1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 //! The region check is a final pass that runs over the AST after we have
12 //! inferred the type constraints but before we have actually finalized
13 //! the types. Its purpose is to embed a variety of region constraints.
14 //! Inserting these constraints as a separate pass is good because (1) it
15 //! localizes the code that has to do with region inference and (2) often
16 //! we cannot know what constraints are needed until the basic types have
19 //! ### Interaction with the borrow checker
21 //! In general, the job of the borrowck module (which runs later) is to
22 //! check that all soundness criteria are met, given a particular set of
23 //! regions. The job of *this* module is to anticipate the needs of the
24 //! borrow checker and infer regions that will satisfy its requirements.
25 //! It is generally true that the inference doesn't need to be sound,
26 //! meaning that if there is a bug and we inferred bad regions, the borrow
27 //! checker should catch it. This is not entirely true though; for
28 //! example, the borrow checker doesn't check subtyping, and it doesn't
29 //! check that region pointers are always live when they are used. It
30 //! might be worthwhile to fix this so that borrowck serves as a kind of
31 //! verification step -- that would add confidence in the overall
32 //! correctness of the compiler, at the cost of duplicating some type
33 //! checks and effort.
35 //! ### Inferring the duration of borrows, automatic and otherwise
37 //! Whenever we introduce a borrowed pointer, for example as the result of
38 //! a borrow expression `let x = &data`, the lifetime of the pointer `x`
39 //! is always specified as a region inference variable. `regionck` has the
40 //! job of adding constraints such that this inference variable is as
41 //! narrow as possible while still accommodating all uses (that is, every
42 //! dereference of the resulting pointer must be within the lifetime).
46 //! Generally speaking, `regionck` does NOT try to ensure that the data
47 //! `data` will outlive the pointer `x`. That is the job of borrowck. The
48 //! one exception is when "re-borrowing" the contents of another borrowed
49 //! pointer. For example, imagine you have a borrowed pointer `b` with
50 //! lifetime L1 and you have an expression `&*b`. The result of this
51 //! expression will be another borrowed pointer with lifetime L2 (which is
52 //! an inference variable). The borrow checker is going to enforce the
53 //! constraint that L2 < L1, because otherwise you are re-borrowing data
54 //! for a lifetime larger than the original loan. However, without the
55 //! routines in this module, the region inferencer would not know of this
56 //! dependency and thus it might infer the lifetime of L2 to be greater
57 //! than L1 (issue #3148).
59 //! There are a number of troublesome scenarios in the tests
60 //! `region-dependent-*.rs`, but here is one example:
62 //! struct Foo { i: i32 }
63 //! struct Bar { foo: Foo }
64 //! fn get_i<'a>(x: &'a Bar) -> &'a i32 {
65 //! let foo = &x.foo; // Lifetime L1
66 //! &foo.i // Lifetime L2
69 //! Note that this comes up either with `&` expressions, `ref`
70 //! bindings, and `autorefs`, which are the three ways to introduce
73 //! The key point here is that when you are borrowing a value that
74 //! is "guaranteed" by a borrowed pointer, you must link the
75 //! lifetime of that borrowed pointer (L1, here) to the lifetime of
76 //! the borrow itself (L2). What do I mean by "guaranteed" by a
77 //! borrowed pointer? I mean any data that is reached by first
78 //! dereferencing a borrowed pointer and then either traversing
79 //! interior offsets or boxes. We say that the guarantor
80 //! of such data is the region of the borrowed pointer that was
81 //! traversed. This is essentially the same as the ownership
82 //! relation, except that a borrowed pointer never owns its
87 use middle
::free_region
::FreeRegionMap
;
88 use middle
::mem_categorization
as mc
;
89 use middle
::mem_categorization
::Categorization
;
90 use middle
::region
::{self, CodeExtent}
;
91 use rustc
::ty
::subst
::Substs
;
93 use rustc
::ty
::{self, Ty, MethodCall, TypeFoldable}
;
94 use rustc
::infer
::{self, GenericKind, SubregionOrigin, VerifyBound}
;
95 use rustc
::ty
::adjustment
;
96 use rustc
::ty
::wf
::ImpliedBound
;
101 use syntax_pos
::Span
;
102 use rustc
::hir
::intravisit
::{self, Visitor, NestedVisitorMap}
;
103 use rustc
::hir
::{self, PatKind}
;
105 use self::SubjectNode
::Subject
;
107 // a variation on try that just returns unit
108 macro_rules
! ignore_err
{
109 ($e
:expr
) => (match $e { Ok(e) => e, Err(_) => return () }
)
112 ///////////////////////////////////////////////////////////////////////////
113 // PUBLIC ENTRY POINTS
115 impl<'a
, 'gcx
, 'tcx
> FnCtxt
<'a
, 'gcx
, 'tcx
> {
116 pub fn regionck_expr(&self, body
: &'gcx hir
::Body
) {
117 let id
= body
.value
.id
;
118 let mut rcx
= RegionCtxt
::new(self, RepeatingScope(id
), id
, Subject(id
));
119 if self.err_count_since_creation() == 0 {
120 // regionck assumes typeck succeeded
121 rcx
.visit_body(body
);
122 rcx
.visit_region_obligations(id
);
124 rcx
.resolve_regions_and_report_errors();
127 /// Region checking during the WF phase for items. `wf_tys` are the
128 /// types from which we should derive implied bounds, if any.
129 pub fn regionck_item(&self,
130 item_id
: ast
::NodeId
,
132 wf_tys
: &[Ty
<'tcx
>]) {
133 debug
!("regionck_item(item.id={:?}, wf_tys={:?}", item_id
, wf_tys
);
134 let mut rcx
= RegionCtxt
::new(self, RepeatingScope(item_id
), item_id
, Subject(item_id
));
135 rcx
.free_region_map
.relate_free_regions_from_predicates(
136 &self.parameter_environment
.caller_bounds
);
137 rcx
.relate_free_regions(wf_tys
, item_id
, span
);
138 rcx
.visit_region_obligations(item_id
);
139 rcx
.resolve_regions_and_report_errors();
142 pub fn regionck_fn(&self,
144 body
: &'gcx hir
::Body
) {
145 debug
!("regionck_fn(id={})", fn_id
);
146 let node_id
= body
.value
.id
;
147 let mut rcx
= RegionCtxt
::new(self, RepeatingScope(node_id
), node_id
, Subject(fn_id
));
149 if self.err_count_since_creation() == 0 {
150 // regionck assumes typeck succeeded
151 rcx
.visit_fn_body(fn_id
, body
, self.tcx
.hir
.span(fn_id
));
154 rcx
.free_region_map
.relate_free_regions_from_predicates(
155 &self.parameter_environment
.caller_bounds
);
157 rcx
.resolve_regions_and_report_errors();
159 // For the top-level fn, store the free-region-map. We don't store
160 // any map for closures; they just share the same map as the
161 // function that created them.
162 self.tcx
.store_free_region_map(fn_id
, rcx
.free_region_map
);
166 ///////////////////////////////////////////////////////////////////////////
169 pub struct RegionCtxt
<'a
, 'gcx
: 'a
+'tcx
, 'tcx
: 'a
> {
170 pub fcx
: &'a FnCtxt
<'a
, 'gcx
, 'tcx
>,
172 region_bound_pairs
: Vec
<(&'tcx ty
::Region
, GenericKind
<'tcx
>)>,
174 free_region_map
: FreeRegionMap
,
176 // id of innermost fn body id
177 body_id
: ast
::NodeId
,
179 // call_site scope of innermost fn
180 call_site_scope
: Option
<CodeExtent
>,
182 // id of innermost fn or loop
183 repeating_scope
: ast
::NodeId
,
185 // id of AST node being analyzed (the subject of the analysis).
