Auto merge of #131628 - matthiaskrgr:rollup-imbojxz, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #128784 (Check ABI target compatibility for function pointers)
 - #130965 (make `Step` doc-comments more clear)
 - #131239 (Don't assume traits used as type are trait objs in 2021 edition)
 - #131277 (Handle `clippy` cases of `rustc::potential_query_instability` lint)
 - #131503 (More clearly document Stdin::read_line)
 - #131567 (Emit an error for unstable attributes that reference already stable features)
 - #131599 (Shallowly match opaque key in storage)
 - #131617 (remove const_cow_is_borrowed feature gate)

Failed merges:

 - #131616 (merge const_ipv4 / const_ipv6 feature gate into 'ip' feature gate)

r? `@ghost`
`@rustbot` modify labels: rollup

2 files changed, 27 insertions, 0 deletions

diff --git a/compiler/rustc_passes/src/errors.rs b/compiler/rustc_passes/src/errors.rs
index 4f00c90fa3b..f9186d3089a 100644
--- a/compiler/rustc_passes/src/errors.rs
+++ b/compiler/rustc_passes/src/errors.rs
@@ -1481,6 +1481,17 @@ pub(crate) struct CannotStabilizeDeprecated {
 }
 
 #[derive(Diagnostic)]
+#[diag(passes_unstable_attr_for_already_stable_feature)]
+pub(crate) struct UnstableAttrForAlreadyStableFeature {
+    #[primary_span]
+    #[label]
+    #[help]
+    pub span: Span,
+    #[label(passes_item)]
+    pub item_sp: Span,
+}
+
+#[derive(Diagnostic)]
 #[diag(passes_missing_stability_attr)]
 pub(crate) struct MissingStabilityAttr<'a> {
     #[primary_span]
diff --git a/compiler/rustc_passes/src/stability.rs b/compiler/rustc_passes/src/stability.rs
index 46b67e930d5..751c87a9fe5 100644
--- a/compiler/rustc_passes/src/stability.rs
+++ b/compiler/rustc_passes/src/stability.rs
@@ -10,6 +10,7 @@ use rustc_attr::{
 };
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::unord::{ExtendUnord, UnordMap, UnordSet};
+use rustc_feature::ACCEPTED_FEATURES;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{CRATE_DEF_ID, LOCAL_CRATE, LocalDefId, LocalModDefId};
@@ -246,12 +247,27 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
                 }
             }
 
+            if let Stability { level: Unstable { .. }, feature } = stab {
+                if ACCEPTED_FEATURES.iter().find(|f| f.name == feature).is_some() {
+                    self.tcx
+                        .dcx()
+                        .emit_err(errors::UnstableAttrForAlreadyStableFeature { span, item_sp });
+                }
+            }
             if let Stability { level: Unstable { implied_by: Some(implied_by), .. }, feature } =
                 stab
             {
                 self.index.implications.insert(implied_by, feature);
             }
 
+            if let Some(ConstStability { level: Unstable { .. }, feature, .. }) = const_stab {
+                if ACCEPTED_FEATURES.iter().find(|f| f.name == feature).is_some() {
+                    self.tcx.dcx().emit_err(errors::UnstableAttrForAlreadyStableFeature {
+                        span: const_span.unwrap(), // If const_stab contains Some(..), same is true for const_span
+                        item_sp,
+                    });
+                }
+            }
             if let Some(ConstStability {
                 level: Unstable { implied_by: Some(implied_by), .. },
                 feature,