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Strict region folders #110312

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Strict region folders #110312

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66314e2
Rewrite `RegionReplacer::fold_region`.
nnethercote Apr 14, 2023
043c1de
Make all region folders strict about which variants they accept.
nnethercote Apr 13, 2023
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6 changes: 4 additions & 2 deletions compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -428,7 +428,7 @@ fn try_extract_error_from_region_constraints<'tcx>(
placeholder_region,
vec![],
),
(Some(error_region), _) => {
(Some(error_region), ty::RePlaceholder(_)) => {
RegionResolutionError::ConcreteFailure(cause.clone(), error_region, placeholder_region)
}
// Note universe here is wrong...
Expand All @@ -439,9 +439,11 @@ fn try_extract_error_from_region_constraints<'tcx>(
cause.clone(),
placeholder_region,
),
(None, _) => {
(None, ty::ReStatic) => {
RegionResolutionError::ConcreteFailure(cause.clone(), sub_region, placeholder_region)
}
(Some(_), r) => bug!("unexpected region with `Some`: {r:?}"),
(None, r) => bug!("unexpected region with `None`: {r:?}"),
};
NiceRegionError::new(&infcx.err_ctxt(), error).try_report_from_nll().or_else(|| {
if let SubregionOrigin::Subtype(trace) = cause {
Expand Down
20 changes: 8 additions & 12 deletions compiler/rustc_borrowck/src/diagnostics/mod.rs
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Expand Up @@ -466,12 +466,10 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
// lifetimes without names with the value `'0`.
if let ty::Ref(region, ..) = ty.kind() {
match **region {
ty::ReLateBound(_, ty::BoundRegion { kind: br, .. })
| ty::RePlaceholder(ty::PlaceholderRegion {
bound: ty::BoundRegion { kind: br, .. },
..
}) => printer.region_highlight_mode.highlighting_bound_region(br, counter),
_ => {}
ty::ReLateBound(_, ty::BoundRegion { kind: br, .. }) => {
printer.region_highlight_mode.highlighting_bound_region(br, counter)
}
r => bug!("unexpected region: {r:?}"),
}
}

Expand All @@ -485,12 +483,10 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {

let region = if let ty::Ref(region, ..) = ty.kind() {
match **region {
ty::ReLateBound(_, ty::BoundRegion { kind: br, .. })
| ty::RePlaceholder(ty::PlaceholderRegion {
bound: ty::BoundRegion { kind: br, .. },
..
}) => printer.region_highlight_mode.highlighting_bound_region(br, counter),
_ => {}
ty::ReLateBound(_, ty::BoundRegion { kind: br, .. }) => {
printer.region_highlight_mode.highlighting_bound_region(br, counter)
}
r => bug!("unexpected region: {r:?}"),
}
region
} else {
Expand Down
6 changes: 1 addition & 5 deletions compiler/rustc_borrowck/src/diagnostics/region_name.rs
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Expand Up @@ -357,11 +357,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
ty::BoundRegionKind::BrAnon(..) => None,
},

ty::ReLateBound(..)
| ty::ReVar(..)
| ty::RePlaceholder(..)
| ty::ReErased
| ty::ReError(_) => None,
r => bug!("unexpected region: {r:?}"),
}
}

Expand Down
50 changes: 29 additions & 21 deletions compiler/rustc_borrowck/src/region_infer/mod.rs
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Expand Up @@ -1127,22 +1127,27 @@ impl<'tcx> RegionInferenceContext<'tcx> {
let ty = ty.fold_with(&mut OpaqueFolder { tcx });

let ty = tcx.fold_regions(ty, |r, _depth| {
let r_vid = self.to_region_vid(r);
let r_scc = self.constraint_sccs.scc(r_vid);

