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use ty::query::Providers;
use hir::def_id::DefId;
use hir;
use ty::TyCtxt;
use syntax_pos::symbol::Symbol;
use hir::map::blocks::FnLikeNode;
use syntax::attr;
use rustc_target::spec::abi;
impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
/// Whether the `def_id` counts as const fn in your current crate, considering all active
/// feature gates
pub fn is_const_fn(self, def_id: DefId) -> bool {
self.is_const_fn_raw(def_id) && match self.lookup_stability(def_id) {
Some(stab) => match stab.const_stability {
// has a `rustc_const_unstable` attribute, check whether the user enabled the
// corresponding feature gate
Some(feature_name) => self.features()
.declared_lib_features
.iter()
.any(|&(sym, _)| sym == feature_name),
// the function has no stability attribute, it is stable as const fn or the user
// needs to use feature gates to use the function at all
None => true,
},
// functions without stability are either stable user written const fn or the user is
// using feature gates and we thus don't care what they do
None => true,
}
}
/// Whether the `def_id` is an unstable const fn and what feature gate is necessary to enable it
pub fn is_unstable_const_fn(self, def_id: DefId) -> Option<Symbol> {
if self.is_const_fn_raw(def_id) {
self.lookup_stability(def_id)?.const_stability
} else {
None
}
}
/// Returns true if this function must conform to `min_const_fn`
pub fn is_min_const_fn(self, def_id: DefId) -> bool {
if self.features().staged_api {
// some intrinsics are waved through if called inside the
// standard library. Users never need to call them directly
if let abi::Abi::RustIntrinsic = self.fn_sig(def_id).abi() {
assert!(!self.is_const_fn(def_id));
match &self.item_name(def_id).as_str()[..] {
| "size_of"
| "min_align_of"
| "needs_drop"
=> return true,
_ => {},
}
}
// in order for a libstd function to be considered min_const_fn
// it needs to be stable and have no `rustc_const_unstable` attribute
match self.lookup_stability(def_id) {
// stable functions with unstable const fn aren't `min_const_fn`
Some(&attr::Stability { const_stability: Some(_), .. }) => false,
// unstable functions don't need to conform
Some(&attr::Stability { ref level, .. }) if level.is_unstable() => false,
// everything else needs to conform, because it would be callable from
// other `min_const_fn` functions
_ => true,
}
} else {
// users enabling the `const_fn` feature gate can do what they want
!self.features().const_fn
}
}
}
pub fn provide<'tcx>(providers: &mut Providers<'tcx>) {
/// only checks whether the function has a `const` modifier
fn is_const_fn_raw<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> bool {
let node_id = tcx.hir.as_local_node_id(def_id)
.expect("Non-local call to local provider is_const_fn");
if let Some(fn_like) = FnLikeNode::from_node(tcx.hir.get(node_id)) {
fn_like.constness() == hir::Constness::Const
} else {
false
}
}
fn is_promotable_const_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> bool {
tcx.is_const_fn(def_id) && match tcx.lookup_stability(def_id) {
Some(stab) => {
if cfg!(debug_assertions) && stab.promotable {
let sig = tcx.fn_sig(def_id);
assert_eq!(
sig.unsafety(),
hir::Unsafety::Normal,
"don't mark const unsafe fns as promotable",
// https://github.com/rust-lang/rust/pull/53851#issuecomment-418760682
);
}
stab.promotable
},
None => false,
}
}
*providers = Providers {
is_const_fn_raw,
is_promotable_const_fn,
..*providers
};
}
|
