (1) is consumed at
402 // point (2), meaning that it must be live across the loop
403 // iteration. The easiest way to guarantee this is to require
404 // that the lifetime of any regions that appear in a
405 // variable's type enclose at least the variable's scope.
406 let var_scope = self.region_scope_tree.var_scope(hir_id.local_id);
407 let var_region = self.tcx.mk_region(ty::ReScope(var_scope));
409 let origin = infer::BindingTypeIsNotValidAtDecl(span);
410 self.type_of_node_must_outlive(origin, hir_id, var_region);
412 let typ = self.resolve_node_type(hir_id);
413 let body_id = self.body_id;
414 let _ = dropck::check_safety_of_destructor_if_necessary(
415 self, typ, span, body_id, var_scope);
420 impl<'a, 'gcx, 'tcx> Visitor<'gcx> for RegionCtxt<'a, 'gcx, 'tcx> {
421 // (..) FIXME(#3238) should use visit_pat, not visit_arm/visit_local,
422 // However, right now we run into an issue whereby some free
423 // regions are not properly related if they appear within the
424 // types of arguments that must be inferred. This could be
425 // addressed by deferring the construction of the region
426 // hierarchy, and in particular the relationships between free
427 // regions, until regionck, as described in #3238.
429 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'gcx> {
430 NestedVisitorMap::None
433 fn visit_fn(&mut self,
434 fk: intravisit::FnKind<'gcx>,
435 _: &'gcx hir::FnDecl,
436 body_id: hir::BodyId,
439 assert!(match fk { intravisit::FnKind::Closure(..) => true, _ => false },
440 "visit_fn invoked for something other than a closure");
442 // Save state of current function before invoking
443 // `visit_fn_body`. We will restore afterwards.
444 let old_body_id = self.body_id;
445 let old_call_site_scope = self.call_site_scope;
446 let env_snapshot = self.outlives_environment.push_snapshot_pre_closure();
448 let body = self.tcx.hir.body(body_id);
449 self.visit_fn_body(id, body, span);
451 // Restore state from previous function.
452 self.outlives_environment.pop_snapshot_post_closure(env_snapshot);
453 self.call_site_scope = old_call_site_scope;
454 self.body_id = old_body_id;
457 //visit_pat: visit_pat, // (..) see above
459 fn visit_arm(&mut self, arm: &'gcx hir::Arm) {
462 self.constrain_bindings_in_pat(p);
464 intravisit::walk_arm(self, arm);
467 fn visit_local(&mut self, l: &'gcx hir::Local) {
469 self.constrain_bindings_in_pat(&l.pat);
471 intravisit::walk_local(self, l);
474 fn visit_expr(&mut self, expr: &'gcx hir::Expr) {
475 debug!("regionck::visit_expr(e={:?}, repeating_scope={})",
476 expr, self.repeating_scope);
478 // No matter what, the type of each expression must outlive the
479 // scope of that expression. This also guarantees basic WF.
480 let expr_ty = self.resolve_node_type(expr.hir_id);
481 // the region corresponding to this expression
482 let expr_region = self.tcx.mk_region(ty::ReScope(
483 region::Scope::Node(expr.hir_id.local_id)));
484 self.type_must_outlive(infer::ExprTypeIsNotInScope(expr_ty, expr.span),
485 expr_ty, expr_region);
487 let is_method_call = self.tables.borrow().is_method_call(expr);
489 // If we are calling a method (either explicitly or via an
490 // overloaded operator), check that all of the types provided as
491 // arguments for its type parameters are well-formed, and all the regions
492 // provided as arguments outlive the call.
494 let origin = match expr.node {
495 hir::ExprMethodCall(..) =>
496 infer::ParameterOrigin::MethodCall,
497 hir::ExprUnary(op, _) if op == hir::UnDeref =>
498 infer::ParameterOrigin::OverloadedDeref,
500 infer::ParameterOrigin::OverloadedOperator
503 let substs = self.tables.borrow().node_substs(expr.hir_id);
504 self.substs_wf_in_scope(origin, substs, expr.span, expr_region);
505 // Arguments (sub-expressions) are checked via `constrain_call`, below.
