rust-lang · bors · Sep 9, 2024 · Sep 6, 2024 · Sep 6, 2024
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -1186,3 +1186,11 @@ pub static BUILTIN_ATTRIBUTE_MAP: LazyLock<FxHashMap<Symbol, &BuiltinAttribute>>
         }
         map
     });
+
+pub fn is_stable_diagnostic_attribute(sym: Symbol, features: &Features) -> bool {
+    match sym {
+        sym::on_unimplemented => true,
+        sym::do_not_recommend => features.do_not_recommend,
+        _ => false,
+    }
+}
diff --git a/compiler/rustc_feature/src/lib.rs b/compiler/rustc_feature/src/lib.rs
@@ -130,8 +130,9 @@ pub fn find_feature_issue(feature: Symbol, issue: GateIssue) -> Option<NonZero<u
 pub use accepted::ACCEPTED_FEATURES;
 pub use builtin_attrs::{
     deprecated_attributes, encode_cross_crate, find_gated_cfg, is_builtin_attr_name,
-    is_valid_for_get_attr, AttributeDuplicates, AttributeGate, AttributeSafety, AttributeTemplate,
-    AttributeType, BuiltinAttribute, GatedCfg, BUILTIN_ATTRIBUTES, BUILTIN_ATTRIBUTE_MAP,
+    is_stable_diagnostic_attribute, is_valid_for_get_attr, AttributeDuplicates, AttributeGate,
+    AttributeSafety, AttributeTemplate, AttributeType, BuiltinAttribute, GatedCfg,
+    BUILTIN_ATTRIBUTES, BUILTIN_ATTRIBUTE_MAP,
 };
 pub use removed::REMOVED_FEATURES;
 pub use unstable::{Features, INCOMPATIBLE_FEATURES, UNSTABLE_FEATURES};
diff --git a/compiler/rustc_hir_analysis/src/collect.rs b/compiler/rustc_hir_analysis/src/collect.rs
@@ -1698,8 +1698,6 @@ fn impl_trait_header(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Option<ty::ImplTrai
             trait_ref: ty::EarlyBinder::bind(trait_ref),
             safety: impl_.safety,
             polarity: polarity_of_impl(tcx, def_id, impl_, item.span),
-            do_not_recommend: tcx.features().do_not_recommend
-                && tcx.has_attrs_with_path(def_id, &[sym::diagnostic, sym::do_not_recommend]),
         }
     })
 }

diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -9,6 +9,7 @@ use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_data_structures::memmap::{Mmap, MmapMut};
 use rustc_data_structures::sync::{join, par_for_each_in, Lrc};
 use rustc_data_structures::temp_dir::MaybeTempDir;
+use rustc_feature::Features;
 use rustc_hir as hir;
 use rustc_hir::def_id::{LocalDefId, LocalDefIdSet, CRATE_DEF_ID, CRATE_DEF_INDEX, LOCAL_CRATE};
 use rustc_hir::definitions::DefPathData;
@@ -797,9 +798,10 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
     }
 }
 
-struct AnalyzeAttrState {
+struct AnalyzeAttrState<'a> {
     is_exported: bool,
     is_doc_hidden: bool,
+    features: &'a Features,
 }
 
 /// Returns whether an attribute needs to be recorded in metadata, that is, if it's usable and
@@ -812,7 +814,7 @@ struct AnalyzeAttrState {
 /// visibility: this is a piece of data that can be computed once per defid, and not once per
 /// attribute. Some attributes would only be usable downstream if they are public.
 #[inline]
-fn analyze_attr(attr: &Attribute, state: &mut AnalyzeAttrState) -> bool {
+fn analyze_attr(attr: &Attribute, state: &mut AnalyzeAttrState<'_>) -> bool {
     let mut should_encode = false;
     if !rustc_feature::encode_cross_crate(attr.name_or_empty()) {
         // Attributes not marked encode-cross-crate don't need to be encoded for downstream crates.
@@ -837,6 +839,9 @@ fn analyze_attr(attr: &Attribute, state: &mut AnalyzeAttrState) -> bool {
                 }
             }
         }
+    } else if attr.path().starts_with(&[sym::diagnostic]) && attr.path().len() == 2 {
+        should_encode =
+            rustc_feature::is_stable_diagnostic_attribute(attr.path()[1], state.features);
     } else {
         should_encode = true;
     }
@@ -1343,6 +1348,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         let mut state = AnalyzeAttrState {
             is_exported: tcx.effective_visibilities(()).is_exported(def_id),
             is_doc_hidden: false,
+            features: &tcx.features(),
         };
         let attr_iter = tcx
             .hir()

diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
@@ -3183,8 +3183,7 @@ impl<'tcx> TyCtxt<'tcx> {
 
     /// Whether this is a trait implementation that has `#[diagnostic::do_not_recommend]`
     pub fn do_not_recommend_impl(self, def_id: DefId) -> bool {
-        matches!(self.def_kind(def_id), DefKind::Impl { of_trait: true })
-            && self.impl_trait_header(def_id).is_some_and(|header| header.do_not_recommend)
+        self.get_diagnostic_attr(def_id, sym::do_not_recommend).is_some()
     }
 }
 

diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
@@ -263,7 +263,6 @@ pub struct ImplTraitHeader<'tcx> {
     pub trait_ref: ty::EarlyBinder<'tcx, ty::TraitRef<'tcx>>,
     pub polarity: ImplPolarity,
     pub safety: hir::Safety,
-    pub do_not_recommend: bool,
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug, TypeFoldable, TypeVisitable)]
@@ -1797,6 +1796,37 @@ impl<'tcx> TyCtxt<'tcx> {
         }
     }
 
+    /// Get an attribute from the diagnostic attribute namespace
+    ///
+    /// This function requests an attribute with the following structure:
+    ///
+    /// `#[diagnostic::$attr]`
+    ///
+    /// This function performs feature checking, so if an attribute is returned
+    /// it can be used by the consumer
+    pub fn get_diagnostic_attr(
+        self,
+        did: impl Into<DefId>,
+        attr: Symbol,
+    ) -> Option<&'tcx ast::Attribute> {
+        let did: DefId = did.into();
+        if did.as_local().is_some() {
+            // it's a crate local item, we need to check feature flags
+            if rustc_feature::is_stable_diagnostic_attribute(attr, self.features()) {
+                self.get_attrs_by_path(did, &[sym::diagnostic, sym::do_not_recommend]).next()
+            } else {
+                None
+            }
+        } else {
+            // we filter out unstable diagnostic attributes before
+            // encoding attributes
+            debug_assert!(rustc_feature::encode_cross_crate(attr));
+            self.item_attrs(did)
+                .iter()
+                .find(|a| matches!(a.path().as_ref(), [sym::diagnostic, a] if *a == attr))
+        }
+    }
+
     pub fn get_attrs_by_path<'attr>(
         self,
         did: DefId,