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Auto merge of #93028 - compiler-errors:const_drop_bounds, r=fee1-dead

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Check `const Drop` impls considering `~const` Bounds

 This PR adds logic to trait selection to account for `~const` bounds in custom `impl const Drop` for types, elaborates the `const Drop` check in `rustc_const_eval` to check those bounds, and steals some drop linting fixes from #92922, thanks `@DrMeepster.`

r? `@fee1-dead` `@oli-obk` <sup>(edit: guess I can't request review from two people, lol)</sup>
since each of you wrote and reviewed #88558, respectively.

Since the logic here is more complicated than what existed, it's possible that this is a perf regression. But it works correctly with tests, and that makes me happy.

Fixes #92881
This commit is contained in:
bors 2022-01-24 08:05:37 +00:00
commit ef119d704d
13 changed files with 384 additions and 244 deletions
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60
compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs
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@ -4,11 +4,12 @@
use rustc_errors::ErrorReported;
use rustc_infer::infer::TyCtxtInferExt;
use rustc_infer::traits::TraitEngine;
use rustc_middle::mir::*;
use rustc_middle::ty::{self, subst::SubstsRef, AdtDef, Ty};
use rustc_span::DUMMY_SP;
use rustc_trait_selection::traits::{
self, ImplSource, Obligation, ObligationCause, SelectionContext,
self, FulfillmentContext, ImplSource, Obligation, ObligationCause, SelectionContext,
};
use super::ConstCx;
@ -145,15 +146,10 @@ impl Qualif for NeedsNonConstDrop {
qualifs.needs_non_const_drop
}
fn in_any_value_of_ty<'tcx>(cx: &ConstCx<'_, 'tcx>, mut ty: Ty<'tcx>) -> bool {
// Avoid selecting for simple cases.
match ty::util::needs_drop_components(ty, &cx.tcx.data_layout).as_deref() {
Ok([]) => return false,
Err(ty::util::AlwaysRequiresDrop) => return true,
// If we've got a single component, select with that
// to increase the chance that we hit the selection cache.
Ok([t]) => ty = t,
Ok([..]) => {}
fn in_any_value_of_ty<'tcx>(cx: &ConstCx<'_, 'tcx>, ty: Ty<'tcx>) -> bool {
// Avoid selecting for simple cases, such as builtin types.
if ty::util::is_trivially_const_drop(ty) {
return false;
}
let Some(drop_trait) = cx.tcx.lang_items().drop_trait() else {
@ -161,28 +157,50 @@ impl Qualif for NeedsNonConstDrop {
// without having the lang item present.
return false;
};
let trait_ref =
ty::TraitRef { def_id: drop_trait, substs: cx.tcx.mk_substs_trait(ty, &[]) };
let obligation = Obligation::new(
ObligationCause::dummy(),
cx.param_env,
ty::Binder::dummy(ty::TraitPredicate {
trait_ref,
trait_ref: ty::TraitRef {
def_id: drop_trait,
substs: cx.tcx.mk_substs_trait(ty, &[]),
},
constness: ty::BoundConstness::ConstIfConst,
polarity: ty::ImplPolarity::Positive,
}),
);
let implsrc = cx.tcx.infer_ctxt().enter(|infcx| {
cx.tcx.infer_ctxt().enter(|infcx| {
let mut selcx = SelectionContext::new(&infcx);
selcx.select(&obligation)
});
!matches!(
implsrc,
Ok(Some(
let Some(impl_src) = selcx.select(&obligation).ok().flatten() else {
// If we couldn't select a const drop candidate, then it's bad
return true;
};
if !matches!(
impl_src,
ImplSource::ConstDrop(_) | ImplSource::Param(_, ty::BoundConstness::ConstIfConst)
))
)
) {
// If our const drop candidate is not ConstDrop or implied by the param env,
// then it's bad
return true;
}
if impl_src.borrow_nested_obligations().is_empty() {
return false;
}
// If we successfully found one, then select all of the predicates
// implied by our const drop impl.
let mut fcx = FulfillmentContext::new();
for nested in impl_src.nested_obligations() {
fcx.register_predicate_obligation(&infcx, nested);
}
// If we had any errors, then it's bad
!fcx.select_all_or_error(&infcx).is_empty()
})
}
fn in_adt_inherently<'tcx>(