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: int }
63 //! struct Bar { foo: Foo }
64 //! fn get_i(x: &'a Bar) -> &'a int {
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 owned pointers. We say that the guarantor
80 //! of such data it 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 check::regionmanip;
90 use middle::mem_categorization as mc;
91 use middle::region::CodeExtent;
93 use middle::ty::{ReScope};
94 use middle::ty::{self, Ty, MethodCall};
95 use middle::infer::{self, GenericKind};
97 use util::ppaux::{ty_to_string, Repr};
99 use syntax::{ast, ast_util};
100 use syntax::codemap::Span;
102 use syntax::visit::Visitor;
104 use self::RepeatingScope::Repeating;
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 pub fn regionck_expr(fcx: &FnCtxt, e: &ast::Expr) {
116 let mut rcx = Rcx::new(fcx, Repeating(e.id), Subject(e.id));
117 if fcx.err_count_since_creation() == 0 {
118 // regionck assumes typeck succeeded
120 rcx.visit_region_obligations(e.id);
122 rcx.resolve_regions_and_report_errors();
125 pub fn regionck_item(fcx: &FnCtxt, item: &ast::Item) {
126 let mut rcx = Rcx::new(fcx, Repeating(item.id), Subject(item.id));
127 rcx.visit_region_obligations(item.id);
128 rcx.resolve_regions_and_report_errors();
131 pub fn regionck_fn(fcx: &FnCtxt, id: ast::NodeId, decl: &ast::FnDecl, blk: &ast::Block) {
132 let mut rcx = Rcx::new(fcx, Repeating(blk.id), Subject(id));
133 if fcx.err_count_since_creation() == 0 {
134 // regionck assumes typeck succeeded
135 rcx.visit_fn_body(id, decl, blk);
138 // Region checking a fn can introduce new trait obligations,
139 // particularly around closure bounds.
140 vtable::select_all_fcx_obligations_or_error(fcx);
142 rcx.resolve_regions_and_report_errors();
145 /// Checks that the types in `component_tys` are well-formed. This will add constraints into the
146 /// region graph. Does *not* run `resolve_regions_and_report_errors` and so forth.
147 pub fn regionck_ensure_component_tys_wf<'a, 'tcx>(fcx: &FnCtxt<'a, 'tcx>,
149 component_tys: &[Ty<'tcx>]) {
150 let mut rcx = Rcx::new(fcx, Repeating(0), SubjectNode::None);
151 for &component_ty in component_tys {
152 // Check that each type outlives the empty region. Since the
153 // empty region is a subregion of all others, this can't fail
154 // unless the type does not meet the well-formedness
156 type_must_outlive(&mut rcx, infer::RelateRegionParamBound(span),
157 component_ty, ty::ReEmpty);
161 ///////////////////////////////////////////////////////////////////////////
164 pub struct Rcx<'a, 'tcx: 'a> {
165 fcx: &'a FnCtxt<'a, 'tcx>,
167 region_bound_pairs: Vec<(ty::Region, GenericKind<'tcx>)>,
169 // id of innermost fn or loop
170 repeating_scope: ast::NodeId,
172 // id of AST node being analyzed (the subject of the analysis).
173 subject: SubjectNode,
176 /// Returns the validity region of `def` -- that is, how long is `def` valid?
177 fn region_of_def(fcx: &FnCtxt, def: def::Def) -> ty::Region {
180 def::DefLocal(node_id) | def::DefUpvar(node_id, _) => {
181 tcx.region_maps.var_region(node_id)
184 tcx.sess.bug(&format!("unexpected def in region_of_def: {:?}",
190 pub enum RepeatingScope { Repeating(ast::NodeId) }
191 pub enum SubjectNode { Subject(ast::NodeId), None }
193 impl<'a, 'tcx> Rcx<'a, 'tcx> {
194 pub fn new(fcx: &'a FnCtxt<'a, 'tcx>,
195 initial_repeating_scope: RepeatingScope,
196 subject: SubjectNode) -> Rcx<'a, 'tcx> {
197 let Repeating(initial_repeating_scope) = initial_repeating_scope;
199 repeating_scope: initial_repeating_scope,
201 region_bound_pairs: Vec::new() }
204 pub fn tcx(&self) -> &'a ty::ctxt<'tcx> {
208 pub fn set_repeating_scope(&mut self, scope: ast::NodeId) -> ast::NodeId {
209 let old_scope = self.repeating_scope;
210 self.repeating_scope = scope;
214 /// Try to resolve the type for the given node, returning t_err if an error results. Note that
215 /// we never care about the details of the error, the same error will be detected and reported
216 /// in the writeback phase.
218 /// Note one important point: we do not attempt to resolve *region variables* here. This is
219 /// because regionck is essentially adding constraints to those region variables and so may yet
220 /// influence how they are resolved.
222 /// Consider this silly example:
225 /// fn borrow(x: &int) -> &int {x}
226 /// fn foo(x: @int) -> int { // block: B
227 /// let b = borrow(x); // region: <R0>
232 /// Here, the region of `b` will be `<R0>`. `<R0>` is constrainted to be some subregion of the
233 /// block B and some superregion of the call. If we forced it now, we'd choose the smaller
234 /// region (the call). But that would make the *b illegal. Since we don't resolve, the type
235 /// of b will be `&<R0>.int` and then `*b` will require that `<R0>` be bigger than the let and
236 /// the `*b` expression, so we will effectively resolve `<R0>` to be the block B.
237 pub fn resolve_type(&self, unresolved_ty: Ty<'tcx>) -> Ty<'tcx> {
238 self.fcx.infcx().resolve_type_vars_if_possible(&unresolved_ty)
241 /// Try to resolve the type for the given node.
242 fn resolve_node_type(&self, id: ast::NodeId) -> Ty<'tcx> {
243 let t = self.fcx.node_ty(id);
247 fn resolve_method_type(&self, method_call: MethodCall) -> Option<Ty<'tcx>> {
248 let method_ty = self.fcx.inh.method_map.borrow()
249 .get(&method_call).map(|method| method.ty);
250 method_ty.map(|method_ty| self.resolve_type(method_ty))
253 /// Try to resolve the type for the given node.