186 subject
: SubjectNode
,
190 impl<'a
, 'gcx
, 'tcx
> Deref
for RegionCtxt
<'a
, 'gcx
, 'tcx
> {
191 type Target
= FnCtxt
<'a
, 'gcx
, 'tcx
>;
192 fn deref(&self) -> &Self::Target
{
197 pub struct RepeatingScope(ast
::NodeId
);
198 pub enum SubjectNode { Subject(ast::NodeId), None }
200 impl<'a
, 'gcx
, 'tcx
> RegionCtxt
<'a
, 'gcx
, 'tcx
> {
201 pub fn new(fcx
: &'a FnCtxt
<'a
, 'gcx
, 'tcx
>,
202 initial_repeating_scope
: RepeatingScope
,
203 initial_body_id
: ast
::NodeId
,
204 subject
: SubjectNode
) -> RegionCtxt
<'a
, 'gcx
, 'tcx
> {
205 let RepeatingScope(initial_repeating_scope
) = initial_repeating_scope
;
208 repeating_scope
: initial_repeating_scope
,
209 body_id
: initial_body_id
,
210 call_site_scope
: None
,
212 region_bound_pairs
: Vec
::new(),
213 free_region_map
: FreeRegionMap
::new(),
217 fn set_call_site_scope(&mut self, call_site_scope
: Option
<CodeExtent
>) -> Option
<CodeExtent
> {
218 mem
::replace(&mut self.call_site_scope
, call_site_scope
)
221 fn set_body_id(&mut self, body_id
: ast
::NodeId
) -> ast
::NodeId
{
222 mem
::replace(&mut self.body_id
, body_id
)
225 fn set_repeating_scope(&mut self, scope
: ast
::NodeId
) -> ast
::NodeId
{
226 mem
::replace(&mut self.repeating_scope
, scope
)
229 /// Try to resolve the type for the given node, returning t_err if an error results. Note that
230 /// we never care about the details of the error, the same error will be detected and reported
231 /// in the writeback phase.
233 /// Note one important point: we do not attempt to resolve *region variables* here. This is
234 /// because regionck is essentially adding constraints to those region variables and so may yet
235 /// influence how they are resolved.
237 /// Consider this silly example:
240 /// fn borrow(x: &i32) -> &i32 {x}
241 /// fn foo(x: @i32) -> i32 { // block: B
242 /// let b = borrow(x); // region: <R0>
247 /// Here, the region of `b` will be `<R0>`. `<R0>` is constrained to be some subregion of the
248 /// block B and some superregion of the call. If we forced it now, we'd choose the smaller
249 /// region (the call). But that would make the *b illegal. Since we don't resolve, the type
250 /// of b will be `&<R0>.i32` and then `*b` will require that `<R0>` be bigger than the let and
251 /// the `*b` expression, so we will effectively resolve `<R0>` to be the block B.
252 pub fn resolve_type(&self, unresolved_ty
: Ty
<'tcx
>) -> Ty
<'tcx
> {
253 self.resolve_type_vars_if_possible(&unresolved_ty
)
256 /// Try to resolve the type for the given node.
257 fn resolve_node_type(&self, id
: ast
::NodeId
) -> Ty
<'tcx
> {
258 let t
= self.node_ty(id
);
262 /// Try to resolve the type for the given node.
263 pub fn resolve_expr_type_adjusted(&mut self, expr
: &hir
::Expr
) -> Ty
<'tcx
> {
264 let ty
= self.tables
.borrow().expr_ty_adjusted(expr
);
265 self.resolve_type(ty
)
268 fn visit_fn_body(&mut self,
269 id
: ast
::NodeId
, // the id of the fn itself
270 body
: &'gcx hir
::Body
,
273 // When we enter a function, we can derive
274 debug
!("visit_fn_body(id={})", id
);
276 let body_id
= body
.id();
278 let call_site
= self.tcx
.region_maps
.lookup_code_extent(
279 region
::CodeExtentData
::CallSiteScope { fn_id: id, body_id: body_id.node_id }
);
280 let old_call_site_scope
= self.set_call_site_scope(Some(call_site
));
283 let fn_sig_map
= &self.tables
.borrow().liberated_fn_sigs
;
284 match fn_sig_map
.get(&id
) {
285 Some(f
) => f
.clone(),
287 bug
!("No fn-sig entry for id={}", id
);
292 let old_region_bounds_pairs_len
= self.region_bound_pairs
.len();
294 // Collect the types from which we create inferred bounds.
295 // For the return type, if diverging, substitute `bool` just
296 // because it will have no effect.
298 // FIXME(#27579) return types should not be implied bounds
299 let fn_sig_tys
: Vec
<_
> =
300 fn_sig
.inputs().iter().cloned().chain(Some(fn_sig
.output())).collect();
302 let old_body_id
= self.set_body_id(body_id
.node_id
);
303 self.relate_free_regions(&fn_sig_tys
[..], body_id
.node_id
, span
);
304 self.link_fn_args(self.tcx
.region_maps
.node_extent(body_id
.node_id
), &body
.arguments
);
305 self.visit_body(body
);
306 self.visit_region_obligations(body_id
.node_id
);
308 let call_site_scope
= self.call_site_scope
.unwrap();
309 debug
!("visit_fn_body body.id {:?} call_site_scope: {:?}",
310 body
.id(), call_site_scope
);
311 let call_site_region
= self.tcx
.mk_region(ty
::ReScope(call_site_scope
));
312 self.type_of_node_must_outlive(infer
::CallReturn(span
),
316 self.region_bound_pairs
.truncate(old_region_bounds_pairs_len
);
318 self.set_body_id(old_body_id
);
319 self.set_call_site_scope(old_call_site_scope
);
322 fn visit_region_obligations(&mut self, node_id
: ast
::NodeId
)
324 debug
!("visit_region_obligations: node_id={}", node_id
);
326 // region checking can introduce new pending obligations
327 // which, when processed, might generate new region
328 // obligations. So make sure we process those.
329 self.select_all_obligations_or_error();
331 // Make a copy of the region obligations vec because we'll need
332 // to be able to borrow the fulfillment-cx below when projecting.
333 let region_obligations
=
336 .region_obligations(node_id
)
339 for r_o
in ®ion_obligations
{
340 debug
!("visit_region_obligations: r_o={:?} cause={:?}",
342 let sup_type
= self.resolve_type(r_o
.sup_type
);
343 let origin
= self.code_to_origin(&r_o
.cause
, sup_type
);
344 self.type_must_outlive(origin
, sup_type
, r_o
.sub_region
);
347 // Processing the region obligations should not cause the list to grow further:
348 assert_eq
!(region_obligations
.len(),
349 self.fulfillment_cx
.borrow().region_obligations(node_id
).len());
352 fn code_to_origin(&self,
353 cause
: &traits
::ObligationCause
<'tcx
>,
355 -> SubregionOrigin
<'tcx
> {
356 SubregionOrigin
::from_obligation_cause(cause
,
357 || infer
::RelateParamBound(cause
.span
, sup_type
))
360 /// This method populates the region map's `free_region_map`. It walks over the transformed
361 /// argument and return types for each function just before we check the body of that function,
362 /// looking for types where you have a borrowed pointer to other borrowed data (e.g., `&'a &'b
363 /// [usize]`. We do not allow references to outlive the things they point at, so we can assume
364 /// that `'a <= 'b`. This holds for both the argument and return types, basically because, on
365 /// the caller side, the caller is responsible for checking that the type of every expression
366 /// (including the actual values for the arguments, as well as the return type of the fn call)
369 /// Tests: `src/test/compile-fail/regions-free-region-ordering-*.rs`
370 fn relate_free_regions(&mut self,
371 fn_sig_tys
: &[Ty
<'tcx
>],
372 body_id
: ast
::NodeId
,
374 debug
!("relate_free_regions >>");
376 for &ty
in fn_sig_tys
{
377 let ty
= self.resolve_type(ty
);
378 debug
!("relate_free_regions(t={:?})", ty
);
379 let implied_bounds
= ty
::wf
::implied_bounds(self, body_id
, ty
, span
);
381 // Record any relations between free regions that we observe into the free-region-map.
382 self.free_region_map
.relate_free_regions_from_implied_bounds(&implied_bounds
);
384 // But also record other relationships, such as `T:'x`,
385 // that don't go into the free-region-map but which we use
387 for implication
in implied_bounds
{
388 debug
!("implication: {:?}", implication
);
390 ImpliedBound
::RegionSubRegion(&ty
::ReFree(free_a
),
391 &ty
::ReVar(vid_b
)) => {
392 self.add_given(free_a
, vid_b
);
394 ImpliedBound
::RegionSubParam(r_a
, param_b
) => {
395 self.region_bound_pairs
.push((r_a
, GenericKind
::Param(param_b
)));
397 ImpliedBound
::RegionSubProjection(r_a
, projection_b
) => {
398 self.region_bound_pairs
.push((r_a
, GenericKind
::Projection(projection_b
)));
400 ImpliedBound
::RegionSubRegion(..) => {
401 // In principle, we could record (and take
402 // advantage of) every relationship here, but
403 // we are also free not to -- it simply means
404 // strictly less that we can successfully type
405 // check. (It may also be that we should
406 // revise our inference system to be more
407 // general and to make use of *every*
408 // relationship that arises here, but
409 // presently we do not.)
