2 use rustc_hir::def_id::{DefId, LocalDefId};
3 use rustc_middle::hir::map::blocks::FnLikeNode;
4 use rustc_middle::ty::query::Providers;
5 use rustc_middle::ty::TyCtxt;
6 use rustc_span::symbol::Symbol;
7 use rustc_target::spec::abi::Abi;
9 /// Whether the `def_id` counts as const fn in your current crate, considering all active
11 pub fn is_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
12 tcx.is_const_fn_raw(def_id)
13 && match is_unstable_const_fn(tcx, def_id) {
14 Some(feature_name) => {
15 // has a `rustc_const_unstable` attribute, check whether the user enabled the
16 // corresponding feature gate.
17 tcx.features().declared_lib_features.iter().any(|&(sym, _)| sym == feature_name)
19 // functions without const stability are either stable user written
20 // const fn or the user is using feature gates and we thus don't
26 /// Whether the `def_id` is an unstable const fn and what feature gate is necessary to enable it
27 pub fn is_unstable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Symbol> {
28 if tcx.is_const_fn_raw(def_id) {
29 let const_stab = tcx.lookup_const_stability(def_id)?;
30 if const_stab.level.is_unstable() { Some(const_stab.feature) } else { None }
36 pub fn is_parent_const_impl_raw(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
37 let parent_id = tcx.hir().get_parent_did(hir_id);
38 if !parent_id.is_top_level_module() { is_const_impl_raw(tcx, parent_id) } else { false }
41 /// Checks whether the function has a `const` modifier or, in case it is an intrinsic, whether
42 /// said intrinsic has a `rustc_const_{un,}stable` attribute.
43 fn is_const_fn_raw(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
44 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
46 let node = tcx.hir().get(hir_id);
48 if let hir::Node::ForeignItem(hir::ForeignItem { kind: hir::ForeignItemKind::Fn(..), .. }) =
51 // Intrinsics use `rustc_const_{un,}stable` attributes to indicate constness. All other
52 // foreign items cannot be evaluated at compile-time.
53 if let Abi::RustIntrinsic | Abi::PlatformIntrinsic = tcx.hir().get_foreign_abi(hir_id) {
54 tcx.lookup_const_stability(def_id).is_some()
58 } else if let Some(fn_like) = FnLikeNode::from_node(node) {
59 if fn_like.constness() == hir::Constness::Const {
63 // If the function itself is not annotated with `const`, it may still be a `const fn`
64 // if it resides in a const trait impl.
65 is_parent_const_impl_raw(tcx, hir_id)
66 } else if let hir::Node::Ctor(_) = node {
73 /// Checks whether the given item is an `impl` that has a `const` modifier.
74 fn is_const_impl_raw(tcx: TyCtxt<'_>, def_id: LocalDefId) -> bool {
75 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
76 let node = tcx.hir().get(hir_id);
79 hir::Node::Item(hir::Item {
80 kind: hir::ItemKind::Impl(hir::Impl { constness: hir::Constness::Const, .. }),
86 fn is_promotable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
87 is_const_fn(tcx, def_id)
88 && match tcx.lookup_const_stability(def_id) {
90 if cfg!(debug_assertions) && stab.promotable {
91 let sig = tcx.fn_sig(def_id);
94 hir::Unsafety::Normal,
95 "don't mark const unsafe fns as promotable",
96 // https://github.com/rust-lang/rust/pull/53851#issuecomment-418760682
105 pub fn provide(providers: &mut Providers) {
106 *providers = Providers {
108 is_const_impl_raw: |tcx, def_id| is_const_impl_raw(tcx, def_id.expect_local()),
109 is_promotable_const_fn,