8e1c34f5cc
instead of during ast lowering, where it's not easily possible to obtain all the right information in time
82 lines
3.4 KiB
Rust
82 lines
3.4 KiB
Rust
use rustc_hir::def_id::{DefId, LocalDefId};
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use rustc_hir::{
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Constness, ExprKind, ForeignItemKind, ImplItem, ImplItemImplKind, ImplItemKind, Item, ItemKind,
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Node, TraitItem, TraitItemKind, VariantData, find_attr,
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};
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use rustc_middle::query::Providers;
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use rustc_middle::ty::TyCtxt;
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/// Checks whether a function-like definition is considered to be `const`. Also stores constness of inherent impls.
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fn constness(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Constness {
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let node = tcx.hir_node_by_def_id(def_id);
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match node {
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Node::Ctor(VariantData::Tuple(..)) => Constness::Const,
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Node::ForeignItem(item) if let ForeignItemKind::Fn(..) = item.kind => {
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// Foreign functions cannot be evaluated at compile-time.
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Constness::NotConst
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}
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Node::Expr(e) if let ExprKind::Closure(c) = e.kind => {
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if let Constness::Const = c.constness && tcx.hir_body_const_context(tcx.local_parent(def_id)).is_none() {
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tcx.dcx().span_err(tcx.def_span(def_id), "cannot use `const` closures outside of const contexts");
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return Constness::NotConst;
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}
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c.constness
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},
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// FIXME(fee1-dead): extract this one out and rename this query to `fn_constness` so we don't need `is_const_fn` anymore.
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Node::Item(i) if let ItemKind::Impl(impl_) = i.kind => impl_.constness,
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Node::Item(Item { kind: ItemKind::Fn { sig, .. }, .. }) => sig.header.constness,
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Node::ImplItem(ImplItem {
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impl_kind: ImplItemImplKind::Trait { .. },
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kind: ImplItemKind::Fn(..),
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..
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}) => tcx.impl_trait_header(tcx.local_parent(def_id)).constness,
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Node::ImplItem(ImplItem {
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impl_kind: ImplItemImplKind::Inherent { .. },
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kind: ImplItemKind::Fn(sig, _),
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..
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}) => {
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match sig.header.constness {
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Constness::Const => Constness::Const,
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// inherent impl could be const
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Constness::NotConst => tcx.constness(tcx.local_parent(def_id)),
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}
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}
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Node::TraitItem(ti @ TraitItem { kind: TraitItemKind::Fn(..), .. }) => {
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if find_attr!(tcx, ti.hir_id(), RustcNonConstTraitMethod) {
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Constness::NotConst
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} else {
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tcx.trait_def(tcx.local_parent(def_id)).constness
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}
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}
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_ => {
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tcx.dcx().span_bug(
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tcx.def_span(def_id),
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format!("should not be requesting the constness of items that can't be const: {node:#?}: {:?}", tcx.def_kind(def_id))
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)
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}
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}
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}
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fn is_promotable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
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tcx.is_const_fn(def_id)
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&& match tcx.lookup_const_stability(def_id) {
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Some(stab) => {
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if cfg!(debug_assertions) && stab.promotable {
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let sig = tcx.fn_sig(def_id);
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assert!(
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sig.skip_binder().safety().is_safe(),
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"don't mark const unsafe fns as promotable",
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// https://github.com/rust-lang/rust/pull/53851#issuecomment-418760682
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);
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}
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stab.promotable
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}
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None => false,
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}
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}
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pub fn provide(providers: &mut Providers) {
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*providers = Providers { constness, is_promotable_const_fn, ..*providers };
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}
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