415 debug
!("<< relate_free_regions");
418 fn resolve_regions_and_report_errors(&self) {
419 let subject_node_id
= match self.subject
{
421 SubjectNode
::None
=> {
422 bug
!("cannot resolve_regions_and_report_errors \
423 without subject node");
427 self.fcx
.resolve_regions_and_report_errors(&self.free_region_map
,
431 fn constrain_bindings_in_pat(&mut self, pat
: &hir
::Pat
) {
433 debug
!("regionck::visit_pat(pat={:?})", pat
);
434 pat
.each_binding(|_
, id
, span
, _
| {
435 // If we have a variable that contains region'd data, that
436 // data will be accessible from anywhere that the variable is
437 // accessed. We must be wary of loops like this:
439 // // from src/test/compile-fail/borrowck-lend-flow.rs
440 // let mut v = box 3, w = box 4;
441 // let mut x = &mut w;
444 // borrow(v); //~ ERROR cannot borrow
445 // x = &mut v; // (1)
448 // Typically, we try to determine the region of a borrow from
449 // those points where it is dereferenced. In this case, one
450 // might imagine that the lifetime of `x` need only be the
451 // body of the loop. But of course this is incorrect because
452 // the pointer that is created at point (1) is consumed at
453 // point (2), meaning that it must be live across the loop
454 // iteration. The easiest way to guarantee this is to require
455 // that the lifetime of any regions that appear in a
456 // variable's type enclose at least the variable's scope.
458 let var_scope
= tcx
.region_maps
.var_scope(id
);
459 let var_region
= self.tcx
.mk_region(ty
::ReScope(var_scope
));
461 let origin
= infer
::BindingTypeIsNotValidAtDecl(span
);
462 self.type_of_node_must_outlive(origin
, id
, var_region
);
464 let typ
= self.resolve_node_type(id
);
465 dropck
::check_safety_of_destructor_if_necessary(self, typ
, span
, var_scope
);
470 impl<'a
, 'gcx
, 'tcx
> Visitor
<'gcx
> for RegionCtxt
<'a
, 'gcx
, 'tcx
> {
471 // (..) FIXME(#3238) should use visit_pat, not visit_arm/visit_local,
472 // However, right now we run into an issue whereby some free
473 // regions are not properly related if they appear within the
474 // types of arguments that must be inferred. This could be
475 // addressed by deferring the construction of the region
476 // hierarchy, and in particular the relationships between free
477 // regions, until regionck, as described in #3238.
479 fn nested_visit_map
<'this
>(&'this
mut self) -> NestedVisitorMap
<'this
, 'gcx
> {
480 NestedVisitorMap
::None
483 fn visit_fn(&mut self, _fk
: intravisit
::FnKind
<'gcx
>, _
: &'gcx hir
::FnDecl
,
484 b
: hir
::BodyId
, span
: Span
, id
: ast
::NodeId
) {
485 let body
= self.tcx
.hir
.body(b
);
486 self.visit_fn_body(id
, body
, span
)
489 //visit_pat: visit_pat, // (..) see above
491 fn visit_arm(&mut self, arm
: &'gcx hir
::Arm
) {
494 self.constrain_bindings_in_pat(p
);
496 intravisit
::walk_arm(self, arm
);
499 fn visit_local(&mut self, l
: &'gcx hir
::Local
) {
501 self.constrain_bindings_in_pat(&l
.pat
);
503 intravisit
::walk_local(self, l
);
506 fn visit_expr(&mut self, expr
: &'gcx hir
::Expr
) {
507 debug
!("regionck::visit_expr(e={:?}, repeating_scope={})",
508 expr
, self.repeating_scope
);
510 // No matter what, the type of each expression must outlive the
511 // scope of that expression. This also guarantees basic WF.
512 let expr_ty
= self.resolve_node_type(expr
.id
);
513 // the region corresponding to this expression
514 let expr_region
= self.tcx
.node_scope_region(expr
.id
);
515 self.type_must_outlive(infer
::ExprTypeIsNotInScope(expr_ty
, expr
.span
),
516 expr_ty
, expr_region
);
518 let method_call
= MethodCall
::expr(expr
.id
);
519 let opt_method_callee
= self.tables
.borrow().method_map
.get(&method_call
).cloned();
520 let has_method_map
= opt_method_callee
.is_some();
522 // If we are calling a method (either explicitly or via an
523 // overloaded operator), check that all of the types provided as
524 // arguments for its type parameters are well-formed, and all the regions
525 // provided as arguments outlive the call.
526 if let Some(callee
) = opt_method_callee
{
527 let origin
= match expr
.node
{
528 hir
::ExprMethodCall(..) =>
529 infer
::ParameterOrigin
::MethodCall
,
530 hir
::ExprUnary(op
, _
) if op
== hir
::UnDeref
=>
531 infer
::ParameterOrigin
::OverloadedDeref
,
533 infer
::ParameterOrigin
::OverloadedOperator
536 self.substs_wf_in_scope(origin
, &callee
.substs
, expr
.span
, expr_region
);
537 self.type_must_outlive(infer
::ExprTypeIsNotInScope(callee
.ty
, expr
.span
),
538 callee
.ty
, expr_region
);
541 // Check any autoderefs or autorefs that appear.
542 let adjustment
= self.tables
.borrow().adjustments
.get(&expr
.id
).map(|a
| a
.clone());
543 if let Some(adjustment
) = adjustment
{
544 debug
!("adjustment={:?}", adjustment
);
545 match adjustment
.kind
{
546 adjustment
::Adjust
::DerefRef { autoderefs, ref autoref, .. }
=> {
547 let expr_ty
= self.resolve_node_type(expr
.id
);
548 self.constrain_autoderefs(expr
, autoderefs
, expr_ty
);
549 if let Some(ref autoref
) = *autoref
{
550 self.link_autoref(expr
, autoderefs
, autoref
);
552 // Require that the resulting region encompasses
555 // FIXME(#6268) remove to support nested method calls
556 self.type_of_node_must_outlive(infer
::AutoBorrow(expr
.span
),
557 expr
.id
, expr_region
);
561 adjustment::AutoObject(_, ref bounds, ..) => {
562 // Determine if we are casting `expr` to a trait
563 // instance. If so, we have to be sure that the type
564 // of the source obeys the new region bound.
565 let source_ty = self.resolve_node_type(expr.id);
566 self.type_must_outlive(infer::RelateObjectBound(expr.span),
567 source_ty, bounds.region_bound);
573 // If necessary, constrain destructors in the unadjusted form of this
576 let mc
= mc
::MemCategorizationContext
::new(self);
577 mc
.cat_expr_unadjusted(expr
)
581 self.check_safety_of_rvalue_destructor_if_necessary(head_cmt
,
585 self.tcx
.sess
.delay_span_bug(expr
.span
, "cat_expr_unadjusted Errd");
590 // If necessary, constrain destructors in this expression. This will be
591 // the adjusted form if there is an adjustment.
593 let mc
= mc
::MemCategorizationContext
::new(self);
598 self.check_safety_of_rvalue_destructor_if_necessary(head_cmt
, expr
.span
);
601 self.tcx
.sess
.delay_span_bug(expr
.span
, "cat_expr Errd");
605 debug
!("regionck::visit_expr(e={:?}, repeating_scope={}) - visiting subexprs",
606 expr
, self.repeating_scope
);
608 hir
::ExprPath(_
) => {
609 self.fcx
.opt_node_ty_substs(expr
.id
, |item_substs
| {
610 let origin
= infer
::ParameterOrigin
::Path
;
611 self.substs_wf_in_scope(origin
, &item_substs
.substs
, expr
.span
, expr_region
);
615 hir
::ExprCall(ref callee
, ref args
) => {
617 self.constrain_call(expr
, Some(&callee
),
618 args
.iter().map(|e
| &*e
), false);
620 self.constrain_callee(callee
.id
, expr
, &callee
);
621 self.constrain_call(expr
, None
,
622 args
.iter().map(|e
| &*e
), false);
625 intravisit
::walk_expr(self, expr
);
628 hir
::ExprMethodCall(.., ref args
) => {
629 self.constrain_call(expr
, Some(&args
[0]),
630 args
[1..].iter().map(|e
| &*e
), false);
632 intravisit
::walk_expr(self, expr
);
635 hir
::ExprAssignOp(_
, ref lhs
, ref rhs
) => {
637 self.constrain_call(expr
, Some(&lhs
),
638 Some(&**rhs
).into_iter(), false);
641 intravisit
::walk_expr(self, expr
);
644 hir
::ExprIndex(ref lhs
, ref rhs
) if has_method_map
=> {
645 self.constrain_call(expr
, Some(&lhs
),
646 Some(&**rhs
).into_iter(), true);
648 intravisit
::walk_expr(self, expr
);
651 hir
::ExprBinary(op
, ref lhs
, ref rhs
) if has_method_map
=> {
652 let implicitly_ref_args
= !op
.node
.is_by_value();
654 // As `expr_method_call`, but the call is via an
655 // overloaded op. Note that we (sadly) currently use an
656 // implicit "by ref" sort of passing style here. This
657 // should be converted to an adjustment!
