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Rollup merge of #132541 - RalfJung:const-stable-extern-crate, r=compiler-errors

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Proper support for cross-crate recursive const stability checks

~~Stacked on top of https://github.com/rust-lang/rust/pull/132492; only the last three commits are new.~~

In a crate without `staged_api` but with `-Zforce-unstable-if-unmarked`, we now subject all functions marked with `#[rustc_const_stable_indirect]` to recursive const stability checks. We require an opt-in so that by default, a crate can be built with `-Zforce-unstable-if-unmarked` and use nightly features as usual. This property is recorded in the crate metadata so when a `staged_api` crate calls such a function, it sees the `#[rustc_const_stable_indirect]` and allows it to be exposed on stable. This, finally, will let us expose `const fn` from hashbrown on stable.

The second commit makes const stability more like regular stability: via `check_missing_const_stability`, we ensure that all publicly reachable functions have a const stability attribute -- both in  `staged_api` crates and `-Zforce-unstable-if-unmarked` crates. To achieve this, we move around the stability computation so that const stability is computed after regular stability is done. This lets us access the final result of the regular stability computation, which we use so that `const fn` can inherit the regular stability (but only if that is "unstable"). Fortunately, this lets us get rid of an `Option` in `ConstStability`.

This is the last PR that I have planned in this series.