254 pub fn resolve_expr_type_adjusted(&mut self, expr: &ast::Expr) -> Ty<'tcx> {
255 let ty_unadjusted = self.resolve_node_type(expr.id);
256 if ty::type_is_error(ty_unadjusted) {
259 let tcx = self.fcx.tcx();
260 ty::adjust_ty(tcx, expr.span, expr.id, ty_unadjusted,
261 self.fcx.inh.adjustments.borrow().get(&expr.id),
262 |method_call| self.resolve_method_type(method_call))
266 fn visit_fn_body(&mut self,
268 fn_decl: &ast::FnDecl,
271 // When we enter a function, we can derive
273 let fn_sig_map = self.fcx.inh.fn_sig_map.borrow();
274 let fn_sig = match fn_sig_map.get(&id) {
278 &format!("No fn-sig entry for id={}", id)[]);
282 let len = self.region_bound_pairs.len();
283 self.relate_free_regions(&fn_sig[], body.id);
284 link_fn_args(self, CodeExtent::from_node_id(body.id), &fn_decl.inputs[]);
285 self.visit_block(body);
286 self.visit_region_obligations(body.id);
287 self.region_bound_pairs.truncate(len);
290 fn visit_region_obligations(&mut self, node_id: ast::NodeId)
292 debug!("visit_region_obligations: node_id={}", node_id);
294 // Make a copy of the region obligations vec because we'll need
295 // to be able to borrow the fulfillment-cx below when projecting.
296 let region_obligations =
297 self.fcx.inh.fulfillment_cx.borrow()
298 .region_obligations(node_id)
301 for r_o in ®ion_obligations {
302 debug!("visit_region_obligations: r_o={}",
303 r_o.repr(self.tcx()));
304 let sup_type = self.resolve_type(r_o.sup_type);
305 let origin = infer::RelateRegionParamBound(r_o.cause.span);
306 type_must_outlive(self, origin, sup_type, r_o.sub_region);
309 // Processing the region obligations should not cause the list to grow further:
310 assert_eq!(region_obligations.len(),
311 self.fcx.inh.fulfillment_cx.borrow().region_obligations(node_id).len());
314 /// This method populates the region map's `free_region_map`. It walks over the transformed
315 /// argument and return types for each function just before we check the body of that function,
316 /// looking for types where you have a borrowed pointer to other borrowed data (e.g., `&'a &'b
317 /// [uint]`. We do not allow references to outlive the things they point at, so we can assume
318 /// that `'a <= 'b`. This holds for both the argument and return types, basically because, on
319 /// the caller side, the caller is responsible for checking that the type of every expression
320 /// (including the actual values for the arguments, as well as the return type of the fn call)
323 /// Tests: `src/test/compile-fail/regions-free-region-ordering-*.rs`
324 fn relate_free_regions(&mut self,
325 fn_sig_tys: &[Ty<'tcx>],
326 body_id: ast::NodeId) {
327 debug!("relate_free_regions >>");
328 let tcx = self.tcx();
330 for &ty in fn_sig_tys {
331 let ty = self.resolve_type(ty);
332 debug!("relate_free_regions(t={})", ty.repr(tcx));
333 let body_scope = CodeExtent::from_node_id(body_id);
334 let body_scope = ty::ReScope(body_scope);
336 regionmanip::region_wf_constraints(
340 for constraint in &constraints {
341 debug!("constraint: {}", constraint.repr(tcx));
343 regionmanip::RegionSubRegionConstraint(_,
345 ty::ReFree(free_b)) => {
346 tcx.region_maps.relate_free_regions(free_a, free_b);
348 regionmanip::RegionSubRegionConstraint(_,
350 ty::ReInfer(ty::ReVar(vid_b))) => {
351 self.fcx.inh.infcx.add_given(free_a, vid_b);
353 regionmanip::RegionSubRegionConstraint(..) => {
354 // In principle, we could record (and take
355 // advantage of) every relationship here, but
356 // we are also free not to -- it simply means
357 // strictly less that we can successfully type
358 // check. (It may also be that we should
359 // revise our inference system to be more
360 // general and to make use of *every*
361 // relationship that arises here, but
362 // presently we do not.)
364 regionmanip::RegionSubGenericConstraint(_, r_a, ref generic_b) => {
365 debug!("RegionSubGenericConstraint: {} <= {}",
366 r_a.repr(tcx), generic_b.repr(tcx));
368 self.region_bound_pairs.push((r_a, generic_b.clone()));
374 debug!("<< relate_free_regions");
377 fn resolve_regions_and_report_errors(&self) {
378 let subject_node_id = match self.subject {
380 SubjectNode::None => {
381 self.tcx().sess.bug("cannot resolve_regions_and_report_errors \
382 without subject node");
386 self.fcx.infcx().resolve_regions_and_report_errors(subject_node_id);
390 impl<'a, 'tcx, 'v> Visitor<'v> for Rcx<'a, 'tcx> {
391 // (..) FIXME(#3238) should use visit_pat, not visit_arm/visit_local,
392 // However, right now we run into an issue whereby some free
393 // regions are not properly related if they appear within the
394 // types of arguments that must be inferred. This could be
395 // addressed by deferring the construction of the region
396 // hierarchy, and in particular the relationships between free
397 // regions, until regionck, as described in #3238.
399 fn visit_fn(&mut self, _fk: visit::FnKind<'v>, fd: &'v ast::FnDecl,
400 b: &'v ast::Block, _s: Span, id: ast::NodeId) {
401 self.visit_fn_body(id, fd, b)
404 fn visit_item(&mut self, i: &ast::Item) { visit_item(self, i); }
406 fn visit_expr(&mut self, ex: &ast::Expr) { visit_expr(self, ex); }
408 //visit_pat: visit_pat, // (..) see above
410 fn visit_arm(&mut self, a: &ast::Arm) { visit_arm(self, a); }
412 fn visit_local(&mut self, l: &ast::Local) { visit_local(self, l); }
414 fn visit_block(&mut self, b: &ast::Block) { visit_block(self, b); }
417 fn visit_item(_rcx: &mut Rcx, _item: &ast::Item) {
421 fn visit_block(rcx: &mut Rcx, b: &ast::Block) {
422 visit::walk_block(rcx, b);
425 fn visit_arm(rcx: &mut Rcx, arm: &ast::Arm) {
428 constrain_bindings_in_pat(&**p, rcx);
431 visit::walk_arm(rcx, arm);
434 fn visit_local(rcx: &mut Rcx, l: &ast::Local) {
436 constrain_bindings_in_pat(&*l.pat, rcx);
438 visit::walk_local(rcx, l);
441 fn constrain_bindings_in_pat(pat: &ast::Pat, rcx: &mut Rcx) {
442 let tcx = rcx.fcx.tcx();
443 debug!("regionck::visit_pat(pat={})", pat.repr(tcx));
444 pat_util::pat_bindings(&tcx.def_map, pat, |_, id, span, _| {
445 // If we have a variable that contains region'd data, that
446 // data will be accessible from anywhere that the variable is
447 // accessed. We must be wary of loops like this:
449 // // from src/test/compile-fail/borrowck-lend-flow.rs
450 // let mut v = box 3, w = box 4;
451 // let mut x = &mut w;
454 // borrow(v); //~ ERROR cannot borrow
455 // x = &mut v; // (1)
458 // Typically, we try to determine the region of a borrow from
459 // those points where it is dereferenced. In this case, one
460 // might imagine that the lifetime of `x` need only be the
461 // body of the loop. But of course this is incorrect because
462 // the pointer that is created at point (1) is consumed at
463 // point (2), meaning that it must be live across the loop
464 // iteration. The easiest way to guarantee this is to require
465 // that the lifetime of any regions that appear in a
466 // variable's type enclose at least the variable's scope.