// The challenge is this. We have some region variable `r`
// whose value is a set of CFG points and universal
// regions. We want to find if that set is *equivalent* to
// any of the named regions found in the closure.
// To do so, we simply check every candidate `u_r` for equality.
self.scc_values
.universal_regions_outlived_by(r_scc)
.filter(|&u_r| !self.universal_regions.is_local_free_region(u_r))
.find(|&u_r| self.eval_equal(u_r, r_vid))
.map(|u_r| tcx.mk_re_var(u_r))
// In the case of a failure, use `ReErased`. We will eventually
// return `None` in this case.
.unwrap_or(tcx.lifetimes.re_erased)
match r.kind() {
ty::ReStatic | ty::ReVar(_) => {
let r_vid = self.to_region_vid(r);
let r_scc = self.constraint_sccs.scc(r_vid);

// The challenge is this. We have some region variable `r`
// whose value is a set of CFG points and universal
// regions. We want to find if that set is *equivalent* to
// any of the named regions found in the closure.
// To do so, we simply check every candidate `u_r` for equality.
self.scc_values
.universal_regions_outlived_by(r_scc)
.filter(|&u_r| !self.universal_regions.is_local_free_region(u_r))
.find(|&u_r| self.eval_equal(u_r, r_vid))
.map(|u_r| tcx.mk_re_var(u_r))
// In the case of a failure, use `ReErased`. We will eventually
// return `None` in this case.
.unwrap_or(tcx.lifetimes.re_erased)
}
r => bug!("unexpected region: {r:?}"),
}
});

debug!("try_promote_type_test_subject: folded ty = {:?}", ty);
Expand Down Expand Up @@ -1332,11 +1337,14 @@ impl<'tcx> RegionInferenceContext<'tcx> {
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
tcx.fold_regions(value, |r, _db| {
let vid = self.to_region_vid(r);
let scc = self.constraint_sccs.scc(vid);
let repr = self.scc_representatives[scc];
tcx.mk_re_var(repr)
tcx.fold_regions(value, |r, _db| match r.kind() {
ty::ReEarlyBound(_) | ty::ReStatic | ty::ReVar(_) => {
let vid = self.to_region_vid(r);
let scc = self.constraint_sccs.scc(vid);
let repr = self.scc_representatives[scc];
tcx.mk_re_var(repr)
}
r => bug!("unexpected region: {r:?}"),
})
}

Expand Down
21 changes: 11 additions & 10 deletions compiler/rustc_borrowck/src/region_infer/opaque_types.rs
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Expand Up @@ -110,14 +110,14 @@ impl<'tcx> RegionInferenceContext<'tcx> {

// Next, insert universal regions from substs, so we can translate regions that appear
// in them but are not subject to member constraints, for instance closure substs.
let universal_substs = infcx.tcx.fold_regions(substs, |region, _| {
if let ty::RePlaceholder(..) = region.kind() {
// Higher kinded regions don't need remapping, they don't refer to anything outside of this the substs.
return region;
}
let vid = self.to_region_vid(region);
to_universal_region(vid, &mut subst_regions)
});
let universal_substs =
infcx.tcx.fold_regions(substs, |region, _| match region.kind() {
ty::ReVar(_) => {
let vid = self.to_region_vid(region);
to_universal_region(vid, &mut subst_regions)
}
r => bug!("unexpected region: {r:?}"),
});
debug!(?universal_substs);
debug!(?subst_regions);

Expand All @@ -132,7 +132,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
.find(|ur_vid| self.eval_equal(vid, **ur_vid))
.and_then(|ur_vid| self.definitions[*ur_vid].external_name)
.unwrap_or(infcx.tcx.lifetimes.re_erased),
_ => region,
ty::ReEarlyBound(_) | ty::ReStatic => region,
r => bug!("unexpected region: {r:?}"),
});
debug!(?universal_concrete_type);