r? `@compiler-errors`
This commit is contained in:
Matthias Krüger 2024-11-12 18:11:04 +01:00 • committed by GitHub
commit 4a699fc475
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18 changed files with 343 additions and 208 deletions
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199
compiler/rustc_passes/src/stability.rs
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@ -16,7 +16,7 @@ use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::{CRATE_DEF_ID, LOCAL_CRATE, LocalDefId, LocalModDefId};
use rustc_hir::hir_id::CRATE_HIR_ID;
use rustc_hir::intravisit::{self, Visitor};
use rustc_hir::{Constness, FieldDef, Item, ItemKind, TraitRef, Ty, TyKind, Variant};
use rustc_hir::{FieldDef, Item, ItemKind, TraitRef, Ty, TyKind, Variant};
use rustc_middle::hir::nested_filter;
use rustc_middle::middle::lib_features::{FeatureStability, LibFeatures};
use rustc_middle::middle::privacy::EffectiveVisibilities;
@ -149,6 +149,11 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
if let Some(stab) = self.parent_stab {
if inherit_deprecation.yes() && stab.is_unstable() {
self.index.stab_map.insert(def_id, stab);
if fn_sig.is_some_and(|s| s.header.is_const()) {
let const_stab =
attr::unmarked_crate_const_stab(self.tcx.sess, attrs, stab);
self.index.const_stab_map.insert(def_id, const_stab);
}
}
}
@ -161,68 +166,11 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
return;
}
// # Regular and body stability
let stab = attr::find_stability(self.tcx.sess, attrs, item_sp);
let const_stab = attr::find_const_stability(
self.tcx.sess,
attrs,
item_sp,
fn_sig.is_some_and(|s| s.header.is_const()),
);
let body_stab = attr::find_body_stability(self.tcx.sess, attrs);
// If the current node is a function with const stability attributes (directly given or
// implied), check if the function/method is const or the parent impl block is const.
if let Some(fn_sig) = fn_sig
&& !fn_sig.header.is_const()
&& const_stab.is_some()
{
self.tcx.dcx().emit_err(errors::MissingConstErr { fn_sig_span: fn_sig.span });
}
// If this is marked const *stable*, it must also be regular-stable.
if let Some((const_stab, const_span)) = const_stab
&& let Some(fn_sig) = fn_sig
&& const_stab.is_const_stable()
&& !stab.is_some_and(|(s, _)| s.is_stable())
{
self.tcx
.dcx()
.emit_err(errors::ConstStableNotStable { fn_sig_span: fn_sig.span, const_span });
}
// Stable *language* features shouldn't be used as unstable library features.
// (Not doing this for stable library features is checked by tidy.)
if let Some((
ConstStability { level: Unstable { .. }, feature: Some(feature), .. },
const_span,
)) = const_stab
{
if ACCEPTED_LANG_FEATURES.iter().find(|f| f.name == feature).is_some() {
self.tcx.dcx().emit_err(errors::UnstableAttrForAlreadyStableFeature {
span: const_span,
item_sp,
});
}
}
let const_stab = const_stab.map(|(const_stab, _span)| {
self.index.const_stab_map.insert(def_id, const_stab);
const_stab
});
// `impl const Trait for Type` items forward their const stability to their
// immediate children.
// FIXME(const_trait_impl): how is this supposed to interact with `#[rustc_const_stable_indirect]`?
// Currently, once that is set, we do not inherit anything from the parent any more.
if const_stab.is_none() {
debug!("annotate: const_stab not found, parent = {:?}", self.parent_const_stab);
if let Some(parent) = self.parent_const_stab {
if parent.is_const_unstable() {
self.index.const_stab_map.insert(def_id, parent);
}
}
}
if let Some((depr, span)) = &depr
&& depr.is_since_rustc_version()
&& stab.is_none()
@ -289,15 +237,6 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
self.index.implications.insert(implied_by, feature);
}
if let Some(ConstStability {
level: Unstable { implied_by: Some(implied_by), .. },
feature,
..
}) = const_stab
{
self.index.implications.insert(implied_by, feature.unwrap());
}
self.index.stab_map.insert(def_id, stab);
stab
});
@ -311,6 +250,91 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
}
}
let final_stab = self.index.stab_map.get(&def_id);
// # Const stability
let const_stab = attr::find_const_stability(self.tcx.sess, attrs, item_sp);
// If the current node is a function with const stability attributes (directly given or
// implied), check if the function/method is const.
if let Some(fn_sig) = fn_sig
&& !fn_sig.header.is_const()
&& const_stab.is_some()
{
self.tcx.dcx().emit_err(errors::MissingConstErr { fn_sig_span: fn_sig.span });
}
// If this is marked const *stable*, it must also be regular-stable.
if let Some((const_stab, const_span)) = const_stab
&& let Some(fn_sig) = fn_sig
&& const_stab.is_const_stable()
&& !stab.is_some_and(|s| s.is_stable())
{
self.tcx
.dcx()
.emit_err(errors::ConstStableNotStable { fn_sig_span: fn_sig.span, const_span });
}
// Stable *language* features shouldn't be used as unstable library features.
// (Not doing this for stable library features is checked by tidy.)
