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Auto merge of rust-lang#118689 - compiler-errors:const-drop, r=fee1-dead
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Fix const drop checking

Fixes confirmation of `~const Destruct` and const drops.

r? fee1-dead
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bors committed Dec 8, 2023
2 parents 5ea6256 + efe8ae7 commit ae612be
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Showing 10 changed files with 57 additions and 67 deletions.
23 changes: 10 additions & 13 deletions compiler/rustc_const_eval/src/transform/check_consts/check.rs
Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,7 @@ use std::mem;
use std::ops::{ControlFlow, Deref};

use super::ops::{self, NonConstOp, Status};
use super::qualifs::{self, CustomEq, HasMutInterior, NeedsDrop};
use super::qualifs::{self, CustomEq, HasMutInterior, NeedsDrop, NeedsNonConstDrop};
use super::resolver::FlowSensitiveAnalysis;
use super::{ConstCx, Qualif};
use crate::const_eval::is_unstable_const_fn;
Expand All @@ -35,7 +35,7 @@ type QualifResults<'mir, 'tcx, Q> =
pub struct Qualifs<'mir, 'tcx> {
has_mut_interior: Option<QualifResults<'mir, 'tcx, HasMutInterior>>,
needs_drop: Option<QualifResults<'mir, 'tcx, NeedsDrop>>,
// needs_non_const_drop: Option<QualifResults<'mir, 'tcx, NeedsNonConstDrop>>,
needs_non_const_drop: Option<QualifResults<'mir, 'tcx, NeedsNonConstDrop>>,
}

impl<'mir, 'tcx> Qualifs<'mir, 'tcx> {
Expand Down Expand Up @@ -78,27 +78,25 @@ impl<'mir, 'tcx> Qualifs<'mir, 'tcx> {
local: Local,
location: Location,
) -> bool {
// FIXME(effects) replace with `NeedsNonconstDrop` after const traits work again
/*
let ty = ccx.body.local_decls[local].ty;
if !NeedsDrop::in_any_value_of_ty(ccx, ty) {
// Peeking into opaque types causes cycles if the current function declares said opaque
// type. Thus we avoid short circuiting on the type and instead run the more expensive
// analysis that looks at the actual usage within this function
if !ty.has_opaque_types() && !NeedsNonConstDrop::in_any_value_of_ty(ccx, ty) {
return false;
}

let needs_non_const_drop = self.needs_non_const_drop.get_or_insert_with(|| {
let ConstCx { tcx, body, .. } = *ccx;

FlowSensitiveAnalysis::new(NeedsDrop, ccx)
.into_engine(tcx, &body)
FlowSensitiveAnalysis::new(NeedsNonConstDrop, ccx)
.into_engine(tcx, body)
.iterate_to_fixpoint()
.into_results_cursor(&body)
.into_results_cursor(body)
});

needs_non_const_drop.seek_before_primary_effect(location);
needs_non_const_drop.get().contains(local)
*/

self.needs_drop(ccx, local, location)
}

/// Returns `true` if `local` is `HasMutInterior` at the given `Location`.
Expand Down Expand Up @@ -1013,9 +1011,8 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
let mut err_span = self.span;
let ty_of_dropped_place = dropped_place.ty(self.body, self.tcx).ty;

// FIXME(effects) replace with `NeedsNonConstDrop` once we fix const traits
let ty_needs_non_const_drop =
qualifs::NeedsDrop::in_any_value_of_ty(self.ccx, ty_of_dropped_place);
qualifs::NeedsNonConstDrop::in_any_value_of_ty(self.ccx, ty_of_dropped_place);

debug!(?ty_of_dropped_place, ?ty_needs_non_const_drop);

Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ use rustc_span::{symbol::sym, Span};

use super::check::Qualifs;
use super::ops::{self, NonConstOp};
use super::qualifs::{NeedsDrop, Qualif};
use super::qualifs::{NeedsNonConstDrop, Qualif};
use super::ConstCx;

/// Returns `true` if we should use the more precise live drop checker that runs after drop
Expand Down Expand Up @@ -83,8 +83,7 @@ impl<'tcx> Visitor<'tcx> for CheckLiveDrops<'_, 'tcx> {
mir::TerminatorKind::Drop { place: dropped_place, .. } => {
let dropped_ty = dropped_place.ty(self.body, self.tcx).ty;

// FIXME(effects) use `NeedsNonConstDrop`
if !NeedsDrop::in_any_value_of_ty(self.ccx, dropped_ty) {
if !NeedsNonConstDrop::in_any_value_of_ty(self.ccx, dropped_ty) {
// Instead of throwing a bug, we just return here. This is because we have to
// run custom `const Drop` impls.
return;
Expand Down
22 changes: 18 additions & 4 deletions compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
Original file line number Diff line number Diff line change
Expand Up @@ -23,8 +23,7 @@ pub fn in_any_value_of_ty<'tcx>(
ConstQualifs {
has_mut_interior: HasMutInterior::in_any_value_of_ty(cx, ty),
needs_drop: NeedsDrop::in_any_value_of_ty(cx, ty),
// FIXME(effects)
needs_non_const_drop: NeedsDrop::in_any_value_of_ty(cx, ty),
needs_non_const_drop: NeedsNonConstDrop::in_any_value_of_ty(cx, ty),
custom_eq: CustomEq::in_any_value_of_ty(cx, ty),
tainted_by_errors,
}
Expand Down Expand Up @@ -155,12 +154,27 @@ impl Qualif for NeedsNonConstDrop {
return false;
}