468 let var_region = tcx.region_maps.var_region(id);
469 type_of_node_must_outlive(
470 rcx, infer::BindingTypeIsNotValidAtDecl(span),
475 fn visit_expr(rcx: &mut Rcx, expr: &ast::Expr) {
476 debug!("regionck::visit_expr(e={}, repeating_scope={})",
477 expr.repr(rcx.fcx.tcx()), rcx.repeating_scope);
479 // No matter what, the type of each expression must outlive the
480 // scope of that expression. This also guarantees basic WF.
481 let expr_ty = rcx.resolve_node_type(expr.id);
483 type_must_outlive(rcx, infer::ExprTypeIsNotInScope(expr_ty, expr.span),
484 expr_ty, ty::ReScope(CodeExtent::from_node_id(expr.id)));
486 let method_call = MethodCall::expr(expr.id);
487 let has_method_map = rcx.fcx.inh.method_map.borrow().contains_key(&method_call);
489 // Check any autoderefs or autorefs that appear.
490 if let Some(adjustment) = rcx.fcx.inh.adjustments.borrow().get(&expr.id) {
491 debug!("adjustment={:?}", adjustment);
493 ty::AdjustDerefRef(ty::AutoDerefRef {autoderefs, autoref: ref opt_autoref}) => {
494 let expr_ty = rcx.resolve_node_type(expr.id);
495 constrain_autoderefs(rcx, expr, autoderefs, expr_ty);
496 if let Some(ref autoref) = *opt_autoref {
497 link_autoref(rcx, expr, autoderefs, autoref);
499 // Require that the resulting region encompasses
502 // FIXME(#6268) remove to support nested method calls
503 type_of_node_must_outlive(
504 rcx, infer::AutoBorrow(expr.span),
505 expr.id, ty::ReScope(CodeExtent::from_node_id(expr.id)));
509 ty::AutoObject(_, ref bounds, _, _) => {
510 // Determine if we are casting `expr` to a trait
511 // instance. If so, we have to be sure that the type
512 // of the source obeys the new region bound.
513 let source_ty = rcx.resolve_node_type(expr.id);
514 type_must_outlive(rcx, infer::RelateObjectBound(expr.span),
515 source_ty, bounds.region_bound);
523 ast::ExprCall(ref callee, ref args) => {
525 constrain_call(rcx, expr, Some(&**callee),
526 args.iter().map(|e| &**e), false);
528 constrain_callee(rcx, callee.id, expr, &**callee);
529 constrain_call(rcx, expr, None,
530 args.iter().map(|e| &**e), false);
533 visit::walk_expr(rcx, expr);
536 ast::ExprMethodCall(_, _, ref args) => {
537 constrain_call(rcx, expr, Some(&*args[0]),
538 args[1..].iter().map(|e| &**e), false);
540 visit::walk_expr(rcx, expr);
543 ast::ExprAssignOp(_, ref lhs, ref rhs) => {
545 constrain_call(rcx, expr, Some(&**lhs),
546 Some(&**rhs).into_iter(), true);
549 visit::walk_expr(rcx, expr);
552 ast::ExprIndex(ref lhs, ref rhs) if has_method_map => {
553 constrain_call(rcx, expr, Some(&**lhs),
554 Some(&**rhs).into_iter(), true);
556 visit::walk_expr(rcx, expr);
559 ast::ExprBinary(op, ref lhs, ref rhs) if has_method_map => {
560 let implicitly_ref_args = !ast_util::is_by_value_binop(op.node);
562 // As `expr_method_call`, but the call is via an
563 // overloaded op. Note that we (sadly) currently use an
564 // implicit "by ref" sort of passing style here. This
565 // should be converted to an adjustment!
566 constrain_call(rcx, expr, Some(&**lhs),
567 Some(&**rhs).into_iter(), implicitly_ref_args);
569 visit::walk_expr(rcx, expr);
572 ast::ExprUnary(op, ref lhs) if has_method_map => {
573 let implicitly_ref_args = !ast_util::is_by_value_unop(op);
576 constrain_call(rcx, expr, Some(&**lhs),
577 None::<ast::Expr>.iter(), implicitly_ref_args);
579 visit::walk_expr(rcx, expr);
582 ast::ExprUnary(ast::UnDeref, ref base) => {
583 // For *a, the lifetime of a must enclose the deref
584 let method_call = MethodCall::expr(expr.id);
585 let base_ty = match rcx.fcx.inh.method_map.borrow().get(&method_call) {
587 constrain_call(rcx, expr, Some(&**base),
588 None::<ast::Expr>.iter(), true);
589 let fn_ret = // late-bound regions in overloaded method calls are instantiated
590 ty::assert_no_late_bound_regions(rcx.tcx(), &ty::ty_fn_ret(method.ty));
593 None => rcx.resolve_node_type(base.id)
595 if let ty::ty_rptr(r_ptr, _) = base_ty.sty {
596 mk_subregion_due_to_dereference(
597 rcx, expr.span, ty::ReScope(CodeExtent::from_node_id(expr.id)), *r_ptr);
600 visit::walk_expr(rcx, expr);
603 ast::ExprIndex(ref vec_expr, _) => {
604 // For a[b], the lifetime of a must enclose the deref
605 let vec_type = rcx.resolve_expr_type_adjusted(&**vec_expr);
606 constrain_index(rcx, expr, vec_type);
608 visit::walk_expr(rcx, expr);
611 ast::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 constrain_cast(rcx, expr, &**source);
616 visit::walk_expr(rcx, expr);
619 ast::ExprAddrOf(m, ref base) => {
620 link_addr_of(rcx, 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(#6268) nested method calls requires that this rule change
629 let ty0 = rcx.resolve_node_type(expr.id);
630 type_must_outlive(rcx, infer::AddrOf(expr.span),
631 ty0, ty::ReScope(CodeExtent::from_node_id(expr.id)));
632 visit::walk_expr(rcx, expr);
635 ast::ExprMatch(ref discr, ref arms, _) => {
636 link_match(rcx, &**discr, &arms[]);
638 visit::walk_expr(rcx, expr);
641 ast::ExprClosure(_, _, _, ref body) => {
642 check_expr_fn_block(rcx, expr, &**body);
645 ast::ExprLoop(ref body, _) => {
646 let repeating_scope = rcx.set_repeating_scope(body.id);
647 visit::walk_expr(rcx, expr);
648 rcx.set_repeating_scope(repeating_scope);
651 ast::ExprWhile(ref cond, ref body, _) => {
652 let repeating_scope = rcx.set_repeating_scope(cond.id);
653 rcx.visit_expr(&**cond);
655 rcx.set_repeating_scope(body.id);
656 rcx.visit_block(&**body);
658 rcx.set_repeating_scope(repeating_scope);
662 visit::walk_expr(rcx, expr);
667 fn constrain_cast(rcx: &mut Rcx,
668 cast_expr: &ast::Expr,
669 source_expr: &ast::Expr)
671 debug!("constrain_cast(cast_expr={}, source_expr={})",
672 cast_expr.repr(rcx.tcx()),
673 source_expr.repr(rcx.tcx()));
675 let source_ty = rcx.resolve_node_type(source_expr.id);
676 let target_ty = rcx.resolve_node_type(cast_expr.id);
678 walk_cast(rcx, cast_expr, source_ty, target_ty);
680 fn walk_cast<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>,
681 cast_expr: &ast::Expr,
684 debug!("walk_cast(from_ty={}, to_ty={})",
685 from_ty.repr(rcx.tcx()),
686 to_ty.repr(rcx.tcx()));
687 match (&from_ty.sty, &to_ty.sty) {
688 /*From:*/ (&ty::ty_rptr(from_r, ref from_mt),
689 /*To: */ &ty::ty_rptr(to_r, ref to_mt)) => {
690 // Target cannot outlive source, naturally.
