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Fixes incorrect handling of ADT's drop requirements #90218

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Oct 28, 2021
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101 changes: 56 additions & 45 deletions compiler/rustc_ty_utils/src/needs_drop.rs
Original file line number Diff line number Diff line change
Expand Up @@ -12,14 +12,12 @@ use rustc_span::{sym, DUMMY_SP};
type NeedsDropResult<T> = Result<T, AlwaysRequiresDrop>;

fn needs_drop_raw<'tcx>(tcx: TyCtxt<'tcx>, query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>) -> bool {
let adt_components =
move |adt_def: &ty::AdtDef, _| tcx.adt_drop_tys(adt_def.did).map(|tys| tys.iter());

// If we don't know a type doesn't need drop, for example if it's a type
// parameter without a `Copy` bound, then we conservatively return that it
// needs drop.
let res =
NeedsDropTypes::new(tcx, query.param_env, query.value, adt_components).next().is_some();
let adt_has_dtor =
|adt_def: &ty::AdtDef| adt_def.destructor(tcx).map(|_| DtorType::Significant);
let res = drop_tys_helper(tcx, query.value, query.param_env, adt_has_dtor).next().is_some();

debug!("needs_drop_raw({:?}) = {:?}", query, res);
res
Expand All @@ -29,12 +27,10 @@ fn has_significant_drop_raw<'tcx>(
tcx: TyCtxt<'tcx>,
query: ty::ParamEnvAnd<'tcx, Ty<'tcx>>,
) -> bool {
let significant_drop_fields = move |adt_def: &ty::AdtDef, _| {
tcx.adt_significant_drop_tys(adt_def.did).map(|tys| tys.iter())
};
let res = NeedsDropTypes::new(tcx, query.param_env, query.value, significant_drop_fields)
.next()
.is_some();
let res =
drop_tys_helper(tcx, query.value, query.param_env, adt_consider_insignificant_dtor(tcx))
.next()
.is_some();
debug!("has_significant_drop_raw({:?}) = {:?}", query, res);
res
}
Expand Down Expand Up @@ -145,10 +141,8 @@ where
Ok(tys) => tys,
};
for required_ty in tys {
let subst_ty = tcx.normalize_erasing_regions(
self.param_env,
required_ty.subst(tcx, substs),
);
let subst_ty =
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Note: I probably would have renamed this variable. I think the reason it was named subst_ty is because it, prior to this PR, had the substs applied to it. But that is no longer the case here, if I understand correctly.

tcx.normalize_erasing_regions(self.param_env, required_ty);
queue_type(self, subst_ty);
}
}
Expand Down Expand Up @@ -187,23 +181,24 @@ enum DtorType {
// Depending on the implentation of `adt_has_dtor`, it is used to check if the
// ADT has a destructor or if the ADT only has a significant destructor. For
// understanding significant destructor look at `adt_significant_drop_tys`.
fn adt_drop_tys_helper<'tcx>(
fn drop_tys_helper<'tcx>(
tcx: TyCtxt<'tcx>,
def_id: DefId,
ty: Ty<'tcx>,
param_env: rustc_middle::ty::ParamEnv<'tcx>,
adt_has_dtor: impl Fn(&ty::AdtDef) -> Option<DtorType>,
) -> Result<&ty::List<Ty<'tcx>>, AlwaysRequiresDrop> {
) -> impl Iterator<Item = NeedsDropResult<Ty<'tcx>>> {
let adt_components = move |adt_def: &ty::AdtDef, substs: SubstsRef<'tcx>| {
if adt_def.is_manually_drop() {
debug!("adt_drop_tys: `{:?}` is manually drop", adt_def);
debug!("drop_tys_helper: `{:?}` is manually drop", adt_def);
return Ok(Vec::new().into_iter());
} else if let Some(dtor_info) = adt_has_dtor(adt_def) {
match dtor_info {
DtorType::Significant => {
debug!("adt_drop_tys: `{:?}` implements `Drop`", adt_def);
debug!("drop_tys_helper: `{:?}` implements `Drop`", adt_def);
return Err(AlwaysRequiresDrop);
}
DtorType::Insignificant => {
debug!("adt_drop_tys: `{:?}` drop is insignificant", adt_def);
debug!("drop_tys_helper: `{:?}` drop is insignificant", adt_def);

