380 lines
14 KiB
Rust
380 lines
14 KiB
Rust
use crate::check::regionck::RegionCtxt;
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use crate::hir;
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use crate::hir::def_id::DefId;
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use crate::util::common::ErrorReported;
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use rustc::infer::outlives::env::OutlivesEnvironment;
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use rustc::infer::{InferOk, SuppressRegionErrors};
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use rustc::middle::region;
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use rustc::traits::{ObligationCause, TraitEngine, TraitEngineExt};
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use rustc::ty::error::TypeError;
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use rustc::ty::relate::{Relate, RelateResult, TypeRelation};
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use rustc::ty::subst::{Subst, SubstsRef};
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use rustc::ty::{self, Predicate, Ty, TyCtxt};
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use rustc_errors::struct_span_err;
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use rustc_span::Span;
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use rustc_error_codes::*;
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/// This function confirms that the `Drop` implementation identified by
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/// `drop_impl_did` is not any more specialized than the type it is
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/// attached to (Issue #8142).
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///
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/// This means:
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///
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/// 1. The self type must be nominal (this is already checked during
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/// coherence),
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///
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/// 2. The generic region/type parameters of the impl's self type must
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/// all be parameters of the Drop impl itself (i.e., no
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/// specialization like `impl Drop for Foo<i32>`), and,
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///
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/// 3. Any bounds on the generic parameters must be reflected in the
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/// struct/enum definition for the nominal type itself (i.e.
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/// cannot do `struct S<T>; impl<T:Clone> Drop for S<T> { ... }`).
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///
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pub fn check_drop_impl(tcx: TyCtxt<'_>, drop_impl_did: DefId) -> Result<(), ErrorReported> {
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let dtor_self_type = tcx.type_of(drop_impl_did);
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let dtor_predicates = tcx.predicates_of(drop_impl_did);
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match dtor_self_type.kind {
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ty::Adt(adt_def, self_to_impl_substs) => {
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ensure_drop_params_and_item_params_correspond(
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tcx,
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drop_impl_did,
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dtor_self_type,
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adt_def.did,
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)?;
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ensure_drop_predicates_are_implied_by_item_defn(
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tcx,
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dtor_predicates,
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adt_def.did,
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self_to_impl_substs,
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)
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}
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_ => {
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// Destructors only work on nominal types. This was
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// already checked by coherence, but compilation may
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// not have been terminated.
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let span = tcx.def_span(drop_impl_did);
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tcx.sess.delay_span_bug(
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span,
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&format!("should have been rejected by coherence check: {}", dtor_self_type),
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);
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Err(ErrorReported)
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}
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}
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}
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fn ensure_drop_params_and_item_params_correspond<'tcx>(
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tcx: TyCtxt<'tcx>,
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drop_impl_did: DefId,
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drop_impl_ty: Ty<'tcx>,
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self_type_did: DefId,
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) -> Result<(), ErrorReported> {
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let drop_impl_hir_id = tcx.hir().as_local_hir_id(drop_impl_did).unwrap();
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// check that the impl type can be made to match the trait type.
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tcx.infer_ctxt().enter(|ref infcx| {
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let impl_param_env = tcx.param_env(self_type_did);
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let tcx = infcx.tcx;
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let mut fulfillment_cx = TraitEngine::new(tcx);
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let named_type = tcx.type_of(self_type_did);
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let drop_impl_span = tcx.def_span(drop_impl_did);
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let fresh_impl_substs = infcx.fresh_substs_for_item(drop_impl_span, drop_impl_did);
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let fresh_impl_self_ty = drop_impl_ty.subst(tcx, fresh_impl_substs);
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let cause = &ObligationCause::misc(drop_impl_span, drop_impl_hir_id);
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match infcx.at(cause, impl_param_env).eq(named_type, fresh_impl_self_ty) {
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Ok(InferOk { obligations, .. }) => {
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fulfillment_cx.register_predicate_obligations(infcx, obligations);
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}
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Err(_) => {
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let item_span = tcx.def_span(self_type_did);
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let self_descr = tcx
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.def_kind(self_type_did)
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.map(|kind| kind.descr(self_type_did))
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.unwrap_or("type");
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struct_span_err!(
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tcx.sess,
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drop_impl_span,
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E0366,
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"`Drop` impls cannot be specialized"
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)
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.span_note(
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item_span,
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&format!(
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"use the same sequence of generic type, lifetime and const parameters \
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as the {} definition",
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self_descr,
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),
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)
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.emit();
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return Err(ErrorReported);
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}
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}
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if let Err(ref errors) = fulfillment_cx.select_all_or_error(&infcx) {
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// this could be reached when we get lazy normalization
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infcx.report_fulfillment_errors(errors, None, false);
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return Err(ErrorReported);
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}
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let region_scope_tree = region::ScopeTree::default();
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// NB. It seems a bit... suspicious to use an empty param-env
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// here. The correct thing, I imagine, would be
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// `OutlivesEnvironment::new(impl_param_env)`, which would
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// allow region solving to take any `a: 'b` relations on the
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// impl into account. But I could not create a test case where
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// it did the wrong thing, so I chose to preserve existing
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// behavior, since it ought to be simply more
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// conservative. -nmatsakis
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let outlives_env = OutlivesEnvironment::new(ty::ParamEnv::empty());
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infcx.resolve_regions_and_report_errors(
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drop_impl_did,
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®ion_scope_tree,
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&outlives_env,
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SuppressRegionErrors::default(),
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);
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Ok(())
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})
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}
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/// Confirms that every predicate imposed by dtor_predicates is
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/// implied by assuming the predicates attached to self_type_did.