691 rcx.fcx.mk_subr(infer::Reborrow(cast_expr.span), *to_r, *from_r);
692 walk_cast(rcx, cast_expr, from_mt.ty, to_mt.ty);
696 /*To: */ &ty::ty_trait(box ty::TyTrait { ref bounds, .. })) => {
697 // When T is existentially quantified as a trait
698 // `Foo+'to`, it must outlive the region bound `'to`.
699 type_must_outlive(rcx, infer::RelateObjectBound(cast_expr.span),
700 from_ty, bounds.region_bound);
703 /*From:*/ (&ty::ty_uniq(from_referent_ty),
704 /*To: */ &ty::ty_uniq(to_referent_ty)) => {
705 walk_cast(rcx, cast_expr, from_referent_ty, to_referent_ty);
713 fn check_expr_fn_block(rcx: &mut Rcx,
716 let tcx = rcx.fcx.tcx();
717 let function_type = rcx.resolve_node_type(expr.id);
719 match function_type.sty {
720 ty::ty_closure(_, region, _) => {
721 ty::with_freevars(tcx, expr.id, |freevars| {
722 constrain_captured_variables(rcx, *region, expr, freevars);
728 let repeating_scope = rcx.set_repeating_scope(body.id);
729 visit::walk_expr(rcx, expr);
730 rcx.set_repeating_scope(repeating_scope);
732 match function_type.sty {
733 ty::ty_closure(_, region, _) => {
734 ty::with_freevars(tcx, expr.id, |freevars| {
735 let bounds = ty::region_existential_bound(*region);
736 ensure_free_variable_types_outlive_closure_bound(rcx, &bounds, expr, freevars);
742 /// Make sure that the type of all free variables referenced inside a closure/proc outlive the
743 /// closure/proc's lifetime bound. This is just a special case of the usual rules about closed
744 /// over values outliving the object's lifetime bound.
745 fn ensure_free_variable_types_outlive_closure_bound(
747 bounds: &ty::ExistentialBounds,
749 freevars: &[ty::Freevar])
751 let tcx = rcx.fcx.ccx.tcx;
753 debug!("ensure_free_variable_types_outlive_closure_bound({}, {})",
754 bounds.region_bound.repr(tcx), expr.repr(tcx));
756 for freevar in freevars {
758 let def_id = freevar.def.def_id();
759 assert!(def_id.krate == ast::LOCAL_CRATE);
763 // Compute the type of the field in the environment that
764 // represents `var_node_id`. For a by-value closure, this
765 // will be the same as the type of the variable. For a
766 // by-reference closure, this will be `&T` where `T` is
767 // the type of the variable.
768 let raw_var_ty = rcx.resolve_node_type(var_node_id);
769 let upvar_id = ty::UpvarId { var_id: var_node_id,
770 closure_expr_id: expr.id };
771 let var_ty = match rcx.fcx.inh.upvar_capture_map.borrow()[upvar_id] {
772 ty::UpvarCapture::ByRef(ref upvar_borrow) => {
773 ty::mk_rptr(rcx.tcx(),
774 rcx.tcx().mk_region(upvar_borrow.region),
775 ty::mt { mutbl: upvar_borrow.kind.to_mutbl_lossy(),
778 ty::UpvarCapture::ByValue => raw_var_ty,
781 // Check that the type meets the criteria of the existential bounds:
782 for builtin_bound in &bounds.builtin_bounds {
783 let code = traits::ClosureCapture(var_node_id, expr.span, builtin_bound);
784 let cause = traits::ObligationCause::new(freevar.span, rcx.fcx.body_id, code);
785 rcx.fcx.register_builtin_bound(var_ty, builtin_bound, cause);
789 rcx, infer::FreeVariable(expr.span, var_node_id),
790 var_ty, bounds.region_bound);
794 /// Make sure that all free variables referenced inside the closure outlive the closure's
795 /// lifetime bound. Also, create an entry in the upvar_borrows map with a region.
796 fn constrain_captured_variables(
798 region_bound: ty::Region,
800 freevars: &[ty::Freevar])
802 let tcx = rcx.fcx.ccx.tcx;
803 debug!("constrain_captured_variables({}, {})",
804 region_bound.repr(tcx), expr.repr(tcx));
805 for freevar in freevars {
806 debug!("constrain_captured_variables: freevar.def={:?}", freevar.def);
808 // Identify the variable being closed over and its node-id.
809 let def = freevar.def;
811 let def_id = def.def_id();
812 assert!(def_id.krate == ast::LOCAL_CRATE);
815 let upvar_id = ty::UpvarId { var_id: var_node_id,
816 closure_expr_id: expr.id };
818 match rcx.fcx.inh.upvar_capture_map.borrow()[upvar_id] {
819 ty::UpvarCapture::ByValue => { }
820 ty::UpvarCapture::ByRef(upvar_borrow) => {
821 rcx.fcx.mk_subr(infer::FreeVariable(freevar.span, var_node_id),
822 region_bound, upvar_borrow.region);
824 // Guarantee that the closure does not outlive the variable itself.