508 // Check any autoderefs or autorefs that appear.
509 let cmt_result = self.constrain_adjustments(expr);
511 // If necessary, constrain destructors in this expression. This will be
512 // the adjusted form if there is an adjustment.
515 self.check_safety_of_rvalue_destructor_if_necessary(&head_cmt, expr.span);
518 self.tcx.sess.delay_span_bug(expr.span, "cat_expr Errd");
522 debug!("regionck::visit_expr(e={:?}, repeating_scope={}) - visiting subexprs",
523 expr, self.repeating_scope);
525 hir::ExprPath(_) => {
526 let substs = self.tables.borrow().node_substs(expr.hir_id);
527 let origin = infer::ParameterOrigin::Path;
528 self.substs_wf_in_scope(origin, substs, expr.span, expr_region);
531 hir::ExprCall(ref callee, ref args) => {
533 self.constrain_call(expr, Some(&callee), args.iter().map(|e| &*e));
535 self.constrain_callee(&callee);
536 self.constrain_call(expr, None, args.iter().map(|e| &*e));
539 intravisit::walk_expr(self, expr);
542 hir::ExprMethodCall(.., ref args) => {
543 self.constrain_call(expr, Some(&args[0]), args[1..].iter().map(|e| &*e));
545 intravisit::walk_expr(self, expr);
548 hir::ExprAssignOp(_, ref lhs, ref rhs) => {
550 self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter());
553 intravisit::walk_expr(self, expr);
556 hir::ExprIndex(ref lhs, ref rhs) if is_method_call => {
557 self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter());
559 intravisit::walk_expr(self, expr);
562 hir::ExprBinary(_, ref lhs, ref rhs) if is_method_call => {
563 // As `ExprMethodCall`, but the call is via an overloaded op.
564 self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter());
566 intravisit::walk_expr(self, expr);
569 hir::ExprBinary(_, ref lhs, ref rhs) => {
570 // If you do `x OP y`, then the types of `x` and `y` must
571 // outlive the operation you are performing.
572 let lhs_ty = self.resolve_expr_type_adjusted(&lhs);
573 let rhs_ty = self.resolve_expr_type_adjusted(&rhs);
574 for &ty in &[lhs_ty, rhs_ty] {
575 self.type_must_outlive(infer::Operand(expr.span),
578 intravisit::walk_expr(self, expr);
581 hir::ExprUnary(hir::UnDeref, ref base) => {
582 // For *a, the lifetime of a must enclose the deref
584 self.constrain_call(expr, Some(base), None::<hir::Expr>.iter());
586 // For overloaded derefs, base_ty is the input to `Deref::deref`,
587 // but it's a reference type uing the same region as the output.
588 let base_ty = self.resolve_expr_type_adjusted(base);
589 if let ty::TyRef(r_ptr, _, _) = base_ty.sty {
590 self.mk_subregion_due_to_dereference(expr.span, expr_region, r_ptr);
593 intravisit::walk_expr(self, expr);
596 hir::ExprUnary(_, ref lhs) if is_method_call => {
598 self.constrain_call(expr, Some(&lhs), None::<hir::Expr>.iter());
600 intravisit::walk_expr(self, expr);
603 hir::ExprIndex(ref vec_expr, _) => {
604 // For a[b], the lifetime of a must enclose the deref
605 let vec_type = self.resolve_expr_type_adjusted(&vec_expr);
606 self.constrain_index(expr, vec_type);
608 intravisit::walk_expr(self, expr);
611 hir::ExprCast(ref source, _) => {
612 // Determine if we are casting `source` to a trait
613 // instance. If so, we have to be sure that the type of
614 // the source obeys the trait's region bound.
