diff --git a/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs b/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs index 25cc6e9f9f2f..aad3c37f84e5 100644 --- a/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs +++ b/compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs @@ -1,73 +1,7 @@ -use crate::infer::at::At; -use crate::infer::canonical::OriginalQueryValues; -use crate::infer::InferOk; - -use rustc_middle::ty::subst::GenericArg; use rustc_middle::ty::{self, Ty, TyCtxt}; pub use rustc_middle::traits::query::{DropckConstraint, DropckOutlivesResult}; -pub trait AtExt<'tcx> { - fn dropck_outlives(&self, ty: Ty<'tcx>) -> InferOk<'tcx, Vec>>; -} - -impl<'cx, 'tcx> AtExt<'tcx> for At<'cx, 'tcx> { - /// Given a type `ty` of some value being dropped, computes a set - /// of "kinds" (types, regions) that must be outlive the execution - /// of the destructor. These basically correspond to data that the - /// destructor might access. This is used during regionck to - /// impose "outlives" constraints on any lifetimes referenced - /// within. - /// - /// The rules here are given by the "dropck" RFCs, notably [#1238] - /// and [#1327]. This is a fixed-point computation, where we - /// explore all the data that will be dropped (transitively) when - /// a value of type `ty` is dropped. For each type T that will be - /// dropped and which has a destructor, we must assume that all - /// the types/regions of T are live during the destructor, unless - /// they are marked with a special attribute (`#[may_dangle]`). - /// - /// [#1238]: https://github.com/rust-lang/rfcs/blob/master/text/1238-nonparametric-dropck.md - /// [#1327]: https://github.com/rust-lang/rfcs/blob/master/text/1327-dropck-param-eyepatch.md - fn dropck_outlives(&self, ty: Ty<'tcx>) -> InferOk<'tcx, Vec>> { - debug!("dropck_outlives(ty={:?}, param_env={:?})", ty, self.param_env,); - - // Quick check: there are a number of cases that we know do not require - // any destructor. - let tcx = self.infcx.tcx; - if trivial_dropck_outlives(tcx, ty) { - return InferOk { value: vec![], obligations: vec![] }; - } - - let mut orig_values = OriginalQueryValues::default(); - let c_ty = self.infcx.canonicalize_query(self.param_env.and(ty), &mut orig_values); - let span = self.cause.span; - debug!("c_ty = {:?}", c_ty); - if let Ok(result) = tcx.dropck_outlives(c_ty) - && result.is_proven() - && let Ok(InferOk { value, obligations }) = - self.infcx.instantiate_query_response_and_region_obligations( - self.cause, - self.param_env, - &orig_values, - result, - ) - { - let ty = self.infcx.resolve_vars_if_possible(ty); - let kinds = value.into_kinds_reporting_overflows(tcx, span, ty); - return InferOk { value: kinds, obligations }; - } - - // Errors and ambiguity in dropck occur in two cases: - // - unresolved inference variables at the end of typeck - // - non well-formed types where projections cannot be resolved - // Either of these should have created an error before. - tcx.sess.delay_span_bug(span, "dtorck encountered internal error"); - - InferOk { value: vec![], obligations: vec![] } - } -} - /// This returns true if the type `ty` is "trivial" for /// dropck-outlives -- that is, if it doesn't require any types to /// outlive. This is similar but not *quite* the same as the @@ -79,6 +13,8 @@ impl<'cx, 'tcx> AtExt<'tcx> for At<'cx, 'tcx> { /// /// Note also that `needs_drop` requires a "global" type (i.e., one /// with erased regions), but this function does not. +/// +// FIXME(@lcnr): remove this module and move this function somewhere else. pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool { match ty.kind() { // None of these types have a destructor and hence they do not @@ -105,7 +41,7 @@ pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool { ty::Array(ty, _) | ty::Slice(ty) => trivial_dropck_outlives(tcx, *ty), // (T1..Tn) and closures have same properties as T1..Tn -- - // check if *any* of those are trivial. + // check if *all* of them are trivial. ty::Tuple(tys) => tys.iter().all(|t| trivial_dropck_outlives(tcx, t)), ty::Closure(_, ref substs) => { trivial_dropck_outlives(tcx, substs.as_closure().tupled_upvars_ty()) diff --git a/compiler/rustc_typeck/src/check/dropck.rs b/compiler/rustc_typeck/src/check/dropck.rs index a4013e10525e..72095c408075 100644 --- a/compiler/rustc_typeck/src/check/dropck.rs +++ b/compiler/rustc_typeck/src/check/dropck.rs @@ -1,5 +1,6 @@ -use crate::check::regionck::RegionCtxt; -use crate::hir; +// FIXME(@lcnr): Move this module out of `rustc_typeck`. +// +// We don't do any drop checking during hir typeck. use crate::hir::def_id::{DefId, LocalDefId}; use rustc_errors::{struct_span_err, ErrorGuaranteed}; use rustc_middle::ty::error::TypeError; @@ -7,7 +8,6 @@ use rustc_middle::ty::relate::{Relate, RelateResult, TypeRelation}; use rustc_middle::ty::subst::SubstsRef; use rustc_middle::ty::util::IgnoreRegions; use rustc_middle::ty::{self, Predicate, Ty, TyCtxt}; -use rustc_span::Span; /// This function confirms that the `Drop` implementation identified by /// `drop_impl_did` is not any more specialized than the type it is @@ -229,19 +229,6 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>( result } -/// This function is not only checking that the dropck obligations are met for -/// the given type, but it's also currently preventing non-regular recursion in -/// types from causing stack overflows (dropck_no_diverge_on_nonregular_*.rs). -/// -/// FIXME: Completely rip out dropck and regionck. -pub(crate) fn check_drop_obligations<'a, 'tcx>( - _rcx: &mut RegionCtxt<'a, 'tcx>, - _ty: Ty<'tcx>, - _span: Span, - _body_id: hir::HirId, -) { -} - // This is an implementation of the TypeRelation trait with the // aim of simply comparing for equality (without side-effects). // It is not intended to be used anywhere else other than here. diff --git a/compiler/rustc_typeck/src/check/mod.rs b/compiler/rustc_typeck/src/check/mod.rs index b812085734dc..dee58791cec1 100644 --- a/compiler/rustc_typeck/src/check/mod.rs +++ b/compiler/rustc_typeck/src/check/mod.rs @@ -368,7 +368,7 @@ fn typeck_with_fallback<'tcx>( let typeck_results = Inherited::build(tcx, def_id).enter(|inh| { let param_env = tcx.param_env(def_id); - let (fcx, wf_tys) = if let Some(hir::FnSig { header, decl, .. }) = fn_sig { + let fcx = if let Some(hir::FnSig { header, decl, .. }) = fn_sig { let fn_sig = if crate::collect::get_infer_ret_ty(&decl.output).is_some() { let fcx = FnCtxt::new(&inh, param_env, body.value.hir_id); >::ty_of_fn(&fcx, id, header.unsafety, header.abi, decl, None, None) @@ -378,13 +378,7 @@ fn typeck_with_fallback<'tcx>( check_abi(tcx, id, span, fn_sig.abi()); - // When normalizing the function signature, we assume all types are - // well-formed. So, we don't need to worry about the obligations - // from normalization. We could just discard these, but to align with - // compare_method and elsewhere, we just add implied bounds for - // these types. - let mut wf_tys = FxHashSet::default(); - // Compute the fty from point of view of inside the fn. + // Compute the function signature from point of view of inside the fn. let fn_sig = tcx.liberate_late_bound_regions(def_id.to_def_id(), fn_sig); let fn_sig = inh.normalize_associated_types_in( body.value.span, @@ -392,10 +386,7 @@ fn typeck_with_fallback<'tcx>( param_env, fn_sig, ); - wf_tys.extend(fn_sig.inputs_and_output.iter()); - - let fcx = check_fn(&inh, param_env, fn_sig, decl, id, body, None, true).0; - (fcx, wf_tys) + check_fn(&inh, param_env, fn_sig, decl, id, body, None, true).0 } else { let fcx = FnCtxt::new(&inh, param_env, body.value.hir_id); let expected_type = body_ty @@ -458,7 +449,7 @@ fn typeck_with_fallback<'tcx>( fcx.write_ty(id, expected_type); - (fcx, FxHashSet::default()) + fcx }; let fallback_has_occurred = fcx.type_inference_fallback(); @@ -490,11 +481,7 @@ fn typeck_with_fallback<'tcx>( fcx.check_asms(); - if fn_sig.is_some() { - fcx.regionck_fn(id, body, wf_tys); - } else { - fcx.regionck_body(body); - } + fcx.infcx.skip_region_resolution(); fcx.resolve_type_vars_in_body(body) }); diff --git a/compiler/rustc_typeck/src/check/regionck.rs b/compiler/rustc_typeck/src/check/regionck.rs index bf30ba2278c7..1c3c5f999bca 100644 --- a/compiler/rustc_typeck/src/check/regionck.rs +++ b/compiler/rustc_typeck/src/check/regionck.rs @@ -1,106 +1,9 @@ -//! 