825 let enclosing_region = region_of_def(rcx.fcx, def);
826 debug!("constrain_captured_variables: enclosing_region = {}",
827 enclosing_region.repr(tcx));
828 rcx.fcx.mk_subr(infer::FreeVariable(freevar.span, var_node_id),
829 region_bound, enclosing_region);
836 fn constrain_callee(rcx: &mut Rcx,
837 callee_id: ast::NodeId,
838 _call_expr: &ast::Expr,
839 _callee_expr: &ast::Expr) {
840 let callee_ty = rcx.resolve_node_type(callee_id);
841 match callee_ty.sty {
842 ty::ty_bare_fn(..) => { }
844 // this should not happen, but it does if the program is
847 // tcx.sess.span_bug(
849 // format!("Calling non-function: {}", callee_ty.repr(tcx)));
854 fn constrain_call<'a, I: Iterator<Item=&'a ast::Expr>>(rcx: &mut Rcx,
855 call_expr: &ast::Expr,
856 receiver: Option<&ast::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 let tcx = rcx.fcx.tcx();
865 debug!("constrain_call(call_expr={}, \
867 implicitly_ref_args={})",
870 implicitly_ref_args);
872 // `callee_region` is the scope representing the time in which the
875 // FIXME(#6268) to support nested method calls, should be callee_id
876 let callee_scope = CodeExtent::from_node_id(call_expr.id);
877 let callee_region = ty::ReScope(callee_scope);
879 debug!("callee_region={}", callee_region.repr(tcx));
881 for arg_expr in arg_exprs {
882 debug!("Argument: {}", arg_expr.repr(tcx));
884 // ensure that any regions appearing in the argument type are
885 // valid for at least the lifetime of the function:
886 type_of_node_must_outlive(
887 rcx, infer::CallArg(arg_expr.span),
888 arg_expr.id, callee_region);
890 // unfortunately, there are two means of taking implicit
891 // references, and we need to propagate constraints as a
892 // result. modes are going away and the "DerefArgs" code
893 // should be ported to use adjustments
894 if implicitly_ref_args {
895 link_by_ref(rcx, arg_expr, callee_scope);
899 // as loop above, but for receiver
900 if let Some(r) = receiver {
901 debug!("receiver: {}", r.repr(tcx));
902 type_of_node_must_outlive(
903 rcx, infer::CallRcvr(r.span),
904 r.id, callee_region);
905 if implicitly_ref_args {
906 link_by_ref(rcx, &*r, callee_scope);
911 /// Invoked on any auto-dereference that occurs. Checks that if this is a region pointer being
912 /// dereferenced, the lifetime of the pointer includes the deref expr.
913 fn constrain_autoderefs<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>,
914 deref_expr: &ast::Expr,
916 mut derefd_ty: Ty<'tcx>)
918 debug!("constrain_autoderefs(deref_expr={}, derefs={}, derefd_ty={})",
919 deref_expr.repr(rcx.tcx()),
921 derefd_ty.repr(rcx.tcx()));
923 let r_deref_expr = ty::ReScope(CodeExtent::from_node_id(deref_expr.id));
924 for i in 0u..derefs {
925 let method_call = MethodCall::autoderef(deref_expr.id, i);
926 debug!("constrain_autoderefs: method_call={:?} (of {:?} total)", method_call, derefs);
928 derefd_ty = match rcx.fcx.inh.method_map.borrow().get(&method_call) {
930 debug!("constrain_autoderefs: #{} is overloaded, method={}",
931 i, method.repr(rcx.tcx()));
933 // Treat overloaded autoderefs as if an AutoRef adjustment
934 // was applied on the base type, as that is always the case.
935 let fn_sig = ty::ty_fn_sig(method.ty);
936 let fn_sig = // late-bound regions should have been instantiated
937 ty::assert_no_late_bound_regions(rcx.tcx(), fn_sig);
938 let self_ty = fn_sig.inputs[0];
939 let (m, r) = match self_ty.sty {
940 ty::ty_rptr(r, ref m) => (m.mutbl, r),
942 rcx.tcx().sess.span_bug(
944 &format!("bad overloaded deref type {}",
945 method.ty.repr(rcx.tcx()))[])
949 debug!("constrain_autoderefs: receiver r={:?} m={:?}",
950 r.repr(rcx.tcx()), m);
953 let mc = mc::MemCategorizationContext::new(rcx.fcx);
954 let self_cmt = ignore_err!(mc.cat_expr_autoderefd(deref_expr, i));
955 debug!("constrain_autoderefs: self_cmt={:?}",
956 self_cmt.repr(rcx.tcx()));
957 link_region(rcx, deref_expr.span, *r,
958 ty::BorrowKind::from_mutbl(m), self_cmt);
961 // Specialized version of constrain_call.
962 type_must_outlive(rcx, infer::CallRcvr(deref_expr.span),
963 self_ty, r_deref_expr);
964 match fn_sig.output {
965 ty::FnConverging(return_type) => {
966 type_must_outlive(rcx, infer::CallReturn(deref_expr.span),
967 return_type, r_deref_expr);
970 ty::FnDiverging => unreachable!()
976 if let ty::ty_rptr(r_ptr, _) = derefd_ty.sty {
977 mk_subregion_due_to_dereference(rcx, deref_expr.span,
978 r_deref_expr, *r_ptr);
981 match ty::deref(derefd_ty, true) {
982 Some(mt) => derefd_ty = mt.ty,
983 /* if this type can't be dereferenced, then there's already an error
984 in the session saying so. Just bail out for now */
990 pub fn mk_subregion_due_to_dereference(rcx: &mut Rcx,
992 minimum_lifetime: ty::Region,
993 maximum_lifetime: ty::Region) {
994 rcx.fcx.mk_subr(infer::DerefPointer(deref_span),
995 minimum_lifetime, maximum_lifetime)
999 /// Invoked on any index expression that occurs. Checks that if this is a slice being indexed, the
1000 /// lifetime of the pointer includes the deref expr.
1001 fn constrain_index<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>,
1002 index_expr: &ast::Expr,
1003 indexed_ty: Ty<'tcx>)
1005 debug!("constrain_index(index_expr=?, indexed_ty={}",
1006 rcx.fcx.infcx().ty_to_string(indexed_ty));
1008 let r_index_expr = ty::ReScope(CodeExtent::from_node_id(index_expr.id));
1009 if let ty::ty_rptr(r_ptr, mt) = indexed_ty.sty {
1011 ty::ty_vec(_, None) | ty::ty_str => {
1012 rcx.fcx.mk_subr(infer::IndexSlice(index_expr.span),
1013 r_index_expr, *r_ptr);
1020 /// Guarantees that any lifetimes which appear in the type of the node `id` (after applying
1021 /// adjustments) are valid for at least `minimum_lifetime`
1022 fn type_of_node_must_outlive<'a, 'tcx>(
1023 rcx: &mut Rcx<'a, 'tcx>,
1024 origin: infer::SubregionOrigin<'tcx>,
1026 minimum_lifetime: ty::Region)
1028 let tcx = rcx.fcx.tcx();
1030 // Try to resolve the type. If we encounter an error, then typeck
1031 // is going to fail anyway, so just stop here and let typeck
1032 // report errors later on in the writeback phase.