615 self.constrain_cast(expr, &source);
616 intravisit::walk_expr(self, expr);
619 hir::ExprAddrOf(m, ref base) => {
620 self.link_addr_of(expr, m, &base);
622 // Require that when you write a `&expr` expression, the
623 // resulting pointer has a lifetime that encompasses the
624 // `&expr` expression itself. Note that we constraining
625 // the type of the node expr.id here *before applying
628 // FIXME(https://github.com/rust-lang/rfcs/issues/811)
629 // nested method calls requires that this rule change
630 let ty0 = self.resolve_node_type(expr.hir_id);
631 self.type_must_outlive(infer::AddrOf(expr.span), ty0, expr_region);
632 intravisit::walk_expr(self, expr);
635 hir::ExprMatch(ref discr, ref arms, _) => {
636 self.link_match(&discr, &arms[..]);
638 intravisit::walk_expr(self, expr);
641 hir::ExprClosure(.., body_id, _, _) => {
642 self.check_expr_fn_block(expr, body_id);
645 hir::ExprLoop(ref body, _, _) => {
646 let repeating_scope = self.set_repeating_scope(body.id);
647 intravisit::walk_expr(self, expr);
648 self.set_repeating_scope(repeating_scope);
651 hir::ExprWhile(ref cond, ref body, _) => {
652 let repeating_scope = self.set_repeating_scope(cond.id);
653 self.visit_expr(&cond);
655 self.set_repeating_scope(body.id);
656 self.visit_block(&body);
658 self.set_repeating_scope(repeating_scope);
661 hir::ExprRet(Some(ref ret_expr)) => {
662 let call_site_scope = self.call_site_scope;
663 debug!("visit_expr ExprRet ret_expr.id {} call_site_scope: {:?}",
664 ret_expr.id, call_site_scope);
665 let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope.unwrap()));
666 self.type_of_node_must_outlive(infer::CallReturn(ret_expr.span),
669 intravisit::walk_expr(self, expr);
673 intravisit::walk_expr(self, expr);
679 impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
680 fn constrain_cast(&mut self,
681 cast_expr: &hir::Expr,
682 source_expr: &hir::Expr)
684 debug!("constrain_cast(cast_expr={:?}, source_expr={:?})",
688 let source_ty = self.resolve_node_type(source_expr.hir_id);
689 let target_ty = self.resolve_node_type(cast_expr.hir_id);
691 self.walk_cast(cast_expr, source_ty, target_ty);
694 fn walk_cast(&mut self,
695 cast_expr: &hir::Expr,
698 debug!("walk_cast(from_ty={:?}, to_ty={:?})",
701 match (&from_ty.sty, &to_ty.sty) {
702 /*From:*/ (&ty::TyRef(from_r, from_ty, _),
703 /*To: */ &ty::TyRef(to_r, to_ty, _)) => {
704 // Target cannot outlive source, naturally.
705 self.sub_regions(infer::Reborrow(cast_expr.span), to_r, from_r);
706 self.walk_cast(cast_expr, from_ty, to_ty);
710 /*To: */ &ty::TyDynamic(.., r)) => {
711 // When T is existentially quantified as a trait
712 // `Foo+'to`, it must outlive the region bound `'to`.
713 self.type_must_outlive(infer::RelateObjectBound(cast_expr.span), from_ty, r);
716 /*From:*/ (&ty::TyAdt(from_def, _),
717 /*To: */ &ty::TyAdt(to_def, _)) if from_def.is_box() && to_def.is_box() => {
718 self.walk_cast(cast_expr, from_ty.boxed_ty(), to_ty.boxed_ty());
725 fn check_expr_fn_block(&mut self,
726 expr: &'gcx hir::Expr,
727 body_id: hir::BodyId) {
728 let repeating_scope = self.set_repeating_scope(body_id.node_id);
729 intravisit::walk_expr(self, expr);
730 self.set_repeating_scope(repeating_scope);
733 fn constrain_callee(&mut self, callee_expr: &hir::Expr) {
734 let callee_ty = self.resolve_node_type(callee_expr.hir_id);
735 match callee_ty.sty {
736 ty::TyFnDef(..) | ty::TyFnPtr(_) => { }
738 // this should not happen, but it does if the program is
743 // "Calling non-function: {}",
749 fn constrain_call<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self,
750 call_expr: &hir::Expr,
751 receiver: Option<&hir::Expr>,
753 //! Invoked on every call site (i.e., normal calls, method calls,
754 //! and overloaded operators). Constrains the regions which appear
755 //! in the type of the function. Also constrains the regions that
756 //! appear in the arguments appropriately.