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::outlives::outlives_bounds::InferCtxtExt as _; -use hir::def_id::LocalDefId; use rustc_data_structures::stable_set::FxHashSet; use rustc_hir as hir; -use rustc_hir::intravisit::{self, Visitor}; -use rustc_hir::PatKind; use rustc_infer::infer::outlives::env::OutlivesEnvironment; -use rustc_infer::infer::{self, InferCtxt, RegionObligation}; -use rustc_middle::hir::place::{PlaceBase, PlaceWithHirId}; -use rustc_middle::ty::adjustment; -use rustc_middle::ty::{self, Ty}; -use rustc_span::Span; -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 (); - } - } - }; -} +use rustc_infer::infer::InferCtxt; +use rustc_middle::ty::Ty; pub(crate) trait OutlivesEnvironmentExt<'tcx> { fn add_implied_bounds( @@ -142,699 +45,3 @@ impl<'tcx> OutlivesEnvironmentExt<'tcx> for OutlivesEnvironment<'tcx> { } } } - -/////////////////////////////////////////////////////////////////////////// -// PUBLIC ENTRY POINTS - -impl<'a, 'tcx> FnCtxt<'a, 'tcx> { - pub fn regionck_body(&self, body: &'tcx hir::Body<'tcx>) { - let body_owner = self.tcx.hir().body_owner_def_id(body.id()); - let mut rcx = RegionCtxt::new(self, body_owner, self.param_env); - - // There are no add'l implied bounds when checking a - // standalone body (e.g., the `E` in a type like `[u32; E]`). - rcx.outlives_environment.save_implied_bounds(rcx.body_id()); - - if !self.errors_reported_since_creation() { - // regionck assumes typeck succeeded - rcx.visit_body(body); - rcx.visit_region_obligations(rcx.body_id()); - } - // Checked by NLL - rcx.fcx.skip_region_resolution(); - } - - /// 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(crate) fn regionck_fn( - &self, - fn_id: hir::HirId, - body: &'tcx hir::Body<'tcx>, - wf_tys: FxHashSet>, - ) { - debug!("regionck_fn(id={})", fn_id); - let body_owner = self.tcx.hir().body_owner_def_id(body.id()); - let mut rcx = RegionCtxt::new(self, body_owner, self.param_env); - // We need to add the implied bounds from the function signature - rcx.outlives_environment.add_implied_bounds(self, wf_tys, fn_id); - rcx.outlives_environment.save_implied_bounds(fn_id); - - if !self.errors_reported_since_creation() { - // regionck assumes typeck succeeded - rcx.visit_fn_body(fn_id, body); - } - - // Checked by NLL - rcx.fcx.skip_region_resolution(); - } -} - -/////////////////////////////////////////////////////////////////////////// -// INTERNALS - -pub struct RegionCtxt<'a, 'tcx> { - pub fcx: &'a FnCtxt<'a, 'tcx>, - - outlives_environment: OutlivesEnvironment<'tcx>, - - body_owner: LocalDefId, -} - -impl<'a, 'tcx> Deref for RegionCtxt<'a, 'tcx> { - type Target = FnCtxt<'a, 'tcx>; - fn deref(&self) -> &Self::Target { - self.fcx - } -} - -impl<'a, 'tcx> RegionCtxt<'a, 'tcx> { - pub fn new( - fcx: &'a FnCtxt<'a, 'tcx>, - body_owner: LocalDefId, - param_env: ty::ParamEnv<'tcx>, - ) -> RegionCtxt<'a, 'tcx> { - let outlives_environment = OutlivesEnvironment::new(param_env); - RegionCtxt { fcx, body_owner, outlives_environment } - } - - /// FIXME: Ideally all the callers would deal with - /// `LocalDefId`s as well. Ah well, this code is going - /// to be removed soon anyways 🤷 - pub fn body_id(&self) -> hir::HirId { - self.tcx.hir().local_def_id_to_hir_id(self.body_owner) - } - - /// 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: - /// - /// ```ignore UNSOLVED (does replacing @i32 with Box preserve the desired semantics for the example?) - /// fn borrow(x: &i32) -> &i32 {x} - /// fn foo(x: @i32) -> i32 { // block: B - /// let b = borrow(x); // region: - /// *b - /// } - /// ``` - /// - /// Here, the region of `b` will be ``. `` 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 `&.i32` and then `*b` will require that `` be bigger than the let and - /// the `*b` expression, so we will effectively resolve `` 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>, - ) { - // When we enter a function, we can derive - debug!("visit_fn_body(id={:?