1033 let ty0 = rcx.resolve_node_type(id);
1034 let ty = ty::adjust_ty(tcx, origin.span(), id, ty0,
1035 rcx.fcx.inh.adjustments.borrow().get(&id),
1036 |method_call| rcx.resolve_method_type(method_call));
1037 debug!("constrain_regions_in_type_of_node(\
1038 ty={}, ty0={}, id={}, minimum_lifetime={:?})",
1039 ty_to_string(tcx, ty), ty_to_string(tcx, ty0),
1040 id, minimum_lifetime);
1041 type_must_outlive(rcx, origin, ty, minimum_lifetime);
1044 /// Computes the guarantor for an expression `&base` and then ensures that the lifetime of the
1045 /// resulting pointer is linked to the lifetime of its guarantor (if any).
1046 fn link_addr_of(rcx: &mut Rcx, expr: &ast::Expr,
1047 mutability: ast::Mutability, base: &ast::Expr) {
1048 debug!("link_addr_of(expr={}, base={})", expr.repr(rcx.tcx()), base.repr(rcx.tcx()));
1051 let mc = mc::MemCategorizationContext::new(rcx.fcx);
1052 ignore_err!(mc.cat_expr(base))
1055 debug!("link_addr_of: cmt={}", cmt.repr(rcx.tcx()));
1057 link_region_from_node_type(rcx, expr.span, expr.id, mutability, cmt);
1060 /// Computes the guarantors for any ref bindings in a `let` and
1061 /// then ensures that the lifetime of the resulting pointer is
1062 /// linked to the lifetime of the initialization expression.
1063 fn link_local(rcx: &Rcx, local: &ast::Local) {
1064 debug!("regionck::for_local()");
1065 let init_expr = match local.init {
1067 Some(ref expr) => &**expr,
1069 let mc = mc::MemCategorizationContext::new(rcx.fcx);
1070 let discr_cmt = ignore_err!(mc.cat_expr(init_expr));
1071 link_pattern(rcx, mc, discr_cmt, &*local.pat);
1074 /// Computes the guarantors for any ref bindings in a match and
1075 /// then ensures that the lifetime of the resulting pointer is
1076 /// linked to the lifetime of its guarantor (if any).
1077 fn link_match(rcx: &Rcx, discr: &ast::Expr, arms: &[ast::Arm]) {
1078 debug!("regionck::for_match()");
1079 let mc = mc::MemCategorizationContext::new(rcx.fcx);
1080 let discr_cmt = ignore_err!(mc.cat_expr(discr));
1081 debug!("discr_cmt={}", discr_cmt.repr(rcx.tcx()));
1083 for root_pat in &arm.pats {
1084 link_pattern(rcx, mc, discr_cmt.clone(), &**root_pat);
1089 /// Computes the guarantors for any ref bindings in a match and
1090 /// then ensures that the lifetime of the resulting pointer is
1091 /// linked to the lifetime of its guarantor (if any).
1092 fn link_fn_args(rcx: &Rcx, body_scope: CodeExtent, args: &[ast::Arg]) {
1093 debug!("regionck::link_fn_args(body_scope={:?})", body_scope);
1094 let mc = mc::MemCategorizationContext::new(rcx.fcx);
1096 let arg_ty = rcx.fcx.node_ty(arg.id);
1097 let re_scope = ty::ReScope(body_scope);
1098 let arg_cmt = mc.cat_rvalue(arg.id, arg.ty.span, re_scope, arg_ty);
1099 debug!("arg_ty={} arg_cmt={}",
1100 arg_ty.repr(rcx.tcx()),
1101 arg_cmt.repr(rcx.tcx()));
1102 link_pattern(rcx, mc, arg_cmt, &*arg.pat);
1106 /// Link lifetimes of any ref bindings in `root_pat` to the pointers found in the discriminant, if
1108 fn link_pattern<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1109 mc: mc::MemCategorizationContext<FnCtxt<'a, 'tcx>>,
1110 discr_cmt: mc::cmt<'tcx>,
1111 root_pat: &ast::Pat) {
1112 debug!("link_pattern(discr_cmt={}, root_pat={})",
1113 discr_cmt.repr(rcx.tcx()),
1114 root_pat.repr(rcx.tcx()));
1115 let _ = mc.cat_pattern(discr_cmt, root_pat, |mc, sub_cmt, sub_pat| {
1116 match sub_pat.node {
1118 ast::PatIdent(ast::BindByRef(mutbl), _, _) => {
1119 link_region_from_node_type(
1120 rcx, sub_pat.span, sub_pat.id,
1124 // `[_, ..slice, _]` pattern
1125 ast::PatVec(_, Some(ref slice_pat), _) => {
1126 match mc.cat_slice_pattern(sub_cmt, &**slice_pat) {
1127 Ok((slice_cmt, slice_mutbl, slice_r)) => {
1128 link_region(rcx, sub_pat.span, slice_r,
1129 ty::BorrowKind::from_mutbl(slice_mutbl),
1140 /// Link lifetime of borrowed pointer resulting from autoref to lifetimes in the value being
1142 fn link_autoref(rcx: &Rcx,
1145 autoref: &ty::AutoRef) {
1147 debug!("link_autoref(autoref={:?})", autoref);
1148 let mc = mc::MemCategorizationContext::new(rcx.fcx);
1149 let expr_cmt = ignore_err!(mc.cat_expr_autoderefd(expr, autoderefs));
1150 debug!("expr_cmt={}", expr_cmt.repr(rcx.tcx()));
1153 ty::AutoPtr(r, m, _) => {
1154 link_region(rcx, expr.span, r,
1155 ty::BorrowKind::from_mutbl(m), expr_cmt);
1158 ty::AutoUnsafe(..) | ty::AutoUnsizeUniq(_) | ty::AutoUnsize(_) => {}
1162 /// Computes the guarantor for cases where the `expr` is being passed by implicit reference and
1163 /// must outlive `callee_scope`.
1164 fn link_by_ref(rcx: &Rcx,
1166 callee_scope: CodeExtent) {
1167 let tcx = rcx.tcx();
1168 debug!("link_by_ref(expr={}, callee_scope={:?})",
1169 expr.repr(tcx), callee_scope);
1170 let mc = mc::MemCategorizationContext::new(rcx.fcx);
1171 let expr_cmt = ignore_err!(mc.cat_expr(expr));
1172 let borrow_region = ty::ReScope(callee_scope);
1173 link_region(rcx, expr.span, borrow_region, ty::ImmBorrow, expr_cmt);
1176 /// Like `link_region()`, except that the region is extracted from the type of `id`, which must be
1177 /// some reference (`&T`, `&str`, etc).
1178 fn link_region_from_node_type<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1181 mutbl: ast::Mutability,
1182 cmt_borrowed: mc::cmt<'tcx>) {
1183 debug!("link_region_from_node_type(id={:?}, mutbl={:?}, cmt_borrowed={})",
1184 id, mutbl, cmt_borrowed.repr(rcx.tcx()));
1186 let rptr_ty = rcx.resolve_node_type(id);
1187 if !ty::type_is_error(rptr_ty) {
1188 let tcx = rcx.fcx.ccx.tcx;
1189 debug!("rptr_ty={}", ty_to_string(tcx, rptr_ty));
1190 let r = ty::ty_region(tcx, span, rptr_ty);
1191 link_region(rcx, span, r, ty::BorrowKind::from_mutbl(mutbl),
1196 /// Informs the inference engine that `borrow_cmt` is being borrowed with kind `borrow_kind` and
1197 /// lifetime `borrow_region`. In order to ensure borrowck is satisfied, this may create constraints
1198 /// between regions, as explained in `link_reborrowed_region()`.
