| //! 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 crate::check::dropck; |
| use crate::check::FnCtxt; |
| use crate::mem_categorization as mc; |
| use crate::middle::region; |
| use rustc_hir as hir; |
| use rustc_hir::def_id::LocalDefId; |
| use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor}; |
| use rustc_hir::PatKind; |
| use rustc_infer::infer::outlives::env::OutlivesEnvironment; |
| use rustc_infer::infer::{self, RegionObligation, RegionckMode}; |
| use rustc_middle::ty::adjustment; |
| use rustc_middle::ty::{self, Ty}; |
| use rustc_span::Span; |
| use rustc_trait_selection::infer::OutlivesEnvironmentExt; |
| use rustc_trait_selection::opaque_types::InferCtxtExt; |
| use std::ops::Deref; |
| |
| // a variation on try that just returns unit |
| macro_rules! ignore_err { |
| ($e:expr) => { |
| match $e { |
| Ok(e) => e, |
| Err(_) => { |
| debug!("ignoring mem-categorization error!"); |
| return (); |
| } |
| } |
| }; |
| } |
| |
| /////////////////////////////////////////////////////////////////////////// |
| // PUBLIC ENTRY POINTS |
| |
| impl<'a, 'tcx> FnCtxt<'a, 'tcx> { |
| pub fn regionck_expr(&self, body: &'tcx hir::Body<'tcx>) { |
| let subject = self.tcx.hir().body_owner_def_id(body.id()); |
| let id = body.value.hir_id; |
| let mut rcx = RegionCtxt::new(self, id, Subject(subject), self.param_env); |
| |
| // There are no add'l implied bounds when checking a |
| // standalone expr (e.g., the `E` in a type like `[u32; E]`). |
| rcx.outlives_environment.save_implied_bounds(id); |
| |
| if !self.errors_reported_since_creation() { |
| // regionck assumes typeck succeeded |
| rcx.visit_body(body); |
| rcx.visit_region_obligations(id); |
| } |
| rcx.resolve_regions_and_report_errors(RegionckMode::for_item_body(self.tcx)); |
| } |
| |
| /// 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: hir::HirId, 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, item_id, Subject(subject), self.param_env); |
| rcx.outlives_environment.add_implied_bounds(self, wf_tys, item_id, span); |
| rcx.outlives_environment.save_implied_bounds(item_id); |
| rcx.visit_region_obligations(item_id); |
| rcx.resolve_regions_and_report_errors(RegionckMode::default()); |
| } |
| |
| /// Region check a function body. Not invoked on closures, but |
| /// only on the "root" fn item (in which closures may be |
| /// embedded). Walks the function body and adds various add'l |
| /// constraints that are needed for region inference. This is |
| /// separated both to isolate "pure" region constraints from the |
| /// rest of type check and because sometimes we need type |
| /// inference to have completed before we can determine which |
| /// constraints to add. |
| pub fn regionck_fn(&self, fn_id: hir::HirId, body: &'tcx hir::Body<'tcx>) { |
| debug!("regionck_fn(id={})", fn_id); |
| let subject = self.tcx.hir().body_owner_def_id(body.id()); |
| let hir_id = body.value.hir_id; |
| let mut rcx = RegionCtxt::new(self, hir_id, Subject(subject), self.param_env); |
| |
| if !self.errors_reported_since_creation() { |
| // regionck assumes typeck succeeded |
| rcx.visit_fn_body(fn_id, body, self.tcx.hir().span(fn_id)); |
| } |
| |
| rcx.resolve_regions_and_report_errors(RegionckMode::for_item_body(self.tcx)); |
| } |
| } |
| |
| /////////////////////////////////////////////////////////////////////////// |
| // INTERNALS |
| |
| pub struct RegionCtxt<'a, 'tcx> { |
| pub fcx: &'a FnCtxt<'a, 'tcx>, |
| |
| pub region_scope_tree: &'tcx region::ScopeTree, |
| |
