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Warn on inductive cycle in coherence leading to impls being considered not overlapping #114023
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compiler-errors:coinductive-cycle-lint
Aug 15, 2023
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2ae4bed
more span info
compiler-errors 56f5704
Implement lint against coinductive impl overlap
compiler-errors d2a14df
nits
compiler-errors ca49a37
Reuse the selection context, compute failing obligations first in amb…
compiler-errors 0e20155
more nits
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Original file line number | Diff line number | Diff line change |
---|---|---|
|
@@ -7,7 +7,7 @@ | |
use crate::infer::outlives::env::OutlivesEnvironment; | ||
use crate::infer::InferOk; | ||
use crate::traits::outlives_bounds::InferCtxtExt as _; | ||
use crate::traits::select::IntercrateAmbiguityCause; | ||
use crate::traits::select::{IntercrateAmbiguityCause, TreatInductiveCycleAs}; | ||
use crate::traits::util::impl_subject_and_oblig; | ||
use crate::traits::SkipLeakCheck; | ||
use crate::traits::{ | ||
|
@@ -24,6 +24,7 @@ use rustc_middle::traits::DefiningAnchor; | |
use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams}; | ||
use rustc_middle::ty::visit::{TypeVisitable, TypeVisitableExt}; | ||
use rustc_middle::ty::{self, Ty, TyCtxt, TypeVisitor}; | ||
use rustc_session::lint::builtin::COINDUCTIVE_OVERLAP_IN_COHERENCE; | ||
use rustc_span::symbol::sym; | ||
use rustc_span::DUMMY_SP; | ||
use std::fmt::Debug; | ||
|
@@ -151,14 +152,16 @@ fn with_fresh_ty_vars<'cx, 'tcx>( | |
.predicates_of(impl_def_id) | ||
.instantiate(tcx, impl_args) | ||
.iter() | ||
.map(|(c, _)| c.as_predicate()) | ||
.map(|(c, s)| (c.as_predicate(), s)) | ||
.collect(), | ||
}; | ||
|
||
let InferOk { value: mut header, obligations } = | ||
selcx.infcx.at(&ObligationCause::dummy(), param_env).normalize(header); | ||
let InferOk { value: mut header, obligations } = selcx | ||
.infcx | ||
.at(&ObligationCause::dummy_with_span(tcx.def_span(impl_def_id)), param_env) | ||
.normalize(header); | ||
|
||
header.predicates.extend(obligations.into_iter().map(|o| o.predicate)); | ||
header.predicates.extend(obligations.into_iter().map(|o| (o.predicate, o.cause.span))); | ||
header | ||
} | ||
|
||
|
@@ -207,16 +210,76 @@ fn overlap<'tcx>( | |
let equate_obligations = equate_impl_headers(selcx.infcx, &impl1_header, &impl2_header)?; | ||
debug!("overlap: unification check succeeded"); | ||
|
||
if overlap_mode.use_implicit_negative() | ||
&& impl_intersection_has_impossible_obligation( | ||
selcx, | ||
param_env, | ||
&impl1_header, | ||
impl2_header, | ||
equate_obligations, | ||
) | ||
{ | ||
return None; | ||
if overlap_mode.use_implicit_negative() { | ||
for mode in [TreatInductiveCycleAs::Ambig, TreatInductiveCycleAs::Recur] { | ||
if let Some(failing_obligation) = selcx.with_treat_inductive_cycle_as(mode, |selcx| { | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. This is gross but needed to make sure we're collecting the right intercrate ambiguity causes. |
||
impl_intersection_has_impossible_obligation( | ||
selcx, | ||
param_env, | ||
&impl1_header, | ||
&impl2_header, | ||
&equate_obligations, | ||
) | ||
}) { | ||
if matches!(mode, TreatInductiveCycleAs::Recur) { | ||
let first_local_impl = impl1_header | ||
.impl_def_id | ||
.as_local() | ||
.or(impl2_header.impl_def_id.as_local()) | ||
.expect("expected one of the impls to be local"); | ||
infcx.tcx.struct_span_lint_hir( | ||
COINDUCTIVE_OVERLAP_IN_COHERENCE, | ||
infcx.tcx.local_def_id_to_hir_id(first_local_impl), | ||
infcx.tcx.def_span(first_local_impl), | ||
format!( | ||
"implementations {} will conflict in the future", | ||
match impl1_header.trait_ref { | ||
Some(trait_ref) => { | ||
let trait_ref = infcx.resolve_vars_if_possible(trait_ref); | ||
format!( | ||
"of `{}` for `{}`", | ||
trait_ref.print_only_trait_path(), | ||
trait_ref.self_ty() | ||
) | ||
} | ||
None => format!( | ||
"for `{}`", | ||
infcx.resolve_vars_if_possible(impl1_header.self_ty) | ||
), | ||
}, | ||
), | ||
|lint| { | ||
lint.note( | ||
"impls that are not considered to overlap may be considered to \ | ||
overlap in the future", | ||
) | ||
.span_label( | ||
infcx.tcx.def_span(impl1_header.impl_def_id), | ||
"the first impl is here", | ||
) | ||
.span_label( | ||
infcx.tcx.def_span(impl2_header.impl_def_id), | ||
"the second impl is here", | ||
); | ||
if !failing_obligation.cause.span.is_dummy() { | ||
lint.span_label( | ||
failing_obligation.cause.span, | ||
format!( | ||
"`{}` may be considered to hold in future releases, \ | ||
causing the impls to overlap", | ||
infcx | ||
.resolve_vars_if_possible(failing_obligation.predicate) | ||
), | ||
); | ||
} | ||
lint | ||
}, | ||
); | ||
} | ||
|
||
return None; | ||
} | ||
} | ||
} | ||
|
||
// We toggle the `leak_check` by using `skip_leak_check` when constructing the | ||
|
