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Auto merge of #76538 - fusion-engineering-forks:check-useless-unstable-trait-impl, r=lcnr

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Warn for #[unstable] on trait impls when it has no effect.

Earlier today I sent a PR with an `#[unstable]` attribute on a trait `impl`, but was informed that this attribute has no effect there. (comment: https://github.com/rust-lang/rust/pull/76525#issuecomment-689678895, issue: https://github.com/rust-lang/rust/issues/55436)

This PR adds a warning for this situation. Trait `impl` blocks with `#[unstable]` where both the type and the trait are stable will result in a warning:

```
warning: An `#[unstable]` annotation here has no effect. See issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information.
   --> library/std/src/panic.rs:235:1
    |
235 | #[unstable(feature = "integer_atomics", issue = "32976")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```

---

It detects three problems in the existing code:

1. A few `RefUnwindSafe` implementations for the atomic integer types in `library/std/src/panic.rs`. Example:
d92155bf6a/library/std/src/panic.rs (L235-L236)
2. An implementation of `Error` for `LayoutErr` in `library/std/srd/error.rs`:
d92155bf6a/library/std/src/error.rs (L392-L397)
3. `From` implementations for `Waker` and `RawWaker` in `library/alloc/src/task.rs`. Example:
d92155bf6a/library/alloc/src/task.rs (L36-L37)

Case 3 interesting: It has a bound with an `#[unstable]` trait (`W: Wake`), so appears to have much effect on stable code. It does however break similar blanket implementations. It would also have immediate effect if `Wake` was implemented for any stable type. (Which is not the case right now, but there are no warnings in place to prevent it.) Whether this case is a problem or not is not clear to me. If it isn't, adding a simple `c.visit_generics(..);` to this PR will stop the warning for this case.
This commit is contained in:
bors 2020-09-12 18:01:33 +00:00
commit 989190874f
7 changed files with 129 additions and 16 deletions
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73
compiler/rustc_passes/src/stability.rs
View file

@ -9,13 +9,14 @@ use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_INDEX, LOCAL_CRATE};
use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
use rustc_hir::{Generics, HirId, Item, StructField, Variant};
use rustc_hir::{Generics, HirId, Item, StructField, TraitRef, Ty, TyKind, Variant};
use rustc_middle::hir::map::Map;
use rustc_middle::middle::privacy::AccessLevels;
use rustc_middle::middle::stability::{DeprecationEntry, Index};
use rustc_middle::ty::query::Providers;
use rustc_middle::ty::TyCtxt;
use rustc_session::lint;
use rustc_session::lint::builtin::INEFFECTIVE_UNSTABLE_TRAIT_IMPL;
use rustc_session::parse::feature_err;
use rustc_session::Session;
use rustc_span::symbol::{sym, Symbol};
@ -538,7 +539,37 @@ impl 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 { of_trait: Some(ref t), items, .. } => {
hir::ItemKind::Impl { of_trait: Some(ref t), self_ty, items, .. } => {
if self.tcx.features().staged_api {
// If this impl block has an #[unstable] attribute, give an
// error if all involved types and traits are stable, because
// it will have no effect.
// See: https://github.com/rust-lang/rust/issues/55436
if let (Some(Stability { level: attr::Unstable { .. }, .. }), _) =
attr::find_stability(&self.tcx.sess, &item.attrs, item.span)
{
let mut c = CheckTraitImplStable { tcx: self.tcx, fully_stable: true };
c.visit_ty(self_ty);
c.visit_trait_ref(t);
if c.fully_stable {
let span = item
.attrs
.iter()
.find(|a| a.has_name(sym::unstable))
.map_or(item.span, |a| a.span);
self.tcx.struct_span_lint_hir(
INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
item.hir_id,
span,
|lint| lint
.build("an `#[unstable]` annotation here has no effect")
.note("see issue #55436 <https://github.com/rust-lang/rust/issues/55436> for more information")
.emit()
);
}
}
}
if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
for impl_item_ref in items {
let impl_item = self.tcx.hir().impl_item(impl_item_ref.id);
@ -598,6 +629,44 @@ impl Visitor<'tcx> for Checker<'tcx> {
}
}
struct CheckTraitImplStable<'tcx> {
tcx: TyCtxt<'tcx>,
fully_stable: bool,
}
impl Visitor<'tcx> for CheckTraitImplStable<'tcx> {
type Map = Map<'tcx>;
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
fn visit_path(&mut self, path: &'tcx hir::Path<'tcx>, _id: hir::HirId) {
if let Some(def_id) = path.res.opt_def_id() {
if let Some(stab) = self.tcx.lookup_stability(def_id) {
self.fully_stable &= stab.level.is_stable();
}
}
intravisit::walk_path(self, path)
}
fn visit_trait_ref(&mut self, t: &'tcx TraitRef<'tcx>) {
if let Res::Def(DefKind::Trait, trait_did) = t.path.res {
if let Some(stab) = self.tcx.lookup_stability(trait_did) {
self.fully_stable &= stab.level.is_stable();
}
}
intravisit::walk_trait_ref(self, t)
}
fn visit_ty(&mut self, t: &'tcx Ty<'tcx>) {
if let TyKind::Never = t.kind {
self.fully_stable = false;
}
intravisit::walk_ty(self, t)
}
}
/// Given the list of enabled features that were not language features (i.e., that
/// were expected to be library features), and the list of features used from
/// libraries, identify activated features that don't exist and error about them.

9
compiler/rustc_session/src/lint/builtin.rs
View file

@ -5,7 +5,7 @@
//! lints are all available in `rustc_lint::builtin`.
use crate::lint::FutureIncompatibleInfo;
use crate::{declare_lint, declare_lint_pass};
use crate::{declare_lint, declare_lint_pass, declare_tool_lint};
use rustc_span::edition::Edition;
use rustc_span::symbol::sym;
@ -555,6 +555,12 @@ declare_lint! {
};
}
declare_tool_lint! {
pub rustc::INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
Deny,
"detects `#[unstable]` on stable trait implementations for stable types"
}
declare_lint_pass! {
/// Does nothing as a lint pass, but registers some `Lint`s
/// that are used by other parts of the compiler.
@ -630,6 +636,7 @@ declare_lint_pass! {
INCOMPLETE_INCLUDE,
CENUM_IMPL_DROP_CAST,
CONST_EVALUATABLE_UNCHECKED,
INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
]
}