758 debug!("constrain_call(call_expr={:?}, receiver={:?})",
762 // `callee_region` is the scope representing the time in which the
765 // FIXME(#6268) to support nested method calls, should be callee_id
766 let callee_scope = region::Scope::Node(call_expr.hir_id.local_id);
767 let callee_region = self.tcx.mk_region(ty::ReScope(callee_scope));
769 debug!("callee_region={:?}", callee_region);
771 for arg_expr in arg_exprs {
772 debug!("Argument: {:?}", arg_expr);
774 // ensure that any regions appearing in the argument type are
775 // valid for at least the lifetime of the function:
776 self.type_of_node_must_outlive(infer::CallArg(arg_expr.span),
781 // as loop above, but for receiver
782 if let Some(r) = receiver {
783 debug!("receiver: {:?}", r);
784 self.type_of_node_must_outlive(infer::CallRcvr(r.span),
790 /// Create a temporary `MemCategorizationContext` and pass it to the closure.
791 fn with_mc<F, R>(&self, f: F) -> R
792 where F: for<'b> FnOnce(mc::MemCategorizationContext<'b, 'gcx, 'tcx>) -> R
794 f(mc::MemCategorizationContext::with_infer(&self.infcx,
795 &self.region_scope_tree,
796 &self.tables.borrow()))
799 /// Invoked on any adjustments that occur. Checks that if this is a region pointer being
800 /// dereferenced, the lifetime of the pointer includes the deref expr.
801 fn constrain_adjustments(&mut self, expr: &hir::Expr) -> mc::McResult<mc::cmt_<'tcx>> {
802 debug!("constrain_adjustments(expr={:?})", expr);
804 let mut cmt = self.with_mc(|mc| mc.cat_expr_unadjusted(expr))?;
806 let tables = self.tables.borrow();
807 let adjustments = tables.expr_adjustments(&expr);
808 if adjustments.is_empty() {
812 debug!("constrain_adjustments: adjustments={:?}", adjustments);
814 // If necessary, constrain destructors in the unadjusted form of this
816 self.check_safety_of_rvalue_destructor_if_necessary(&cmt, expr.span);
818 let expr_region = self.tcx.mk_region(ty::ReScope(
819 region::Scope::Node(expr.hir_id.local_id)));
820 for adjustment in adjustments {
821 debug!("constrain_adjustments: adjustment={:?}, cmt={:?}",
824 if let adjustment::Adjust::Deref(Some(deref)) = adjustment.kind {
825 debug!("constrain_adjustments: overloaded deref: {:?}", deref);
827 // Treat overloaded autoderefs as if an AutoBorrow adjustment
828 // was applied on the base type, as that is always the case.
829 let input = self.tcx.mk_ref(deref.region, ty::TypeAndMut {
833 let output = self.tcx.mk_ref(deref.region, ty::TypeAndMut {
834 ty: adjustment.target,
838 self.link_region(expr.span, deref.region,
839 ty::BorrowKind::from_mutbl(deref.mutbl), &cmt);
841 // Specialized version of constrain_call.
842 self.type_must_outlive(infer::CallRcvr(expr.span),
844 self.type_must_outlive(infer::CallReturn(expr.span),
845 output, expr_region);
848 if let adjustment::Adjust::Borrow(ref autoref) = adjustment.kind {
849 self.link_autoref(expr, &cmt, autoref);
851 // Require that the resulting region encompasses
854 // FIXME(#6268) remove to support nested method calls
855 self.type_of_node_must_outlive(infer::AutoBorrow(expr.span),
860 cmt = self.with_mc(|mc| mc.cat_expr_adjusted(expr, cmt, &adjustment))?;
862 if let Categorization::Deref(_, mc::BorrowedPtr(_, r_ptr)) = cmt.cat {
863 self.mk_subregion_due_to_dereference(expr.span,
871 pub fn mk_subregion_due_to_dereference(&mut self,
873 minimum_lifetime: ty::Region<'tcx>,
874 maximum_lifetime: ty::Region<'tcx>) {
875 self.sub_regions(infer::DerefPointer(deref_span),
876 minimum_lifetime, maximum_lifetime)
879 fn check_safety_of_rvalue_destructor_if_necessary(&mut self,
880 cmt: &mc::cmt_<'tcx>,
883 Categorization::Rvalue(region) => {
885 ty::ReScope(rvalue_scope) => {
886 let typ = self.resolve_type(cmt.ty);
887 let body_id = self.body_id;
888 let _ = dropck::check_safety_of_destructor_if_necessary(
889 self, typ, span, body_id, rvalue_scope);
894 "unexpected rvalue region in rvalue \
895 destructor safety checking: `{:?}`",
904 /// Invoked on any index expression that occurs. Checks that if this is a slice
905 /// being indexed, the lifetime of the pointer includes the deref expr.
