| // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| //! The region check is a final pass that runs over the AST after we have |
| //! inferred the type constraints but before we have actually finalized |
| //! the types. Its purpose is to embed a variety of region constraints. |
| //! Inserting these constraints as a separate pass is good because (1) it |
| //! localizes the code that has to do with region inference and (2) often |
| //! we cannot know what constraints are needed until the basic types have |
| //! been inferred. |
| //! |
| //! ### Interaction with the borrow checker |
| //! |
| //! In general, the job of the borrowck module (which runs later) is to |
| //! check that all soundness criteria are met, given a particular set of |
| //! regions. The job of *this* module is to anticipate the needs of the |
| //! borrow checker and infer regions that will satisfy its requirements. |
| //! It is generally true that the inference doesn't need to be sound, |
| //! meaning that if there is a bug and we inferred bad regions, the borrow |
| //! checker should catch it. This is not entirely true though; for |
| //! example, the borrow checker doesn't check subtyping, and it doesn't |
| //! check that region pointers are always live when they are used. It |
| //! might be worthwhile to fix this so that borrowck serves as a kind of |
| //! verification step -- that would add confidence in the overall |
| //! correctness of the compiler, at the cost of duplicating some type |
| //! checks and effort. |
| //! |
| //! ### Inferring the duration of borrows, automatic and otherwise |
| //! |
| //! Whenever we introduce a borrowed pointer, for example as the result of |
| //! a borrow expression `let x = &data`, the lifetime of the pointer `x` |
| //! is always specified as a region inference variable. `regionck` has the |
| //! job of adding constraints such that this inference variable is as |
| //! narrow as possible while still accommodating all uses (that is, every |
| //! dereference of the resulting pointer must be within the lifetime). |
| //! |
| //! #### Reborrows |
| //! |
| //! Generally speaking, `regionck` does NOT try to ensure that the data |
| //! `data` will outlive the pointer `x`. That is the job of borrowck. The |
| //! one exception is when "re-borrowing" the contents of another borrowed |
| //! pointer. For example, imagine you have a borrowed pointer `b` with |
| //! lifetime L1 and you have an expression `&*b`. The result of this |
| //! expression will be another borrowed pointer with lifetime L2 (which is |
| //! an inference variable). The borrow checker is going to enforce the |
| //! constraint that L2 < L1, because otherwise you are re-borrowing data |
| //! for a lifetime larger than the original loan. However, without the |
| //! routines in this module, the region inferencer would not know of this |
| //! dependency and thus it might infer the lifetime of L2 to be greater |
| //! than L1 (issue #3148). |
| //! |
| //! There are a number of troublesome scenarios in the tests |
| //! `region-dependent-*.rs`, but here is one example: |
| //! |
| //! struct Foo { i: i32 } |
| //! struct Bar { foo: Foo } |
| //! fn get_i<'a>(x: &'a Bar) -> &'a i32 { |
| //! let foo = &x.foo; // Lifetime L1 |
| //! &foo.i // Lifetime L2 |
| //! } |
| //! |
| //! Note that this comes up either with `&` expressions, `ref` |
| //! bindings, and `autorefs`, which are the three ways to introduce |
| //! a borrow. |
| //! |
| //! The key point here is that when you are borrowing a value that |
| //! is "guaranteed" by a borrowed pointer, you must link the |
| //! lifetime of that borrowed pointer (L1, here) to the lifetime of |
| //! the borrow itself (L2). What do I mean by "guaranteed" by a |
| //! borrowed pointer? I mean any data that is reached by first |
| //! dereferencing a borrowed pointer and then either traversing |
| //! interior offsets or boxes. We say that the guarantor |
| //! of such data is the region of the borrowed pointer that was |
| //! traversed. This is essentially the same as the ownership |
| //! relation, except that a borrowed pointer never owns its |
| //! contents. |
| |
| use check::dropck; |
| use check::FnCtxt; |
| use middle::free_region::FreeRegionMap; |
| use middle::mem_categorization as mc; |
| use middle::mem_categorization::Categorization; |
| use middle::region; |
| use rustc::hir::def_id::DefId; |
| use rustc::ty::subst::Substs; |
| use rustc::traits; |
| use rustc::ty::{self, Ty, TypeFoldable}; |
| use rustc::infer::{self, GenericKind, SubregionOrigin, VerifyBound}; |
| use rustc::ty::adjustment; |
| use rustc::ty::outlives::Component; |
| use rustc::ty::wf; |
| |
| use std::mem; |
| use std::ops::Deref; |
| use std::rc::Rc; |
| use syntax::ast; |
| use syntax_pos::Span; |
| use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap}; |
| use rustc::hir::{self, PatKind}; |
| |
| // a variation on try that just returns unit |
| macro_rules! ignore_err { |
| ($e:expr) => (match $e { Ok(e) => e, Err(_) => return () }) |
| } |
| |
| /////////////////////////////////////////////////////////////////////////// |
| // PUBLIC ENTRY POINTS |
| |
| impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> { |
| pub fn regionck_expr(&self, body: &'gcx hir::Body) { |
| let subject = self.tcx.hir.body_owner_def_id(body.id()); |
| let id = body.value.id; |
| let mut rcx = RegionCtxt::new(self, RepeatingScope(id), id, Subject(subject)); |
| if self.err_count_since_creation() == 0 { |
| // regionck assumes typeck succeeded |
| rcx.visit_body(body); |
| rcx.visit_region_obligations(id); |
| } |
| rcx.resolve_regions_and_report_errors(); |
| |
| assert!(self.tables.borrow().free_region_map.is_empty()); |
| self.tables.borrow_mut().free_region_map = rcx.free_region_map; |
| } |
| |
| /// Region checking during the WF phase for items. `wf_tys` are the |
| /// types from which we should derive implied bounds, if any. |
| pub fn regionck_item(&self, |
| item_id: ast::NodeId, |
| span: Span, |
| wf_tys: &[Ty<'tcx>]) { |
| debug!("regionck_item(item.id={:?}, wf_tys={:?}", item_id, wf_tys); |
| let subject = self.tcx.hir.local_def_id(item_id); |
| let mut rcx = RegionCtxt::new(self, RepeatingScope(item_id), item_id, Subject(subject)); |
| rcx.free_region_map.relate_free_regions_from_predicates( |
| &self.param_env.caller_bounds); |
| rcx.relate_free_regions(wf_tys, item_id, span); |
| rcx.visit_region_obligations(item_id); |
| rcx.resolve_regions_and_report_errors(); |
| } |
| |
| pub fn regionck_fn(&self, |
| fn_id: ast::NodeId, |
| body: &'gcx hir::Body) { |
| debug!("regionck_fn(id={})", fn_id); |
| let subject = self.tcx.hir.body_owner_def_id(body.id()); |
| let node_id = body.value.id; |
| let mut rcx = RegionCtxt::new(self, RepeatingScope(node_id), node_id, Subject(subject)); |
| |
| if self.err_count_since_creation() == 0 { |
| // regionck assumes typeck succeeded |
| rcx.visit_fn_body(fn_id, body, self.tcx.hir.span(fn_id)); |
| } |
| |
| rcx.free_region_map.relate_free_regions_from_predicates( |
| &self.param_env.caller_bounds); |
| |
| rcx.resolve_regions_and_report_errors(); |
| |
| // In this mode, we also copy the free-region-map into the |
| // tables of the enclosing fcx. In the other regionck modes |
| // (e.g., `regionck_item`), we don't have an enclosing tables. |
| assert!(self.tables.borrow().free_region_map.is_empty()); |
| self.tables.borrow_mut().free_region_map = rcx.free_region_map; |
| } |
| } |
| |
| /////////////////////////////////////////////////////////////////////////// |
| // INTERNALS |
| |
| pub struct RegionCtxt<'a, 'gcx: 'a+'tcx, 'tcx: 'a> { |
| pub fcx: &'a FnCtxt<'a, 'gcx, 'tcx>, |
| |
| region_bound_pairs: Vec<(ty::Region<'tcx>, GenericKind<'tcx>)>, |
| |
| pub region_scope_tree: Rc<region::ScopeTree>, |
| |
| free_region_map: FreeRegionMap<'tcx>, |
| |
| // id of innermost fn body id |
| body_id: ast::NodeId, |
| |
| // call_site scope of innermost fn |
| call_site_scope: Option<region::Scope>, |
| |
| // id of innermost fn or loop |
| repeating_scope: ast::NodeId, |
| |
| // id of AST node being analyzed (the subject of the analysis). |
| subject_def_id: DefId, |
| |
| } |
| |
| /// Implied bounds are region relationships that we deduce |
| /// automatically. The idea is that (e.g.) a caller must check that a |