Expand Down Expand Up @@ -201,7 +202,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
}
}
}
_ => region,
r => bug!("unexpected region: {r:?}"),
})
}
}
Expand Down
7 changes: 5 additions & 2 deletions compiler/rustc_borrowck/src/renumber.rs
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Expand Up @@ -75,8 +75,11 @@ impl<'a, 'tcx> RegionRenumberer<'a, 'tcx> {
F: Fn() -> RegionCtxt,
{
let origin = NllRegionVariableOrigin::Existential { from_forall: false };
self.infcx.tcx.fold_regions(value, |_region, _depth| {
self.infcx.next_nll_region_var(origin, || region_ctxt_fn())
self.infcx.tcx.fold_regions(value, |region, _depth| match region.kind() {
ty::ReErased | ty::ReError(_) => {
self.infcx.next_nll_region_var(origin, || region_ctxt_fn())
}
r => bug!("unexpected region: {r:?}"),
})
}
}
Expand Down
3 changes: 2 additions & 1 deletion compiler/rustc_borrowck/src/type_check/constraint_conversion.rs
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Expand Up @@ -178,7 +178,8 @@ impl<'a, 'tcx> ConstraintConversion<'a, 'tcx> {
ty::RePlaceholder(placeholder) => {
self.constraints.placeholder_region(self.infcx, placeholder)
}
_ => r,
ty::ReStatic | ty::ReVar(_) => r,
r => bug!("unexpected region: {r:?}"),
})
} else {
value
Expand Down
19 changes: 13 additions & 6 deletions compiler/rustc_borrowck/src/universal_regions.rs
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Expand Up @@ -757,11 +757,13 @@ impl<'cx, 'tcx> InferCtxtExt<'tcx> for BorrowckInferCtxt<'cx, 'tcx> {
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
self.infcx.tcx.fold_regions(value, |region, _depth| {
let name = region.get_name_or_anon();
debug!(?region, ?name);

self.next_nll_region_var(origin, || RegionCtxt::Free(name))
self.infcx.tcx.fold_regions(value, |region, _depth| match region.kind() {
ty::ReEarlyBound(_) | ty::ReStatic | ty::ReErased | ty::ReError(_) => {
let name = region.get_name_or_anon();
debug!(?region, ?name);
self.next_nll_region_var(origin, || RegionCtxt::Free(name))
}
r => bug!("unexpected region: {r:?}"),
})
}

Expand Down Expand Up @@ -889,7 +891,12 @@ impl<'tcx> UniversalRegionIndices<'tcx> {
where
T: TypeFoldable<TyCtxt<'tcx>>,
{
tcx.fold_regions(value, |region, _| tcx.mk_re_var(self.to_region_vid(region)))
tcx.fold_regions(value, |region, _| match region.kind() {
ty::ReEarlyBound(_) | ty::ReStatic | ty::ReError(_) => {
tcx.mk_re_var(self.to_region_vid(region))
}
r => bug!("unexpected region: {r:?}"),
})
}
}

Expand Down
5 changes: 3 additions & 2 deletions compiler/rustc_hir_analysis/src/astconv/mod.rs
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Expand Up @@ -3226,8 +3226,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
}
hir::TyKind::Typeof(e) => {
let ty_erased = tcx.type_of(e.def_id).subst_identity();
let ty = tcx.fold_regions(ty_erased, |r, _| {
if r.is_erased() { tcx.lifetimes.re_static } else { r }
let ty = tcx.fold_regions(ty_erased, |r, _| match r.kind() {
ty::ReErased => tcx.lifetimes.re_static,
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I think ReErased is the only kind we expect here.

r => bug!("unexpected region: {r:?}"),
});
let span = ast_ty.span;
let (ty, opt_sugg) = if let Some(ty) = ty.make_suggestable(tcx, false) {
Expand Down
3 changes: 2 additions & 1 deletion compiler/rustc_hir_analysis/src/check/check.rs
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Expand Up @@ -419,7 +419,8 @@ fn check_opaque_meets_bounds<'tcx>(
let hidden_ty = tcx.type_of(def_id.to_def_id()).subst(tcx, substs);
let hidden_ty = tcx.fold_regions(hidden_ty, |re, _dbi| match re.kind() {
ty::ReErased => infcx.next_region_var(RegionVariableOrigin::MiscVariable(span)),
_ => re,
ty::ReEarlyBound(_) | ty::ReStatic | ty::ReError(_) => re,
r => bug!("unexpected region: {r:?}"),
});

let misc_cause = traits::ObligationCause::misc(span, def_id);
Expand Down
20 changes: 12 additions & 8 deletions compiler/rustc_hir_analysis/src/check/compare_impl_item.rs
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Expand Up @@ -458,13 +458,13 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for RemapLateBound<'_, 'tcx> {
}

fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
if let ty::ReFree(fr) = *r {
self.tcx.mk_re_free(
match r.kind() {
ty::ReFree(fr) => self.tcx.mk_re_free(
fr.scope,
self.mapping.get(&fr.bound_region).copied().unwrap_or(fr.bound_region),
)
} else {
r
),
ty::ReEarlyBound(_) | ty::ReStatic => r,
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Probably need to support ReError here, but after staring at this code for the last hour or so I am starting to get exhausted providing examples 😅

r => bug!("unexpected region: {r:?}"),
}
}
}
Expand Down Expand Up @@ -765,11 +765,15 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
let num_impl_substs = tcx.generics_of(impl_m.container_id(tcx)).params.len();
let ty = tcx.fold_regions(ty, |region, _| {
match region.kind() {
// Remap all free regions, which correspond to late-bound regions in the function.
// Remap all free regions, which correspond to late-bound regions in the
// function.
ty::ReFree(_) => {}
// Remap early-bound regions as long as they don't come from the `impl` itself.
// Remap early-bound regions as long as they don't come from the `impl`
// itself.
ty::ReEarlyBound(ebr) if tcx.parent(ebr.def_id) != impl_m.container_id(tcx) => {}
_ => return region,
ty::ReEarlyBound(_) |
ty::ReStatic => return region,
r => bug!("unexpected region: {r:?}"),
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ReError here

}
let Some(ty::ReEarlyBound(e)) = map.get(&region.into()).map(|r| r.expect_region().kind())
else {
Expand Down
15 changes: 4 additions & 11 deletions compiler/rustc_hir_analysis/src/check/wfcheck.rs
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Expand Up @@ -1574,17 +1574,10 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ImplTraitInTraitFinder<'_, 'tcx> {
&& let hir::OpaqueTyOrigin::FnReturn(source) | hir::OpaqueTyOrigin::AsyncFn(source) = opaque.origin
&& source == self.fn_def_id
{
let opaque_ty = tcx.fold_regions(unshifted_opaque_ty, |re, depth| {
if let ty::ReLateBound(index, bv) = re.kind() {
if depth != ty::INNERMOST {
return tcx.mk_re_error_with_message(
DUMMY_SP,
"we shouldn't walk non-predicate binders with `impl Trait`...",
);
}
tcx.mk_re_late_bound(index.shifted_out_to_binder(self.depth), bv)
} else {
re
let opaque_ty = tcx.fold_regions(unshifted_opaque_ty, |re, _depth| {
match re.kind() {
ty::ReEarlyBound(_) | ty::ReFree(_) => re,
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Probably need to support ReError here, but actually, but I guess I never noticed that all the late-bound lifetimes are liberated here, so that's good news I guess. Simplifes the logic a bit.

r => bug!("unexpected region: {r:?}"),
}
});
for (bound, bound_span) in tcx
Expand Down
8 changes: 5 additions & 3 deletions compiler/rustc_hir_analysis/src/collect.rs
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Expand Up @@ -387,8 +387,10 @@ impl<'tcx> AstConv<'tcx> for ItemCtxt<'tcx> {

fn ct_infer(&self, ty: Ty<'tcx>, _: Option<&ty::GenericParamDef>, span: Span) -> Const<'tcx> {
let ty = self.tcx.fold_regions(ty, |r, _| match *r {
ty::ReErased => self.tcx.lifetimes.re_static,
_ => r,
// This is never reached in practice. If it ever is reached,
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We do not hit this in practice, I checked. But as far as I know, ReErased is the only region we should see... anyways, this is fine to keep here I guess.