})", id); - let body_id = body.id(); - self.body_owner = self.tcx.hir().body_owner_def_id(body_id); - - let Some(fn_sig) = self.typeck_results.borrow().liberated_fn_sigs().get(id) else { - 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: FxHashSet<_> = - 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); - 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); - } - - fn visit_inline_const(&mut self, id: hir::HirId, body: &'tcx hir::Body<'tcx>) { - debug!("visit_inline_const(id={:?})", id); - - // Save state of current function. We will restore afterwards. - let old_body_owner = self.body_owner; - let env_snapshot = self.outlives_environment.push_snapshot_pre_typeck_child(); - - let body_id = body.id(); - self.body_owner = self.tcx.hir().body_owner_def_id(body_id); - - self.outlives_environment.save_implied_bounds(body_id.hir_id); - - self.visit_body(body); - self.visit_region_obligations(body_id.hir_id); - - // Restore state from previous function. - self.outlives_environment.pop_snapshot_post_typeck_child(env_snapshot); - self.body_owner = old_body_owner; - } - - 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 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; - 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. - - fn visit_fn( - &mut self, - fk: intravisit::FnKind<'tcx>, - _: &'tcx hir::FnDecl<'tcx>, - body_id: hir::BodyId, - _span: Span, - hir_id: hir::HirId, - ) { - assert!( - matches!(fk, intravisit::FnKind::Closure), - "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_owner = self.body_owner; - let env_snapshot = self.outlives_environment.push_snapshot_pre_typeck_child(); - - let body = self.tcx.hir().body(body_id); - self.visit_fn_body(hir_id, body); - - // Restore state from previous function. - self.outlives_environment.pop_snapshot_post_typeck_child(env_snapshot); - 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, arms, _) => { - self.link_match(discr, arms); - - intravisit::walk_expr(self, expr); - } - - hir::ExprKind::ConstBlock(anon_const) => { - let body = self.tcx.hir().body(anon_const.body); - self.visit_inline_const(anon_const.hir_id, body); - } - - _ => intravisit::walk_expr(self, expr), - } - } -} - -impl<'a, 'tcx> RegionCtxt<'a, 'tcx> { - /// Creates a temporary `MemCategorizationContext` and pass it to the closure. - fn with_mc(&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.typeck_results.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> { - debug!("constrain_adjustments(expr={:?})", expr); - - let mut place = self.with_mc(|mc| mc.cat_expr_unadjusted(expr))?; - - let typeck_results = self.typeck_results.borrow(); - let adjustments = typeck_results.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: &PlaceWithHirId<'tcx>, - span: Span, - ) { - if let 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; - 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(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, param.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: 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 - && let Some(ty::BindByReference(mutbl)) = mc.typeck_results.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: &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: &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: &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 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. - let closure_local_def_id = upvar_id.closure_expr_id; - let mut all_captures_are_imm_borrow = true; - for captured_place in self - .typeck_results - .borrow() - .closure_min_captures - .get(&closure_local_def_id.to_def_id()) - .and_then(|root_var_min_cap| root_var_min_cap.get(&upvar_id.var_path.hir_id)) - .into_iter() - .flatten() - { - match captured_place.info.capture_kind { - ty::UpvarCapture::ByRef(upvar_borrow) => { - self.sub_regions( - infer::ReborrowUpvar(span, upvar_id), - borrow_region, - captured_place.region.unwrap(), - ); - if let ty::ImmBorrow = upvar_borrow { - debug!("link_upvar_region: capture by shared ref"); - } else { - all_captures_are_imm_borrow = false; - } - } - ty::UpvarCapture::ByValue => { - all_captures_are_imm_borrow = false; - } - } - } - if all_captures_are_imm_borrow { - return; - } - let fn_hir_id = self.tcx.hir().local_def_id_to_hir_id(closure_local_def_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"); - } - } - } - } -}