906 fn constrain_index(&mut self,
907 index_expr: &hir::Expr,
908 indexed_ty: Ty<'tcx>)
910 debug!("constrain_index(index_expr=?, indexed_ty={}",
911 self.ty_to_string(indexed_ty));
913 let r_index_expr = ty::ReScope(region::Scope::Node(index_expr.hir_id.local_id));
914 if let ty::TyRef(r_ptr, r_ty, _) = indexed_ty.sty {
916 ty::TySlice(_) | ty::TyStr => {
917 self.sub_regions(infer::IndexSlice(index_expr.span),
918 self.tcx.mk_region(r_index_expr), r_ptr);
925 /// Guarantees that any lifetimes which appear in the type of the node `id` (after applying
926 /// adjustments) are valid for at least `minimum_lifetime`
927 fn type_of_node_must_outlive(&mut self,
928 origin: infer::SubregionOrigin<'tcx>,
930 minimum_lifetime: ty::Region<'tcx>)
932 // Try to resolve the type. If we encounter an error, then typeck
933 // is going to fail anyway, so just stop here and let typeck
934 // report errors later on in the writeback phase.
935 let ty0 = self.resolve_node_type(hir_id);
941 .and_then(|adj| adj.last())
942 .map_or(ty0, |adj| adj.target);
943 let ty = self.resolve_type(ty);
944 debug!("constrain_regions_in_type_of_node(\
945 ty={}, ty0={}, id={:?}, minimum_lifetime={:?})",
947 hir_id, minimum_lifetime);
948 self.type_must_outlive(origin, ty, minimum_lifetime);
951 /// Adds constraints to inference such that `T: 'a` holds (or
952 /// reports an error if it cannot).
956 /// - `origin`, the reason we need this constraint
957 /// - `ty`, the type `T`
958 /// - `region`, the region `'a`
959 pub fn type_must_outlive(&self,
960 origin: infer::SubregionOrigin<'tcx>,
962 region: ty::Region<'tcx>)
964 self.infcx.type_must_outlive(self.outlives_environment.region_bound_pairs(),
965 self.implicit_region_bound,
972 /// Computes the guarantor for an expression `&base` and then ensures that the lifetime of the
973 /// resulting pointer is linked to the lifetime of its guarantor (if any).
974 fn link_addr_of(&mut self, expr: &hir::Expr,
975 mutability: hir::Mutability, base: &hir::Expr) {
976 debug!("link_addr_of(expr={:?}, base={:?})", expr, base);
978 let cmt = ignore_err!(self.with_mc(|mc| mc.cat_expr(base)));
980 debug!("link_addr_of: cmt={:?}", cmt);
982 self.link_region_from_node_type(expr.span, expr.hir_id, mutability, &cmt);
985 /// Computes the guarantors for any ref bindings in a `let` and
986 /// then ensures that the lifetime of the resulting pointer is
987 /// linked to the lifetime of the initialization expression.
988 fn link_local(&self, local: &hir::Local) {
989 debug!("regionck::for_local()");
990 let init_expr = match local.init {
992 Some(ref expr) => &**expr,
994 let discr_cmt = Rc::new(ignore_err!(self.with_mc(|mc| mc.cat_expr(init_expr))));
995 self.link_pattern(discr_cmt, &local.pat);
998 /// Computes the guarantors for any ref bindings in a match and
999 /// then ensures that the lifetime of the resulting pointer is
1000 /// linked to the lifetime of its guarantor (if any).
