Auto merge of #114417 - chinedufn:fix-expect-unused-in-impl-block-rust-issue-114416, r=cjgillot

Fix multiple `expect` attribs in impl block

Closes #114416

compiler/rustc_passes/src/dead.rs

@@ -1,6 +1,7 @@
-// This implements the dead-code warning pass. It follows middle::reachable
-// closely. The idea is that all reachable symbols are live, codes called
-// from live codes are live, and everything else is dead.
+// This implements the dead-code warning pass.
+// All reachable symbols are live, code called from live code is live, code with certain lint
+// expectations such as `#[expect(unused)]` and `#[expect(dead_code)]` is live, and everything else
+// is dead.
 
 use hir::def_id::{LocalDefIdMap, LocalDefIdSet};
 use itertools::Itertools;
@@ -747,7 +748,7 @@ fn live_symbols_and_ignored_derived_traits(
     (symbol_visitor.live_symbols, symbol_visitor.ignored_derived_traits)
 }
 
-struct DeadVariant {
+struct DeadItem {
     def_id: LocalDefId,
     name: Symbol,
     level: lint::Level,
@@ -785,7 +786,13 @@ impl<'tcx> DeadVisitor<'tcx> {
         ShouldWarnAboutField::Yes(is_positional)
     }
 
-    fn warn_multiple_dead_codes(
+    // # Panics
+    // All `dead_codes` must have the same lint level, otherwise we will intentionally ICE.
+    // This is because we emit a multi-spanned lint using the lint level of the `dead_codes`'s
+    // first local def id.
+    // Prefer calling `Self.warn_dead_code` or `Self.warn_dead_code_grouped_by_lint_level`
+    // since those methods group by lint level before calling this method.
+    fn lint_at_single_level(
         &self,
         dead_codes: &[LocalDefId],
         participle: &str,
@@ -796,6 +803,15 @@ impl<'tcx> DeadVisitor<'tcx> {
             return;
         };
         let tcx = self.tcx;
+
+        let first_hir_id = tcx.hir().local_def_id_to_hir_id(first_id);
+        let first_lint_level = tcx.lint_level_at_node(lint::builtin::DEAD_CODE, first_hir_id).0;
+        assert!(dead_codes.iter().skip(1).all(|id| {
+            let hir_id = tcx.hir().local_def_id_to_hir_id(*id);
+            let level = tcx.lint_level_at_node(lint::builtin::DEAD_CODE, hir_id).0;
+            level == first_lint_level
+        }));
+
         let names: Vec<_> =
             dead_codes.iter().map(|&def_id| tcx.item_name(def_id.to_def_id())).collect();
         let spans: Vec<_> = dead_codes
@@ -876,31 +892,26 @@ impl<'tcx> DeadVisitor<'tcx> {
             }
         };
 
-        self.tcx.emit_spanned_lint(
-            lint,
-            tcx.hir().local_def_id_to_hir_id(first_id),
-            MultiSpan::from_spans(spans),
-            diag,
-        );
+        self.tcx.emit_spanned_lint(lint, first_hir_id, MultiSpan::from_spans(spans), diag);
     }
 
-    fn warn_dead_fields_and_variants(
+    fn warn_multiple(
         &self,
         def_id: LocalDefId,
         participle: &str,
-        dead_codes: Vec<DeadVariant>,
+        dead_codes: Vec<DeadItem>,
         is_positional: bool,
     ) {
         let mut dead_codes = dead_codes
             .iter()
             .filter(|v| !v.name.as_str().starts_with('_'))
-            .collect::<Vec<&DeadVariant>>();
+            .collect::<Vec<&DeadItem>>();
         if dead_codes.is_empty() {
             return;
         }
         dead_codes.sort_by_key(|v| v.level);
         for (_, group) in &dead_codes.into_iter().group_by(|v| v.level) {
-            self.warn_multiple_dead_codes(
+            self.lint_at_single_level(
                 &group.map(|v| v.def_id).collect::<Vec<_>>(),
                 participle,
                 Some(def_id),
@@ -910,7 +921,7 @@ impl<'tcx> DeadVisitor<'tcx> {
     }
 