658 self.constrain_call(expr
, Some(&lhs
),
659 Some(&**rhs
).into_iter(), implicitly_ref_args
);
661 intravisit
::walk_expr(self, expr
);
664 hir
::ExprBinary(_
, ref lhs
, ref rhs
) => {
665 // If you do `x OP y`, then the types of `x` and `y` must
666 // outlive the operation you are performing.
667 let lhs_ty
= self.resolve_expr_type_adjusted(&lhs
);
668 let rhs_ty
= self.resolve_expr_type_adjusted(&rhs
);
669 for &ty
in &[lhs_ty
, rhs_ty
] {
670 self.type_must_outlive(infer
::Operand(expr
.span
),
673 intravisit
::walk_expr(self, expr
);
676 hir
::ExprUnary(op
, ref lhs
) if has_method_map
=> {
677 let implicitly_ref_args
= !op
.is_by_value();
680 self.constrain_call(expr
, Some(&lhs
),
681 None
::<hir
::Expr
>.iter(), implicitly_ref_args
);
683 intravisit
::walk_expr(self, expr
);
686 hir
::ExprUnary(hir
::UnDeref
, ref base
) => {
687 // For *a, the lifetime of a must enclose the deref
688 let method_call
= MethodCall
::expr(expr
.id
);
689 let base_ty
= match self.tables
.borrow().method_map
.get(&method_call
) {
691 self.constrain_call(expr
, Some(&base
),
692 None
::<hir
::Expr
>.iter(), true);
693 // late-bound regions in overloaded method calls are instantiated
694 let fn_ret
= self.tcx
.no_late_bound_regions(&method
.ty
.fn_ret());
697 None
=> self.resolve_node_type(base
.id
)
699 if let ty
::TyRef(r_ptr
, _
) = base_ty
.sty
{
700 self.mk_subregion_due_to_dereference(expr
.span
, expr_region
, r_ptr
);
703 intravisit
::walk_expr(self, expr
);
706 hir
::ExprIndex(ref vec_expr
, _
) => {
707 // For a[b], the lifetime of a must enclose the deref
708 let vec_type
= self.resolve_expr_type_adjusted(&vec_expr
);
709 self.constrain_index(expr
, vec_type
);
711 intravisit
::walk_expr(self, expr
);
714 hir
::ExprCast(ref source
, _
) => {
715 // Determine if we are casting `source` to a trait
716 // instance. If so, we have to be sure that the type of
717 // the source obeys the trait's region bound.
718 self.constrain_cast(expr
, &source
);
719 intravisit
::walk_expr(self, expr
);
722 hir
::ExprAddrOf(m
, ref base
) => {
723 self.link_addr_of(expr
, m
, &base
);
725 // Require that when you write a `&expr` expression, the
726 // resulting pointer has a lifetime that encompasses the
727 // `&expr` expression itself. Note that we constraining
728 // the type of the node expr.id here *before applying
731 // FIXME(#6268) nested method calls requires that this rule change
732 let ty0
= self.resolve_node_type(expr
.id
);
733 self.type_must_outlive(infer
::AddrOf(expr
.span
), ty0
, expr_region
);
734 intravisit
::walk_expr(self, expr
);
737 hir
::ExprMatch(ref discr
, ref arms
, _
) => {
738 self.link_match(&discr
, &arms
[..]);
740 intravisit
::walk_expr(self, expr
);
743 hir
::ExprClosure(.., body_id
, _
) => {
744 self.check_expr_fn_block(expr
, body_id
);
747 hir
::ExprLoop(ref body
, _
, _
) => {
748 let repeating_scope
= self.set_repeating_scope(body
.id
);
749 intravisit
::walk_expr(self, expr
);
750 self.set_repeating_scope(repeating_scope
);
753 hir
::ExprWhile(ref cond
, ref body
, _
) => {
754 let repeating_scope
= self.set_repeating_scope(cond
.id
);
755 self.visit_expr(&cond
);
757 self.set_repeating_scope(body
.id
);
758 self.visit_block(&body
);
760 self.set_repeating_scope(repeating_scope
);
763 hir
::ExprRet(Some(ref ret_expr
)) => {
764 let call_site_scope
= self.call_site_scope
;
765 debug
!("visit_expr ExprRet ret_expr.id {} call_site_scope: {:?}",
766 ret_expr
.id
, call_site_scope
);
767 let call_site_region
= self.tcx
.mk_region(ty
::ReScope(call_site_scope
.unwrap()));
768 self.type_of_node_must_outlive(infer
::CallReturn(ret_expr
.span
),
771 intravisit
::walk_expr(self, expr
);
775 intravisit
::walk_expr(self, expr
);
781 impl<'a
, 'gcx
, 'tcx
> RegionCtxt
<'a
, 'gcx
, 'tcx
> {
782 fn constrain_cast(&mut self,
783 cast_expr
: &hir
::Expr
,
784 source_expr
: &hir
::Expr
)
786 debug
!("constrain_cast(cast_expr={:?}, source_expr={:?})",
790 let source_ty
= self.resolve_node_type(source_expr
.id
);
791 let target_ty
= self.resolve_node_type(cast_expr
.id
);
793 self.walk_cast(cast_expr
, source_ty
, target_ty
);
796 fn walk_cast(&mut self,
797 cast_expr
: &hir
::Expr
,
800 debug
!("walk_cast(from_ty={:?}, to_ty={:?})",
803 match (&from_ty
.sty
, &to_ty
.sty
) {
804 /*From:*/ (&ty
::TyRef(from_r
, ref from_mt
),
805 /*To: */ &ty
::TyRef(to_r
, ref to_mt
)) => {
806 // Target cannot outlive source, naturally.
807 self.sub_regions(infer
::Reborrow(cast_expr
.span
), to_r
, from_r
);
808 self.walk_cast(cast_expr
, from_mt
.ty
, to_mt
.ty
);
812 /*To: */ &ty
::TyDynamic(.., r
)) => {
813 // When T is existentially quantified as a trait
814 // `Foo+'to`, it must outlive the region bound `'to`.
815 self.type_must_outlive(infer
::RelateObjectBound(cast_expr
.span
), from_ty
, r
);
818 /*From:*/ (&ty
::TyAdt(from_def
, _
),
819 /*To: */ &ty
::TyAdt(to_def
, _
)) if from_def
.is_box() && to_def
.is_box() => {
820 self.walk_cast(cast_expr
, from_ty
.boxed_ty(), to_ty
.boxed_ty());
827 fn check_expr_fn_block(&mut self,
828 expr
: &'gcx hir
::Expr
,
829 body_id
: hir
::BodyId
) {
830 let repeating_scope
= self.set_repeating_scope(body_id
.node_id
);
831 intravisit
::walk_expr(self, expr
);
832 self.set_repeating_scope(repeating_scope
);
835 fn constrain_callee(&mut self,
836 callee_id
: ast
::NodeId
,
837 _call_expr
: &hir
::Expr
,
838 _callee_expr
: &hir
::Expr
) {
839 let callee_ty
= self.resolve_node_type(callee_id
);
840 match callee_ty
.sty
{
841 ty
::TyFnDef(..) | ty
::TyFnPtr(_
) => { }
843 // this should not happen, but it does if the program is
848 // "Calling non-function: {}",
854 fn constrain_call
<'b
, I
: Iterator
<Item
=&'b hir
::Expr
>>(&mut self,
855 call_expr
: &hir
::Expr
,
856 receiver
: Option
<&hir
::Expr
>,
858 implicitly_ref_args
: bool
) {
859 //! Invoked on every call site (i.e., normal calls, method calls,
860 //! and overloaded operators). Constrains the regions which appear
861 //! in the type of the function. Also constrains the regions that
862 //! appear in the arguments appropriately.