1001 fn link_match(&self, discr: &hir::Expr, arms: &[hir::Arm]) {
1002 debug!("regionck::for_match()");
1003 let discr_cmt = Rc::new(ignore_err!(self.with_mc(|mc| mc.cat_expr(discr))));
1004 debug!("discr_cmt={:?}", discr_cmt);
1006 for root_pat in &arm.pats {
1007 self.link_pattern(discr_cmt.clone(), &root_pat);
1012 /// Computes the guarantors for any ref bindings in a match and
1013 /// then ensures that the lifetime of the resulting pointer is
1014 /// linked to the lifetime of its guarantor (if any).
1015 fn link_fn_args(&self, body_scope: region::Scope, args: &[hir::Arg]) {
1016 debug!("regionck::link_fn_args(body_scope={:?})", body_scope);
1018 let arg_ty = self.node_ty(arg.hir_id);
1019 let re_scope = self.tcx.mk_region(ty::ReScope(body_scope));
1020 let arg_cmt = self.with_mc(|mc| {
1021 Rc::new(mc.cat_rvalue(arg.hir_id, arg.pat.span, re_scope, arg_ty))
1023 debug!("arg_ty={:?} arg_cmt={:?} arg={:?}",
1027 self.link_pattern(arg_cmt, &arg.pat);
1031 /// Link lifetimes of any ref bindings in `root_pat` to the pointers found
1032 /// in the discriminant, if needed.
1033 fn link_pattern(&self, discr_cmt: mc::cmt<'tcx>, root_pat: &hir::Pat) {
1034 debug!("link_pattern(discr_cmt={:?}, root_pat={:?})",
1037 let _ = self.with_mc(|mc| {
1038 mc.cat_pattern(discr_cmt, root_pat, |sub_cmt, sub_pat| {
1039 match sub_pat.node {
1041 PatKind::Binding(..) => {
1042 let bm = *mc.tables.pat_binding_modes().get(sub_pat.hir_id)
1043 .expect("missing binding mode");
1044 if let ty::BindByReference(mutbl) = bm {
1045 self.link_region_from_node_type(sub_pat.span, sub_pat.hir_id,
1055 /// Link lifetime of borrowed pointer resulting from autoref to lifetimes in the value being
1057 fn link_autoref(&self,
1059 expr_cmt: &mc::cmt_<'tcx>,
1060 autoref: &adjustment::AutoBorrow<'tcx>)
1062 debug!("link_autoref(autoref={:?}, expr_cmt={:?})", autoref, expr_cmt);
1065 adjustment::AutoBorrow::Ref(r, m) => {
1066 self.link_region(expr.span, r, ty::BorrowKind::from_mutbl(m.into()), expr_cmt);
1069 adjustment::AutoBorrow::RawPtr(m) => {
1070 let r = self.tcx.mk_region(ty::ReScope(region::Scope::Node(expr.hir_id.local_id)));
1071 self.link_region(expr.span, r, ty::BorrowKind::from_mutbl(m), expr_cmt);
1076 /// Like `link_region()`, except that the region is extracted from the type of `id`,
1077 /// which must be some reference (`&T`, `&str`, etc).
1078 fn link_region_from_node_type(&self,
1081 mutbl: hir::Mutability,
1082 cmt_borrowed: &mc::cmt_<'tcx>) {
1083 debug!("link_region_from_node_type(id={:?}, mutbl={:?}, cmt_borrowed={:?})",
1084 id, mutbl, cmt_borrowed);
1086 let rptr_ty = self.resolve_node_type(id);
1087 if let ty::TyRef(r, _, _) = rptr_ty.sty {
1088 debug!("rptr_ty={}", rptr_ty);
1089 self.link_region(span, r, ty::BorrowKind::from_mutbl(mutbl), cmt_borrowed);
1093 /// Informs the inference engine that `borrow_cmt` is being borrowed with
1094 /// kind `borrow_kind` and lifetime `borrow_region`.
1095 /// In order to ensure borrowck is satisfied, this may create constraints
1096 /// between regions, as explained in `link_reborrowed_region()`.
