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rip out RegionCtxt from hir typeck

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This commit is contained in:
lcnr 2022-06-29 17:46:16 +02:00
parent 68d70fc5bd
commit e78e0e2ad0
4 changed files with 13 additions and 896 deletions
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70
compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs
View file

@ -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}; use rustc_middle::ty::{self, Ty, TyCtxt};
pub use rustc_middle::traits::query::{DropckConstraint, DropckOutlivesResult}; pub use rustc_middle::traits::query::{DropckConstraint, DropckOutlivesResult};
pub trait AtExt<'tcx> {
fn dropck_outlives(&self, ty: Ty<'tcx>) -> InferOk<'tcx, Vec<GenericArg<'tcx>>>;
}
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<GenericArg<'tcx>>> {
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 /// This returns true if the type `ty` is "trivial" for
/// dropck-outlives -- that is, if it doesn't require any types to /// dropck-outlives -- that is, if it doesn't require any types to
/// outlive. This is similar but not *quite* the same as the /// 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 /// Note also that `needs_drop` requires a "global" type (i.e., one
/// with erased regions), but this function does not. /// 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 { pub fn trivial_dropck_outlives<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
match ty.kind() { match ty.kind() {
// None of these types have a destructor and hence they do not // 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), ty::Array(ty, _) | ty::Slice(ty) => trivial_dropck_outlives(tcx, *ty),
// (T1..Tn) and closures have same properties as T1..Tn -- // (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::Tuple(tys) => tys.iter().all(|t| trivial_dropck_outlives(tcx, t)),
ty::Closure(_, ref substs) => { ty::Closure(_, ref substs) => {
trivial_dropck_outlives(tcx, substs.as_closure().tupled_upvars_ty()) trivial_dropck_outlives(tcx, substs.as_closure().tupled_upvars_ty())

19
compiler/rustc_typeck/src/check/dropck.rs
View file

@ -1,5 +1,6 @@
use crate::check::regionck::RegionCtxt; // FIXME(@lcnr): Move this module out of `rustc_typeck`.
use crate::hir; //
// We don't do any drop checking during hir typeck.
use crate::hir::def_id::{DefId, LocalDefId}; use crate::hir::def_id::{DefId, LocalDefId};
use rustc_errors::{struct_span_err, ErrorGuaranteed}; use rustc_errors::{struct_span_err, ErrorGuaranteed};
use rustc_middle::ty::error::TypeError; 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::subst::SubstsRef;
use rustc_middle::ty::util::IgnoreRegions; use rustc_middle::ty::util::IgnoreRegions;
use rustc_middle::ty::{self, Predicate, Ty, TyCtxt}; use rustc_middle::ty::{self, Predicate, Ty, TyCtxt};
use rustc_span::Span;
/// This function confirms that the `Drop` implementation identified by /// This function confirms that the `Drop` implementation identified by
/// `drop_impl_did` is not any more specialized than the type it is /// `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 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 // This is an implementation of the TypeRelation trait with the
// aim of simply comparing for equality (without side-effects). // aim of simply comparing for equality (without side-effects).
// It is not intended to be used anywhere else other than here. // It is not intended to be used anywhere else other than here.

23
compiler/rustc_typeck/src/check/mod.rs
View file

@ -368,7 +368,7 @@ fn typeck_with_fallback<'tcx>(
let typeck_results = Inherited::build(tcx, def_id).enter(|inh| { let typeck_results = Inherited::build(tcx, def_id).enter(|inh| {
let param_env = tcx.param_env(def_id); 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 fn_sig = if crate::collect::get_infer_ret_ty(&decl.output).is_some() {
let fcx = FnCtxt::new(&inh, param_env, body.value.hir_id); let fcx = FnCtxt::new(&inh, param_env, body.value.hir_id);
<dyn AstConv<'_>>::ty_of_fn(&fcx, id, header.unsafety, header.abi, decl, None, None) <dyn AstConv<'_>>::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()); check_abi(tcx, id, span, fn_sig.abi());
// When normalizing the function signature, we assume all types are // Compute the function signature from point of view of inside the fn.
// 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.
let fn_sig = tcx.liberate_late_bound_regions(def_id.to_def_id(), fn_sig); let fn_sig = tcx.liberate_late_bound_regions(def_id.to_def_id(), fn_sig);
let fn_sig = inh.normalize_associated_types_in( let fn_sig = inh.normalize_associated_types_in(
body.value.span, body.value.span,
@ -392,10 +386,7 @@ fn typeck_with_fallback<'tcx>(
param_env, param_env,
fn_sig, fn_sig,
); );
wf_tys.extend(fn_sig.inputs_and_output.iter()); check_fn(&inh, param_env, fn_sig, decl, id, body, None, true).0
let fcx = check_fn(&inh, param_env, fn_sig, decl, id, body, None, true).0;
(fcx, wf_tys)
} else { } else {
let fcx = FnCtxt::new(&inh, param_env, body.value.hir_id); let fcx = FnCtxt::new(&inh, param_env, body.value.hir_id);
let expected_type = body_ty let expected_type = body_ty
@ -458,7 +449,7 @@ fn typeck_with_fallback<'tcx>(
fcx.write_ty(id, expected_type); fcx.write_ty(id, expected_type);
(fcx, FxHashSet::default()) fcx
}; };
let fallback_has_occurred = fcx.type_inference_fallback(); let fallback_has_occurred = fcx.type_inference_fallback();
@ -490,11 +481,7 @@ fn typeck_with_fallback<'tcx>(
fcx.check_asms(); fcx.check_asms();
if fn_sig.is_some() { fcx.infcx.skip_region_resolution();
fcx.regionck_fn(id, body, wf_tys);
} else {
fcx.regionck_body(body);
}
fcx.resolve_type_vars_in_body(body) fcx.resolve_type_vars_in_body(body)
}); });

797
compiler/rustc_typeck/src/check/regionck.rs
View file

@ -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 crate::outlives::outlives_bounds::InferCtxtExt as _;
use hir::def_id::LocalDefId;
use rustc_data_structures::stable_set::FxHashSet; use rustc_data_structures::stable_set::FxHashSet;
use rustc_hir as hir; 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::outlives::env::OutlivesEnvironment;
use rustc_infer::infer::{self, InferCtxt, RegionObligation}; use rustc_infer::infer::InferCtxt;
use rustc_middle::hir::place::{PlaceBase, PlaceWithHirId}; use rustc_middle::ty::Ty;
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 ();
}
}
};
}
pub(crate) trait OutlivesEnvironmentExt<'tcx> { pub(crate) trait OutlivesEnvironmentExt<'tcx> {
fn add_implied_bounds( 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<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);
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<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>,
) {
// 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<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");
}
}
}
}
}