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fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
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tcx: TyCtxt<'tcx>,
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dtor_predicates: ty::GenericPredicates<'tcx>,
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self_type_did: DefId,
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self_to_impl_substs: SubstsRef<'tcx>,
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) -> Result<(), ErrorReported> {
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let mut result = Ok(());
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// Here is an example, analogous to that from
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// `compare_impl_method`.
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//
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// Consider a struct type:
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//
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// struct Type<'c, 'b:'c, 'a> {
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// x: &'a Contents // (contents are irrelevant;
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// y: &'c Cell<&'b Contents>, // only the bounds matter for our purposes.)
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// }
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//
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// and a Drop impl:
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//
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// impl<'z, 'y:'z, 'x:'y> Drop for P<'z, 'y, 'x> {
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// fn drop(&mut self) { self.y.set(self.x); } // (only legal if 'x: 'y)
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// }
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//
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// We start out with self_to_impl_substs, that maps the generic
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// parameters of Type to that of the Drop impl.
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//
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// self_to_impl_substs = {'c => 'z, 'b => 'y, 'a => 'x}
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//
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// Applying this to the predicates (i.e., assumptions) provided by the item
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// definition yields the instantiated assumptions:
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//
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// ['y : 'z]
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//
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// We then check all of the predicates of the Drop impl:
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//
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// ['y:'z, 'x:'y]
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//
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// and ensure each is in the list of instantiated
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// assumptions. Here, `'y:'z` is present, but `'x:'y` is
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// absent. So we report an error that the Drop impl injected a
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// predicate that is not present on the struct definition.
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let self_type_hir_id = tcx.hir().as_local_hir_id(self_type_did).unwrap();
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// We can assume the predicates attached to struct/enum definition
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// hold.
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let generic_assumptions = tcx.predicates_of(self_type_did);
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let assumptions_in_impl_context = generic_assumptions.instantiate(tcx, &self_to_impl_substs);
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let assumptions_in_impl_context = assumptions_in_impl_context.predicates;
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let self_param_env = tcx.param_env(self_type_did);
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// An earlier version of this code attempted to do this checking
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// via the traits::fulfill machinery. However, it ran into trouble
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// since the fulfill machinery merely turns outlives-predicates
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// 'a:'b and T:'b into region inference constraints. It is simpler
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// just to look for all the predicates directly.
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assert_eq!(dtor_predicates.parent, None);
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for (predicate, predicate_sp) in dtor_predicates.predicates {
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// (We do not need to worry about deep analysis of type
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// expressions etc because the Drop impls are already forced
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// to take on a structure that is roughly an alpha-renaming of
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// the generic parameters of the item definition.)
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// This path now just checks *all* predicates via an instantiation of
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// the `SimpleEqRelation`, which simply forwards to the `relate` machinery
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// after taking care of anonymizing late bound regions.
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//
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// However, it may be more efficient in the future to batch
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// the analysis together via the fulfill (see comment above regarding
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// the usage of the fulfill machinery), rather than the
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// repeated `.iter().any(..)` calls.
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// This closure is a more robust way to check `Predicate` equality
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// than simple `==` checks (which were the previous implementation).
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// It relies on `ty::relate` for `TraitPredicate` and `ProjectionPredicate`
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// (which implement the Relate trait), while delegating on simple equality
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// for the other `Predicate`.
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// This implementation solves (Issue #59497) and (Issue #58311).
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// It is unclear to me at the moment whether the approach based on `relate`
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// could be extended easily also to the other `Predicate`.
