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add new attribute rustc_insignificant_dtor and a query to check if a type has a significant drop

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This commit is contained in:
Dhruv Jauhar 2021-04-13 03:43:11 -04:00
parent 1025db84a6
commit a7e1cec621
11 changed files with 333 additions and 13 deletions
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55
compiler/rustc_ty_utils/src/needs_drop.rs
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@ -6,7 +6,7 @@ use rustc_middle::ty::subst::Subst;
use rustc_middle::ty::util::{needs_drop_components, AlwaysRequiresDrop};
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_session::Limit;
use rustc_span::DUMMY_SP;
use rustc_span::{sym, DUMMY_SP};
type NeedsDropResult<T> = Result<T, AlwaysRequiresDrop>;
@ -21,6 +21,19 @@ fn needs_drop_raw<'tcx>(tcx: TyCtxt<'tcx>, query: ty::ParamEnvAnd<'tcx, Ty<'tcx>
res
}
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();
debug!("has_significant_drop_raw({:?}) = {:?}", query, res);
res
}
struct NeedsDropTypes<'tcx, F> {
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
@ -155,12 +168,20 @@ where
}
}
fn adt_drop_tys(tcx: TyCtxt<'_>, def_id: DefId) -> Result<&ty::List<Ty<'_>>, AlwaysRequiresDrop> {
// This is a helper function for `adt_drop_tys` and `adt_significant_drop_tys`.
// 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: TyCtxt<'_>,
def_id: DefId,
adt_has_dtor: impl Fn(&ty::AdtDef) -> bool,
) -> Result<&ty::List<Ty<'_>>, AlwaysRequiresDrop> {
let adt_components = move |adt_def: &ty::AdtDef| {
if adt_def.is_manually_drop() {
debug!("adt_drop_tys: `{:?}` is manually drop", adt_def);
return Ok(Vec::new().into_iter());
} else if adt_def.destructor(tcx).is_some() {
} else if adt_has_dtor(adt_def) {
debug!("adt_drop_tys: `{:?}` implements `Drop`", adt_def);
return Err(AlwaysRequiresDrop);
} else if adt_def.is_union() {
@ -179,6 +200,30 @@ fn adt_drop_tys(tcx: TyCtxt<'_>, def_id: DefId) -> Result<&ty::List<Ty<'_>>, Alw
res.map(|components| tcx.intern_type_list(&components))
}
pub(crate) fn provide(providers: &mut ty::query::Providers) {
*providers = ty::query::Providers { needs_drop_raw, adt_drop_tys, ..*providers };
fn adt_drop_tys(tcx: TyCtxt<'_>, def_id: DefId) -> Result<&ty::List<Ty<'_>>, AlwaysRequiresDrop> {
let adt_has_dtor = |adt_def: &ty::AdtDef| adt_def.destructor(tcx).is_some();
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| {
adt_def
.destructor(tcx)
.map(|dtor| !tcx.has_attr(dtor.did, sym::rustc_insignificant_dtor))
.unwrap_or(false)
};
adt_drop_tys_helper(tcx, def_id, adt_has_dtor)
}
pub(crate) fn provide(providers: &mut ty::query::Providers) {
*providers = ty::query::Providers {
needs_drop_raw,
has_significant_drop_raw,
adt_drop_tys,
adt_significant_drop_tys,
..*providers
};
}