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Rollup merge of #95354 - dtolnay:rustc_const_stable, r=lcnr

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Handle rustc_const_stable attribute in library feature collector

The library feature collector in [compiler/rustc_passes/src/lib_features.rs](551b4fa395/compiler/rustc_passes/src/lib_features.rs) has only been looking at `#[stable(…)]`, `#[unstable(…)]`, and `#[rustc_const_unstable(…)]` attributes, while ignoring `#[rustc_const_stable(…)]`. The consequences of this were:

- When any const feature got stabilized (changing one or more `rustc_const_unstable` to `rustc_const_stable`), users who had previously enabled that unstable feature using `#![feature(…)]` would get told "unknown feature", rather than rustc's nicer "the feature … has been stable since … and no longer requires an attribute to enable".

    This can be seen in the way that https://github.com/rust-lang/rust/pull/93957#issuecomment-1079794660 failed after rebase:

    ```console
    error[E0635]: unknown feature `const_ptr_offset`
      --> $DIR/offset_from_ub.rs:1:35
       |
    LL | #![feature(const_ptr_offset_from, const_ptr_offset)]
       |                                   ^^^^^^^^^^^^^^^^
    ```

- We weren't enforcing that a particular feature is either stable everywhere or unstable everywhere, and that a feature that has been stabilized has the same stabilization version everywhere, both of which we enforce for the other stability attributes.

This PR updates the library feature collector to handle `rustc_const_stable`, and fixes places in the standard library and test suite where `rustc_const_stable` was being used in a way that does not meet the rules for a stability attribute.
This commit is contained in:
Dylan DPC 2022-04-02 03:34:21 +02:00 • committed by GitHub
commit d7a24003d8
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21 changed files with 69 additions and 68 deletions
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11
compiler/rustc_passes/src/lib_features.rs
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@ -29,10 +29,11 @@ impl<'tcx> LibFeatureCollector<'tcx> {
}
fn extract(&self, attr: &Attribute) -> Option<(Symbol, Option<Symbol>, Span)> {
let stab_attrs = [sym::stable, sym::unstable, sym::rustc_const_unstable];
let stab_attrs =
[sym::stable, sym::unstable, sym::rustc_const_stable, sym::rustc_const_unstable];
// Find a stability attribute (i.e., `#[stable (..)]`, `#[unstable (..)]`,
// `#[rustc_const_unstable (..)]`).
// Find a stability attribute: one of #[stable(…)], #[unstable(…)],
// #[rustc_const_stable(…)], or #[rustc_const_unstable(…)].
if let Some(stab_attr) = stab_attrs.iter().find(|stab_attr| attr.has_name(**stab_attr)) {
let meta_kind = attr.meta_kind();
if let Some(MetaItemKind::List(ref metas)) = meta_kind {
@ -52,7 +53,9 @@ impl<'tcx> LibFeatureCollector<'tcx> {
// This additional check for stability is to make sure we
// don't emit additional, irrelevant errors for malformed
// attributes.
if *stab_attr != sym::stable || since.is_some() {
let is_unstable =
matches!(*stab_attr, sym::unstable | sym::rustc_const_unstable);
if since.is_some() || is_unstable {
return Some((feature, since, attr.span));
}
}