1097 fn link_region(&self,
1099 borrow_region: ty::Region<'tcx>,
1100 borrow_kind: ty::BorrowKind,
1101 borrow_cmt: &mc::cmt_<'tcx>) {
1102 let origin = infer::DataBorrowed(borrow_cmt.ty, span);
1103 self.type_must_outlive(origin, borrow_cmt.ty, borrow_region);
1105 let mut borrow_kind = borrow_kind;
1106 let mut borrow_cmt_cat = borrow_cmt.cat.clone();
1109 debug!("link_region(borrow_region={:?}, borrow_kind={:?}, borrow_cmt={:?})",
1113 match borrow_cmt_cat {
1114 Categorization::Deref(ref_cmt, mc::BorrowedPtr(ref_kind, ref_region)) => {
1115 match self.link_reborrowed_region(span,
1116 borrow_region, borrow_kind,
1117 ref_cmt, ref_region, ref_kind,
1120 borrow_cmt_cat = c.cat.clone();
1129 Categorization::Downcast(cmt_base, _) |
1130 Categorization::Deref(cmt_base, mc::Unique) |
1131 Categorization::Interior(cmt_base, _) => {
1132 // Borrowing interior or owned data requires the base
1133 // to be valid and borrowable in the same fashion.
1134 borrow_cmt_cat = cmt_base.cat.clone();
1135 borrow_kind = borrow_kind;
1138 Categorization::Deref(_, mc::UnsafePtr(..)) |
1139 Categorization::StaticItem |
1140 Categorization::Upvar(..) |
1141 Categorization::Local(..) |
1142 Categorization::Rvalue(..) => {
1143 // These are all "base cases" with independent lifetimes
1144 // that are not subject to inference
1151 /// This is the most complicated case: the path being borrowed is
1152 /// itself the referent of a borrowed pointer. Let me give an
1153 /// example fragment of code to make clear(er) the situation:
1155 /// let r: &'a mut T = ...; // the original reference "r" has lifetime 'a
1157 /// &'z *r // the reborrow has lifetime 'z
1159 /// Now, in this case, our primary job is to add the inference
1160 /// constraint that `'z <= 'a`. Given this setup, let's clarify the
1161 /// parameters in (roughly) terms of the example:
1163 /// ```plain,ignore (pseudo-Rust)
1164 /// A borrow of: `& 'z bk * r` where `r` has type `& 'a bk T`
1165 /// borrow_region ^~ ref_region ^~
1166 /// borrow_kind ^~ ref_kind ^~
1170 /// Here `bk` stands for some borrow-kind (e.g., `mut`, `uniq`, etc).
1172 /// Unfortunately, there are some complications beyond the simple
1173 /// scenario I just painted:
1175 /// 1. The reference `r` might in fact be a "by-ref" upvar. In that
1176 /// case, we have two jobs. First, we are inferring whether this reference
1177 /// should be an `&T`, `&mut T`, or `&uniq T` reference, and we must
1178 /// adjust that based on this borrow (e.g., if this is an `&mut` borrow,
1179 /// then `r` must be an `&mut` reference). Second, whenever we link
1180 /// two regions (here, `'z <= 'a`), we supply a *cause*, and in this
1181 /// case we adjust the cause to indicate that the reference being
1182 /// "reborrowed" is itself an upvar. This provides a nicer error message
1183 /// should something go wrong.
1185 /// 2. There may in fact be more levels of reborrowing. In the
1186 /// example, I said the borrow was like `&'z *r`, but it might
1187 /// in fact be a borrow like `&'z **q` where `q` has type `&'a
1188 /// &'b mut T`. In that case, we want to ensure that `'z <= 'a`
1189 /// and `'z <= 'b`. This is explained more below.
1191 /// The return value of this function indicates whether we need to
1192 /// recurse and process `ref_cmt` (see case 2 above).