| /// function's argument types are well-formed immediately before |
| /// calling that fn, and hence the *callee* can assume that its |
| /// argument types are well-formed. This may imply certain relationships |
| /// between generic parameters. For example: |
| /// |
| /// fn foo<'a,T>(x: &'a T) |
| /// |
| /// can only be called with a `'a` and `T` such that `&'a T` is WF. |
| /// For `&'a T` to be WF, `T: 'a` must hold. So we can assume `T: 'a`. |
| #[derive(Debug)] |
| enum ImpliedBound<'tcx> { |
| RegionSubRegion(ty::Region<'tcx>, ty::Region<'tcx>), |
| RegionSubParam(ty::Region<'tcx>, ty::ParamTy), |
| RegionSubProjection(ty::Region<'tcx>, ty::ProjectionTy<'tcx>), |
| } |
| |
| impl<'a, 'gcx, 'tcx> Deref for RegionCtxt<'a, 'gcx, 'tcx> { |
| type Target = FnCtxt<'a, 'gcx, 'tcx>; |
| fn deref(&self) -> &Self::Target { |
| &self.fcx |
| } |
| } |
| |
| pub struct RepeatingScope(ast::NodeId); |
| pub struct Subject(DefId); |
| |
| impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> { |
| pub fn new(fcx: &'a FnCtxt<'a, 'gcx, 'tcx>, |
| RepeatingScope(initial_repeating_scope): RepeatingScope, |
| initial_body_id: ast::NodeId, |
| Subject(subject): Subject) -> RegionCtxt<'a, 'gcx, 'tcx> { |
| let region_scope_tree = fcx.tcx.region_scope_tree(subject); |
| RegionCtxt { |
| fcx, |
| region_scope_tree, |
| repeating_scope: initial_repeating_scope, |
| body_id: initial_body_id, |
| call_site_scope: None, |
| subject_def_id: subject, |
| region_bound_pairs: Vec::new(), |
| free_region_map: FreeRegionMap::new(), |
| } |
| } |
| |
| fn set_call_site_scope(&mut self, call_site_scope: Option<region::Scope>) |
| -> Option<region::Scope> { |
| mem::replace(&mut self.call_site_scope, call_site_scope) |
| } |
| |
| fn set_body_id(&mut self, body_id: ast::NodeId) -> ast::NodeId { |
| mem::replace(&mut self.body_id, body_id) |
| } |
| |
| fn set_repeating_scope(&mut self, scope: ast::NodeId) -> ast::NodeId { |
| mem::replace(&mut self.repeating_scope, scope) |
| } |
| |
| /// Try to resolve the type for the given node, returning t_err if an error results. Note that |
| /// we never care about the details of the error, the same error will be detected and reported |
| /// in the writeback phase. |
| /// |
| /// Note one important point: we do not attempt to resolve *region variables* here. This is |
| /// because regionck is essentially adding constraints to those region variables and so may yet |
| /// influence how they are resolved. |
| /// |
| /// Consider this silly example: |
| /// |
| /// ``` |
| /// fn borrow(x: &i32) -> &i32 {x} |
| /// fn foo(x: @i32) -> i32 { // block: B |
| /// let b = borrow(x); // region: <R0> |
| /// *b |
| /// } |
| /// ``` |
| /// |
| /// Here, the region of `b` will be `<R0>`. `<R0>` is constrained to be some subregion of the |
| /// block B and some superregion of the call. If we forced it now, we'd choose the smaller |
| /// region (the call). But that would make the *b illegal. Since we don't resolve, the type |
| /// of b will be `&<R0>.i32` and then `*b` will require that `<R0>` be bigger than the let and |
| /// the `*b` expression, so we will effectively resolve `<R0>` to be the block B. |
| pub fn resolve_type(&self, unresolved_ty: Ty<'tcx>) -> Ty<'tcx> { |
| self.resolve_type_vars_if_possible(&unresolved_ty) |
| } |
| |
| /// Try to resolve the type for the given node. |
| fn resolve_node_type(&self, id: hir::HirId) -> Ty<'tcx> { |
| let t = self.node_ty(id); |
| self.resolve_type(t) |
| } |
| |
| /// Try to resolve the type for the given node. |
| pub fn resolve_expr_type_adjusted(&mut self, expr: &hir::Expr) -> Ty<'tcx> { |
| let ty = self.tables.borrow().expr_ty_adjusted(expr); |
| self.resolve_type(ty) |
| } |
| |
| fn visit_fn_body(&mut self, |
| id: ast::NodeId, // the id of the fn itself |
| body: &'gcx hir::Body, |
| span: Span) |
| { |
| // When we enter a function, we can derive |
| debug!("visit_fn_body(id={})", id); |
| |
| let body_id = body.id(); |
| |
| let call_site = region::Scope::CallSite(body.value.hir_id.local_id); |
| let old_call_site_scope = self.set_call_site_scope(Some(call_site)); |
| |
| let fn_sig = { |
| let fn_hir_id = self.tcx.hir.node_to_hir_id(id); |
| match self.tables.borrow().liberated_fn_sigs().get(fn_hir_id) { |
| Some(f) => f.clone(), |
| None => { |
| bug!("No fn-sig entry for id={}", id); |
| } |
| } |
| }; |
| |
| let old_region_bounds_pairs_len = self.region_bound_pairs.len(); |
| |
| // Collect the types from which we create inferred bounds. |
| // For the return type, if diverging, substitute `bool` just |
| // because it will have no effect. |
| // |
| // FIXME(#27579) return types should not be implied bounds |
| let fn_sig_tys: Vec<_> = |
| fn_sig.inputs().iter().cloned().chain(Some(fn_sig.output())).collect(); |
| |
| let old_body_id = self.set_body_id(body_id.node_id); |
| self.relate_free_regions(&fn_sig_tys[..], body_id.node_id, span); |
| self.link_fn_args(region::Scope::Node(body.value.hir_id.local_id), &body.arguments); |
| self.visit_body(body); |
| self.visit_region_obligations(body_id.node_id); |
| |
| let call_site_scope = self.call_site_scope.unwrap(); |
| debug!("visit_fn_body body.id {:?} call_site_scope: {:?}", |
| body.id(), call_site_scope); |
| let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope)); |
| let body_hir_id = self.tcx.hir.node_to_hir_id(body_id.node_id); |
| self.type_of_node_must_outlive(infer::CallReturn(span), |
| body_hir_id, |
| call_site_region); |
| |
| self.region_bound_pairs.truncate(old_region_bounds_pairs_len); |
| |
| self.set_body_id(old_body_id); |
| self.set_call_site_scope(old_call_site_scope); |
| } |
| |
| fn visit_region_obligations(&mut self, node_id: ast::NodeId) |
| { |
| debug!("visit_region_obligations: node_id={}", node_id); |
| |
| // region checking can introduce new pending obligations |
| // which, when processed, might generate new region |
| // obligations. So make sure we process those. |
| self.select_all_obligations_or_error(); |
| |
| // Make a copy of the region obligations vec because we'll need |
| // to be able to borrow the fulfillment-cx below when projecting. |
| let region_obligations = |
| self.fulfillment_cx |
| .borrow() |
| .region_obligations(node_id) |
| .to_vec(); |
| |
| for r_o in ®ion_obligations { |
| debug!("visit_region_obligations: r_o={:?} cause={:?}", |
| r_o, r_o.cause); |
| let sup_type = self.resolve_type(r_o.sup_type); |
| let origin = self.code_to_origin(&r_o.cause, sup_type); |
| self.type_must_outlive(origin, sup_type, r_o.sub_region); |
| } |
| |
| // Processing the region obligations should not cause the list to grow further: |
| assert_eq!(region_obligations.len(), |
| self.fulfillment_cx.borrow().region_obligations(node_id).len()); |
| } |
| |
| fn code_to_origin(&self, |
| cause: &traits::ObligationCause<'tcx>, |
| sup_type: Ty<'tcx>) |
| -> SubregionOrigin<'tcx> { |
| SubregionOrigin::from_obligation_cause(cause, |
| || infer::RelateParamBound(cause.span, sup_type)) |
| } |
| |
| /// This method populates the region map's `free_region_map`. It walks over the transformed |
| /// argument and return types for each function just before we check the body of that function, |
| /// looking for types where you have a borrowed pointer to other borrowed data (e.g., `&'a &'b |
| /// [usize]`. We do not allow references to outlive the things they point at, so we can assume |
| /// that `'a <= 'b`. This holds for both the argument and return types, basically because, on |
| /// the caller side, the caller is responsible for checking that the type of every expression |
| /// (including the actual values for the arguments, as well as the return type of the fn call) |
| /// is well-formed. |
| /// |
| /// Tests: `src/test/compile-fail/regions-free-region-ordering-*.rs` |
| fn relate_free_regions(&mut self, |
| fn_sig_tys: &[Ty<'tcx>], |
| body_id: ast::NodeId, |
| span: Span) { |
| debug!("relate_free_regions >>"); |
| |
| for &ty in fn_sig_tys { |
| let ty = self.resolve_type(ty); |
| debug!("relate_free_regions(t={:?})", ty); |
| let implied_bounds = self.implied_bounds(body_id, ty, span); |
| |
| // But also record other relationships, such as `T:'x`, |
| // that don't go into the free-region-map but which we use |
| // here. |
| for implication in implied_bounds { |
| debug!("implication: {:?}", implication); |