// Since the destructor is insignificant, we just want to make sure all of
// the passed in type parameters are also insignificant.
Expand All @@ -212,34 +207,27 @@ fn adt_drop_tys_helper<'tcx>(
}
}
} else if adt_def.is_union() {
debug!("adt_drop_tys: `{:?}` is a union", adt_def);
debug!("drop_tys_helper: `{:?}` is a union", adt_def);
return Ok(Vec::new().into_iter());
}
Ok(adt_def.all_fields().map(|field| tcx.type_of(field.did)).collect::<Vec<_>>().into_iter())
Ok(adt_def
.all_fields()
.map(|field| {
let r = tcx.type_of(field.did).subst(tcx, substs);
debug!("drop_tys_helper: Subst into {:?} with {:?} gettng {:?}", field, substs, r);
r
})
.collect::<Vec<_>>()
.into_iter())
};

let adt_ty = tcx.type_of(def_id);
let param_env = tcx.param_env(def_id);
let res: Result<Vec<_>, _> =
NeedsDropTypes::new(tcx, param_env, adt_ty, adt_components).collect();

debug!("adt_drop_tys(`{}`) = `{:?}`", tcx.def_path_str(def_id), res);
res.map(|components| tcx.intern_type_list(&components))
NeedsDropTypes::new(tcx, param_env, ty, adt_components)
}

fn adt_drop_tys(tcx: TyCtxt<'_>, def_id: DefId) -> Result<&ty::List<Ty<'_>>, AlwaysRequiresDrop> {
// This is for the "needs_drop" query, that considers all `Drop` impls, therefore all dtors are
// significant.
let adt_has_dtor =
|adt_def: &ty::AdtDef| adt_def.destructor(tcx).map(|_| DtorType::Significant);
adt_drop_tys_helper(tcx, def_id, adt_has_dtor)
}

fn adt_significant_drop_tys(
tcx: TyCtxt<'_>,
def_id: DefId,
) -> Result<&ty::List<Ty<'_>>, AlwaysRequiresDrop> {
let adt_has_dtor = |adt_def: &ty::AdtDef| {
fn adt_consider_insignificant_dtor<'tcx>(
tcx: TyCtxt<'tcx>,
) -> impl Fn(&ty::AdtDef) -> Option<DtorType> + 'tcx {
move |adt_def: &ty::AdtDef| {
let is_marked_insig = tcx.has_attr(adt_def.did, sym::rustc_insignificant_dtor);
if is_marked_insig {
// In some cases like `std::collections::HashMap` where the struct is a wrapper around
Expand All @@ -256,8 +244,31 @@ fn adt_significant_drop_tys(
// treat this as the simple case of Drop impl for type.
None
}
};
adt_drop_tys_helper(tcx, def_id, adt_has_dtor)
}
}

fn adt_drop_tys(tcx: TyCtxt<'_>, def_id: DefId) -> Result<&ty::List<Ty<'_>>, AlwaysRequiresDrop> {
// This is for the "adt_drop_tys" query, that considers all `Drop` impls, therefore all dtors are
// significant.
let adt_has_dtor =
|adt_def: &ty::AdtDef| adt_def.destructor(tcx).map(|_| DtorType::Significant);
drop_tys_helper(tcx, tcx.type_of(def_id), tcx.param_env(def_id), adt_has_dtor)
.collect::<Result<Vec<_>, _>>()
.map(|components| tcx.intern_type_list(&components))
}

fn adt_significant_drop_tys(
tcx: TyCtxt<'_>,
def_id: DefId,
) -> Result<&ty::List<Ty<'_>>, AlwaysRequiresDrop> {
drop_tys_helper(
tcx,
tcx.type_of(def_id),
tcx.param_env(def_id),
adt_consider_insignificant_dtor(tcx),
)
.collect::<Result<Vec<_>, _>>()
.map(|components| tcx.intern_type_list(&components))
}

pub(crate) fn provide(providers: &mut ty::query::Providers) {
Expand Down
Original file line number Diff line number Diff line change
@@ -0,0 +1,37 @@
// Test that rustc doesn't ICE as in #90024.
// check-pass
// edition=2018

#![warn(rust_2021_incompatible_closure_captures)]

// Checks there's no double-subst into the generic args, otherwise we get OOB
// MCVE by @lqd
pub struct Graph<N, E, Ix> {
_edges: E,
_nodes: N,
_ix: Vec<Ix>,
}
fn graph<N, E>() -> Graph<N, E, i32> {
todo!()
}
fn first_ice() {
let g = graph::<i32, i32>();
let _ = || g;
}

// Checks that there is a subst into the fields, otherwise we get normalization error
// MCVE by @cuviper
use std::iter::Empty;
struct Foo<I: Iterator> {
data: Vec<I::Item>,
}
pub fn second_ice() {
let v = Foo::<Empty<()>> { data: vec![] };

(|| v.data[0])();
}

pub fn main() {
first_ice();
second_ice();
}