@@ -284,40 +347,30 @@ fn impl_intersection_has_impossible_obligation<'cx, 'tcx>( | |
selcx: &mut SelectionContext<'cx, 'tcx>, | ||
param_env: ty::ParamEnv<'tcx>, | ||
impl1_header: &ty::ImplHeader<'tcx>, | ||
impl2_header: ty::ImplHeader<'tcx>, | ||
obligations: PredicateObligations<'tcx>, | ||
) -> bool { | ||
impl2_header: &ty::ImplHeader<'tcx>, | ||
obligations: &PredicateObligations<'tcx>, | ||
) -> Option<PredicateObligation<'tcx>> { | ||
let infcx = selcx.infcx; | ||
|
||
let obligation_guaranteed_to_fail = move |obligation: &PredicateObligation<'tcx>| { | ||
if infcx.next_trait_solver() { | ||
infcx.evaluate_obligation(obligation).map_or(false, |result| !result.may_apply()) | ||
} else { | ||
// We use `evaluate_root_obligation` to correctly track | ||
// intercrate ambiguity clauses. We do not need this in the | ||
// new solver. | ||
selcx.evaluate_root_obligation(obligation).map_or( | ||
false, // Overflow has occurred, and treat the obligation as possibly holding. | ||
|result| !result.may_apply(), | ||
) | ||
} | ||
}; | ||
|
||
let opt_failing_obligation = [&impl1_header.predicates, &impl2_header.predicates] | ||
[&impl1_header.predicates, &impl2_header.predicates] | ||
.into_iter() | ||
.flatten() | ||
.map(|&predicate| { | ||
Obligation::new(infcx.tcx, ObligationCause::dummy(), param_env, predicate) | ||
.map(|&(predicate, span)| { | ||
Obligation::new(infcx.tcx, ObligationCause::dummy_with_span(span), param_env, predicate) | ||
}) | ||
.chain(obligations.into_iter().cloned()) | ||
.find(|obligation: &PredicateObligation<'tcx>| { | ||
if infcx.next_trait_solver() { | ||
infcx.evaluate_obligation(obligation).map_or(false, |result| !result.may_apply()) | ||
} else { | ||
// We use `evaluate_root_obligation` to correctly track intercrate | ||
// ambiguity clauses. We cannot use this in the new solver. | ||
selcx.evaluate_root_obligation(obligation).map_or( | ||
false, // Overflow has occurred, and treat the obligation as possibly holding. | ||
|result| !result.may_apply(), | ||
) | ||
} | ||
}) | ||
.chain(obligations) | ||
.find(obligation_guaranteed_to_fail); | ||
|
||
if let Some(failing_obligation) = opt_failing_obligation { | ||
debug!("overlap: obligation unsatisfiable {:?}", failing_obligation); | ||
true | ||
} else { | ||
false | ||
} | ||
} | ||
|
||
/// Check if both impls can be satisfied by a common type by considering whether | ||
|
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35 changes: 35 additions & 0 deletions
35
tests/ui/coherence/warn-when-cycle-is-error-in-coherence.rs
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,35 @@ | ||
#![deny(coinductive_overlap_in_coherence)] | ||
|
||
use std::borrow::Borrow; | ||
use std::cmp::Ordering; | ||
use std::marker::PhantomData; | ||
|
||
#[derive(PartialEq, Default)] | ||
pub(crate) struct Interval<T>(PhantomData<T>); | ||
|
||
// This impl overlaps with the `derive` unless we reject the nested | ||
// `Interval<?1>: PartialOrd<Interval<?1>>` candidate which results | ||
// in a - currently inductive - cycle. | ||
impl<T, Q> PartialEq<Q> for Interval<T> | ||
//~^ ERROR implementations of `PartialEq<Interval<_>>` for `Interval<_>` will conflict in the future | ||
//~| WARN this was previously accepted by the compiler but is being phased out | ||
where | ||
T: Borrow<Q>, | ||
Q: ?Sized + PartialOrd, | ||
{ | ||
fn eq(&self, _: &Q) -> bool { | ||
true | ||
} | ||
} | ||
|
||
impl<T, Q> PartialOrd<Q> for Interval<T> | ||
where | ||
T: Borrow<Q>, | ||
Q: ?Sized + PartialOrd, | ||
{ | ||
fn partial_cmp(&self, _: &Q) -> Option<Ordering> { | ||
None | ||
} | ||
} | ||
|
||
fn main() {} |
23 changes: 23 additions & 0 deletions
23
tests/ui/coherence/warn-when-cycle-is-error-in-coherence.stderr
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,23 @@ | ||
error: implementations of `PartialEq<Interval<_>>` for `Interval<_>` will conflict in the future | ||
--> $DIR/warn-when-cycle-is-error-in-coherence.rs:13:1 | ||
| | ||
LL | #[derive(PartialEq, Default)] | ||
| --------- the second impl is here | ||
... | ||
LL | impl<T, Q> PartialEq<Q> for Interval<T> | ||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the first impl is here | ||
... | ||
LL | Q: ?Sized + PartialOrd, | ||
| ---------- `Interval<_>: PartialOrd` may be considered to hold in future releases, causing the impls to overlap | ||
| | ||
= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! | ||
= note: for more information, see issue #114040 <https://github.com/rust-lang/rust/issues/114040> | ||
= note: impls that are not considered to overlap may be considered to overlap in the future | ||
note: the lint level is defined here | ||
--> $DIR/warn-when-cycle-is-error-in-coherence.rs:1:9 | ||
| | ||
LL | #![deny(coinductive_overlap_in_coherence)] | ||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | ||
|
||
error: aborting due to previous error | ||
|
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