| match implication { |
| ImpliedBound::RegionSubRegion(r_a @ &ty::ReEarlyBound(_), |
| &ty::ReVar(vid_b)) | |
| ImpliedBound::RegionSubRegion(r_a @ &ty::ReFree(_), |
| &ty::ReVar(vid_b)) => { |
| self.add_given(r_a, vid_b); |
| } |
| ImpliedBound::RegionSubParam(r_a, param_b) => { |
| self.region_bound_pairs.push((r_a, GenericKind::Param(param_b))); |
| } |
| ImpliedBound::RegionSubProjection(r_a, projection_b) => { |
| self.region_bound_pairs.push((r_a, GenericKind::Projection(projection_b))); |
| } |
| ImpliedBound::RegionSubRegion(r_a, r_b) => { |
| // In principle, we could record (and take |
| // advantage of) every relationship here, but |
| // we are also free not to -- it simply means |
| // strictly less that we can successfully type |
| // check. Right now we only look for things |
| // relationships between free regions. (It may |
| // also be that we should revise our inference |
| // system to be more general and to make use |
| // of *every* relationship that arises here, |
| // but presently we do not.) |
| self.free_region_map.relate_regions(r_a, r_b); |
| } |
| } |
| } |
| } |
| |
| debug!("<< relate_free_regions"); |
| } |
| |
| /// Compute the implied bounds that a callee/impl can assume based on |
| /// the fact that caller/projector has ensured that `ty` is WF. See |
| /// the `ImpliedBound` type for more details. |
| fn implied_bounds(&mut self, body_id: ast::NodeId, ty: Ty<'tcx>, span: Span) |
| -> Vec<ImpliedBound<'tcx>> { |
| // Sometimes when we ask what it takes for T: WF, we get back that |
| // U: WF is required; in that case, we push U onto this stack and |
| // process it next. Currently (at least) these resulting |
| // predicates are always guaranteed to be a subset of the original |
| // type, so we need not fear non-termination. |
| let mut wf_types = vec![ty]; |
| |
| let mut implied_bounds = vec![]; |
| |
| while let Some(ty) = wf_types.pop() { |
| // Compute the obligations for `ty` to be well-formed. If `ty` is |
| // an unresolved inference variable, just substituted an empty set |
| // -- because the return type here is going to be things we *add* |
| // to the environment, it's always ok for this set to be smaller |
| // than the ultimate set. (Note: normally there won't be |
| // unresolved inference variables here anyway, but there might be |
| // during typeck under some circumstances.) |
| let obligations = |
| wf::obligations(self, self.fcx.param_env, body_id, ty, span) |
| .unwrap_or(vec![]); |
| |
| // NB: All of these predicates *ought* to be easily proven |
| // true. In fact, their correctness is (mostly) implied by |
| // other parts of the program. However, in #42552, we had |
| // an annoying scenario where: |
| // |
| // - Some `T::Foo` gets normalized, resulting in a |
| // variable `_1` and a `T: Trait<Foo=_1>` constraint |
| // (not sure why it couldn't immediately get |
| // solved). This result of `_1` got cached. |
| // - These obligations were dropped on the floor here, |
| // rather than being registered. |
| // - Then later we would get a request to normalize |
| // `T::Foo` which would result in `_1` being used from |
| // the cache, but hence without the `T: Trait<Foo=_1>` |
| // constraint. As a result, `_1` never gets resolved, |
| // and we get an ICE (in dropck). |
| // |
| // Therefore, we register any predicates involving |
| // inference variables. We restrict ourselves to those |
| // involving inference variables both for efficiency and |
| // to avoids duplicate errors that otherwise show up. |
| self.fcx.register_predicates( |
| obligations.iter() |
| .filter(|o| o.predicate.has_infer_types()) |
| .cloned()); |
| |
| // From the full set of obligations, just filter down to the |
| // region relationships. |
| implied_bounds.extend( |
| obligations |
| .into_iter() |
| .flat_map(|obligation| { |
| assert!(!obligation.has_escaping_regions()); |
| match obligation.predicate { |
| ty::Predicate::Trait(..) | |
| ty::Predicate::Equate(..) | |
| ty::Predicate::Subtype(..) | |
| ty::Predicate::Projection(..) | |
| ty::Predicate::ClosureKind(..) | |
| ty::Predicate::ObjectSafe(..) | |
| ty::Predicate::ConstEvaluatable(..) => |
| vec![], |
| |
| ty::Predicate::WellFormed(subty) => { |
| wf_types.push(subty); |
| vec![] |
| } |
| |
| ty::Predicate::RegionOutlives(ref data) => |
| match self.tcx.no_late_bound_regions(data) { |
| None => |
| vec![], |
| Some(ty::OutlivesPredicate(r_a, r_b)) => |
| vec![ImpliedBound::RegionSubRegion(r_b, r_a)], |
| }, |
| |
| ty::Predicate::TypeOutlives(ref data) => |
| match self.tcx.no_late_bound_regions(data) { |
| None => vec![], |
| Some(ty::OutlivesPredicate(ty_a, r_b)) => { |
| let ty_a = self.resolve_type_vars_if_possible(&ty_a); |
| let components = self.tcx.outlives_components(ty_a); |
| self.implied_bounds_from_components(r_b, components) |
| } |
| }, |
| }})); |
| } |
| |
| implied_bounds |
| } |
| |
| /// When we have an implied bound that `T: 'a`, we can further break |
| /// this down to determine what relationships would have to hold for |
| /// `T: 'a` to hold. We get to assume that the caller has validated |
| /// those relationships. |
| fn implied_bounds_from_components(&self, |
| sub_region: ty::Region<'tcx>, |
| sup_components: Vec<Component<'tcx>>) |
| -> Vec<ImpliedBound<'tcx>> |
| { |
| sup_components |
| .into_iter() |
| .flat_map(|component| { |
| match component { |
| Component::Region(r) => |
| vec![ImpliedBound::RegionSubRegion(sub_region, r)], |
| Component::Param(p) => |
| vec![ImpliedBound::RegionSubParam(sub_region, p)], |
| Component::Projection(p) => |
| vec![ImpliedBound::RegionSubProjection(sub_region, p)], |
| Component::EscapingProjection(_) => |
| // If the projection has escaping regions, don't |
| // try to infer any implied bounds even for its |
| // free components. This is conservative, because |
| // the caller will still have to prove that those |
| // free components outlive `sub_region`. But the |
| // idea is that the WAY that the caller proves |
| // that may change in the future and we want to |
| // give ourselves room to get smarter here. |
| vec![], |
| Component::UnresolvedInferenceVariable(..) => |
| vec![], |
| } |
| }) |
| .collect() |
| } |
| |
| fn resolve_regions_and_report_errors(&self) { |
| self.fcx.resolve_regions_and_report_errors(self.subject_def_id, |
| &self.region_scope_tree, |
| &self.free_region_map); |
| } |
| |
| fn constrain_bindings_in_pat(&mut self, pat: &hir::Pat) { |
| debug!("regionck::visit_pat(pat={:?})", pat); |
| pat.each_binding(|_, id, span, _| { |
| // If we have a variable that contains region'd data, that |
| // data will be accessible from anywhere that the variable is |
| // accessed. We must be wary of loops like this: |
| // |
| // // from src/test/compile-fail/borrowck-lend-flow.rs |
| // let mut v = box 3, w = box 4; |
| // let mut x = &mut w; |
| // loop { |
| // **x += 1; // (2) |
| // borrow(v); //~ ERROR cannot borrow |
| // x = &mut v; // (1) |
| // } |
| // |
| // Typically, we try to determine the region of a borrow from |
| // those points where it is dereferenced. In this case, one |
| // might imagine that the lifetime of `x` need only be the |
| // body of the loop. But of course this is incorrect because |
| // the pointer that is created at point (1) is consumed at |
| // point (2), meaning that it must be live across the loop |
| // iteration. The easiest way to guarantee this is to require |
| // that the lifetime of any regions that appear in a |
| // variable's type enclose at least the variable's scope. |
| |
| let hir_id = self.tcx.hir.node_to_hir_id(id); |
| let var_scope = self.region_scope_tree.var_scope(hir_id.local_id); |
| let var_region = self.tcx.mk_region(ty::ReScope(var_scope)); |
| |
| let origin = infer::BindingTypeIsNotValidAtDecl(span); |
| self.type_of_node_must_outlive(origin, hir_id, var_region); |
| |
| let typ = self.resolve_node_type(hir_id); |
| let _ = dropck::check_safety_of_destructor_if_necessary( |
| self, typ, span, var_scope); |
| }) |
| } |
| } |
| |
| impl<'a, 'gcx, 'tcx> Visitor<'gcx> for RegionCtxt<'a, 'gcx, 'tcx> { |
| // (..) FIXME(#3238) should use visit_pat, not visit_arm/visit_local, |
| // However, right now we run into an issue whereby some free |
| // regions are not properly related if they appear within the |
| // types of arguments that must be inferred. This could be |