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let predicate_matches_closure = |p: &'_ Predicate<'tcx>| {
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let mut relator: SimpleEqRelation<'tcx> = SimpleEqRelation::new(tcx, self_param_env);
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match (predicate, p) {
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(Predicate::Trait(a), Predicate::Trait(b)) => relator.relate(a, b).is_ok(),
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(Predicate::Projection(a), Predicate::Projection(b)) => {
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relator.relate(a, b).is_ok()
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}
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_ => predicate == p,
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}
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};
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if !assumptions_in_impl_context.iter().any(predicate_matches_closure) {
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let item_span = tcx.hir().span(self_type_hir_id);
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let self_descr =
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tcx.def_kind(self_type_did).map(|kind| kind.descr(self_type_did)).unwrap_or("type");
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struct_span_err!(
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tcx.sess,
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*predicate_sp,
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E0367,
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"`Drop` impl requires `{}` but the {} it is implemented for does not",
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predicate,
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self_descr,
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)
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.span_note(item_span, "the implementor must specify the same requirement")
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.emit();
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result = Err(ErrorReported);
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}
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}
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result
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}
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/// This function is not only checking that the dropck obligations are met for
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/// the given type, but it's also currently preventing non-regular recursion in
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/// types from causing stack overflows (dropck_no_diverge_on_nonregular_*.rs).
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crate fn check_drop_obligations<'a, 'tcx>(
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rcx: &mut RegionCtxt<'a, 'tcx>,
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ty: Ty<'tcx>,
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span: Span,
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body_id: hir::HirId,
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) -> Result<(), ErrorReported> {
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debug!("check_drop_obligations typ: {:?}", ty);
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let cause = &ObligationCause::misc(span, body_id);
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let infer_ok = rcx.infcx.at(cause, rcx.fcx.param_env).dropck_outlives(ty);
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debug!("dropck_outlives = {:#?}", infer_ok);
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rcx.fcx.register_infer_ok_obligations(infer_ok);
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Ok(())
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}
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// This is an implementation of the TypeRelation trait with the
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// aim of simply comparing for equality (without side-effects).
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// It is not intended to be used anywhere else other than here.
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crate struct SimpleEqRelation<'tcx> {
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tcx: TyCtxt<'tcx>,
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param_env: ty::ParamEnv<'tcx>,
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}
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impl<'tcx> SimpleEqRelation<'tcx> {
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fn new(tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> SimpleEqRelation<'tcx> {
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SimpleEqRelation { tcx, param_env }
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}
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}
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impl TypeRelation<'tcx> for SimpleEqRelation<'tcx> {
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fn tcx(&self) -> TyCtxt<'tcx> {
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self.tcx
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}
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fn param_env(&self) -> ty::ParamEnv<'tcx> {
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self.param_env
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}
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fn tag(&self) -> &'static str {
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"dropck::SimpleEqRelation"
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}
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fn a_is_expected(&self) -> bool {
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true
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}
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fn relate_with_variance<T: Relate<'tcx>>(
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&mut self,
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_: ty::Variance,
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a: &T,
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b: &T,
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) -> RelateResult<'tcx, T> {
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// Here we ignore variance because we require drop impl's types
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// to be *exactly* the same as to the ones in the struct definition.
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self.relate(a, b)
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}
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fn tys(&mut self, a: Ty<'tcx>, b: Ty<'tcx>) -> RelateResult<'tcx, Ty<'tcx>> {
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debug!("SimpleEqRelation::tys(a={:?}, b={:?})", a, b);
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ty::relate::super_relate_tys(self, a, b)
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}
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fn regions(
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&mut self,
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a: ty::Region<'tcx>,
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b: ty::Region<'tcx>,
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) -> RelateResult<'tcx, ty::Region<'tcx>> {
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debug!("SimpleEqRelation::regions(a={:?}, b={:?})", a, b);
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// We can just equate the regions because LBRs have been
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// already anonymized.
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if a == b {
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Ok(a)
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} else {
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// I'm not sure is this `TypeError` is the right one, but
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// it should not matter as it won't be checked (the dropck
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// will emit its own, more informative and higher-level errors
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// in case anything goes wrong).
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Err(TypeError::RegionsPlaceholderMismatch)
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}
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}
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fn consts(
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&mut self,
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a: &'tcx ty::Const<'tcx>,
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b: &'tcx ty::Const<'tcx>,
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) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
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debug!("SimpleEqRelation::consts(a={:?}, b={:?})", a, b);
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ty::relate::super_relate_consts(self, a, b)
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}
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fn binders<T>(
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&mut self,
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a: &ty::Binder<T>,
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b: &ty::Binder<T>,
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) -> RelateResult<'tcx, ty::Binder<T>>
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where
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T: Relate<'tcx>,
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{
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debug!("SimpleEqRelation::binders({:?}: {:?}", a, b);
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// Anonymizing the LBRs is necessary to solve (Issue #59497).
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// After we do so, it should be totally fine to skip the binders.
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let anon_a = self.tcx.anonymize_late_bound_regions(a);
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let anon_b = self.tcx.anonymize_late_bound_regions(b);
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self.relate(anon_a.skip_binder(), anon_b.skip_binder())?;
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Ok(a.clone())
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}
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}
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