864 debug
!("constrain_call(call_expr={:?}, \
866 implicitly_ref_args={})",
869 implicitly_ref_args
);
871 // `callee_region` is the scope representing the time in which the
874 // FIXME(#6268) to support nested method calls, should be callee_id
875 let callee_scope
= self.tcx
.region_maps
.node_extent(call_expr
.id
);
876 let callee_region
= self.tcx
.mk_region(ty
::ReScope(callee_scope
));
878 debug
!("callee_region={:?}", callee_region
);
880 for arg_expr
in arg_exprs
{
881 debug
!("Argument: {:?}", arg_expr
);
883 // ensure that any regions appearing in the argument type are
884 // valid for at least the lifetime of the function:
885 self.type_of_node_must_outlive(infer
::CallArg(arg_expr
.span
),
886 arg_expr
.id
, callee_region
);
888 // unfortunately, there are two means of taking implicit
889 // references, and we need to propagate constraints as a
890 // result. modes are going away and the "DerefArgs" code
891 // should be ported to use adjustments
892 if implicitly_ref_args
{
893 self.link_by_ref(arg_expr
, callee_scope
);
897 // as loop above, but for receiver
898 if let Some(r
) = receiver
{
899 debug
!("receiver: {:?}", r
);
900 self.type_of_node_must_outlive(infer
::CallRcvr(r
.span
),
901 r
.id
, callee_region
);
902 if implicitly_ref_args
{
903 self.link_by_ref(&r
, callee_scope
);
908 /// Invoked on any auto-dereference that occurs. Checks that if this is a region pointer being
909 /// dereferenced, the lifetime of the pointer includes the deref expr.
910 fn constrain_autoderefs(&mut self,
911 deref_expr
: &hir
::Expr
,
913 mut derefd_ty
: Ty
<'tcx
>)
915 debug
!("constrain_autoderefs(deref_expr={:?}, derefs={}, derefd_ty={:?})",
920 let r_deref_expr
= self.tcx
.node_scope_region(deref_expr
.id
);
922 let method_call
= MethodCall
::autoderef(deref_expr
.id
, i
as u32);
923 debug
!("constrain_autoderefs: method_call={:?} (of {:?} total)", method_call
, derefs
);
925 let method
= self.tables
.borrow().method_map
.get(&method_call
).map(|m
| m
.clone());
927 derefd_ty
= match method
{
929 debug
!("constrain_autoderefs: #{} is overloaded, method={:?}",
932 let origin
= infer
::ParameterOrigin
::OverloadedDeref
;
933 self.substs_wf_in_scope(origin
, method
.substs
, deref_expr
.span
, r_deref_expr
);
935 // Treat overloaded autoderefs as if an AutoBorrow adjustment
936 // was applied on the base type, as that is always the case.
937 let fn_sig
= method
.ty
.fn_sig();
938 let fn_sig
= // late-bound regions should have been instantiated
939 self.tcx
.no_late_bound_regions(fn_sig
).unwrap();
940 let self_ty
= fn_sig
.inputs()[0];
941 let (m
, r
) = match self_ty
.sty
{
942 ty
::TyRef(r
, ref m
) => (m
.mutbl
, r
),
946 "bad overloaded deref type {:?}",
951 debug
!("constrain_autoderefs: receiver r={:?} m={:?}",
955 let mc
= mc
::MemCategorizationContext
::new(self);
956 let self_cmt
= ignore_err
!(mc
.cat_expr_autoderefd(deref_expr
, i
));
957 debug
!("constrain_autoderefs: self_cmt={:?}",
959 self.link_region(deref_expr
.span
, r
,
960 ty
::BorrowKind
::from_mutbl(m
), self_cmt
);
963 // Specialized version of constrain_call.
964 self.type_must_outlive(infer
::CallRcvr(deref_expr
.span
),
965 self_ty
, r_deref_expr
);
966 self.type_must_outlive(infer
::CallReturn(deref_expr
.span
),
967 fn_sig
.output(), r_deref_expr
);
973 if let ty
::TyRef(r_ptr
, _
) = derefd_ty
.sty
{
974 self.mk_subregion_due_to_dereference(deref_expr
.span
,
975 r_deref_expr
, r_ptr
);
978 match derefd_ty
.builtin_deref(true, ty
::NoPreference
) {
979 Some(mt
) => derefd_ty
= mt
.ty
,
980 /* if this type can't be dereferenced, then there's already an error
981 in the session saying so. Just bail out for now */
987 pub fn mk_subregion_due_to_dereference(&mut self,
989 minimum_lifetime
: &'tcx ty
::Region
,
990 maximum_lifetime
: &'tcx ty
::Region
) {
991 self.sub_regions(infer
::DerefPointer(deref_span
),
992 minimum_lifetime
, maximum_lifetime
)
995 fn check_safety_of_rvalue_destructor_if_necessary(&mut self,
999 Categorization
::Rvalue(region
, _
) => {
1001 ty
::ReScope(rvalue_scope
) => {
1002 let typ
= self.resolve_type(cmt
.ty
);
1003 dropck
::check_safety_of_destructor_if_necessary(self,
1011 "unexpected rvalue region in rvalue \
1012 destructor safety checking: `{:?}`",
1021 /// Invoked on any index expression that occurs. Checks that if this is a slice
1022 /// being indexed, the lifetime of the pointer includes the deref expr.
1023 fn constrain_index(&mut self,
1024 index_expr
: &hir
::Expr
,
1025 indexed_ty
: Ty
<'tcx
>)
1027 debug
!("constrain_index(index_expr=?, indexed_ty={}",
1028 self.ty_to_string(indexed_ty
));
1030 let r_index_expr
= ty
::ReScope(self.tcx
.region_maps
.node_extent(index_expr
.id
));
1031 if let ty
::TyRef(r_ptr
, mt
) = indexed_ty
.sty
{
1033 ty
::TySlice(_
) | ty
::TyStr
=> {
1034 self.sub_regions(infer
::IndexSlice(index_expr
.span
),
1035 self.tcx
.mk_region(r_index_expr
), r_ptr
);
1042 /// Guarantees that any lifetimes which appear in the type of the node `id` (after applying
1043 /// adjustments) are valid for at least `minimum_lifetime`
1044 fn type_of_node_must_outlive(&mut self,
1045 origin
: infer
::SubregionOrigin
<'tcx
>,
1047 minimum_lifetime
: &'tcx ty
::Region
)
1049 // Try to resolve the type. If we encounter an error, then typeck
1050 // is going to fail anyway, so just stop here and let typeck
1051 // report errors later on in the writeback phase.
1052 let ty0
= self.resolve_node_type(id
);
1053 let ty
= self.tables
.borrow().adjustments
.get(&id
).map_or(ty0
, |adj
| adj
.target
);
1054 let ty
= self.resolve_type(ty
);
1055 debug
!("constrain_regions_in_type_of_node(\
1056 ty={}, ty0={}, id={}, minimum_lifetime={:?})",
1058 id
, minimum_lifetime
);
1059 self.type_must_outlive(origin
, ty
, minimum_lifetime
);
1062 /// Computes the guarantor for an expression `&base` and then ensures that the lifetime of the
1063 /// resulting pointer is linked to the lifetime of its guarantor (if any).
1064 fn link_addr_of(&mut self, expr
: &hir
::Expr
,
1065 mutability
: hir
::Mutability
, base
: &hir
::Expr
) {
1066 debug
!("link_addr_of(expr={:?}, base={:?})", expr
, base
);
1069 let mc
= mc
::MemCategorizationContext
::new(self);
1070 ignore_err
!(mc
.cat_expr(base
))
1073 debug
!("link_addr_of: cmt={:?}", cmt
);
1075 self.link_region_from_node_type(expr
.span
, expr
.id
, mutability
, cmt
);
1078 /// Computes the guarantors for any ref bindings in a `let` and
1079 /// then ensures that the lifetime of the resulting pointer is
1080 /// linked to the lifetime of the initialization expression.
1081 fn link_local(&self, local
: &hir
::Local
) {
1082 debug
!("regionck::for_local()");
1083 let init_expr
= match local
.init
{
1085 Some(ref expr
) => &**expr
,
1087 let mc
= mc
::MemCategorizationContext
::new(self);
1088 let discr_cmt
= ignore_err
!(mc
.cat_expr(init_expr
));
1089 self.link_pattern(mc
, discr_cmt
, &local
.pat
);
1092 /// Computes the guarantors for any ref bindings in a match and
1093 /// then ensures that the lifetime of the resulting pointer is
1094 /// linked to the lifetime of its guarantor (if any).
1095 fn link_match(&self, discr
: &hir
::Expr
, arms
: &[hir
::Arm
]) {
1096 debug
!("regionck::for_match()");
1097 let mc
= mc
::MemCategorizationContext
::new(self);
1098 let discr_cmt
= ignore_err
!(mc
.cat_expr(discr
));
1099 debug
!("discr_cmt={:?}", discr_cmt
);
1101 for root_pat
in &arm
.pats
{
1102 self.link_pattern(mc
, discr_cmt
.clone(), &root_pat
);
1107 /// Computes the guarantors for any ref bindings in a match and
1108 /// then ensures that the lifetime of the resulting pointer is
1109 /// linked to the lifetime of its guarantor (if any).