1199 fn link_region<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1201 borrow_region: ty::Region,
1202 borrow_kind: ty::BorrowKind,
1203 borrow_cmt: mc::cmt<'tcx>) {
1204 let mut borrow_cmt = borrow_cmt;
1205 let mut borrow_kind = borrow_kind;
1208 debug!("link_region(borrow_region={}, borrow_kind={}, borrow_cmt={})",
1209 borrow_region.repr(rcx.tcx()),
1210 borrow_kind.repr(rcx.tcx()),
1211 borrow_cmt.repr(rcx.tcx()));
1212 match borrow_cmt.cat.clone() {
1213 mc::cat_deref(ref_cmt, _,
1214 mc::Implicit(ref_kind, ref_region)) |
1215 mc::cat_deref(ref_cmt, _,
1216 mc::BorrowedPtr(ref_kind, ref_region)) => {
1217 match link_reborrowed_region(rcx, span,
1218 borrow_region, borrow_kind,
1219 ref_cmt, ref_region, ref_kind,
1231 mc::cat_downcast(cmt_base, _) |
1232 mc::cat_deref(cmt_base, _, mc::Unique) |
1233 mc::cat_interior(cmt_base, _) => {
1234 // Borrowing interior or owned data requires the base
1235 // to be valid and borrowable in the same fashion.
1236 borrow_cmt = cmt_base;
1237 borrow_kind = borrow_kind;
1240 mc::cat_deref(_, _, mc::UnsafePtr(..)) |
1241 mc::cat_static_item |
1244 mc::cat_rvalue(..) => {
1245 // These are all "base cases" with independent lifetimes
1246 // that are not subject to inference
1253 /// This is the most complicated case: the path being borrowed is
1254 /// itself the referent of a borrowed pointer. Let me give an
1255 /// example fragment of code to make clear(er) the situation:
1257 /// let r: &'a mut T = ...; // the original reference "r" has lifetime 'a
1259 /// &'z *r // the reborrow has lifetime 'z
1261 /// Now, in this case, our primary job is to add the inference
1262 /// constraint that `'z <= 'a`. Given this setup, let's clarify the
1263 /// parameters in (roughly) terms of the example:
1265 /// A borrow of: `& 'z bk * r` where `r` has type `& 'a bk T`
1266 /// borrow_region ^~ ref_region ^~
1267 /// borrow_kind ^~ ref_kind ^~
1270 /// Here `bk` stands for some borrow-kind (e.g., `mut`, `uniq`, etc).
1272 /// Unfortunately, there are some complications beyond the simple
1273 /// scenario I just painted:
1275 /// 1. The reference `r` might in fact be a "by-ref" upvar. In that
1276 /// case, we have two jobs. First, we are inferring whether this reference
1277 /// should be an `&T`, `&mut T`, or `&uniq T` reference, and we must
1278 /// adjust that based on this borrow (e.g., if this is an `&mut` borrow,
1279 /// then `r` must be an `&mut` reference). Second, whenever we link
1280 /// two regions (here, `'z <= 'a`), we supply a *cause*, and in this
1281 /// case we adjust the cause to indicate that the reference being
1282 /// "reborrowed" is itself an upvar. This provides a nicer error message
1283 /// should something go wrong.
1285 /// 2. There may in fact be more levels of reborrowing. In the
1286 /// example, I said the borrow was like `&'z *r`, but it might
1287 /// in fact be a borrow like `&'z **q` where `q` has type `&'a
1288 /// &'b mut T`. In that case, we want to ensure that `'z <= 'a`
1289 /// and `'z <= 'b`. This is explained more below.
1291 /// The return value of this function indicates whether we need to
1292 /// recurse and process `ref_cmt` (see case 2 above).
1293 fn link_reborrowed_region<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1295 borrow_region: ty::Region,
1296 borrow_kind: ty::BorrowKind,
1297 ref_cmt: mc::cmt<'tcx>,
1298 ref_region: ty::Region,
1299 mut ref_kind: ty::BorrowKind,
1301 -> Option<(mc::cmt<'tcx>, ty::BorrowKind)>
1303 // Possible upvar ID we may need later to create an entry in the
1306 // Detect by-ref upvar `x`:
1307 let cause = match note {
1308 mc::NoteUpvarRef(ref upvar_id) => {
1309 let upvar_capture_map = rcx.fcx.inh.upvar_capture_map.borrow_mut();
1310 match upvar_capture_map.get(upvar_id) {
1311 Some(&ty::UpvarCapture::ByRef(ref upvar_borrow)) => {
1312 // The mutability of the upvar may have been modified
1313 // by the above adjustment, so update our local variable.
1314 ref_kind = upvar_borrow.kind;
1316 infer::ReborrowUpvar(span, *upvar_id)
1319 rcx.tcx().sess.span_bug(
1321 &format!("Illegal upvar id: {}",
1322 upvar_id.repr(rcx.tcx()))[]);
1326 mc::NoteClosureEnv(ref upvar_id) => {
1327 // We don't have any mutability changes to propagate, but
1328 // we do want to note that an upvar reborrow caused this
1330 infer::ReborrowUpvar(span, *upvar_id)
1333 infer::Reborrow(span)
1337 debug!("link_reborrowed_region: {} <= {}",
1338 borrow_region.repr(rcx.tcx()),
1339 ref_region.repr(rcx.tcx()));
1340 rcx.fcx.mk_subr(cause, borrow_region, ref_region);
1342 // If we end up needing to recurse and establish a region link
1343 // with `ref_cmt`, calculate what borrow kind we will end up
1344 // needing. This will be used below.
1346 // One interesting twist is that we can weaken the borrow kind
1347 // when we recurse: to reborrow an `&mut` referent as mutable,
1348 // borrowck requires a unique path to the `&mut` reference but not
1349 // necessarily a *mutable* path.