| // addressed by deferring the construction of the region |
| // hierarchy, and in particular the relationships between free |
| // regions, until regionck, as described in #3238. |
| |
| fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'gcx> { |
| NestedVisitorMap::None |
| } |
| |
| fn visit_fn(&mut self, _fk: intravisit::FnKind<'gcx>, _: &'gcx hir::FnDecl, |
| b: hir::BodyId, span: Span, id: ast::NodeId) { |
| let body = self.tcx.hir.body(b); |
| self.visit_fn_body(id, body, span) |
| } |
| |
| //visit_pat: visit_pat, // (..) see above |
| |
| fn visit_arm(&mut self, arm: &'gcx hir::Arm) { |
| // see above |
| for p in &arm.pats { |
| self.constrain_bindings_in_pat(p); |
| } |
| intravisit::walk_arm(self, arm); |
| } |
| |
| fn visit_local(&mut self, l: &'gcx hir::Local) { |
| // see above |
| self.constrain_bindings_in_pat(&l.pat); |
| self.link_local(l); |
| intravisit::walk_local(self, l); |
| } |
| |
| fn visit_expr(&mut self, expr: &'gcx hir::Expr) { |
| debug!("regionck::visit_expr(e={:?}, repeating_scope={})", |
| expr, self.repeating_scope); |
| |
| // No matter what, the type of each expression must outlive the |
| // scope of that expression. This also guarantees basic WF. |
| let expr_ty = self.resolve_node_type(expr.hir_id); |
| // the region corresponding to this expression |
| let expr_region = self.tcx.mk_region(ty::ReScope( |
| region::Scope::Node(expr.hir_id.local_id))); |
| self.type_must_outlive(infer::ExprTypeIsNotInScope(expr_ty, expr.span), |
| expr_ty, expr_region); |
| |
| let is_method_call = self.tables.borrow().is_method_call(expr); |
| |
| // If we are calling a method (either explicitly or via an |
| // overloaded operator), check that all of the types provided as |
| // arguments for its type parameters are well-formed, and all the regions |
| // provided as arguments outlive the call. |
| if is_method_call { |
| let origin = match expr.node { |
| hir::ExprMethodCall(..) => |
| infer::ParameterOrigin::MethodCall, |
| hir::ExprUnary(op, _) if op == hir::UnDeref => |
| infer::ParameterOrigin::OverloadedDeref, |
| _ => |
| infer::ParameterOrigin::OverloadedOperator |
| }; |
| |
| let substs = self.tables.borrow().node_substs(expr.hir_id); |
| self.substs_wf_in_scope(origin, substs, expr.span, expr_region); |
| // Arguments (sub-expressions) are checked via `constrain_call`, below. |
| } |
| |
| // Check any autoderefs or autorefs that appear. |
| let cmt_result = self.constrain_adjustments(expr); |
| |
| // If necessary, constrain destructors in this expression. This will be |
| // the adjusted form if there is an adjustment. |
| match cmt_result { |
| Ok(head_cmt) => { |
| self.check_safety_of_rvalue_destructor_if_necessary(head_cmt, expr.span); |
| } |
| Err(..) => { |
| self.tcx.sess.delay_span_bug(expr.span, "cat_expr Errd"); |
| } |
| } |
| |
| debug!("regionck::visit_expr(e={:?}, repeating_scope={}) - visiting subexprs", |
| expr, self.repeating_scope); |
| match expr.node { |
| hir::ExprPath(_) => { |
| let substs = self.tables.borrow().node_substs(expr.hir_id); |
| let origin = infer::ParameterOrigin::Path; |
| self.substs_wf_in_scope(origin, substs, expr.span, expr_region); |
| } |
| |
| hir::ExprCall(ref callee, ref args) => { |
| if is_method_call { |
| self.constrain_call(expr, Some(&callee), args.iter().map(|e| &*e)); |
| } else { |
| self.constrain_callee(&callee); |
| self.constrain_call(expr, None, args.iter().map(|e| &*e)); |
| } |
| |
| intravisit::walk_expr(self, expr); |
| } |
| |
| hir::ExprMethodCall(.., ref args) => { |
| self.constrain_call(expr, Some(&args[0]), args[1..].iter().map(|e| &*e)); |
| |
| intravisit::walk_expr(self, expr); |
| } |
| |
| hir::ExprAssignOp(_, ref lhs, ref rhs) => { |
| if is_method_call { |
| self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter()); |
| } |
| |
| intravisit::walk_expr(self, expr); |
| } |
| |
| hir::ExprIndex(ref lhs, ref rhs) if is_method_call => { |
| self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter()); |
| |
| intravisit::walk_expr(self, expr); |
| }, |
| |
| hir::ExprBinary(_, ref lhs, ref rhs) if is_method_call => { |
| // As `ExprMethodCall`, but the call is via an overloaded op. |
| self.constrain_call(expr, Some(&lhs), Some(&**rhs).into_iter()); |
| |
| intravisit::walk_expr(self, expr); |
| } |
| |
| hir::ExprBinary(_, ref lhs, ref rhs) => { |
| // If you do `x OP y`, then the types of `x` and `y` must |
| // outlive the operation you are performing. |
| let lhs_ty = self.resolve_expr_type_adjusted(&lhs); |
| let rhs_ty = self.resolve_expr_type_adjusted(&rhs); |
| for &ty in &[lhs_ty, rhs_ty] { |
| self.type_must_outlive(infer::Operand(expr.span), |
| ty, expr_region); |
| } |
| intravisit::walk_expr(self, expr); |
| } |
| |
| hir::ExprUnary(hir::UnDeref, ref base) => { |
| // For *a, the lifetime of a must enclose the deref |
| if is_method_call { |
| self.constrain_call(expr, Some(base), None::<hir::Expr>.iter()); |
| } |
| // For overloaded derefs, base_ty is the input to `Deref::deref`, |
| // but it's a reference type uing the same region as the output. |
| let base_ty = self.resolve_expr_type_adjusted(base); |
| if let ty::TyRef(r_ptr, _) = base_ty.sty { |
| self.mk_subregion_due_to_dereference(expr.span, expr_region, r_ptr); |
| } |
| |
| intravisit::walk_expr(self, expr); |
| } |
| |
| hir::ExprUnary(_, ref lhs) if is_method_call => { |
| // As above. |
| self.constrain_call(expr, Some(&lhs), None::<hir::Expr>.iter()); |
| |
| intravisit::walk_expr(self, expr); |
| } |
| |
| hir::ExprIndex(ref vec_expr, _) => { |
| // For a[b], the lifetime of a must enclose the deref |
| let vec_type = self.resolve_expr_type_adjusted(&vec_expr); |
| self.constrain_index(expr, vec_type); |
| |
| intravisit::walk_expr(self, expr); |
| } |
| |
| hir::ExprCast(ref source, _) => { |
| // Determine if we are casting `source` to a trait |
| // instance. If so, we have to be sure that the type of |
| // the source obeys the trait's region bound. |
| self.constrain_cast(expr, &source); |
| intravisit::walk_expr(self, expr); |
| } |
| |
| hir::ExprAddrOf(m, ref base) => { |
| self.link_addr_of(expr, m, &base); |
| |
| // Require that when you write a `&expr` expression, the |
| // resulting pointer has a lifetime that encompasses the |
| // `&expr` expression itself. Note that we constraining |
| // the type of the node expr.id here *before applying |
| // adjustments*. |
| // |
| // FIXME(https://github.com/rust-lang/rfcs/issues/811) |
| // nested method calls requires that this rule change |
| let ty0 = self.resolve_node_type(expr.hir_id); |
| self.type_must_outlive(infer::AddrOf(expr.span), ty0, expr_region); |
| intravisit::walk_expr(self, expr); |
| } |
| |
| hir::ExprMatch(ref discr, ref arms, _) => { |
| self.link_match(&discr, &arms[..]); |
| |
| intravisit::walk_expr(self, expr); |
| } |
| |
| hir::ExprClosure(.., body_id, _, _) => { |
| self.check_expr_fn_block(expr, body_id); |
| } |
| |
| hir::ExprLoop(ref body, _, _) => { |
| let repeating_scope = self.set_repeating_scope(body.id); |
| intravisit::walk_expr(self, expr); |
| self.set_repeating_scope(repeating_scope); |
| } |
| |
| hir::ExprWhile(ref cond, ref body, _) => { |
| let repeating_scope = self.set_repeating_scope(cond.id); |
| self.visit_expr(&cond); |
| |
| self.set_repeating_scope(body.id); |
| self.visit_block(&body); |
| |
| self.set_repeating_scope(repeating_scope); |
| } |
| |
| hir::ExprRet(Some(ref ret_expr)) => { |
| let call_site_scope = self.call_site_scope; |
| debug!("visit_expr ExprRet ret_expr.id {} call_site_scope: {:?}", |
| ret_expr.id, call_site_scope); |
| let call_site_region = self.tcx.mk_region(ty::ReScope(call_site_scope.unwrap())); |
| self.type_of_node_must_outlive(infer::CallReturn(ret_expr.span), |
| ret_expr.hir_id, |
| call_site_region); |
| intravisit::walk_expr(self, expr); |
| } |
| |
| _ => { |
| intravisit::walk_expr(self, expr); |
| } |
| } |
| } |
| } |
| |
| impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> { |
| fn constrain_cast(&mut self, |
| cast_expr: &hir::Expr, |
| source_expr: &hir::Expr) |
| { |
| debug!("constrain_cast(cast_expr={:?}, source_expr={:?})", |
| cast_expr, |
| source_expr); |
| |
| let source_ty = self.resolve_node_type(source_expr.hir_id); |
| let target_ty = self.resolve_node_type(cast_expr.hir_id); |
| |