1110 fn link_fn_args(&self, body_scope
: CodeExtent
, args
: &[hir
::Arg
]) {
1111 debug
!("regionck::link_fn_args(body_scope={:?})", body_scope
);
1112 let mc
= mc
::MemCategorizationContext
::new(self);
1114 let arg_ty
= self.node_ty(arg
.id
);
1115 let re_scope
= self.tcx
.mk_region(ty
::ReScope(body_scope
));
1116 let arg_cmt
= mc
.cat_rvalue(
1117 arg
.id
, arg
.pat
.span
, re_scope
, re_scope
, arg_ty
);
1118 debug
!("arg_ty={:?} arg_cmt={:?} arg={:?}",
1122 self.link_pattern(mc
, arg_cmt
, &arg
.pat
);
1126 /// Link lifetimes of any ref bindings in `root_pat` to the pointers found
1127 /// in the discriminant, if needed.
1128 fn link_pattern
<'t
>(&self,
1129 mc
: mc
::MemCategorizationContext
<'a
, 'gcx
, 'tcx
>,
1130 discr_cmt
: mc
::cmt
<'tcx
>,
1131 root_pat
: &hir
::Pat
) {
1132 debug
!("link_pattern(discr_cmt={:?}, root_pat={:?})",
1135 let _
= mc
.cat_pattern(discr_cmt
, root_pat
, |_
, sub_cmt
, sub_pat
| {
1136 match sub_pat
.node
{
1138 PatKind
::Binding(hir
::BindByRef(mutbl
), ..) => {
1139 self.link_region_from_node_type(sub_pat
.span
, sub_pat
.id
,
1147 /// Link lifetime of borrowed pointer resulting from autoref to lifetimes in the value being
1149 fn link_autoref(&self,
1152 autoref
: &adjustment
::AutoBorrow
<'tcx
>)
1154 debug
!("link_autoref(autoderefs={}, autoref={:?})", autoderefs
, autoref
);
1155 let mc
= mc
::MemCategorizationContext
::new(self);
1156 let expr_cmt
= ignore_err
!(mc
.cat_expr_autoderefd(expr
, autoderefs
));
1157 debug
!("expr_cmt={:?}", expr_cmt
);
1160 adjustment
::AutoBorrow
::Ref(r
, m
) => {
1161 self.link_region(expr
.span
, r
,
1162 ty
::BorrowKind
::from_mutbl(m
), expr_cmt
);
1165 adjustment
::AutoBorrow
::RawPtr(m
) => {
1166 let r
= self.tcx
.node_scope_region(expr
.id
);
1167 self.link_region(expr
.span
, r
, ty
::BorrowKind
::from_mutbl(m
), expr_cmt
);
1172 /// Computes the guarantor for cases where the `expr` is being passed by implicit reference and
1173 /// must outlive `callee_scope`.
1174 fn link_by_ref(&self,
1176 callee_scope
: CodeExtent
) {
1177 debug
!("link_by_ref(expr={:?}, callee_scope={:?})",
1178 expr
, callee_scope
);
1179 let mc
= mc
::MemCategorizationContext
::new(self);
1180 let expr_cmt
= ignore_err
!(mc
.cat_expr(expr
));
1181 let borrow_region
= self.tcx
.mk_region(ty
::ReScope(callee_scope
));
1182 self.link_region(expr
.span
, borrow_region
, ty
::ImmBorrow
, expr_cmt
);
1185 /// Like `link_region()`, except that the region is extracted from the type of `id`,
1186 /// which must be some reference (`&T`, `&str`, etc).
1187 fn link_region_from_node_type(&self,
1190 mutbl
: hir
::Mutability
,
1191 cmt_borrowed
: mc
::cmt
<'tcx
>) {
1192 debug
!("link_region_from_node_type(id={:?}, mutbl={:?}, cmt_borrowed={:?})",
1193 id
, mutbl
, cmt_borrowed
);
1195 let rptr_ty
= self.resolve_node_type(id
);
1196 if let ty
::TyRef(r
, _
) = rptr_ty
.sty
{
1197 debug
!("rptr_ty={}", rptr_ty
);
1198 self.link_region(span
, r
, ty
::BorrowKind
::from_mutbl(mutbl
),
1203 /// Informs the inference engine that `borrow_cmt` is being borrowed with
1204 /// kind `borrow_kind` and lifetime `borrow_region`.
1205 /// In order to ensure borrowck is satisfied, this may create constraints
1206 /// between regions, as explained in `link_reborrowed_region()`.
1207 fn link_region(&self,
1209 borrow_region
: &'tcx ty
::Region
,
1210 borrow_kind
: ty
::BorrowKind
,
1211 borrow_cmt
: mc
::cmt
<'tcx
>) {
1212 let mut borrow_cmt
= borrow_cmt
;
1213 let mut borrow_kind
= borrow_kind
;
1215 let origin
= infer
::DataBorrowed(borrow_cmt
.ty
, span
);
1216 self.type_must_outlive(origin
, borrow_cmt
.ty
, borrow_region
);
1219 debug
!("link_region(borrow_region={:?}, borrow_kind={:?}, borrow_cmt={:?})",
1223 match borrow_cmt
.cat
.clone() {
1224 Categorization
::Deref(ref_cmt
, _
,
1225 mc
::Implicit(ref_kind
, ref_region
)) |
1226 Categorization
::Deref(ref_cmt
, _
,
1227 mc
::BorrowedPtr(ref_kind
, ref_region
)) => {
1228 match self.link_reborrowed_region(span
,
1229 borrow_region
, borrow_kind
,
1230 ref_cmt
, ref_region
, ref_kind
,
1242 Categorization
::Downcast(cmt_base
, _
) |
1243 Categorization
::Deref(cmt_base
, _
, mc
::Unique
) |
1244 Categorization
::Interior(cmt_base
, _
) => {
1245 // Borrowing interior or owned data requires the base
1246 // to be valid and borrowable in the same fashion.
1247 borrow_cmt
= cmt_base
;
1248 borrow_kind
= borrow_kind
;
1251 Categorization
::Deref(.., mc
::UnsafePtr(..)) |
1252 Categorization
::StaticItem
|
1253 Categorization
::Upvar(..) |
1254 Categorization
::Local(..) |
1255 Categorization
::Rvalue(..) => {
1256 // These are all "base cases" with independent lifetimes
1257 // that are not subject to inference
1264 /// This is the most complicated case: the path being borrowed is
1265 /// itself the referent of a borrowed pointer. Let me give an
1266 /// example fragment of code to make clear(er) the situation:
1268 /// let r: &'a mut T = ...; // the original reference "r" has lifetime 'a
1270 /// &'z *r // the reborrow has lifetime 'z
1272 /// Now, in this case, our primary job is to add the inference
1273 /// constraint that `'z <= 'a`. Given this setup, let's clarify the
1274 /// parameters in (roughly) terms of the example:
1276 /// A borrow of: `& 'z bk * r` where `r` has type `& 'a bk T`
1277 /// borrow_region ^~ ref_region ^~
1278 /// borrow_kind ^~ ref_kind ^~
1281 /// Here `bk` stands for some borrow-kind (e.g., `mut`, `uniq`, etc).
1283 /// Unfortunately, there are some complications beyond the simple
1284 /// scenario I just painted:
1286 /// 1. The reference `r` might in fact be a "by-ref" upvar. In that
1287 /// case, we have two jobs. First, we are inferring whether this reference
1288 /// should be an `&T`, `&mut T`, or `&uniq T` reference, and we must
1289 /// adjust that based on this borrow (e.g., if this is an `&mut` borrow,
1290 /// then `r` must be an `&mut` reference). Second, whenever we link
1291 /// two regions (here, `'z <= 'a`), we supply a *cause*, and in this
1292 /// case we adjust the cause to indicate that the reference being
1293 /// "reborrowed" is itself an upvar. This provides a nicer error message
1294 /// should something go wrong.
1296 /// 2. There may in fact be more levels of reborrowing. In the
1297 /// example, I said the borrow was like `&'z *r`, but it might
1298 /// in fact be a borrow like `&'z **q` where `q` has type `&'a
1299 /// &'b mut T`. In that case, we want to ensure that `'z <= 'a`
1300 /// and `'z <= 'b`. This is explained more below.
1302 /// The return value of this function indicates whether we need to
1303 /// recurse and process `ref_cmt` (see case 2 above).