1350 let new_borrow_kind = match borrow_kind {
1353 ty::MutBorrow | ty::UniqueImmBorrow =>
1357 // Decide whether we need to recurse and link any regions within
1358 // the `ref_cmt`. This is concerned for the case where the value
1359 // being reborrowed is in fact a borrowed pointer found within
1360 // another borrowed pointer. For example:
1362 // let p: &'b &'a mut T = ...;
1366 // What makes this case particularly tricky is that, if the data
1367 // being borrowed is a `&mut` or `&uniq` borrow, borrowck requires
1368 // not only that `'z <= 'a`, (as before) but also `'z <= 'b`
1369 // (otherwise the user might mutate through the `&mut T` reference
1370 // after `'b` expires and invalidate the borrow we are looking at
1373 // So let's re-examine our parameters in light of this more
1374 // complicated (possible) scenario:
1376 // A borrow of: `& 'z bk * * p` where `p` has type `&'b bk & 'a bk T`
1377 // borrow_region ^~ ref_region ^~
1378 // borrow_kind ^~ ref_kind ^~
1381 // (Note that since we have not examined `ref_cmt.cat`, we don't
1382 // know whether this scenario has occurred; but I wanted to show
1383 // how all the types get adjusted.)
1386 // The reference being reborrowed is a sharable ref of
1387 // type `&'a T`. In this case, it doesn't matter where we
1388 // *found* the `&T` pointer, the memory it references will
1389 // be valid and immutable for `'a`. So we can stop here.
1391 // (Note that the `borrow_kind` must also be ImmBorrow or
1392 // else the user is borrowed imm memory as mut memory,
1393 // which means they'll get an error downstream in borrowck
1398 ty::MutBorrow | ty::UniqueImmBorrow => {
1399 // The reference being reborrowed is either an `&mut T` or
1400 // `&uniq T`. This is the case where recursion is needed.
1401 return Some((ref_cmt, new_borrow_kind));
1406 /// Ensures that all borrowed data reachable via `ty` outlives `region`.
1407 fn type_must_outlive<'a, 'tcx>(rcx: &mut Rcx<'a, 'tcx>,
1408 origin: infer::SubregionOrigin<'tcx>,
1412 debug!("type_must_outlive(ty={}, region={})",
1414 region.repr(rcx.tcx()));
1417 regionmanip::region_wf_constraints(
1421 for constraint in &constraints {
1422 debug!("constraint: {}", constraint.repr(rcx.tcx()));
1424 regionmanip::RegionSubRegionConstraint(None, r_a, r_b) => {
1425 rcx.fcx.mk_subr(origin.clone(), r_a, r_b);
1427 regionmanip::RegionSubRegionConstraint(Some(ty), r_a, r_b) => {
1428 let o1 = infer::ReferenceOutlivesReferent(ty, origin.span());
1429 rcx.fcx.mk_subr(o1, r_a, r_b);
1431 regionmanip::RegionSubGenericConstraint(None, r_a, ref generic_b) => {
1432 generic_must_outlive(rcx, origin.clone(), r_a, generic_b);
1434 regionmanip::RegionSubGenericConstraint(Some(ty), r_a, ref generic_b) => {
1435 let o1 = infer::ReferenceOutlivesReferent(ty, origin.span());
1436 generic_must_outlive(rcx, o1, r_a, generic_b);
1442 fn generic_must_outlive<'a, 'tcx>(rcx: &Rcx<'a, 'tcx>,
1443 origin: infer::SubregionOrigin<'tcx>,
1445 generic: &GenericKind<'tcx>) {
1446 let param_env = &rcx.fcx.inh.param_env;
1448 debug!("param_must_outlive(region={}, generic={})",
1449 region.repr(rcx.tcx()),
1450 generic.repr(rcx.tcx()));
1452 // To start, collect bounds from user:
1453 let mut param_bounds =
1454 ty::required_region_bounds(rcx.tcx(),
1455 generic.to_ty(rcx.tcx()),
1456 param_env.caller_bounds.clone());
1458 // In the case of a projection T::Foo, we may be able to extract bounds from the trait def:
1460 GenericKind::Param(..) => { }
1461 GenericKind::Projection(ref projection_ty) => {
1462 param_bounds.push_all(
1463 &projection_bounds(rcx, origin.span(), projection_ty)[]);
1467 // Add in the default bound of fn body that applies to all in
1468 // scope type parameters:
1469 param_bounds.push(param_env.implicit_region_bound);
1471 // Finally, collect regions we scraped from the well-formedness
1472 // constraints in the fn signature. To do that, we walk the list
1473 // of known relations from the fn ctxt.
1475 // This is crucial because otherwise code like this fails:
1477 // fn foo<'a, A>(x: &'a A) { x.bar() }
1479 // The problem is that the type of `x` is `&'a A`. To be
1480 // well-formed, then, A must be lower-generic by `'a`, but we
1481 // don't know that this holds from first principles.
1482 for &(ref r, ref p) in &rcx.region_bound_pairs {
1483 debug!("generic={} p={}",
1484 generic.repr(rcx.tcx()),
1487 param_bounds.push(*r);
1491 // Inform region inference that this generic must be properly
1493 rcx.fcx.infcx().verify_generic_bound(origin,
1499 fn projection_bounds<'a,'tcx>(rcx: &Rcx<'a, 'tcx>,
1501 projection_ty: &ty::ProjectionTy<'tcx>)
1505 let tcx = fcx.tcx();
1506 let infcx = fcx.infcx();
1508 debug!("projection_bounds(projection_ty={})",
1509 projection_ty.repr(tcx));
1511 let ty = ty::mk_projection(tcx, projection_ty.trait_ref.clone(), projection_ty.item_name);
1513 // Say we have a projection `<T as SomeTrait<'a>>::SomeType`. We are interested
1514 // in looking for a trait definition like:
1517 // trait SomeTrait<'a> {
1518 // type SomeType : 'a;
1522 // we can thus deduce that `<T as SomeTrait<'a>>::SomeType : 'a`.
1523 let trait_def = ty::lookup_trait_def(tcx, projection_ty.trait_ref.def_id);
1524 let predicates = trait_def.generics.predicates.as_slice().to_vec();
1525 traits::elaborate_predicates(tcx, predicates)
1526 .filter_map(|predicate| {
1527 // we're only interesting in `T : 'a` style predicates:
1528 let outlives = match predicate {
1529 ty::Predicate::TypeOutlives(data) => data,
1530 _ => { return None; }
1533 debug!("projection_bounds: outlives={} (1)",
1534 outlives.repr(tcx));
1536 // apply the substitutions (and normalize any projected types)
1537 let outlives = fcx.instantiate_type_scheme(span,
1538 projection_ty.trait_ref.substs,
1541 debug!("projection_bounds: outlives={} (2)",
1542 outlives.repr(tcx));
1544 let region_result = infcx.try(|_| {
1546 infcx.replace_late_bound_regions_with_fresh_var(
1548 infer::AssocTypeProjection(projection_ty.item_name),
1551 debug!("projection_bounds: outlives={} (3)",
1552 outlives.repr(tcx));
1554 // check whether this predicate applies to our current projection
1555 match infer::mk_eqty(infcx, false, infer::Misc(span), ty, outlives.0) {
1556 Ok(()) => { Ok(outlives.1) }
1557 Err(_) => { Err(()) }
1561 debug!("projection_bounds: region_result={}",
1562 region_result.repr(tcx));