-//! 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(
infcx: &InferCtxt<'_, 'tcx>,
fn_sig_tys: FxHashSet<Ty<'tcx>>,
body_id: hir::HirId,
- span: Span,
);
}
infcx: &InferCtxt<'a, 'tcx>,
fn_sig_tys: FxHashSet<Ty<'tcx>>,
body_id: hir::HirId,
- span: Span,
) {
for ty in fn_sig_tys {
let ty = infcx.resolve_vars_if_possible(ty);
- let implied_bounds = infcx.implied_outlives_bounds(self.param_env, body_id, ty, span);
+ let implied_bounds = infcx.implied_outlives_bounds(self.param_env, body_id, ty);
self.add_outlives_bounds(Some(infcx), implied_bounds)
}
}
}
-
-///////////////////////////////////////////////////////////////////////////
-// 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 checking during the WF phase for items. `wf_tys` are the
- /// types from which we should derive implied bounds, if any.
- #[instrument(level = "debug", skip(self))]
- pub fn regionck_item(&self, item_id: hir::HirId, span: Span, wf_tys: FxHashSet<Ty<'tcx>>) {
- let body_owner = self.tcx.hir().local_def_id(item_id);
- let mut rcx = RegionCtxt::new(self, body_owner, self.param_env);
- rcx.outlives_environment.add_implied_bounds(self, wf_tys, item_id, span);
- rcx.outlives_environment.save_implied_bounds(rcx.body_id());
- rcx.visit_region_obligations(item_id);
- rcx.resolve_regions_and_report_errors();
- }
-
- /// 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>,
- span: Span,
- wf_tys: FxHashSet<Ty<'tcx>>,
- ) {
- 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, span);
- 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, self.tcx.hir().span(fn_id));
- }
-
- // 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<i32> 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: <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_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, 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);
- }
-
- 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 resolve_regions_and_report_errors(&self) {
- self.infcx.process_registered_region_obligations(
- self.outlives_environment.region_bound_pairs_map(),
- self.param_env,
- );
-
- self.fcx.resolve_regions_and_report_errors(&self.outlives_environment);
- }
-
- 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, span);
-
- // 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<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.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<PlaceWithHirId<'tcx>> {
- 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");
- }
- }
- }
- }
-}
projects / rust.git / blobdiff