1304 fn link_reborrowed_region(&self,
1306 borrow_region
: &'tcx ty
::Region
,
1307 borrow_kind
: ty
::BorrowKind
,
1308 ref_cmt
: mc
::cmt
<'tcx
>,
1309 ref_region
: &'tcx ty
::Region
,
1310 mut ref_kind
: ty
::BorrowKind
,
1312 -> Option
<(mc
::cmt
<'tcx
>, ty
::BorrowKind
)>
1314 // Possible upvar ID we may need later to create an entry in the
1317 // Detect by-ref upvar `x`:
1318 let cause
= match note
{
1319 mc
::NoteUpvarRef(ref upvar_id
) => {
1320 let upvar_capture_map
= &self.tables
.borrow_mut().upvar_capture_map
;
1321 match upvar_capture_map
.get(upvar_id
) {
1322 Some(&ty
::UpvarCapture
::ByRef(ref upvar_borrow
)) => {
1323 // The mutability of the upvar may have been modified
1324 // by the above adjustment, so update our local variable.
1325 ref_kind
= upvar_borrow
.kind
;
1327 infer
::ReborrowUpvar(span
, *upvar_id
)
1330 span_bug
!( span
, "Illegal upvar id: {:?}", upvar_id
);
1334 mc
::NoteClosureEnv(ref upvar_id
) => {
1335 // We don't have any mutability changes to propagate, but
1336 // we do want to note that an upvar reborrow caused this
1338 infer
::ReborrowUpvar(span
, *upvar_id
)
1341 infer
::Reborrow(span
)
1345 debug
!("link_reborrowed_region: {:?} <= {:?}",
1348 self.sub_regions(cause
, borrow_region
, ref_region
);
1350 // If we end up needing to recurse and establish a region link
1351 // with `ref_cmt`, calculate what borrow kind we will end up
1352 // needing. This will be used below.
1354 // One interesting twist is that we can weaken the borrow kind
1355 // when we recurse: to reborrow an `&mut` referent as mutable,
1356 // borrowck requires a unique path to the `&mut` reference but not
1357 // necessarily a *mutable* path.
1358 let new_borrow_kind
= match borrow_kind
{
1361 ty
::MutBorrow
| ty
::UniqueImmBorrow
=>
1365 // Decide whether we need to recurse and link any regions within
1366 // the `ref_cmt`. This is concerned for the case where the value
1367 // being reborrowed is in fact a borrowed pointer found within
1368 // another borrowed pointer. For example:
1370 // let p: &'b &'a mut T = ...;
1374 // What makes this case particularly tricky is that, if the data
1375 // being borrowed is a `&mut` or `&uniq` borrow, borrowck requires
1376 // not only that `'z <= 'a`, (as before) but also `'z <= 'b`
1377 // (otherwise the user might mutate through the `&mut T` reference
1378 // after `'b` expires and invalidate the borrow we are looking at
1381 // So let's re-examine our parameters in light of this more
1382 // complicated (possible) scenario:
1384 // A borrow of: `& 'z bk * * p` where `p` has type `&'b bk & 'a bk T`
1385 // borrow_region ^~ ref_region ^~
1386 // borrow_kind ^~ ref_kind ^~
1389 // (Note that since we have not examined `ref_cmt.cat`, we don't
1390 // know whether this scenario has occurred; but I wanted to show
1391 // how all the types get adjusted.)
1394 // The reference being reborrowed is a sharable ref of
1395 // type `&'a T`. In this case, it doesn't matter where we
1396 // *found* the `&T` pointer, the memory it references will
1397 // be valid and immutable for `'a`. So we can stop here.
1399 // (Note that the `borrow_kind` must also be ImmBorrow or
1400 // else the user is borrowed imm memory as mut memory,
1401 // which means they'll get an error downstream in borrowck
1406 ty
::MutBorrow
| ty
::UniqueImmBorrow
=> {
1407 // The reference being reborrowed is either an `&mut T` or
1408 // `&uniq T`. This is the case where recursion is needed.
1409 return Some((ref_cmt
, new_borrow_kind
));
1414 /// Checks that the values provided for type/region arguments in a given
1415 /// expression are well-formed and in-scope.
1416 fn substs_wf_in_scope(&mut self,
1417 origin
: infer
::ParameterOrigin
,
1418 substs
: &Substs
<'tcx
>,
1420 expr_region
: &'tcx ty
::Region
) {
1421 debug
!("substs_wf_in_scope(substs={:?}, \
1425 substs
, expr_region
, origin
, expr_span
);
1427 let origin
= infer
::ParameterInScope(origin
, expr_span
);
1429 for region
in substs
.regions() {
1430 self.sub_regions(origin
.clone(), expr_region
, region
);
1433 for ty
in substs
.types() {
1434 let ty
= self.resolve_type(ty
);
1435 self.type_must_outlive(origin
.clone(), ty
, expr_region
);
1439 /// Ensures that type is well-formed in `region`, which implies (among
1440 /// other things) that all borrowed data reachable via `ty` outlives
1442 pub fn type_must_outlive(&self,
1443 origin
: infer
::SubregionOrigin
<'tcx
>,
1445 region
: &'tcx ty
::Region
)
1447 let ty
= self.resolve_type(ty
);
1449 debug
!("type_must_outlive(ty={:?}, region={:?}, origin={:?})",
1454 assert
!(!ty
.has_escaping_regions());
1456 let components
= self.tcx
.outlives_components(ty
);
1457 self.components_must_outlive(origin
, components
, region
);
1460 fn components_must_outlive(&self,
1461 origin
: infer
::SubregionOrigin
<'tcx
>,
1462 components
: Vec
<ty
::outlives
::Component
<'tcx
>>,
1463 region
: &'tcx ty
::Region
)
1465 for component
in components
{
1466 let origin
= origin
.clone();
1468 ty
::outlives
::Component
::Region(region1
) => {
1469 self.sub_regions(origin
, region
, region1
);
1471 ty
::outlives
::Component
::Param(param_ty
) => {
1472 self.param_ty_must_outlive(origin
, region
, param_ty
);
1474 ty
::outlives
::Component
::Projection(projection_ty
) => {
1475 self.projection_must_outlive(origin
, region
, projection_ty
);
1477 ty
::outlives
::Component
::EscapingProjection(subcomponents
) => {
1478 self.components_must_outlive(origin
, subcomponents
, region
);
1480 ty
::outlives
::Component
::UnresolvedInferenceVariable(v
) => {
1481 // ignore this, we presume it will yield an error
1482 // later, since if a type variable is not resolved by
1483 // this point it never will be
1484 self.tcx
.sess
.delay_span_bug(
1486 &format
!("unresolved inference variable in outlives: {:?}", v
));
1492 fn param_ty_must_outlive(&self,
1493 origin
: infer
::SubregionOrigin
<'tcx
>,
1494 region
: &'tcx ty
::Region
,
1495 param_ty
: ty
::ParamTy
) {
1496 debug
!("param_ty_must_outlive(region={:?}, param_ty={:?}, origin={:?})",
1497 region
, param_ty
, origin
);
1499 let verify_bound
= self.param_bound(param_ty
);
1500 let generic
= GenericKind
::Param(param_ty
);
1501 self.verify_generic_bound(origin
, generic
, region
, verify_bound
);
1504 fn projection_must_outlive(&self,
1505 origin
: infer
::SubregionOrigin
<'tcx
>,
1506 region
: &'tcx ty
::Region
,
1507 projection_ty
: ty
::ProjectionTy
<'tcx
>)
1509 debug
!("projection_must_outlive(region={:?}, projection_ty={:?}, origin={:?})",
1510 region
, projection_ty
, origin
);
1512 // This case is thorny for inference. The fundamental problem is
1513 // that there are many cases where we have choice, and inference
1514 // doesn't like choice (the current region inference in
1515 // particular). :) First off, we have to choose between using the
1516 // OutlivesProjectionEnv, OutlivesProjectionTraitDef, and
1517 // OutlivesProjectionComponent rules, any one of which is
1518 // sufficient. If there are no inference variables involved, it's
1519 // not hard to pick the right rule, but if there are, we're in a
1520 // bit of a catch 22: if we picked which rule we were going to
1521 // use, we could add constraints to the region inference graph
1522 // that make it apply, but if we don't add those constraints, the
1523 // rule might not apply (but another rule might). For now, we err
1524 // on the side of adding too few edges into the graph.
1526 // Compute the bounds we can derive from the environment or trait
1527 // definition. We know that the projection outlives all the
1528 // regions in this list.
1529 let env_bounds
= self.projection_declared_bounds(origin
.span(), projection_ty
);
1531 debug
!("projection_must_outlive: env_bounds={:?}",
1534 // If we know that the projection outlives 'static, then we're
1536 if env_bounds
.contains(&&ty
::ReStatic
) {
1537 debug
!("projection_must_outlive: 'static as declared bound");
1541 // If declared bounds list is empty, the only applicable rule is
1542 // OutlivesProjectionComponent. If there are inference variables,
1543 // then, we can break down the outlives into more primitive
1544 // components without adding unnecessary edges.
