rustc_const_eval/const_eval/
fn_queries.rs

1use rustc_hir::def_id::{DefId, LocalDefId};
2use rustc_hir::{
3    Constness, ExprKind, ForeignItemKind, ImplItem, ImplItemImplKind, ImplItemKind, Item, ItemKind,
4    Node, TraitItem, TraitItemKind, VariantData,
5};
6use rustc_middle::query::Providers;
7use rustc_middle::ty::TyCtxt;
8
9/// Checks whether a function-like definition is considered to be `const`. Also stores constness of inherent impls.
10fn constness(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Constness {
11    let node = tcx.hir_node_by_def_id(def_id);
12
13    match node {
14        Node::Ctor(VariantData::Tuple(..)) => Constness::Const,
15        Node::ForeignItem(item) if let ForeignItemKind::Fn(..) = item.kind => {
16            // Foreign functions cannot be evaluated at compile-time.
17            Constness::NotConst
18        }
19        Node::Expr(e) if let ExprKind::Closure(c) = e.kind => c.constness,
20        // FIXME(fee1-dead): extract this one out and rename this query to `fn_constness` so we don't need `is_const_fn` anymore.
21        Node::Item(i) if let ItemKind::Impl(impl_) = i.kind => impl_.constness,
22        Node::Item(Item { kind: ItemKind::Fn { sig, .. }, .. }) => sig.header.constness,
23        Node::ImplItem(ImplItem {
24            impl_kind: ImplItemImplKind::Trait { .. },
25            kind: ImplItemKind::Fn(..),
26            ..
27        }) => tcx.impl_trait_header(tcx.local_parent(def_id)).constness,
28        Node::ImplItem(ImplItem {
29            impl_kind: ImplItemImplKind::Inherent { .. },
30            kind: ImplItemKind::Fn(sig, _),
31            ..
32        }) => {
33            match sig.header.constness {
34                Constness::Const => Constness::Const,
35                // inherent impl could be const
36                Constness::NotConst => tcx.constness(tcx.local_parent(def_id)),
37            }
38        }
39        Node::TraitItem(TraitItem { kind: TraitItemKind::Fn(..), .. }) => tcx.trait_def(tcx.local_parent(def_id)).constness,
40        _ => {
41            tcx.dcx().span_bug(
42                tcx.def_span(def_id),
43                format!("should not be requesting the constness of items that can't be const: {node:#?}: {:?}", tcx.def_kind(def_id))
44            )
45        }
46    }
47}
48
49fn is_promotable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
50    tcx.is_const_fn(def_id)
51        && match tcx.lookup_const_stability(def_id) {
52            Some(stab) => {
53                if cfg!(debug_assertions) && stab.promotable {
54                    let sig = tcx.fn_sig(def_id);
55                    assert!(
56                        sig.skip_binder().safety().is_safe(),
57                        "don't mark const unsafe fns as promotable",
58                        // https://github.com/rust-lang/rust/pull/53851#issuecomment-418760682
59                    );
60                }
61                stab.promotable
62            }
63            None => false,
64        }
65}
66
67pub fn provide(providers: &mut Providers) {
68    *providers = Providers { constness, is_promotable_const_fn, ..*providers };
69}
rustc_const_eval/const_eval/fn_queries.rs

rustc_const_eval/const_eval/
fn_queries.rs