| outlives_environment: OutlivesEnvironment<'tcx>, |
| |
| // id of innermost fn body id |
| body_id: hir::HirId, |
| body_owner: LocalDefId, |
| |
| // id of AST node being analyzed (the subject of the analysis). |
| subject_def_id: LocalDefId, |
| } |
| |
| impl<'a, 'tcx> Deref for RegionCtxt<'a, 'tcx> { |
| type Target = FnCtxt<'a, 'tcx>; |
| fn deref(&self) -> &Self::Target { |
| &self.fcx |
| } |
| } |
| |
| pub struct Subject(LocalDefId); |
| |
| impl<'a, 'tcx> RegionCtxt<'a, 'tcx> { |
| pub fn new( |
| fcx: &'a FnCtxt<'a, 'tcx>, |
| initial_body_id: hir::HirId, |
| Subject(subject): Subject, |
| param_env: ty::ParamEnv<'tcx>, |
| ) -> RegionCtxt<'a, 'tcx> { |
| let region_scope_tree = fcx.tcx.region_scope_tree(subject); |
| let outlives_environment = OutlivesEnvironment::new(param_env); |
| RegionCtxt { |
| fcx, |
| region_scope_tree, |
| body_id: initial_body_id, |
| body_owner: subject, |
| subject_def_id: subject, |
| outlives_environment, |
| } |
| } |
| |
| /// 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_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) |
| } |
| |
| /// This is the "main" function when region-checking a function item or a |
| /// closure within a function item. It begins by updating various fields |
| /// (e.g., `outlives_environment`) to be appropriate to the function and |
| /// then adds constraints derived from the function body. |
| /// |
| /// Note that it does **not** restore the state of the fields that |
| /// it updates! This is intentional, since -- for the main |
| /// function -- we wish to be able to read the final |
| /// `outlives_environment` and other fields from the caller. For |
| /// closures, however, we save and restore any "scoped state" |
| /// before we invoke this function. (See `visit_fn` in the |
| /// `intravisit::Visitor` impl below.) |
| fn visit_fn_body( |
| &mut self, |
| id: hir::HirId, // the id of the fn itself |
| body: &'tcx hir::Body<'tcx>, |
| span: Span, |
| ) { |
| // When we enter a function, we can derive |
| debug!("visit_fn_body(id={:?})", id); |
| |
| let body_id = body.id(); |
| self.body_id = body_id.hir_id; |
| self.body_owner = self.tcx.hir().body_owner_def_id(body_id); |
| |
| let fn_sig = { |
| match self.tables.borrow().liberated_fn_sigs().get(id) { |
| Some(f) => *f, |
| None => { |
| bug!("No fn-sig entry for id={:?}", id); |
| } |
| } |
| }; |
| |
| // 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(); |
| |
| self.outlives_environment.add_implied_bounds( |
| self.fcx, |
| &fn_sig_tys[..], |
| body_id.hir_id, |
| span, |
| ); |
| self.outlives_environment.save_implied_bounds(body_id.hir_id); |
| self.link_fn_params(&body.params); |
| self.visit_body(body); |
| self.visit_region_obligations(body_id.hir_id); |
| |
| self.constrain_opaque_types( |
| &self.fcx.opaque_types.borrow(), |
| self.outlives_environment.free_region_map(), |
| ); |
| } |
| |
| fn visit_region_obligations(&mut self, hir_id: hir::HirId) { |
| debug!("visit_region_obligations: hir_id={:?}", hir_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(); |
| } |
| |
| fn resolve_regions_and_report_errors(&self, mode: RegionckMode) { |
| self.infcx.process_registered_region_obligations( |
| self.outlives_environment.region_bound_pairs_map(), |
| self.implicit_region_bound, |
| self.param_env, |
| ); |
| |
| self.fcx.resolve_regions_and_report_errors( |
| self.subject_def_id.to_def_id(), |
| &self.outlives_environment, |
| mode, |
| ); |
| } |
| |
| fn constrain_bindings_in_pat(&mut self, pat: &hir::Pat<'_>) { |