1193 fn link_reborrowed_region(&self,
1195 borrow_region: ty::Region<'tcx>,
1196 borrow_kind: ty::BorrowKind,
1197 ref_cmt: mc::cmt<'tcx>,
1198 ref_region: ty::Region<'tcx>,
1199 mut ref_kind: ty::BorrowKind,
1201 -> Option<(mc::cmt<'tcx>, ty::BorrowKind)>
1203 // Possible upvar ID we may need later to create an entry in the
1206 // Detect by-ref upvar `x`:
1207 let cause = match note {
1208 mc::NoteUpvarRef(ref upvar_id) => {
1209 match self.tables.borrow().upvar_capture_map.get(upvar_id) {
1210 Some(&ty::UpvarCapture::ByRef(ref upvar_borrow)) => {
1211 // The mutability of the upvar may have been modified
1212 // by the above adjustment, so update our local variable.
1213 ref_kind = upvar_borrow.kind;
1215 infer::ReborrowUpvar(span, *upvar_id)
1218 span_bug!( span, "Illegal upvar id: {:?}", upvar_id);
1222 mc::NoteClosureEnv(ref upvar_id) => {
1223 // We don't have any mutability changes to propagate, but
1224 // we do want to note that an upvar reborrow caused this
1226 infer::ReborrowUpvar(span, *upvar_id)
1229 infer::Reborrow(span)
1233 debug!("link_reborrowed_region: {:?} <= {:?}",
1236 self.sub_regions(cause, borrow_region, ref_region);
1238 // If we end up needing to recurse and establish a region link
1239 // with `ref_cmt`, calculate what borrow kind we will end up
1240 // needing. This will be used below.
1242 // One interesting twist is that we can weaken the borrow kind
1243 // when we recurse: to reborrow an `&mut` referent as mutable,
1244 // borrowck requires a unique path to the `&mut` reference but not
1245 // necessarily a *mutable* path.
1246 let new_borrow_kind = match borrow_kind {
1249 ty::MutBorrow | ty::UniqueImmBorrow =>
1253 // Decide whether we need to recurse and link any regions within
1254 // the `ref_cmt`. This is concerned for the case where the value
1255 // being reborrowed is in fact a borrowed pointer found within
1256 // another borrowed pointer. For example:
1258 // let p: &'b &'a mut T = ...;
1262 // What makes this case particularly tricky is that, if the data
1263 // being borrowed is a `&mut` or `&uniq` borrow, borrowck requires
1264 // not only that `'z <= 'a`, (as before) but also `'z <= 'b`
1265 // (otherwise the user might mutate through the `&mut T` reference
1266 // after `'b` expires and invalidate the borrow we are looking at
1269 // So let's re-examine our parameters in light of this more
1270 // complicated (possible) scenario:
1272 // A borrow of: `& 'z bk * * p` where `p` has type `&'b bk & 'a bk T`
1273 // borrow_region ^~ ref_region ^~
1274 // borrow_kind ^~ ref_kind ^~
1277 // (Note that since we have not examined `ref_cmt.cat`, we don't
1278 // know whether this scenario has occurred; but I wanted to show
1279 // how all the types get adjusted.)
1282 // The reference being reborrowed is a sharable ref of
1283 // type `&'a T`. In this case, it doesn't matter where we
1284 // *found* the `&T` pointer, the memory it references will
1285 // be valid and immutable for `'a`. So we can stop here.
1287 // (Note that the `borrow_kind` must also be ImmBorrow or
1288 // else the user is borrowed imm memory as mut memory,
1289 // which means they'll get an error downstream in borrowck
1294 ty::MutBorrow | ty::UniqueImmBorrow => {
1295 // The reference being reborrowed is either an `&mut T` or
1296 // `&uniq T`. This is the case where recursion is needed.
1297 return Some((ref_cmt, new_borrow_kind));
1302 /// Checks that the values provided for type/region arguments in a given
1303 /// expression are well-formed and in-scope.
1304 fn substs_wf_in_scope(&mut self,
1305 origin: infer::ParameterOrigin,
1306 substs: &Substs<'tcx>,
1308 expr_region: ty::Region<'tcx>) {
1309 debug!("substs_wf_in_scope(substs={:?}, \
1313 substs, expr_region, origin, expr_span);
1315 let origin = infer::ParameterInScope(origin, expr_span);
1317 for region in substs.regions() {
1318 self.sub_regions(origin.clone(), expr_region, region);
1321 for ty in substs.types() {
1322 let ty = self.resolve_type(ty);
1323 self.type_must_outlive(origin.clone(), ty, expr_region);