// FIXME(effects) constness
// FIXME(effects): If `destruct` is not a `const_trait`,
// or effects are disabled in this crate, then give up.
let destruct_def_id = cx.tcx.require_lang_item(LangItem::Destruct, Some(cx.body.span));
if cx.tcx.generics_of(destruct_def_id).host_effect_index.is_none()
|| !cx.tcx.features().effects
{
return NeedsDrop::in_any_value_of_ty(cx, ty);
}

let obligation = Obligation::new(
cx.tcx,
ObligationCause::dummy_with_span(cx.body.span),
cx.param_env,
ty::TraitRef::from_lang_item(cx.tcx, LangItem::Destruct, cx.body.span, [ty]),
ty::TraitRef::new(
cx.tcx,
destruct_def_id,
[
ty::GenericArg::from(ty),
ty::GenericArg::from(cx.tcx.expected_const_effect_param_for_body(cx.def_id())),
],
),
);

let infcx = cx.tcx.infer_ctxt().build();
Expand Down
6 changes: 3 additions & 3 deletions compiler/rustc_middle/src/ty/util.rs
Original file line number Diff line number Diff line change
Expand Up @@ -781,9 +781,9 @@ impl<'tcx> TyCtxt<'tcx> {
}

pub fn expected_const_effect_param_for_body(self, def_id: LocalDefId) -> ty::Const<'tcx> {
// if the callee does have the param, we need to equate the param to some const
// value no matter whether the effects feature is enabled in the local crate,
// because inference will fail if we don't.
// FIXME(effects): This is suspicious and should probably not be done,
// especially now that we enforce host effects and then properly handle
// effect vars during fallback.
let mut host_always_on =
!self.features().effects || self.sess.opts.unstable_opts.unleash_the_miri_inside_of_you;

Expand Down
Original file line number Diff line number Diff line change
Expand Up @@ -872,9 +872,18 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
) {
// If the predicate is `~const Destruct` in a non-const environment, we don't actually need
// to check anything. We'll short-circuit checking any obligations in confirmation, too.
// FIXME(effects)
if true {
candidates.vec.push(ConstDestructCandidate(None));
let Some(host_effect_index) =
self.tcx().generics_of(obligation.predicate.def_id()).host_effect_index
else {
candidates.vec.push(BuiltinCandidate { has_nested: false });
return;
};
// If the obligation has `host = true`, then the obligation is non-const and it's always
// trivially implemented.
if obligation.predicate.skip_binder().trait_ref.args.const_at(host_effect_index)
== self.tcx().consts.true_
{
candidates.vec.push(BuiltinCandidate { has_nested: false });
return;
}

Expand Down
16 changes: 9 additions & 7 deletions compiler/rustc_trait_selection/src/traits/select/confirmation.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1172,11 +1172,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
obligation: &PolyTraitObligation<'tcx>,
impl_def_id: Option<DefId>,
) -> Result<Vec<PredicateObligation<'tcx>>, SelectionError<'tcx>> {
// `~const Destruct` in a non-const environment is always trivially true, since our type is `Drop`
// FIXME(effects)
if true {
return Ok(vec![]);
}
let Some(host_effect_index) =
self.tcx().generics_of(obligation.predicate.def_id()).host_effect_index
else {
bug!()
};
let host_effect_param: ty::GenericArg<'tcx> =
obligation.predicate.skip_binder().trait_ref.args.const_at(host_effect_index).into();

let drop_trait = self.tcx().require_lang_item(LangItem::Drop, None);

Expand Down Expand Up @@ -1284,7 +1286,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
self.tcx(),
LangItem::Destruct,
cause.span,
[nested_ty],
[nested_ty.into(), host_effect_param],
),
polarity: ty::ImplPolarity::Positive,
}),
Expand All @@ -1310,7 +1312,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
self.tcx(),
LangItem::Destruct,
cause.span,
[nested_ty],
[nested_ty.into(), host_effect_param],
),
polarity: ty::ImplPolarity::Positive,
});
Expand Down
7 changes: 1 addition & 6 deletions tests/ui/consts/precise-drop-with-promoted.rs
Original file line number Diff line number Diff line change
@@ -1,11 +1,6 @@
// Regression test for issue #89938.
// check-pass
// compile-flags: --crate-type=lib
// known-bug: #103507
// failure-status: 101
// normalize-stderr-test "note: .*\n\n" -> ""
// normalize-stderr-test "thread 'rustc' panicked.*\n.*\n" -> ""
// normalize-stderr-test "(error: internal compiler error: [^:]+):\d+:\d+: " -> "$1:LL:CC: "
// rustc-env:RUST_BACKTRACE=0

#![feature(const_precise_live_drops)]

Expand Down
6 changes: 0 additions & 6 deletions tests/ui/consts/precise-drop-with-promoted.stderr

This file was deleted.

4 changes: 2 additions & 2 deletions tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.rs
Original file line number Diff line number Diff line change
@@ -1,3 +1,5 @@
// check-pass

#![crate_type = "lib"]
#![feature(no_core, lang_items, unboxed_closures, auto_traits, intrinsics, rustc_attrs)]
#![feature(fundamental)]
Expand All @@ -6,8 +8,6 @@
#![no_std]
#![no_core]

// known-bug: #110395

#[lang = "sized"]
trait Sized {}
#[lang = "copy"]
Expand Down
20 changes: 0 additions & 20 deletions tests/ui/rfcs/rfc-2632-const-trait-impl/effects/minicore.stderr

This file was deleted.

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