| debug!("regionck::visit_pat(pat={:?})", pat); |
| pat.each_binding(|_, hir_id, span, _| { |
| let typ = self.resolve_node_type(hir_id); |
| let body_id = self.body_id; |
| let _ = dropck::check_drop_obligations(self, typ, span, body_id); |
| }) |
| } |
| } |
| |
| impl<'a, 'tcx> Visitor<'tcx> for RegionCtxt<'a, '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. |
| |
| type Map = intravisit::ErasedMap<'tcx>; |
| |
| fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> { |
| NestedVisitorMap::None |
| } |
| |
| fn visit_fn( |
| &mut self, |
| fk: intravisit::FnKind<'tcx>, |
| _: &'tcx hir::FnDecl<'tcx>, |
| body_id: hir::BodyId, |
| span: Span, |
| hir_id: hir::HirId, |
| ) { |
| assert!( |
| match fk { |
| intravisit::FnKind::Closure(..) => true, |
| _ => false, |
| }, |
| "visit_fn invoked for something other than a closure" |
| ); |
| |
| // Save state of current function before invoking |
| // `visit_fn_body`. We will restore afterwards. |
| let old_body_id = self.body_id; |
| let old_body_owner = self.body_owner; |
| let env_snapshot = self.outlives_environment.push_snapshot_pre_closure(); |
| |
| let body = self.tcx.hir().body(body_id); |
| self.visit_fn_body(hir_id, body, span); |
| |
| // Restore state from previous function. |
| self.outlives_environment.pop_snapshot_post_closure(env_snapshot); |
| self.body_id = old_body_id; |
| self.body_owner = old_body_owner; |
| } |
| |
| //visit_pat: visit_pat, // (..) see above |
| |
| fn visit_arm(&mut self, arm: &'tcx hir::Arm<'tcx>) { |
| // see above |
| self.constrain_bindings_in_pat(&arm.pat); |
| intravisit::walk_arm(self, arm); |
| } |
| |
| fn visit_local(&mut self, l: &'tcx hir::Local<'tcx>) { |
| // see above |
| self.constrain_bindings_in_pat(&l.pat); |
| self.link_local(l); |
| intravisit::walk_local(self, l); |
| } |
| |
| fn visit_expr(&mut self, expr: &'tcx hir::Expr<'tcx>) { |
| // 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"); |
| } |
| } |
| |
| match expr.kind { |
| hir::ExprKind::AddrOf(hir::BorrowKind::Ref, m, ref base) => { |
| self.link_addr_of(expr, m, &base); |
| |
| intravisit::walk_expr(self, expr); |
| } |
| |
| hir::ExprKind::Match(ref discr, ref arms, _) => { |
| self.link_match(&discr, &arms[..]); |
| |
| intravisit::walk_expr(self, expr); |
| } |
| |
| _ => intravisit::walk_expr(self, expr), |
| } |
| } |
| } |
| |
| impl<'a, 'tcx> RegionCtxt<'a, 'tcx> { |
| /// Creates 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, 'tcx>) -> R, |
| { |
| f(mc::MemCategorizationContext::new( |
| &self.infcx, |
| self.outlives_environment.param_env, |
| self.body_owner, |
| &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::PlaceWithHirId<'tcx>> { |
| debug!("constrain_adjustments(expr={:?})", expr); |
| |
| let mut place = 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(place); |
| } |
| |
| debug!("constrain_adjustments: adjustments={:?}", adjustments); |
| |
| // If necessary, constrain destructors in the unadjusted form of this |
| // expression. |
| self.check_safety_of_rvalue_destructor_if_necessary(&place, expr.span); |
| |
| for adjustment in adjustments { |
| debug!("constrain_adjustments: adjustment={:?}, place={:?}", adjustment, place); |
| |
| if let adjustment::Adjust::Deref(Some(deref)) = adjustment.kind { |
| self.link_region( |
| expr.span, |
| deref.region, |
| ty::BorrowKind::from_mutbl(deref.mutbl), |
| &place, |
| ); |
| } |
| |
| if let adjustment::Adjust::Borrow(ref autoref) = adjustment.kind { |
| self.link_autoref(expr, &place, autoref); |
| } |
