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Implement MIR const trait stability checks

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This commit is contained in:
Deadbeef
2025-01-25 21:38:15 +08:00
parent 0df0662ee0
commit 4aaf467e26
9 changed files with 232 additions and 120 deletions
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20
compiler/rustc_const_eval/src/check_consts/mod.rs
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@@ -56,7 +56,7 @@ impl<'mir, 'tcx> ConstCx<'mir, 'tcx> {
self.const_kind == Some(hir::ConstContext::ConstFn)
&& (self.tcx.features().staged_api()
|| self.tcx.sess.opts.unstable_opts.force_unstable_if_unmarked)
&& is_safe_to_expose_on_stable_const_fn(self.tcx, self.def_id().to_def_id())
&& is_fn_or_trait_safe_to_expose_on_stable(self.tcx, self.def_id().to_def_id())
}
fn is_async(&self) -> bool {
@@ -84,28 +84,14 @@ pub fn rustc_allow_const_fn_unstable(
attr::rustc_allow_const_fn_unstable(tcx.sess, attrs).any(|name| name == feature_gate)
}
/// Returns `true` if the given `const fn` is "safe to expose on stable".
///
/// Panics if the given `DefId` does not refer to a `const fn`.
/// Returns `true` if the given `def_id` (trait or function) is "safe to expose on stable".
///
/// This is relevant within a `staged_api` crate. Unlike with normal features, the use of unstable
/// const features *recursively* taints the functions that use them. This is to avoid accidentally
/// exposing e.g. the implementation of an unstable const intrinsic on stable. So we partition the
/// world into two functions: those that are safe to expose on stable (and hence may not use
/// unstable features, not even recursively), and those that are not.
pub fn is_safe_to_expose_on_stable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
// A default body in a `#[const_trait]` is not const-stable because const trait fns currently
// cannot be const-stable. These functions can't be called from anything stable, so we shouldn't
// restrict them to only call const-stable functions.
if tcx.is_const_default_method(def_id) {
// FIXME(const_trait_impl): we have to eventually allow some of these if these things can ever be stable.
// They should probably behave like regular `const fn` for that...
return false;
}
// Const-stability is only relevant for `const fn`.
assert!(tcx.is_const_fn(def_id));
pub fn is_fn_or_trait_safe_to_expose_on_stable(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
match tcx.lookup_const_stability(def_id) {
None => {
// In a `staged_api` crate, we do enforce recursive const stability for all unmarked