| self.walk_cast(cast_expr, source_ty, target_ty); |
| } |
| |
| fn walk_cast(&mut self, |
| cast_expr: &hir::Expr, |
| from_ty: Ty<'tcx>, |
| to_ty: Ty<'tcx>) { |
| debug!("walk_cast(from_ty={:?}, to_ty={:?})", |
| from_ty, |
| to_ty); |
| match (&from_ty.sty, &to_ty.sty) { |
| /*From:*/ (&ty::TyRef(from_r, ref from_mt), |
| /*To: */ &ty::TyRef(to_r, ref to_mt)) => { |
| // Target cannot outlive source, naturally. |
| self.sub_regions(infer::Reborrow(cast_expr.span), to_r, from_r); |
| self.walk_cast(cast_expr, from_mt.ty, to_mt.ty); |
| } |
| |
| /*From:*/ (_, |
| /*To: */ &ty::TyDynamic(.., r)) => { |
| // When T is existentially quantified as a trait |
| // `Foo+'to`, it must outlive the region bound `'to`. |
| self.type_must_outlive(infer::RelateObjectBound(cast_expr.span), from_ty, r); |
| } |
| |
| /*From:*/ (&ty::TyAdt(from_def, _), |
| /*To: */ &ty::TyAdt(to_def, _)) if from_def.is_box() && to_def.is_box() => { |
| self.walk_cast(cast_expr, from_ty.boxed_ty(), to_ty.boxed_ty()); |
| } |
| |
| _ => { } |
| } |
| } |
| |
| fn check_expr_fn_block(&mut self, |
| expr: &'gcx hir::Expr, |
| body_id: hir::BodyId) { |
| let repeating_scope = self.set_repeating_scope(body_id.node_id); |
| intravisit::walk_expr(self, expr); |
| self.set_repeating_scope(repeating_scope); |
| } |
| |
| fn constrain_callee(&mut self, callee_expr: &hir::Expr) { |
| let callee_ty = self.resolve_node_type(callee_expr.hir_id); |
| match callee_ty.sty { |
| ty::TyFnDef(..) | ty::TyFnPtr(_) => { } |
| _ => { |
| // this should not happen, but it does if the program is |
| // erroneous |
| // |
| // bug!( |
| // callee_expr.span, |
| // "Calling non-function: {}", |
| // callee_ty); |
| } |
| } |
| } |
| |
| fn constrain_call<'b, I: Iterator<Item=&'b hir::Expr>>(&mut self, |
| call_expr: &hir::Expr, |
| receiver: Option<&hir::Expr>, |
| arg_exprs: I) { |
| //! Invoked on every call site (i.e., normal calls, method calls, |
| //! and overloaded operators). Constrains the regions which appear |
| //! in the type of the function. Also constrains the regions that |
| //! appear in the arguments appropriately. |
| |
| debug!("constrain_call(call_expr={:?}, receiver={:?})", |
| call_expr, |
| receiver); |
| |
| // `callee_region` is the scope representing the time in which the |
| // call occurs. |
| // |
| // FIXME(#6268) to support nested method calls, should be callee_id |
| let callee_scope = region::Scope::Node(call_expr.hir_id.local_id); |
| let callee_region = self.tcx.mk_region(ty::ReScope(callee_scope)); |
| |
| debug!("callee_region={:?}", callee_region); |
| |
| for arg_expr in arg_exprs { |
| debug!("Argument: {:?}", arg_expr); |
| |
| // ensure that any regions appearing in the argument type are |
| // valid for at least the lifetime of the function: |
| self.type_of_node_must_outlive(infer::CallArg(arg_expr.span), |
| arg_expr.hir_id, |
| callee_region); |
| } |
| |
| // as loop above, but for receiver |
| if let Some(r) = receiver { |
| debug!("receiver: {:?}", r); |
| self.type_of_node_must_outlive(infer::CallRcvr(r.span), |
| r.hir_id, |
| callee_region); |
| } |
| } |
| |
| /// Create a temporary `MemCategorizationContext` and pass it to the closure. |
| fn with_mc<F, R>(&self, f: F) -> R |
| where F: for<'b> FnOnce(mc::MemCategorizationContext<'b, 'gcx, 'tcx>) -> R |
| { |
| f(mc::MemCategorizationContext::with_infer(&self.infcx, |
| &self.region_scope_tree, |
| &self.tables.borrow())) |
| } |
| |
| /// Invoked on any adjustments that occur. Checks that if this is a region pointer being |
| /// dereferenced, the lifetime of the pointer includes the deref expr. |
| fn constrain_adjustments(&mut self, expr: &hir::Expr) -> mc::McResult<mc::cmt<'tcx>> { |
| debug!("constrain_adjustments(expr={:?})", expr); |
| |
| let mut cmt = self.with_mc(|mc| mc.cat_expr_unadjusted(expr))?; |
| |
| let tables = self.tables.borrow(); |
| let adjustments = tables.expr_adjustments(&expr); |
| if adjustments.is_empty() { |
| return Ok(cmt); |
| } |
| |
| debug!("constrain_adjustments: adjustments={:?}", adjustments); |
| |
| // If necessary, constrain destructors in the unadjusted form of this |
| // expression. |
| self.check_safety_of_rvalue_destructor_if_necessary(cmt.clone(), expr.span); |
| |
| let expr_region = self.tcx.mk_region(ty::ReScope( |
| region::Scope::Node(expr.hir_id.local_id))); |
| for adjustment in adjustments { |
| debug!("constrain_adjustments: adjustment={:?}, cmt={:?}", |
| adjustment, cmt); |
| |
| if let adjustment::Adjust::Deref(Some(deref)) = adjustment.kind { |
| debug!("constrain_adjustments: overloaded deref: {:?}", deref); |
| |
| // Treat overloaded autoderefs as if an AutoBorrow adjustment |
| // was applied on the base type, as that is always the case. |
| let input = self.tcx.mk_ref(deref.region, ty::TypeAndMut { |
| ty: cmt.ty, |
| mutbl: deref.mutbl, |
| }); |
| let output = self.tcx.mk_ref(deref.region, ty::TypeAndMut { |
| ty: adjustment.target, |
| mutbl: deref.mutbl, |
| }); |
| |
| self.link_region(expr.span, deref.region, |
| ty::BorrowKind::from_mutbl(deref.mutbl), cmt.clone()); |
| |
| // Specialized version of constrain_call. |
| self.type_must_outlive(infer::CallRcvr(expr.span), |
| input, expr_region); |
| self.type_must_outlive(infer::CallReturn(expr.span), |
| output, expr_region); |
| } |
| |
| if let adjustment::Adjust::Borrow(ref autoref) = adjustment.kind { |
| self.link_autoref(expr, cmt.clone(), autoref); |
| |
| // Require that the resulting region encompasses |
| // the current node. |
| // |
| // FIXME(#6268) remove to support nested method calls |
| self.type_of_node_must_outlive(infer::AutoBorrow(expr.span), |
| expr.hir_id, |
| expr_region); |
| } |
| |
| cmt = self.with_mc(|mc| mc.cat_expr_adjusted(expr, cmt, &adjustment))?; |
| |
| if let Categorization::Deref(_, mc::BorrowedPtr(_, r_ptr)) = cmt.cat { |
| self.mk_subregion_due_to_dereference(expr.span, |
| expr_region, r_ptr); |
| } |
| } |
| |
| Ok(cmt) |
| } |
| |
| pub fn mk_subregion_due_to_dereference(&mut self, |
| deref_span: Span, |
| minimum_lifetime: ty::Region<'tcx>, |
| maximum_lifetime: ty::Region<'tcx>) { |
| self.sub_regions(infer::DerefPointer(deref_span), |
| minimum_lifetime, maximum_lifetime) |
| } |
| |
| fn check_safety_of_rvalue_destructor_if_necessary(&mut self, |
| cmt: mc::cmt<'tcx>, |
| span: Span) { |
| match cmt.cat { |
| Categorization::Rvalue(region) => { |
| match *region { |
| ty::ReScope(rvalue_scope) => { |
| let typ = self.resolve_type(cmt.ty); |
| let _ = dropck::check_safety_of_destructor_if_necessary( |
| self, typ, span, rvalue_scope); |
| } |
| ty::ReStatic => {} |
| _ => { |
| span_bug!(span, |
| "unexpected rvalue region in rvalue \ |
| destructor safety checking: `{:?}`", |
| region); |
| } |
| } |
| } |
| _ => {} |
| } |
| } |
| |
| /// Invoked on any index expression that occurs. Checks that if this is a slice |
| /// being indexed, the lifetime of the pointer includes the deref expr. |
| fn constrain_index(&mut self, |
| index_expr: &hir::Expr, |
| indexed_ty: Ty<'tcx>) |
| { |
| debug!("constrain_index(index_expr=?, indexed_ty={}", |
| self.ty_to_string(indexed_ty)); |
| |
| let r_index_expr = ty::ReScope(region::Scope::Node(index_expr.hir_id.local_id)); |
| if let ty::TyRef(r_ptr, mt) = indexed_ty.sty { |
| match mt.ty.sty { |
| ty::TySlice(_) | ty::TyStr => { |
| self.sub_regions(infer::IndexSlice(index_expr.span), |
| self.tcx.mk_region(r_index_expr), r_ptr); |
| } |
| _ => {} |
| } |
| } |
| } |
| |
| /// Guarantees that any lifetimes which appear in the type of the node `id` (after applying |
| /// adjustments) are valid for at least `minimum_lifetime` |
| fn type_of_node_must_outlive(&mut self, |
| origin: infer::SubregionOrigin<'tcx>, |
| hir_id: hir::HirId, |
| minimum_lifetime: ty::Region<'tcx>) |
| { |
| // Try to resolve the type. If we encounter an error, then typeck |
| // is going to fail anyway, so just stop here and let typeck |
| // report errors later on in the writeback phase. |
| let ty0 = self.resolve_node_type(hir_id); |
| |
| let ty = self.tables |
| .borrow() |
| .adjustments() |
| .get(hir_id) |
| .and_then(|adj| adj.last()) |
| .map_or(ty0, |adj| adj.target); |
| let ty = self.resolve_type(ty); |
| debug!("constrain_regions_in_type_of_node(\ |
| ty={}, ty0={}, id={:?}, minimum_lifetime={:?})", |
| ty, ty0, |
| hir_id, minimum_lifetime); |