     fn warn_dead_code(&mut self, id: LocalDefId, participle: &str) {
-        self.warn_multiple_dead_codes(&[id], participle, None, false);
+        self.lint_at_single_level(&[id], participle, None, false);
     }
 
     fn check_definition(&mut self, def_id: LocalDefId) {
@@ -954,17 +965,16 @@ fn check_mod_deathness(tcx: TyCtxt<'_>, module: LocalModDefId) {
         if let hir::ItemKind::Impl(impl_item) = tcx.hir().item(item).kind {
             let mut dead_items = Vec::new();
             for item in impl_item.items {
-                let did = item.id.owner_id.def_id;
-                if !visitor.is_live_code(did) {
-                    dead_items.push(did)
+                let def_id = item.id.owner_id.def_id;
+                if !visitor.is_live_code(def_id) {
+                    let name = tcx.item_name(def_id.to_def_id());
+                    let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
+                    let level = tcx.lint_level_at_node(lint::builtin::DEAD_CODE, hir_id).0;
+
+                    dead_items.push(DeadItem { def_id, name, level })
                 }
             }
-            visitor.warn_multiple_dead_codes(
-                &dead_items,
-                "used",
-                Some(item.owner_id.def_id),
-                false,
-            );
+            visitor.warn_multiple(item.owner_id.def_id, "used", dead_items, false);
         }
 
         if !live_symbols.contains(&item.owner_id.def_id) {
@@ -988,7 +998,7 @@ fn check_mod_deathness(tcx: TyCtxt<'_>, module: LocalModDefId) {
                     // Record to group diagnostics.
                     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
                     let level = tcx.lint_level_at_node(lint::builtin::DEAD_CODE, hir_id).0;
-                    dead_variants.push(DeadVariant { def_id, name: variant.name, level });
+                    dead_variants.push(DeadItem { def_id, name: variant.name, level });
                     continue;
                 }
 
@@ -1013,21 +1023,16 @@ fn check_mod_deathness(tcx: TyCtxt<'_>, module: LocalModDefId) {
                                     hir_id,
                                 )
                                 .0;
-                            Some(DeadVariant { def_id, name: field.name, level })
+                            Some(DeadItem { def_id, name: field.name, level })
                         } else {
                             None
                         }
                     })
                     .collect();
-                visitor.warn_dead_fields_and_variants(def_id, "read", dead_fields, is_positional)
+                visitor.warn_multiple(def_id, "read", dead_fields, is_positional);
             }
 
-            visitor.warn_dead_fields_and_variants(
-                item.owner_id.def_id,
-                "constructed",
-                dead_variants,
-                false,
-            );
+            visitor.warn_multiple(item.owner_id.def_id, "constructed", dead_variants, false);
         }
     }
 

tests/ui/lint/rfc-2383-lint-reason/expect_unused_inside_impl_block.rs

@@ -0,0 +1,30 @@
+// check-pass
+// incremental
+
+#![feature(lint_reasons)]
+#![warn(unused)]
+
+struct OneUnused;
+struct TwoUnused;
+
+impl OneUnused {
+    #[expect(unused)]
+    fn unused() {}
+}
+
+impl TwoUnused {
+    #[expect(unused)]
+    fn unused1(){}
+
+    // This unused method has `#[expect(unused)]`, so the compiler should not emit a warning.
+    // This ui test was added after a regression in the compiler where it did not recognize multiple
+    // `#[expect(unused)]` annotations inside of impl blocks.
+    // issue 114416
+    #[expect(unused)]
+    fn unused2(){}
+}
+
+fn main() {
+    let _ = OneUnused;
+    let _ = TwoUnused;
+}