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hack: don't normalize xform_ret_ty for trait/object candidates unless needed

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This commit is contained in:
Michael Goulet 2023-01-09 06:53:11 +00:00
parent 2600d6245b
commit 4f15034b55
3 changed files with 42 additions and 39 deletions
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67
compiler/rustc_hir_typeck/src/method/probe.rs
View File

@ -1523,30 +1523,11 @@ fn consider_probe(
};
let mut result = ProbeResult::Match;
let mut xform_ret_ty = probe.xform_ret_ty;
debug!(?xform_ret_ty);
let cause = traits::ObligationCause::misc(self.span, self.body_id);
let xform_ret_ty = if let Some(xform_ret_ty) = probe.xform_ret_ty {
// `xform_ret_ty` hasn't been normalized yet, only `xform_self_ty`,
// see the reasons mentioned in the comments in `assemble_inherent_impl_probe`
// for why this is necessary
let InferOk {
value: normalized_xform_ret_ty,
obligations: normalization_obligations,
} = self.fcx.at(&cause, self.param_env).normalize(xform_ret_ty);
debug!("xform_ret_ty after normalization: {:?}", normalized_xform_ret_ty);
for o in normalization_obligations {
if !self.predicate_may_hold(&o) {
possibly_unsatisfied_predicates.push((o.predicate, None, Some(o.cause)));
result = ProbeResult::NoMatch;
}
}
Some(normalized_xform_ret_ty)
} else {
None
};
let mut parent_pred = None;
// If so, impls may carry other conditions (e.g., where
@ -1555,6 +1536,16 @@ fn consider_probe(
// don't have enough information to fully evaluate).
match probe.kind {
InherentImplCandidate(ref substs, ref ref_obligations) => {
// `xform_ret_ty` hasn't been normalized yet, only `xform_self_ty`,
// see the reasons mentioned in the comments in `assemble_inherent_impl_probe`
// for why this is necessary
let InferOk {
value: normalized_xform_ret_ty,
obligations: normalization_obligations,
} = self.fcx.at(&cause, self.param_env).normalize(xform_ret_ty);
xform_ret_ty = normalized_xform_ret_ty;
debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty);
// Check whether the impl imposes obligations we have to worry about.
let impl_def_id = probe.item.container_id(self.tcx);
let impl_bounds = self.tcx.predicates_of(impl_def_id);
@ -1572,7 +1563,8 @@ fn consider_probe(
let candidate_obligations = impl_obligations
.chain(norm_obligations.into_iter())
.chain(ref_obligations.iter().cloned());
.chain(ref_obligations.iter().cloned())
.chain(normalization_obligations.into_iter());
// Evaluate those obligations to see if they might possibly hold.
for o in candidate_obligations {
@ -1668,8 +1660,33 @@ fn consider_probe(
if let ProbeResult::Match = result
&& let Some(return_ty) = self.return_type
&& let Some(xform_ret_ty) = xform_ret_ty
&& let Some(mut xform_ret_ty) = xform_ret_ty
{
// `xform_ret_ty` has only been normalized for `InherentImplCandidate`.
// We don't normalize the other candidates for perf/backwards-compat reasons...
// but `self.return_type` is only set on the diagnostic-path, so we
// should be okay doing it here.
if !matches!(probe.kind, InherentImplCandidate(..)) {
let InferOk {
value: normalized_xform_ret_ty,
obligations: normalization_obligations,
} = self.fcx.at(&cause, self.param_env).normalize(xform_ret_ty);
xform_ret_ty = normalized_xform_ret_ty;
debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty);
// Evaluate those obligations to see if they might possibly hold.
for o in normalization_obligations {
let o = self.resolve_vars_if_possible(o);
if !self.predicate_may_hold(&o) {
result = ProbeResult::NoMatch;
possibly_unsatisfied_predicates.push((
o.predicate,
None,
Some(o.cause),
));
}
}
}
debug!(
"comparing return_ty {:?} with xform ret ty {:?}",
return_ty, xform_ret_ty
@ -1681,7 +1698,7 @@ fn consider_probe(
.sup(return_ty, xform_ret_ty)
.is_err()
{
return ProbeResult::BadReturnType;
result = ProbeResult::BadReturnType;
}
}

7
src/test/ui/trait-bounds/impl-derived-implicit-sized-bound-2.stderr
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@ -17,13 +17,6 @@ LL | impl<'a, T: Perpetrator /*+ ?Sized*/> VictimTrait for Victim<'a, T> {
| ^ ----------- -------------
| |
| unsatisfied trait bound introduced here
= note: the following trait bounds were not satisfied:
`&Victim<'_, Self>: VictimTrait`
`&mut Victim<'_, Self>: VictimTrait`
help: consider relaxing the type parameter's implicit `Sized` bound
|
LL | impl<'a, T: ?Sized + Perpetrator /*+ ?Sized*/> VictimTrait for Victim<'a, T> {
| ++++++++
help: consider relaxing the type parameter's implicit `Sized` bound
|
LL | impl<'a, T: ?Sized + Perpetrator /*+ ?Sized*/> VictimTrait for Victim<'a, T> {

7
src/test/ui/trait-bounds/impl-derived-implicit-sized-bound.stderr
View File

@ -17,13 +17,6 @@ LL | impl<'a, T: Perpetrator /*+ ?Sized*/> VictimTrait for Victim<'a, T> {
| ^ ----------- -------------
| |
| unsatisfied trait bound introduced here
= note: the following trait bounds were not satisfied:
`&Victim<'_, Self>: VictimTrait`
`&mut Victim<'_, Self>: VictimTrait`
help: consider relaxing the type parameter's implicit `Sized` bound
|
LL | impl<'a, T: ?Sized + Perpetrator /*+ ?Sized*/> VictimTrait for Victim<'a, T> {
| ++++++++
help: consider relaxing the type parameter's implicit `Sized` bound
|
LL | impl<'a, T: ?Sized + Perpetrator /*+ ?Sized*/> VictimTrait for Victim<'a, T> {