From 8f21bfc774b63389a1359b286cf051a46039ae0f Mon Sep 17 00:00:00 2001
From: Gurinder Singh <frederick.the.fool@gmail.com>
Date: Mon, 29 Jul 2024 08:00:58 +0530
Subject: [PATCH] Consider const fn with `&self` while checking liveness

---
 compiler/rustc_passes/src/dead.rs             |  5 ++--
 ...false-positive-builder-with-self-128272.rs | 25 +++++++++++++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)
 create mode 100644 tests/ui/lint/dead-code/false-positive-builder-with-self-128272.rs

diff --git a/compiler/rustc_passes/src/dead.rs b/compiler/rustc_passes/src/dead.rs
index 239bc8e7accfc..bbf38a478f9f0 100644
--- a/compiler/rustc_passes/src/dead.rs
+++ b/compiler/rustc_passes/src/dead.rs
@@ -833,8 +833,9 @@ fn check_item<'tcx>(
                 if let Some(fn_sig) =
                     tcx.hir().fn_sig_by_hir_id(tcx.local_def_id_to_hir_id(local_def_id))
                 {
-                    may_construct_self =
-                        matches!(fn_sig.decl.implicit_self, hir::ImplicitSelfKind::None);
+                    may_construct_self = matches!(fn_sig.decl.implicit_self, hir::ImplicitSelfKind::None)
+                            // Also considering const functions with `&self` to fix #128272
+                            || fn_sig.header.is_const() && matches!(fn_sig.decl.implicit_self, hir::ImplicitSelfKind::RefImm);
                 }
 
                 // for trait impl blocks,
diff --git a/tests/ui/lint/dead-code/false-positive-builder-with-self-128272.rs b/tests/ui/lint/dead-code/false-positive-builder-with-self-128272.rs
new file mode 100644
index 0000000000000..bcef76d555e70
--- /dev/null
+++ b/tests/ui/lint/dead-code/false-positive-builder-with-self-128272.rs
@@ -0,0 +1,25 @@
+// Regression test for #128272
+// Tests that we do not consider a struct
+// dead code if it is constructed in a
+// const function taking `&self`
+
+
+//@ check-pass
+
+#![deny(dead_code)]
+
+pub struct Foo {
+    _f: i32
+}
+
+impl Foo {
+    // This function constructs Foo but in #128272
+    // the compiler warned that Foo is never constructed
+    pub const fn new(&self) -> Foo {
+        Foo { _f: 5 }
+    }
+}
+
+fn main() {
+    static _X: Foo = _X.new();
+}