// `ReErased` should be changed to `ReStatic`, and any other region
// left alone.
r => bug!("unexpected region: {r:?}"),
});
self.tcx().const_error_with_message(ty, span, "bad placeholder constant")
}
Expand Down Expand Up @@ -1142,7 +1144,7 @@ fn infer_return_ty_for_fn_sig<'tcx>(
// Typeck doesn't expect erased regions to be returned from `type_of`.
let fn_sig = tcx.fold_regions(fn_sig, |r, _| match *r {
ty::ReErased => tcx.lifetimes.re_static,
_ => r,
r => bug!("unexpected region: {r:?}"),
});

let mut visitor = HirPlaceholderCollector::default();
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_hir_analysis/src/collect/type_of.rs
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Expand Up @@ -933,7 +933,7 @@ fn infer_placeholder_type<'a>(
// Typeck doesn't expect erased regions to be returned from `type_of`.
tcx.fold_regions(ty, |r, _| match *r {
ty::ReErased => tcx.lifetimes.re_static,
_ => r,
r => bug!("unexpected region: {r:?}"),
})
}

Expand Down
6 changes: 5 additions & 1 deletion compiler/rustc_hir_analysis/src/hir_wf_check.rs
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Expand Up @@ -194,6 +194,10 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for EraseAllBoundRegions<'tcx> {
self.tcx
}
fn fold_region(&mut self, r: Region<'tcx>) -> Region<'tcx> {
if r.is_late_bound() { self.tcx.lifetimes.re_erased } else { r }
match r.kind() {
ty::ReLateBound(..) => self.tcx.lifetimes.re_erased,
ty::ReEarlyBound(_) | ty::ReStatic | ty::ReError(_) => r,
r => bug!("unexpected region: {r:?}"),
}
}
}
5 changes: 4 additions & 1 deletion compiler/rustc_hir_typeck/src/demand.rs
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Expand Up @@ -270,7 +270,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
// Hack to make equality checks on types with inference variables and regions useful.
let mut eraser = BottomUpFolder {
tcx: self.tcx,
lt_op: |_| self.tcx.lifetimes.re_erased,
lt_op: |r| match r.kind() {
ty::ReStatic | ty::ReVar(_) | ty::ReErased => self.tcx.lifetimes.re_erased,
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This ICEs on ReEarlyBound. Probably needs to handle ReError too, now that I think of it.

struct Wrapper<'a, T>(&'a T);

fn foo<'a, T>() -> Wrapper<'a, T> {}
fn needs_i32(_: Wrapper<'static, i32>) {}

fn test<'a>() {
    let x = foo::<'a, ()>();
    needs_i32(x);
}

fn main() {}

But also, I just rewrote all this code in #108687, so whatever.

r => bug!("unexpected region: {r:?}"),
},
ct_op: |c| c,
ty_op: |t| match *t.kind() {
ty::Infer(ty::TyVar(_)) => self.tcx.mk_ty_var(ty::TyVid::from_u32(0)),
Expand Down
9 changes: 5 additions & 4 deletions compiler/rustc_hir_typeck/src/generator_interior/mod.rs
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Expand Up @@ -257,19 +257,20 @@ pub fn resolve_interior<'a, 'tcx>(
_ => mk_bound_region(None),
}
}
// FIXME: these should use `BrNamed`
// // FIXME: these should use `BrNamed`
ty::ReEarlyBound(region) => {
mk_bound_region(Some(fcx.tcx.def_span(region.def_id)))
}
ty::ReLateBound(_, ty::BoundRegion { kind, .. })
| ty::ReFree(ty::FreeRegion { bound_region: kind, .. }) => match kind {
// ty::ReLateBound(_, ty::BoundRegion { kind, .. })
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Stray comment? I think it's ok to ICE on ReLateBound here... I think...

ty::ReFree(ty::FreeRegion { bound_region: kind, .. }) => match kind {
ty::BoundRegionKind::BrAnon(span) => mk_bound_region(span),
ty::BoundRegionKind::BrNamed(def_id, _) => {
mk_bound_region(Some(fcx.tcx.def_span(def_id)))
}
ty::BoundRegionKind::BrEnv => mk_bound_region(None),
},
_ => mk_bound_region(None),
ty::ReStatic | ty::ReErased => mk_bound_region(None),
r => bug!("unexpected region: {r:?}"),
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We must handle ReError here:

fn missing() -> &'missing () {  &() }

async fn async_fn() {}

fn main() {
    async {
        let x = missing();
        async_fn().await;
        drop(x);
    };
}

};
let r = fcx.tcx.mk_re_late_bound(current_depth, br);
r
Expand Down
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