| self.type_must_outlive(origin, ty, minimum_lifetime); |
| } |
| |
| /// Computes the guarantor for an expression `&base` and then ensures that the lifetime of the |
| /// resulting pointer is linked to the lifetime of its guarantor (if any). |
| fn link_addr_of(&mut self, expr: &hir::Expr, |
| mutability: hir::Mutability, base: &hir::Expr) { |
| debug!("link_addr_of(expr={:?}, base={:?})", expr, base); |
| |
| let cmt = ignore_err!(self.with_mc(|mc| mc.cat_expr(base))); |
| |
| debug!("link_addr_of: cmt={:?}", cmt); |
| |
| self.link_region_from_node_type(expr.span, expr.hir_id, mutability, cmt); |
| } |
| |
| /// Computes the guarantors for any ref bindings in a `let` and |
| /// then ensures that the lifetime of the resulting pointer is |
| /// linked to the lifetime of the initialization expression. |
| fn link_local(&self, local: &hir::Local) { |
| debug!("regionck::for_local()"); |
| let init_expr = match local.init { |
| None => { return; } |
| Some(ref expr) => &**expr, |
| }; |
| let discr_cmt = ignore_err!(self.with_mc(|mc| mc.cat_expr(init_expr))); |
| self.link_pattern(discr_cmt, &local.pat); |
| } |
| |
| /// Computes the guarantors for any ref bindings in a match and |
| /// then ensures that the lifetime of the resulting pointer is |
| /// linked to the lifetime of its guarantor (if any). |
| fn link_match(&self, discr: &hir::Expr, arms: &[hir::Arm]) { |
| debug!("regionck::for_match()"); |
| let discr_cmt = ignore_err!(self.with_mc(|mc| mc.cat_expr(discr))); |
| debug!("discr_cmt={:?}", discr_cmt); |
| for arm in arms { |
| for root_pat in &arm.pats { |
| self.link_pattern(discr_cmt.clone(), &root_pat); |
| } |
| } |
| } |
| |
| /// Computes the guarantors for any ref bindings in a match and |
| /// then ensures that the lifetime of the resulting pointer is |
| /// linked to the lifetime of its guarantor (if any). |
| fn link_fn_args(&self, body_scope: region::Scope, args: &[hir::Arg]) { |
| debug!("regionck::link_fn_args(body_scope={:?})", body_scope); |
| for arg in args { |
| let arg_ty = self.node_ty(arg.hir_id); |
| let re_scope = self.tcx.mk_region(ty::ReScope(body_scope)); |
| let arg_cmt = self.with_mc(|mc| { |
| mc.cat_rvalue(arg.id, arg.pat.span, re_scope, arg_ty) |
| }); |
| debug!("arg_ty={:?} arg_cmt={:?} arg={:?}", |
| arg_ty, |
| arg_cmt, |
| arg); |
| self.link_pattern(arg_cmt, &arg.pat); |
| } |
| } |
| |
| /// Link lifetimes of any ref bindings in `root_pat` to the pointers found |
| /// in the discriminant, if needed. |
| fn link_pattern(&self, discr_cmt: mc::cmt<'tcx>, root_pat: &hir::Pat) { |
| debug!("link_pattern(discr_cmt={:?}, root_pat={:?})", |
| discr_cmt, |
| root_pat); |
| let _ = self.with_mc(|mc| { |
| mc.cat_pattern(discr_cmt, root_pat, |sub_cmt, sub_pat| { |
| match sub_pat.node { |
| // `ref x` pattern |
| PatKind::Binding(..) => { |
| let bm = *mc.tables.pat_binding_modes().get(sub_pat.hir_id) |
| .expect("missing binding mode"); |
| if let ty::BindByReference(mutbl) = bm { |
| self.link_region_from_node_type(sub_pat.span, sub_pat.hir_id, |
| mutbl, sub_cmt); |
| } |
| } |
| _ => {} |
| } |
| }) |
| }); |
| } |
| |
| /// Link lifetime of borrowed pointer resulting from autoref to lifetimes in the value being |
| /// autoref'd. |
| fn link_autoref(&self, |
| expr: &hir::Expr, |
| expr_cmt: mc::cmt<'tcx>, |
| autoref: &adjustment::AutoBorrow<'tcx>) |
| { |
| debug!("link_autoref(autoref={:?}, expr_cmt={:?})", autoref, expr_cmt); |
| |
| match *autoref { |
| adjustment::AutoBorrow::Ref(r, m) => { |
| self.link_region(expr.span, r, |
| ty::BorrowKind::from_mutbl(m), expr_cmt); |
| } |
| |
| adjustment::AutoBorrow::RawPtr(m) => { |
| let r = self.tcx.mk_region(ty::ReScope(region::Scope::Node(expr.hir_id.local_id))); |
| self.link_region(expr.span, r, ty::BorrowKind::from_mutbl(m), expr_cmt); |
| } |
| } |
| } |
| |
| /// Like `link_region()`, except that the region is extracted from the type of `id`, |
| /// which must be some reference (`&T`, `&str`, etc). |
| fn link_region_from_node_type(&self, |
| span: Span, |
| id: hir::HirId, |
| mutbl: hir::Mutability, |
| cmt_borrowed: mc::cmt<'tcx>) { |
| debug!("link_region_from_node_type(id={:?}, mutbl={:?}, cmt_borrowed={:?})", |
| id, mutbl, cmt_borrowed); |
| |
| let rptr_ty = self.resolve_node_type(id); |
| if let ty::TyRef(r, _) = rptr_ty.sty { |
| debug!("rptr_ty={}", rptr_ty); |
| self.link_region(span, r, ty::BorrowKind::from_mutbl(mutbl), |
| cmt_borrowed); |
| } |
| } |
| |
| /// Informs the inference engine that `borrow_cmt` is being borrowed with |
| /// kind `borrow_kind` and lifetime `borrow_region`. |
| /// In order to ensure borrowck is satisfied, this may create constraints |
| /// between regions, as explained in `link_reborrowed_region()`. |
| fn link_region(&self, |
| span: Span, |
| borrow_region: ty::Region<'tcx>, |
| borrow_kind: ty::BorrowKind, |
| borrow_cmt: mc::cmt<'tcx>) { |
| let mut borrow_cmt = borrow_cmt; |
| let mut borrow_kind = borrow_kind; |
| |
| let origin = infer::DataBorrowed(borrow_cmt.ty, span); |
| self.type_must_outlive(origin, borrow_cmt.ty, borrow_region); |
| |
| loop { |
| debug!("link_region(borrow_region={:?}, borrow_kind={:?}, borrow_cmt={:?})", |
| borrow_region, |
| borrow_kind, |
| borrow_cmt); |
| match borrow_cmt.cat.clone() { |
| Categorization::Deref(ref_cmt, mc::Implicit(ref_kind, ref_region)) | |
| Categorization::Deref(ref_cmt, mc::BorrowedPtr(ref_kind, ref_region)) => { |
| match self.link_reborrowed_region(span, |
| borrow_region, borrow_kind, |
| ref_cmt, ref_region, ref_kind, |
| borrow_cmt.note) { |
| Some((c, k)) => { |
| borrow_cmt = c; |
| borrow_kind = k; |
| } |
| None => { |
| return; |
| } |
| } |
| } |
| |
| Categorization::Downcast(cmt_base, _) | |
| Categorization::Deref(cmt_base, mc::Unique) | |
| Categorization::Interior(cmt_base, _) => { |
| // Borrowing interior or owned data requires the base |
| // to be valid and borrowable in the same fashion. |
| borrow_cmt = cmt_base; |
| borrow_kind = borrow_kind; |
| } |
| |
| Categorization::Deref(_, mc::UnsafePtr(..)) | |
| Categorization::StaticItem | |
| Categorization::Upvar(..) | |
| Categorization::Local(..) | |
| Categorization::Rvalue(..) => { |
| // These are all "base cases" with independent lifetimes |
| // that are not subject to inference |
| return; |
| } |
| } |
| } |
| } |
| |
| /// This is the most complicated case: the path being borrowed is |
| /// itself the referent of a borrowed pointer. Let me give an |
| /// example fragment of code to make clear(er) the situation: |
| /// |
| /// let r: &'a mut T = ...; // the original reference "r" has lifetime 'a |
| /// ... |
| /// &'z *r // the reborrow has lifetime 'z |
| /// |
| /// Now, in this case, our primary job is to add the inference |
| /// constraint that `'z <= 'a`. Given this setup, let's clarify the |
| /// parameters in (roughly) terms of the example: |
| /// |
| /// A borrow of: `& 'z bk * r` where `r` has type `& 'a bk T` |
| /// borrow_region ^~ ref_region ^~ |
| /// borrow_kind ^~ ref_kind ^~ |
| /// ref_cmt ^ |
| /// |
| /// Here `bk` stands for some borrow-kind (e.g., `mut`, `uniq`, etc). |
| /// |
| /// Unfortunately, there are some complications beyond the simple |
| /// scenario I just painted: |
| /// |
| /// 1. The reference `r` might in fact be a "by-ref" upvar. In that |
| /// case, we have two jobs. First, we are inferring whether this reference |
| /// should be an `&T`, `&mut T`, or `&uniq T` reference, and we must |
| /// adjust that based on this borrow (e.g., if this is an `&mut` borrow, |
| /// then `r` must be an `&mut` reference). Second, whenever we link |
| /// two regions (here, `'z <= 'a`), we supply a *cause*, and in this |
| /// case we adjust the cause to indicate that the reference being |
| /// "reborrowed" is itself an upvar. This provides a nicer error message |
| /// should something go wrong. |
| /// |
| /// 2. There may in fact be more levels of reborrowing. In the |
| /// example, I said the borrow was like `&'z *r`, but it might |
| /// in fact be a borrow like `&'z **q` where `q` has type `&'a |
| /// &'b mut T`. In that case, we want to ensure that `'z <= 'a` |
| /// and `'z <= 'b`. This is explained more below. |
| /// |
| /// The return value of this function indicates whether we need to |
| /// recurse and process `ref_cmt` (see case 2 above). |
