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Rollup merge of #102830 - compiler-errors:constness-parity, r=fee1-dead

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Unify `tcx.constness` query and param env constness checks

The checks that we do in the `constness` query seem inconsistent with the checks that we do to determine if an item's param-env is const, so I merged them into the `constness` query and call that from the `param_env` query.

I'm not sure if this totally makes sense -- is there a case where `tcx.param_env()` would return a const param-env for an item whose `tcx.constness()` is `Constness::NotConst`? Because if not, it seems a bit dangerous that these two differ.

Luckily, not many places actually use `tcx.constness()`, and the checks in `tcx.param_env()` seem stricter than the checks in `tcx.constness()` (at least for the types of items we type-check).

Also, due to the way that `tcx.param_env()` is implemented, it _never_ used to return a const param-env for a item coming from a different crate, which also seems dangerous (though also probably not weaponizable currently, because we seldom actually compute the param-env for a non-local item).
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Dylan DPC 2022-10-12 22:13:25 +05:30 • committed by GitHub
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69
compiler/rustc_ty_utils/src/ty.rs
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@ -137,77 +137,10 @@ fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
let local_did = def_id.as_local();
let hir_id = local_did.map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id));
let constness = match hir_id {
Some(hir_id) => match tcx.hir().get(hir_id) {
hir::Node::TraitItem(hir::TraitItem { kind: hir::TraitItemKind::Fn(..), .. })
if tcx.is_const_default_method(def_id) =>
{
hir::Constness::Const
}
hir::Node::Item(hir::Item { kind: hir::ItemKind::Const(..), .. })
| hir::Node::Item(hir::Item { kind: hir::ItemKind::Static(..), .. })
| hir::Node::TraitItem(hir::TraitItem {
kind: hir::TraitItemKind::Const(..), ..
})
| hir::Node::AnonConst(_)
| hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Const(..), .. })
| hir::Node::ImplItem(hir::ImplItem {
kind:
hir::ImplItemKind::Fn(
hir::FnSig {
header: hir::FnHeader { constness: hir::Constness::Const, .. },
..
},
..,
),
..
}) => hir::Constness::Const,
hir::Node::ImplItem(hir::ImplItem {
kind: hir::ImplItemKind::Type(..) | hir::ImplItemKind::Fn(..),
..
}) => {
let parent_hir_id = tcx.hir().get_parent_node(hir_id);
match tcx.hir().get(parent_hir_id) {
hir::Node::Item(hir::Item {
kind: hir::ItemKind::Impl(hir::Impl { constness, .. }),
..
}) => *constness,
_ => span_bug!(
tcx.def_span(parent_hir_id.owner),
"impl item's parent node is not an impl",
),
}
}
hir::Node::Item(hir::Item {
kind:
hir::ItemKind::Fn(hir::FnSig { header: hir::FnHeader { constness, .. }, .. }, ..),
..
})
| hir::Node::TraitItem(hir::TraitItem {
kind:
hir::TraitItemKind::Fn(
hir::FnSig { header: hir::FnHeader { constness, .. }, .. },
..,
),
..
})
| hir::Node::Item(hir::Item {
kind: hir::ItemKind::Impl(hir::Impl { constness, .. }),
..
}) => *constness,
_ => hir::Constness::NotConst,
},
None => hir::Constness::NotConst,
};
let unnormalized_env = ty::ParamEnv::new(
tcx.intern_predicates(&predicates),
traits::Reveal::UserFacing,
constness,
tcx.constness(def_id),
);
let body_id =