if let Some((ConstStability { level: Unstable { .. }, feature, .. }, const_span)) =
const_stab
{
if ACCEPTED_LANG_FEATURES.iter().find(|f| f.name == feature).is_some() {
self.tcx.dcx().emit_err(errors::UnstableAttrForAlreadyStableFeature {
span: const_span,
item_sp,
});
}
}
// After checking the immediate attributes, get rid of the span and compute implied
// const stability: inherit feature gate from regular stability.
let mut const_stab = const_stab.map(|(stab, _span)| stab);
// If this is a const fn but not annotated with stability markers, see if we can inherit regular stability.
if fn_sig.is_some_and(|s| s.header.is_const()) && const_stab.is_none() &&
// We only ever inherit unstable features.
let Some(inherit_regular_stab) =
final_stab.filter(|s| s.is_unstable())
{
const_stab = Some(ConstStability {
// We subject these implicitly-const functions to recursive const stability.
const_stable_indirect: true,
promotable: false,
level: inherit_regular_stab.level,
feature: inherit_regular_stab.feature,
});
}
// Now that everything is computed, insert it into the table.
const_stab.inspect(|const_stab| {
self.index.const_stab_map.insert(def_id, *const_stab);
});
if let Some(ConstStability {
level: Unstable { implied_by: Some(implied_by), .. },
feature,
..
}) = const_stab
{
self.index.implications.insert(implied_by, feature);
}
// `impl const Trait for Type` items forward their const stability to their
// immediate children.
// FIXME(const_trait_impl): how is this supposed to interact with `#[rustc_const_stable_indirect]`?
// Currently, once that is set, we do not inherit anything from the parent any more.
if const_stab.is_none() {
debug!("annotate: const_stab not found, parent = {:?}", self.parent_const_stab);
if let Some(parent) = self.parent_const_stab {
if parent.is_const_unstable() {
self.index.const_stab_map.insert(def_id, parent);
}
}
}
self.recurse_with_stability_attrs(
depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
stab,
@ -565,13 +589,7 @@ impl<'tcx> MissingStabilityAnnotations<'tcx> {
}
}
fn check_missing_or_wrong_const_stability(&self, def_id: LocalDefId, span: Span) {
// The visitor runs for "unstable-if-unmarked" crates, but we don't yet support
// that on the const side.
if !self.tcx.features().staged_api() {
return;
}
fn check_missing_const_stability(&self, def_id: LocalDefId, span: Span) {
// if the const impl is derived using the `derive_const` attribute,
// then it would be "stable" at least for the impl.
// We gate usages of it using `feature(const_trait_impl)` anyways
@ -582,12 +600,12 @@ impl<'tcx> MissingStabilityAnnotations<'tcx> {
let is_const = self.tcx.is_const_fn(def_id.to_def_id())
|| self.tcx.is_const_trait_impl(def_id.to_def_id());
let is_stable =
self.tcx.lookup_stability(def_id).is_some_and(|stability| stability.level.is_stable());
let missing_const_stability_attribute =
self.tcx.lookup_const_stability(def_id).is_none_or(|s| s.feature.is_none());
if is_const && is_stable && missing_const_stability_attribute {
// Reachable const fn must have a stability attribute.
if is_const
&& self.effective_visibilities.is_reachable(def_id)
&& self.tcx.lookup_const_stability(def_id).is_none()
{
let descr = self.tcx.def_descr(def_id.to_def_id());
self.tcx.dcx().emit_err(errors::MissingConstStabAttr { span, descr });
}
@ -615,7 +633,7 @@ impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
}
// Ensure stable `const fn` have a const stability attribute.
self.check_missing_or_wrong_const_stability(i.owner_id.def_id, i.span);
self.check_missing_const_stability(i.owner_id.def_id, i.span);
intravisit::walk_item(self, i)
}
@ -629,7 +647,7 @@ impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
let impl_def_id = self.tcx.hir().get_parent_item(ii.hir_id());
if self.tcx.impl_trait_ref(impl_def_id).is_none() {
self.check_missing_stability(ii.owner_id.def_id, ii.span);
self.check_missing_or_wrong_const_stability(ii.owner_id.def_id, ii.span);
self.check_missing_const_stability(ii.owner_id.def_id, ii.span);
}
intravisit::walk_impl_item(self, ii);
}
@ -760,23 +778,12 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
// For implementations of traits, check the stability of each item
// individually as it's possible to have a stable trait with unstable
// items.
hir::ItemKind::Impl(hir::Impl {
constness,
of_trait: Some(ref t),
self_ty,
items,
..
}) => {
hir::ItemKind::Impl(hir::Impl { of_trait: Some(ref t), self_ty, items, .. }) => {
let features = self.tcx.features();
if features.staged_api() {
let attrs = self.tcx.hir().attrs(item.hir_id());
let stab = attr::find_stability(self.tcx.sess, attrs, item.span);
let const_stab = attr::find_const_stability(
self.tcx.sess,
attrs,
item.span,
matches!(constness, Constness::Const),
);
let const_stab = attr::find_const_stability(self.tcx.sess, attrs, item.span);
// If this impl block has an #[unstable] attribute, give an
// error if all involved types and traits are stable, because