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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
Dylan-DPC authored Oct 12, 2022
2 parents 40deece + bef8681 commit c763ebc
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Showing 3 changed files with 98 additions and 99 deletions.
72 changes: 56 additions & 16 deletions compiler/rustc_const_eval/src/const_eval/fn_queries.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -25,12 +25,10 @@ pub fn is_parent_const_impl_raw(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
/// report whether said intrinsic has a `rustc_const_{un,}stable` attribute. Otherwise, return
/// `Constness::NotConst`.
fn constness(tcx: TyCtxt<'_>, def_id: DefId) -> hir::Constness {
let def_id = def_id.expect_local();
let node = tcx.hir().get_by_def_id(def_id);

match node {
let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
match tcx.hir().get(hir_id) {
hir::Node::Ctor(_) => hir::Constness::Const,
hir::Node::Item(hir::Item { kind: hir::ItemKind::Impl(impl_), .. }) => impl_.constness,

hir::Node::ForeignItem(hir::ForeignItem { kind: hir::ForeignItemKind::Fn(..), .. }) => {
// Intrinsics use `rustc_const_{un,}stable` attributes to indicate constness. All other
// foreign items cannot be evaluated at compile-time.
Expand All @@ -41,20 +39,62 @@ fn constness(tcx: TyCtxt<'_>, def_id: DefId) -> hir::Constness {
};
if is_const { hir::Constness::Const } else { hir::Constness::NotConst }
}
_ => {
if let Some(fn_kind) = node.fn_kind() {
if fn_kind.constness() == hir::Constness::Const {
return hir::Constness::Const;
}

// If the function itself is not annotated with `const`, it may still be a `const fn`
// if it resides in a const trait impl.
let is_const = is_parent_const_impl_raw(tcx, def_id);
if is_const { hir::Constness::Const } else { hir::Constness::NotConst }
} else {
hir::Constness::NotConst
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,
}
}

Expand Down
56 changes: 41 additions & 15 deletions compiler/rustc_metadata/src/rmeta/encoder.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1059,6 +1059,43 @@ fn should_encode_const(def_kind: DefKind) -> bool {
}
}

fn should_encode_constness(def_kind: DefKind) -> bool {
match def_kind {
DefKind::Struct
| DefKind::Union
| DefKind::Enum
| DefKind::Trait
| DefKind::AssocTy
| DefKind::Fn
| DefKind::Const
| DefKind::Static(..)
| DefKind::Ctor(..)
| DefKind::AssocFn
| DefKind::AssocConst
| DefKind::AnonConst
| DefKind::InlineConst
| DefKind::OpaqueTy
| DefKind::ImplTraitPlaceholder
| DefKind::Impl
| DefKind::Closure
| DefKind::Generator
| DefKind::TyAlias => true,
DefKind::Variant
| DefKind::TraitAlias
| DefKind::ForeignTy
| DefKind::Field
| DefKind::TyParam
| DefKind::Mod
| DefKind::ForeignMod
| DefKind::ConstParam
| DefKind::Macro(..)
| DefKind::Use
| DefKind::LifetimeParam
| DefKind::GlobalAsm
| DefKind::ExternCrate => false,
}
}

fn should_encode_trait_impl_trait_tys<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
if tcx.def_kind(def_id) != DefKind::AssocFn {
return false;
Expand Down Expand Up @@ -1165,6 +1202,9 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
{
record!(self.tables.trait_impl_trait_tys[def_id] <- table);
}
if should_encode_constness(def_kind) {
self.tables.constness.set(def_id.index, tcx.constness(def_id));
}
}
let inherent_impls = tcx.crate_inherent_impls(());
for (def_id, implementations) in inherent_impls.inherent_impls.iter() {
Expand Down Expand Up @@ -1192,7 +1232,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
};

record!(self.tables.variant_data[def_id] <- data);
self.tables.constness.set(def_id.index, hir::Constness::Const);
record_array!(self.tables.children[def_id] <- variant.fields.iter().map(|f| {
assert!(f.did.is_local());
f.did.index
Expand Down Expand Up @@ -1220,7 +1259,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
};

record!(self.tables.variant_data[def_id] <- data);
self.tables.constness.set(def_id.index, hir::Constness::Const);
if variant.ctor_kind == CtorKind::Fn {
record!(self.tables.fn_sig[def_id] <- tcx.fn_sig(def_id));
}
Expand Down Expand Up @@ -1284,7 +1322,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {

record!(self.tables.repr_options[def_id] <- adt_def.repr());
record!(self.tables.variant_data[def_id] <- data);
self.tables.constness.set(def_id.index, hir::Constness::Const);
if variant.ctor_kind == CtorKind::Fn {
record!(self.tables.fn_sig[def_id] <- tcx.fn_sig(def_id));
}
Expand Down Expand Up @@ -1320,7 +1357,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
}
};
self.tables.asyncness.set(def_id.index, m_sig.header.asyncness);
self.tables.constness.set(def_id.index, hir::Constness::NotConst);
}
ty::AssocKind::Type => {
self.encode_explicit_item_bounds(def_id);
Expand All @@ -1345,13 +1381,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
let hir::ImplItemKind::Fn(ref sig, body) = ast_item.kind else { bug!() };
self.tables.asyncness.set(def_id.index, sig.header.asyncness);
record_array!(self.tables.fn_arg_names[def_id] <- self.tcx.hir().body_param_names(body));
// Can be inside `impl const Trait`, so using sig.header.constness is not reliable
let constness = if self.tcx.is_const_fn_raw(def_id) {
hir::Constness::Const
} else {
hir::Constness::NotConst
};
self.tables.constness.set(def_id.index, constness);
}
ty::AssocKind::Const | ty::AssocKind::Type => {}
}
Expand Down Expand Up @@ -1474,7 +1503,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
hir::ItemKind::Fn(ref sig, .., body) => {
self.tables.asyncness.set(def_id.index, sig.header.asyncness);
record_array!(self.tables.fn_arg_names[def_id] <- self.tcx.hir().body_param_names(body));
self.tables.constness.set(def_id.index, sig.header.constness);
}
hir::ItemKind::Macro(ref macro_def, _) => {
if macro_def.macro_rules {
Expand All @@ -1495,7 +1523,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
hir::ItemKind::Struct(ref struct_def, _) => {
let adt_def = self.tcx.adt_def(def_id);
record!(self.tables.repr_options[def_id] <- adt_def.repr());
self.tables.constness.set(def_id.index, hir::Constness::Const);

// Encode def_ids for each field and method
// for methods, write all the stuff get_trait_method
Expand Down Expand Up @@ -1524,9 +1551,8 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
is_non_exhaustive: variant.is_field_list_non_exhaustive(),
});
}
hir::ItemKind::Impl(hir::Impl { defaultness, constness, .. }) => {
hir::ItemKind::Impl(hir::Impl { defaultness, .. }) => {
self.tables.impl_defaultness.set(def_id.index, *defaultness);
self.tables.constness.set(def_id.index, *constness);

let trait_ref = self.tcx.impl_trait_ref(def_id);
if let Some(trait_ref) = trait_ref {
Expand Down
69 changes: 1 addition & 68 deletions compiler/rustc_ty_utils/src/ty.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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 =
Expand Down

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