| fn link_reborrowed_region(&self, |
| span: Span, |
| borrow_region: ty::Region<'tcx>, |
| borrow_kind: ty::BorrowKind, |
| ref_cmt: mc::cmt<'tcx>, |
| ref_region: ty::Region<'tcx>, |
| mut ref_kind: ty::BorrowKind, |
| note: mc::Note) |
| -> Option<(mc::cmt<'tcx>, ty::BorrowKind)> |
| { |
| // Possible upvar ID we may need later to create an entry in the |
| // maybe link map. |
| |
| // Detect by-ref upvar `x`: |
| let cause = match note { |
| mc::NoteUpvarRef(ref upvar_id) => { |
| match self.tables.borrow().upvar_capture_map.get(upvar_id) { |
| Some(&ty::UpvarCapture::ByRef(ref upvar_borrow)) => { |
| // The mutability of the upvar may have been modified |
| // by the above adjustment, so update our local variable. |
| ref_kind = upvar_borrow.kind; |
| |
| infer::ReborrowUpvar(span, *upvar_id) |
| } |
| _ => { |
| span_bug!( span, "Illegal upvar id: {:?}", upvar_id); |
| } |
| } |
| } |
| mc::NoteClosureEnv(ref upvar_id) => { |
| // We don't have any mutability changes to propagate, but |
| // we do want to note that an upvar reborrow caused this |
| // link |
| infer::ReborrowUpvar(span, *upvar_id) |
| } |
| _ => { |
| infer::Reborrow(span) |
| } |
| }; |
| |
| debug!("link_reborrowed_region: {:?} <= {:?}", |
| borrow_region, |
| ref_region); |
| self.sub_regions(cause, borrow_region, ref_region); |
| |
| // If we end up needing to recurse and establish a region link |
| // with `ref_cmt`, calculate what borrow kind we will end up |
| // needing. This will be used below. |
| // |
| // One interesting twist is that we can weaken the borrow kind |
| // when we recurse: to reborrow an `&mut` referent as mutable, |
| // borrowck requires a unique path to the `&mut` reference but not |
| // necessarily a *mutable* path. |
| let new_borrow_kind = match borrow_kind { |
| ty::ImmBorrow => |
| ty::ImmBorrow, |
| ty::MutBorrow | ty::UniqueImmBorrow => |
| ty::UniqueImmBorrow |
| }; |
| |
| // Decide whether we need to recurse and link any regions within |
| // the `ref_cmt`. This is concerned for the case where the value |
| // being reborrowed is in fact a borrowed pointer found within |
| // another borrowed pointer. For example: |
| // |
| // let p: &'b &'a mut T = ...; |
| // ... |
| // &'z **p |
| // |
| // What makes this case particularly tricky is that, if the data |
| // being borrowed is a `&mut` or `&uniq` borrow, borrowck requires |
| // not only that `'z <= 'a`, (as before) but also `'z <= 'b` |
| // (otherwise the user might mutate through the `&mut T` reference |
| // after `'b` expires and invalidate the borrow we are looking at |
| // now). |
| // |
| // So let's re-examine our parameters in light of this more |
| // complicated (possible) scenario: |
| // |
| // A borrow of: `& 'z bk * * p` where `p` has type `&'b bk & 'a bk T` |
| // borrow_region ^~ ref_region ^~ |
| // borrow_kind ^~ ref_kind ^~ |
| // ref_cmt ^~~ |
| // |
| // (Note that since we have not examined `ref_cmt.cat`, we don't |
| // know whether this scenario has occurred; but I wanted to show |
| // how all the types get adjusted.) |
| match ref_kind { |
| ty::ImmBorrow => { |
| // The reference being reborrowed is a sharable ref of |
| // type `&'a T`. In this case, it doesn't matter where we |
| // *found* the `&T` pointer, the memory it references will |
| // be valid and immutable for `'a`. So we can stop here. |
| // |
| // (Note that the `borrow_kind` must also be ImmBorrow or |
| // else the user is borrowed imm memory as mut memory, |
| // which means they'll get an error downstream in borrowck |
| // anyhow.) |
| return None; |
| } |
| |
| ty::MutBorrow | ty::UniqueImmBorrow => { |
| // The reference being reborrowed is either an `&mut T` or |
| // `&uniq T`. This is the case where recursion is needed. |
| return Some((ref_cmt, new_borrow_kind)); |
| } |
| } |
| } |
| |
| /// Checks that the values provided for type/region arguments in a given |
| /// expression are well-formed and in-scope. |
| fn substs_wf_in_scope(&mut self, |
| origin: infer::ParameterOrigin, |
| substs: &Substs<'tcx>, |
| expr_span: Span, |
| expr_region: ty::Region<'tcx>) { |
| debug!("substs_wf_in_scope(substs={:?}, \ |
| expr_region={:?}, \ |
| origin={:?}, \ |
| expr_span={:?})", |
| substs, expr_region, origin, expr_span); |
| |
| let origin = infer::ParameterInScope(origin, expr_span); |
| |
| for region in substs.regions() { |
| self.sub_regions(origin.clone(), expr_region, region); |
| } |
| |
| for ty in substs.types() { |
| let ty = self.resolve_type(ty); |
| self.type_must_outlive(origin.clone(), ty, expr_region); |
| } |
| } |
| |
| /// Ensures that type is well-formed in `region`, which implies (among |
| /// other things) that all borrowed data reachable via `ty` outlives |
| /// `region`. |
| pub fn type_must_outlive(&self, |
| origin: infer::SubregionOrigin<'tcx>, |
| ty: Ty<'tcx>, |
| region: ty::Region<'tcx>) |
| { |
| let ty = self.resolve_type(ty); |
| |
| debug!("type_must_outlive(ty={:?}, region={:?}, origin={:?})", |
| ty, |
| region, |
| origin); |
| |
| assert!(!ty.has_escaping_regions()); |
| |
| let components = self.tcx.outlives_components(ty); |
| self.components_must_outlive(origin, components, region); |
| } |
| |
| fn components_must_outlive(&self, |
| origin: infer::SubregionOrigin<'tcx>, |
| components: Vec<Component<'tcx>>, |
| region: ty::Region<'tcx>) |
| { |
| for component in components { |
| let origin = origin.clone(); |
| match component { |
| Component::Region(region1) => { |
| self.sub_regions(origin, region, region1); |
| } |
| Component::Param(param_ty) => { |
| self.param_ty_must_outlive(origin, region, param_ty); |
| } |
| Component::Projection(projection_ty) => { |
| self.projection_must_outlive(origin, region, projection_ty); |
| } |
| Component::EscapingProjection(subcomponents) => { |
| self.components_must_outlive(origin, subcomponents, region); |
| } |
| Component::UnresolvedInferenceVariable(v) => { |
| // ignore this, we presume it will yield an error |
| // later, since if a type variable is not resolved by |
| // this point it never will be |
| self.tcx.sess.delay_span_bug( |
| origin.span(), |
| &format!("unresolved inference variable in outlives: {:?}", v)); |
| } |
| } |
| } |
| } |
| |
| fn param_ty_must_outlive(&self, |
| origin: infer::SubregionOrigin<'tcx>, |
| region: ty::Region<'tcx>, |
| param_ty: ty::ParamTy) { |
| debug!("param_ty_must_outlive(region={:?}, param_ty={:?}, origin={:?})", |
| region, param_ty, origin); |
| |
| let verify_bound = self.param_bound(param_ty); |
| let generic = GenericKind::Param(param_ty); |
| self.verify_generic_bound(origin, generic, region, verify_bound); |
| } |
| |
| fn projection_must_outlive(&self, |
| origin: infer::SubregionOrigin<'tcx>, |
| region: ty::Region<'tcx>, |
| projection_ty: ty::ProjectionTy<'tcx>) |
| { |
| debug!("projection_must_outlive(region={:?}, projection_ty={:?}, origin={:?})", |
| region, projection_ty, origin); |
| |
| // This case is thorny for inference. The fundamental problem is |
| // that there are many cases where we have choice, and inference |
| // doesn't like choice (the current region inference in |
| // particular). :) First off, we have to choose between using the |
| // OutlivesProjectionEnv, OutlivesProjectionTraitDef, and |
| // OutlivesProjectionComponent rules, any one of which is |
| // sufficient. If there are no inference variables involved, it's |
| // not hard to pick the right rule, but if there are, we're in a |
| // bit of a catch 22: if we picked which rule we were going to |
| // use, we could add constraints to the region inference graph |
| // that make it apply, but if we don't add those constraints, the |
| // rule might not apply (but another rule might). For now, we err |
| // on the side of adding too few edges into the graph. |
| |
| // Compute the bounds we can derive from the environment or trait |
| // definition. We know that the projection outlives all the |
| // regions in this list. |
| let env_bounds = self.projection_declared_bounds(origin.span(), projection_ty); |
| |
| debug!("projection_must_outlive: env_bounds={:?}", |
| env_bounds); |
| |
| // If we know that the projection outlives 'static, then we're |
| // done here. |
| if env_bounds.contains(&&ty::ReStatic) { |
| debug!("projection_must_outlive: 'static as declared bound"); |
| return; |
| } |
| |
