From eed7d10b5cd724a55c5451cd9adafa00828680e0 Mon Sep 17 00:00:00 2001
From: Raghavender Singh <itsraghavchouhan23@gmail.com>
Date: Sat, 11 Apr 2026 14:16:11 +0530
Subject: [PATCH] Fix ICE when using attributes on delegation items

Delegation items are skipped by `hir_walk_toplevel_module` (via
`visit_if_delayed`), so they were never added to `delayed_lint_items`.
This caused a debug assertion failure in `emit_ast_lowering_delayed_lints`
when an attribute like `#[deprecated]` generated a delayed lint on the item.

The FIXME in `ItemCollector::new` already noted this gap.
---
 compiler/rustc_middle/src/hir/map.rs        |  5 ++++-
 tests/ui/delegation/ice-issue-155127.rs     | 17 +++++++++++++++++
 tests/ui/delegation/ice-issue-155127.stderr | 12 ++++++++++++
 3 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/delegation/ice-issue-155127.rs
 create mode 100644 tests/ui/delegation/ice-issue-155127.stderr

diff --git a/compiler/rustc_middle/src/hir/map.rs b/compiler/rustc_middle/src/hir/map.rs
index 450b9d6c6bbc6..65c8867424d80 100644
--- a/compiler/rustc_middle/src/hir/map.rs
+++ b/compiler/rustc_middle/src/hir/map.rs
@@ -1335,7 +1335,7 @@ impl<'tcx> ItemCollector<'tcx> {
             let delayed_kinds =
                 krate.delayed_ids.iter().copied().map(|id| (id, krate.owners[id].expect_delayed()));
 
-            // FIXME(fn_delegation): need to add delayed lints, eiis
+            // FIXME(fn_delegation): need to add eiis
             for (def_id, kind) in delayed_kinds {
                 let owner_id = OwnerId { def_id };
 
@@ -1350,6 +1350,9 @@ impl<'tcx> ItemCollector<'tcx> {
                 };
 
                 collector.body_owners.push(def_id);
+                // Delegation items are skipped by the HIR walk (see `visit_if_delayed`),
+                // so we have to account for their delayed lints manually.
+                collector.delayed_lint_items.push(owner_id);
             }
         }
 
diff --git a/tests/ui/delegation/ice-issue-155127.rs b/tests/ui/delegation/ice-issue-155127.rs
new file mode 100644
index 0000000000000..f23170fa45063
--- /dev/null
+++ b/tests/ui/delegation/ice-issue-155127.rs
@@ -0,0 +1,17 @@
+// https://github.com/rust-lang/rust/issues/155127
+
+#![feature(fn_delegation)]
+#![allow(incomplete_features)]
+
+struct S;
+
+fn foo() {}
+
+impl S {
+    #[deprecated]
+    //~^ ERROR `#[deprecated]` attribute cannot be used on delegations
+    //~| WARN this was previously accepted by the compiler but is being phased out
+    reuse foo;
+}
+
+fn main() {}
diff --git a/tests/ui/delegation/ice-issue-155127.stderr b/tests/ui/delegation/ice-issue-155127.stderr
new file mode 100644
index 0000000000000..a743c3e92f0c8
--- /dev/null
+++ b/tests/ui/delegation/ice-issue-155127.stderr
@@ -0,0 +1,12 @@
+error: `#[deprecated]` attribute cannot be used on delegations
+  --> $DIR/ice-issue-155127.rs:11:5
+   |
+LL |     #[deprecated]
+   |     ^^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = help: `#[deprecated]` can be applied to associated consts, associated types, constants, crates, data types, enum variants, foreign statics, functions, inherent impl blocks, macro defs, modules, statics, struct fields, traits, type aliases, and use statements
+   = note: `#[deny(useless_deprecated)]` on by default
+
+error: aborting due to 1 previous error
+