| |
| place = self.with_mc(|mc| mc.cat_expr_adjusted(expr, place, &adjustment))?; |
| } |
| |
| Ok(place) |
| } |
| |
| fn check_safety_of_rvalue_destructor_if_necessary( |
| &mut self, |
| place_with_id: &mc::PlaceWithHirId<'tcx>, |
| span: Span, |
| ) { |
| if let mc::PlaceBase::Rvalue = place_with_id.place.base { |
| if place_with_id.place.projections.is_empty() { |
| let typ = self.resolve_type(place_with_id.place.ty()); |
| let body_id = self.body_id; |
| let _ = dropck::check_drop_obligations(self, typ, span, body_id); |
| } |
| } |
| } |
| /// Adds constraints to inference such that `T: 'a` holds (or |
| /// reports an error if it cannot). |
| /// |
| /// # Parameters |
| /// |
| /// - `origin`, the reason we need this constraint |
| /// - `ty`, the type `T` |
| /// - `region`, the region `'a` |
| pub fn type_must_outlive( |
| &self, |
| origin: infer::SubregionOrigin<'tcx>, |
| ty: Ty<'tcx>, |
| region: ty::Region<'tcx>, |
| ) { |
| self.infcx.register_region_obligation( |
| self.body_id, |
| RegionObligation { sub_region: region, sup_type: ty, origin }, |
| ); |
| } |
| |
| /// 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 { |
| self.link_pattern(discr_cmt.clone(), &arm.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_params(&self, params: &[hir::Param<'_>]) { |
| for param in params { |
| let param_ty = self.node_ty(param.hir_id); |
| let param_cmt = |
| self.with_mc(|mc| mc.cat_rvalue(param.hir_id, param.pat.span, param_ty)); |
| debug!("param_ty={:?} param_cmt={:?} param={:?}", param_ty, param_cmt, param); |
| self.link_pattern(param_cmt, ¶m.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::PlaceWithHirId<'tcx>, root_pat: &hir::Pat<'_>) { |
| debug!("link_pattern(discr_cmt={:?}, root_pat={:?})", discr_cmt, root_pat); |
| ignore_err!(self.with_mc(|mc| { |
| mc.cat_pattern(discr_cmt, root_pat, |sub_cmt, hir::Pat { kind, span, hir_id }| { |
| // `ref x` pattern |
| if let PatKind::Binding(..) = kind { |
| if let Some(ty::BindByReference(mutbl)) = |
| mc.tables.extract_binding_mode(self.tcx.sess, *hir_id, *span) |
| { |
| self.link_region_from_node_type(*span, *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::PlaceWithHirId<'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.into()), expr_cmt); |
| } |
| |
| adjustment::AutoBorrow::RawPtr(_) => {} |
| } |
| } |
| |
| /// 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::PlaceWithHirId<'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::Ref(r, _, _) = rptr_ty.kind { |
| 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_place: &mc::PlaceWithHirId<'tcx>, |
| ) { |
| let origin = infer::DataBorrowed(borrow_place.place.ty(), span); |
| self.type_must_outlive(origin, borrow_place.place.ty(), borrow_region); |
| |
| for pointer_ty in borrow_place.place.deref_tys() { |
| debug!( |
| "link_region(borrow_region={:?}, borrow_kind={:?}, pointer_ty={:?})", |
| borrow_region, borrow_kind, borrow_place |
| ); |
| match pointer_ty.kind { |
| ty::RawPtr(_) => return, |
| ty::Ref(ref_region, _, ref_mutability) => { |
| if self.link_reborrowed_region(span, borrow_region, ref_region, ref_mutability) |
| { |
| return; |
| } |
| } |
| _ => assert!(pointer_ty.is_box(), "unexpected built-in deref type {}", pointer_ty), |
| } |
| } |
| if let mc::PlaceBase::Upvar(upvar_id) = borrow_place.place.base { |
| self.link_upvar_region(span, borrow_region, upvar_id); |
| } |
| } |
| |
| /// 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: |
| /// |
| /// ```ignore (incomplete Rust code) |