| // If declared bounds list is empty, the only applicable rule is |
| // OutlivesProjectionComponent. If there are inference variables, |
| // then, we can break down the outlives into more primitive |
| // components without adding unnecessary edges. |
| // |
| // If there are *no* inference variables, however, we COULD do |
| // this, but we choose not to, because the error messages are less |
| // good. For example, a requirement like `T::Item: 'r` would be |
| // translated to a requirement that `T: 'r`; when this is reported |
| // to the user, it will thus say "T: 'r must hold so that T::Item: |
| // 'r holds". But that makes it sound like the only way to fix |
| // the problem is to add `T: 'r`, which isn't true. So, if there are no |
| // inference variables, we use a verify constraint instead of adding |
| // edges, which winds up enforcing the same condition. |
| let needs_infer = projection_ty.needs_infer(); |
| if env_bounds.is_empty() && needs_infer { |
| debug!("projection_must_outlive: no declared bounds"); |
| |
| for component_ty in projection_ty.substs.types() { |
| self.type_must_outlive(origin.clone(), component_ty, region); |
| } |
| |
| for r in projection_ty.substs.regions() { |
| self.sub_regions(origin.clone(), region, r); |
| } |
| |
| return; |
| } |
| |
| // If we find that there is a unique declared bound `'b`, and this bound |
| // appears in the trait reference, then the best action is to require that `'b:'r`, |
| // so do that. This is best no matter what rule we use: |
| // |
| // - OutlivesProjectionEnv or OutlivesProjectionTraitDef: these would translate to |
| // the requirement that `'b:'r` |
| // - OutlivesProjectionComponent: this would require `'b:'r` in addition to |
| // other conditions |
| if !env_bounds.is_empty() && env_bounds[1..].iter().all(|b| *b == env_bounds[0]) { |
| let unique_bound = env_bounds[0]; |
| debug!("projection_must_outlive: unique declared bound = {:?}", unique_bound); |
| if projection_ty.substs.regions().any(|r| env_bounds.contains(&r)) { |
| debug!("projection_must_outlive: unique declared bound appears in trait ref"); |
| self.sub_regions(origin.clone(), region, unique_bound); |
| return; |
| } |
| } |
| |
| // Fallback to verifying after the fact that there exists a |
| // declared bound, or that all the components appearing in the |
| // projection outlive; in some cases, this may add insufficient |
| // edges into the inference graph, leading to inference failures |
| // even though a satisfactory solution exists. |
| let verify_bound = self.projection_bound(origin.span(), env_bounds, projection_ty); |
| let generic = GenericKind::Projection(projection_ty); |
| self.verify_generic_bound(origin, generic.clone(), region, verify_bound); |
| } |
| |
| fn type_bound(&self, span: Span, ty: Ty<'tcx>) -> VerifyBound<'tcx> { |
| match ty.sty { |
| ty::TyParam(p) => { |
| self.param_bound(p) |
| } |
| ty::TyProjection(data) => { |
| let declared_bounds = self.projection_declared_bounds(span, data); |
| self.projection_bound(span, declared_bounds, data) |
| } |
| _ => { |
| self.recursive_type_bound(span, ty) |
| } |
| } |
| } |
| |
| fn param_bound(&self, param_ty: ty::ParamTy) -> VerifyBound<'tcx> { |
| debug!("param_bound(param_ty={:?})", |
| param_ty); |
| |
| let mut param_bounds = self.declared_generic_bounds_from_env(GenericKind::Param(param_ty)); |
| |
| // Add in the default bound of fn body that applies to all in |
| // scope type parameters: |
| param_bounds.extend(self.implicit_region_bound); |
| |
| VerifyBound::AnyRegion(param_bounds) |
| } |
| |
| fn projection_declared_bounds(&self, |
| span: Span, |
| projection_ty: ty::ProjectionTy<'tcx>) |
| -> Vec<ty::Region<'tcx>> |
| { |
| // First assemble bounds from where clauses and traits. |
| |
| let mut declared_bounds = |
| self.declared_generic_bounds_from_env(GenericKind::Projection(projection_ty)); |
| |
| declared_bounds.extend_from_slice( |
| &self.declared_projection_bounds_from_trait(span, projection_ty)); |
| |
| declared_bounds |
| } |
| |
| fn projection_bound(&self, |
| span: Span, |
| declared_bounds: Vec<ty::Region<'tcx>>, |
| projection_ty: ty::ProjectionTy<'tcx>) |
| -> VerifyBound<'tcx> { |
| debug!("projection_bound(declared_bounds={:?}, projection_ty={:?})", |
| declared_bounds, projection_ty); |
| |
| // see the extensive comment in projection_must_outlive |
| let ty = self.tcx.mk_projection(projection_ty.item_def_id, projection_ty.substs); |
| let recursive_bound = self.recursive_type_bound(span, ty); |
| |
| VerifyBound::AnyRegion(declared_bounds).or(recursive_bound) |
| } |
| |
| fn recursive_type_bound(&self, span: Span, ty: Ty<'tcx>) -> VerifyBound<'tcx> { |
| let mut bounds = vec![]; |
| |
| for subty in ty.walk_shallow() { |
| bounds.push(self.type_bound(span, subty)); |
| } |
| |
| let mut regions = ty.regions(); |
| regions.retain(|r| !r.is_late_bound()); // ignore late-bound regions |
| bounds.push(VerifyBound::AllRegions(regions)); |
| |
| // remove bounds that must hold, since they are not interesting |
| bounds.retain(|b| !b.must_hold()); |
| |
| if bounds.len() == 1 { |
| bounds.pop().unwrap() |
| } else { |
| VerifyBound::AllBounds(bounds) |
| } |
| } |
| |
| fn declared_generic_bounds_from_env(&self, generic: GenericKind<'tcx>) |
| -> Vec<ty::Region<'tcx>> |
| { |
| let param_env = &self.param_env; |
| |
| // To start, collect bounds from user: |
| let mut param_bounds = self.tcx.required_region_bounds(generic.to_ty(self.tcx), |
| param_env.caller_bounds.to_vec()); |
| |
| // Next, collect regions we scraped from the well-formedness |
| // constraints in the fn signature. To do that, we walk the list |
| // of known relations from the fn ctxt. |
| // |
| // This is crucial because otherwise code like this fails: |
| // |
| // fn foo<'a, A>(x: &'a A) { x.bar() } |
| // |
| // The problem is that the type of `x` is `&'a A`. To be |
| // well-formed, then, A must be lower-generic by `'a`, but we |
| // don't know that this holds from first principles. |
| for &(r, p) in &self.region_bound_pairs { |
| debug!("generic={:?} p={:?}", |
| generic, |
| p); |
| if generic == p { |
| param_bounds.push(r); |
| } |
| } |
| |
| param_bounds |
| } |
| |
| fn declared_projection_bounds_from_trait(&self, |
| span: Span, |
| projection_ty: ty::ProjectionTy<'tcx>) |
| -> Vec<ty::Region<'tcx>> |
| { |
| debug!("projection_bounds(projection_ty={:?})", |
| projection_ty); |
| let ty = self.tcx.mk_projection(projection_ty.item_def_id, projection_ty.substs); |
| |
| // Say we have a projection `<T as SomeTrait<'a>>::SomeType`. We are interested |
| // in looking for a trait definition like: |
| // |
| // ``` |
| // trait SomeTrait<'a> { |
| // type SomeType : 'a; |
| // } |
| // ``` |
| // |
| // we can thus deduce that `<T as SomeTrait<'a>>::SomeType : 'a`. |
| let trait_predicates = self.tcx.predicates_of(projection_ty.trait_ref(self.tcx).def_id); |
| assert_eq!(trait_predicates.parent, None); |
| let predicates = trait_predicates.predicates.as_slice().to_vec(); |
| traits::elaborate_predicates(self.tcx, predicates) |
| .filter_map(|predicate| { |
| // we're only interesting in `T : 'a` style predicates: |
| let outlives = match predicate { |
| ty::Predicate::TypeOutlives(data) => data, |
| _ => { return None; } |
| }; |
| |
| debug!("projection_bounds: outlives={:?} (1)", |
| outlives); |
| |
| // apply the substitutions (and normalize any projected types) |
| let outlives = self.instantiate_type_scheme(span, |
| projection_ty.substs, |
| &outlives); |
| |
| debug!("projection_bounds: outlives={:?} (2)", |
| outlives); |
| |
| let region_result = self.commit_if_ok(|_| { |
| let (outlives, _) = |
| self.replace_late_bound_regions_with_fresh_var( |
| span, |
| infer::AssocTypeProjection(projection_ty.item_def_id), |
| &outlives); |
| |
| debug!("projection_bounds: outlives={:?} (3)", |
| outlives); |
| |
| // check whether this predicate applies to our current projection |
| let cause = self.fcx.misc(span); |
| match self.at(&cause, self.fcx.param_env).eq(outlives.0, ty) { |
| Ok(ok) => Ok((ok, outlives.1)), |
| Err(_) => Err(()) |
| } |
| }).map(|(ok, result)| { |
| self.register_infer_ok_obligations(ok); |
| result |
| }); |
| |
| debug!("projection_bounds: region_result={:?}", |
| region_result); |
| |
| region_result.ok() |
| }) |
| .collect() |
| } |
| } |