1546 // If there are *no* inference variables, however, we COULD do
1547 // this, but we choose not to, because the error messages are less
1548 // good. For example, a requirement like `T::Item: 'r` would be
1549 // translated to a requirement that `T: 'r`; when this is reported
1550 // to the user, it will thus say "T: 'r must hold so that T::Item:
1551 // 'r holds". But that makes it sound like the only way to fix
1552 // the problem is to add `T: 'r`, which isn't true. So, if there are no
1553 // inference variables, we use a verify constraint instead of adding
1554 // edges, which winds up enforcing the same condition.
1555 let needs_infer
= projection_ty
.trait_ref
.needs_infer();
1556 if env_bounds
.is_empty() && needs_infer
{
1557 debug
!("projection_must_outlive: no declared bounds");
1559 for component_ty
in projection_ty
.trait_ref
.substs
.types() {
1560 self.type_must_outlive(origin
.clone(), component_ty
, region
);
1563 for r
in projection_ty
.trait_ref
.substs
.regions() {
1564 self.sub_regions(origin
.clone(), region
, r
);
1570 // If we find that there is a unique declared bound `'b`, and this bound
1571 // appears in the trait reference, then the best action is to require that `'b:'r`,
1572 // so do that. This is best no matter what rule we use:
1574 // - OutlivesProjectionEnv or OutlivesProjectionTraitDef: these would translate to
1575 // the requirement that `'b:'r`
1576 // - OutlivesProjectionComponent: this would require `'b:'r` in addition to
1578 if !env_bounds
.is_empty() && env_bounds
[1..].iter().all(|b
| *b
== env_bounds
[0]) {
1579 let unique_bound
= env_bounds
[0];
1580 debug
!("projection_must_outlive: unique declared bound = {:?}", unique_bound
);
1581 if projection_ty
.trait_ref
.substs
.regions().any(|r
| env_bounds
.contains(&r
)) {
1582 debug
!("projection_must_outlive: unique declared bound appears in trait ref");
1583 self.sub_regions(origin
.clone(), region
, unique_bound
);
1588 // Fallback to verifying after the fact that there exists a
1589 // declared bound, or that all the components appearing in the
1590 // projection outlive; in some cases, this may add insufficient
1591 // edges into the inference graph, leading to inference failures
1592 // even though a satisfactory solution exists.
1593 let verify_bound
= self.projection_bound(origin
.span(), env_bounds
, projection_ty
);
1594 let generic
= GenericKind
::Projection(projection_ty
);
1595 self.verify_generic_bound(origin
, generic
.clone(), region
, verify_bound
);
1598 fn type_bound(&self, span
: Span
, ty
: Ty
<'tcx
>) -> VerifyBound
<'tcx
> {
1603 ty
::TyProjection(data
) => {
1604 let declared_bounds
= self.projection_declared_bounds(span
, data
);
1605 self.projection_bound(span
, declared_bounds
, data
)
1608 self.recursive_type_bound(span
, ty
)
1613 fn param_bound(&self, param_ty
: ty
::ParamTy
) -> VerifyBound
<'tcx
> {
1614 let param_env
= &self.parameter_environment
;
1616 debug
!("param_bound(param_ty={:?})",
1619 let mut param_bounds
= self.declared_generic_bounds_from_env(GenericKind
::Param(param_ty
));
1621 // Add in the default bound of fn body that applies to all in
1622 // scope type parameters:
1623 param_bounds
.push(param_env
.implicit_region_bound
);
1625 VerifyBound
::AnyRegion(param_bounds
)
1628 fn projection_declared_bounds(&self,
1630 projection_ty
: ty
::ProjectionTy
<'tcx
>)
1631 -> Vec
<&'tcx ty
::Region
>
1633 // First assemble bounds from where clauses and traits.
1635 let mut declared_bounds
=
1636 self.declared_generic_bounds_from_env(GenericKind
::Projection(projection_ty
));
1638 declared_bounds
.extend_from_slice(
1639 &self.declared_projection_bounds_from_trait(span
, projection_ty
));
1644 fn projection_bound(&self,
1646 declared_bounds
: Vec
<&'tcx ty
::Region
>,
1647 projection_ty
: ty
::ProjectionTy
<'tcx
>)
1648 -> VerifyBound
<'tcx
> {
1649 debug
!("projection_bound(declared_bounds={:?}, projection_ty={:?})",
1650 declared_bounds
, projection_ty
);
1652 // see the extensive comment in projection_must_outlive
1654 let ty
= self.tcx
.mk_projection(projection_ty
.trait_ref
, projection_ty
.item_name
);
1655 let recursive_bound
= self.recursive_type_bound(span
, ty
);
1657 VerifyBound
::AnyRegion(declared_bounds
).or(recursive_bound
)
1660 fn recursive_type_bound(&self, span
: Span
, ty
: Ty
<'tcx
>) -> VerifyBound
<'tcx
> {
1661 let mut bounds
= vec
![];
1663 for subty
in ty
.walk_shallow() {
1664 bounds
.push(self.type_bound(span
, subty
));
1667 let mut regions
= ty
.regions();
1668 regions
.retain(|r
| !r
.is_bound()); // ignore late-bound regions
1669 bounds
.push(VerifyBound
::AllRegions(regions
));
1671 // remove bounds that must hold, since they are not interesting
1672 bounds
.retain(|b
| !b
.must_hold());
1674 if bounds
.len() == 1 {
1675 bounds
.pop().unwrap()
1677 VerifyBound
::AllBounds(bounds
)
1681 fn declared_generic_bounds_from_env(&self, generic
: GenericKind
<'tcx
>)
1682 -> Vec
<&'tcx ty
::Region
>
1684 let param_env
= &self.parameter_environment
;
1686 // To start, collect bounds from user:
1687 let mut param_bounds
= self.tcx
.required_region_bounds(generic
.to_ty(self.tcx
),
1688 param_env
.caller_bounds
.clone());
1690 // Next, collect regions we scraped from the well-formedness
1691 // constraints in the fn signature. To do that, we walk the list
1692 // of known relations from the fn ctxt.
1694 // This is crucial because otherwise code like this fails:
1696 // fn foo<'a, A>(x: &'a A) { x.bar() }
1698 // The problem is that the type of `x` is `&'a A`. To be
1699 // well-formed, then, A must be lower-generic by `'a`, but we
1700 // don't know that this holds from first principles.
1701 for &(r
, p
) in &self.region_bound_pairs
{
1702 debug
!("generic={:?} p={:?}",
1706 param_bounds
.push(r
);
1713 fn declared_projection_bounds_from_trait(&self,
1715 projection_ty
: ty
::ProjectionTy
<'tcx
>)
1716 -> Vec
<&'tcx ty
::Region
>
1718 debug
!("projection_bounds(projection_ty={:?})",
1721 let ty
= self.tcx
.mk_projection(projection_ty
.trait_ref
.clone(),
1722 projection_ty
.item_name
);
1724 // Say we have a projection `<T as SomeTrait<'a>>::SomeType`. We are interested
1725 // in looking for a trait definition like:
1728 // trait SomeTrait<'a> {
1729 // type SomeType : 'a;
1733 // we can thus deduce that `<T as SomeTrait<'a>>::SomeType : 'a`.
1734 let trait_predicates
= self.tcx
.item_predicates(projection_ty
.trait_ref
.def_id
);
1735 assert_eq
!(trait_predicates
.parent
, None
);
1736 let predicates
= trait_predicates
.predicates
.as_slice().to_vec();
1737 traits
::elaborate_predicates(self.tcx
, predicates
)
1738 .filter_map(|predicate
| {
1739 // we're only interesting in `T : 'a` style predicates:
1740 let outlives
= match predicate
{
1741 ty
::Predicate
::TypeOutlives(data
) => data
,
1742 _
=> { return None; }
1745 debug
!("projection_bounds: outlives={:?} (1)",
1748 // apply the substitutions (and normalize any projected types)
1749 let outlives
= self.instantiate_type_scheme(span
,
1750 projection_ty
.trait_ref
.substs
,
1753 debug
!("projection_bounds: outlives={:?} (2)",
1756 let region_result
= self.commit_if_ok(|_
| {
1758 self.replace_late_bound_regions_with_fresh_var(
1760 infer
::AssocTypeProjection(projection_ty
.item_name
),
1763 debug
!("projection_bounds: outlives={:?} (3)",
1766 // check whether this predicate applies to our current projection
1767 let cause
= self.fcx
.misc(span
);
1768 match self.eq_types(false, &cause
, ty
, outlives
.0) {
1770 self.register_infer_ok_obligations(ok
);
1773 Err(_
) => { Err(()) }
1777 debug
!("projection_bounds: region_result={:?}",