| /// 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: |
| /// |
| /// ```plain,ignore (pseudo-Rust) |
| /// 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). |
| /// |
| /// There is a complication beyond the simple scenario I just painted: 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`. |
| /// |
| /// The return value of this function indicates whether we *don't* need to |
| /// the recurse to the next reference up. |
| /// |
| /// This is explained more below. |
| fn link_reborrowed_region( |
| &self, |
| span: Span, |
| borrow_region: ty::Region<'tcx>, |
| ref_region: ty::Region<'tcx>, |
| ref_mutability: hir::Mutability, |
| ) -> bool { |
| debug!("link_reborrowed_region: {:?} <= {:?}", borrow_region, ref_region); |
| self.sub_regions(infer::Reborrow(span), borrow_region, ref_region); |
| |
| // 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_mutability { |
| hir::Mutability::Not => { |
| // The reference being reborrowed is a shareable 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. |
| true |
| } |
| |
| hir::Mutability::Mut => { |
| // The reference being reborrowed is either an `&mut T`. This is |
| // the case where recursion is needed. |
| false |
| } |
| } |
| } |
| |
| /// An upvar may be behind up to 2 references: |
| /// |
| /// * One can come from the reference to a "by-reference" upvar. |
| /// * Another one can come from the reference to the closure itself if it's |
| /// a `FnMut` or `Fn` closure. |
| /// |
| /// This function links the lifetimes of those references to the lifetime |
| /// of the borrow that's provided. See [RegionCtxt::link_reborrowed_region] for some |
| /// more explanation of this in the general case. |
| /// |
| /// We also supply a *cause*, and in this case we set the cause to |
| /// indicate that the reference being "reborrowed" is itself an upvar. This |
| /// provides a nicer error message should something go wrong. |
| fn link_upvar_region( |
| &self, |
| span: Span, |
| borrow_region: ty::Region<'tcx>, |
| upvar_id: ty::UpvarId, |
| ) { |
| debug!("link_upvar_region(borrorw_region={:?}, upvar_id={:?}", borrow_region, upvar_id); |
| // A by-reference upvar can't be borrowed for longer than the |
| // upvar is borrowed from the environment. |
| match self.tables.borrow().upvar_capture(upvar_id) { |
| ty::UpvarCapture::ByRef(upvar_borrow) => { |
| self.sub_regions( |
| infer::ReborrowUpvar(span, upvar_id), |
| borrow_region, |
| upvar_borrow.region, |
| ); |
| if let ty::ImmBorrow = upvar_borrow.kind { |
| debug!("link_upvar_region: capture by shared ref"); |
| return; |
| } |
| } |
| ty::UpvarCapture::ByValue => {} |
| } |
| let fn_hir_id = self.tcx.hir().local_def_id_to_hir_id(upvar_id.closure_expr_id); |
| let ty = self.resolve_node_type(fn_hir_id); |
| debug!("link_upvar_region: ty={:?}", ty); |
| |
| // A closure capture can't be borrowed for longer than the |
| // reference to the closure. |
| if let ty::Closure(_, substs) = ty.kind { |
| match self.infcx.closure_kind(substs) { |
| Some(ty::ClosureKind::Fn | ty::ClosureKind::FnMut) => { |
| // Region of environment pointer |
| let env_region = self.tcx.mk_region(ty::ReFree(ty::FreeRegion { |
| scope: upvar_id.closure_expr_id.to_def_id(), |
| bound_region: ty::BrEnv, |
| })); |
| self.sub_regions( |
| infer::ReborrowUpvar(span, upvar_id), |
| borrow_region, |
| env_region, |
| ); |
| } |
| Some(ty::ClosureKind::FnOnce) => {} |
| None => { |
| span_bug!(span, "Have not inferred closure kind before regionck"); |
| } |
| } |
| } |
| } |
| } |
