From 2169c1630ca9262a1b01a5ea2fdc8468f39ec841 Mon Sep 17 00:00:00 2001
From: durationextender <durationextender@gmail.com>
Date: Fri, 5 Jun 2026 17:46:50 +0200
Subject: [PATCH] fixes issue 17162 false positive for never type impls

---
 clippy_lints/src/unused_async.rs        | 20 ++++++++++++++------
 tests/ui/unused_async_trait_impl.fixed  | 12 ++++++++++++
 tests/ui/unused_async_trait_impl.rs     | 11 +++++++++++
 tests/ui/unused_async_trait_impl.stderr | 10 +++++-----
 4 files changed, 42 insertions(+), 11 deletions(-)

diff --git a/clippy_lints/src/unused_async.rs b/clippy_lints/src/unused_async.rs
index 456b98e6459d..b351fa084aa8 100644
--- a/clippy_lints/src/unused_async.rs
+++ b/clippy_lints/src/unused_async.rs
@@ -257,13 +257,21 @@ impl<'tcx> LateLintPass<'tcx> for UnusedAsync {
             visitor.visit_nested_body(body_id);
 
             if !visitor.found_await
-                && let Some(builtin_crate) = clippy_utils::std_or_core(cx)
-                && let Some(inner) = unpack_async_fn_body(cx, body)
-                // Find the tail expression contained in the async fn (if any),
-                // which will be wrapped in std::future::ready.
-                && let ExprKind::Block(block, _) = inner.kind
-                && let Some(tail_expr) = block.expr
+                    && let Some(builtin_crate) = clippy_utils::std_or_core(cx)
+                    && let Some(inner) = unpack_async_fn_body(cx, body)
+                    // Find the tail expression contained in the async fn (if any),
+                    // which will be wrapped in std::future::ready.
+                    && let ExprKind::Block(block, _) = inner.kind
+                    && let Some(tail_expr) = block.expr
             {
+                let parent = cx.tcx.hir_get_parent_item(impl_item.hir_id()).def_id;
+                let item = cx.tcx.hir_expect_item(parent);
+                let self_ty = cx.tcx.type_of(item.owner_id).instantiate_identity().skip_norm_wip();
+                //check if self.ty is never type ! if it is, then we don't want to lint because the function can
+                // never be called and thus doesn't need to be async
+                if self_ty.is_never() {
+                    return;
+                }
                 span_lint_and_then(
                     cx,
                     UNUSED_ASYNC_TRAIT_IMPL,
diff --git a/tests/ui/unused_async_trait_impl.fixed b/tests/ui/unused_async_trait_impl.fixed
index 384bb3449f90..1986105e2d76 100644
--- a/tests/ui/unused_async_trait_impl.fixed
+++ b/tests/ui/unused_async_trait_impl.fixed
@@ -1,4 +1,5 @@
 #![warn(clippy::unused_async_trait_impl)]
+#![feature(never_type)]
 
 trait HasAsyncMethod {
     async fn do_something() -> u32;
@@ -107,3 +108,14 @@ mod macros {
         }
     }
 }
+
+
+mod issue17162 {
+    // Should not lint when async trait impl is for `!` (never type)
+    
+    impl crate::HasAsyncMethod for ! {
+        async fn do_something() -> u32 {
+            unreachable!()
+        }
+    }
+}
\ No newline at end of file
diff --git a/tests/ui/unused_async_trait_impl.rs b/tests/ui/unused_async_trait_impl.rs
index 0a93635c264f..1a07dc9109df 100644
--- a/tests/ui/unused_async_trait_impl.rs
+++ b/tests/ui/unused_async_trait_impl.rs
@@ -1,4 +1,5 @@
 #![warn(clippy::unused_async_trait_impl)]
+#![feature(never_type)]
 
 trait HasAsyncMethod {
     async fn do_something() -> u32;
@@ -107,3 +108,13 @@ mod macros {
         }
     }
 }
+
+mod issue17162 {
+    // Should not lint when async trait impl is for `!` (never type)
+
+    impl crate::HasAsyncMethod for ! {
+        async fn do_something() -> u32 {
+            unreachable!()
+        }
+    }
+}
diff --git a/tests/ui/unused_async_trait_impl.stderr b/tests/ui/unused_async_trait_impl.stderr
index 7265dc2dd059..1d4b54a4be61 100644
--- a/tests/ui/unused_async_trait_impl.stderr
+++ b/tests/ui/unused_async_trait_impl.stderr
@@ -1,5 +1,5 @@
 error: unused `async` for async trait impl function with no `.await` statements
-  --> tests/ui/unused_async_trait_impl.rs:16:9
+  --> tests/ui/unused_async_trait_impl.rs:17:9
    |
 LL | /         async fn do_something() -> u32 {
 LL | |
@@ -18,7 +18,7 @@ LL ~             std::future::ready(1)
    |
 
 error: unused `async` for async trait impl function with no `.await` statements
-  --> tests/ui/unused_async_trait_impl.rs:40:9
+  --> tests/ui/unused_async_trait_impl.rs:41:9
    |
 LL | /         async fn do_something() -> u32 {
 LL | |
@@ -40,7 +40,7 @@ LL ~             std::future::ready(x)
    |
 
 error: unused `async` for async trait impl function with no `.await` statements
-  --> tests/ui/unused_async_trait_impl.rs:63:9
+  --> tests/ui/unused_async_trait_impl.rs:64:9
    |
 LL | /         async fn do_something() -> u32 {
 LL | |
@@ -57,7 +57,7 @@ LL ~             std::future::ready(5)
    |
 
 error: unused `async` for async trait impl function with no `.await` statements
-  --> tests/ui/unused_async_trait_impl.rs:97:9
+  --> tests/ui/unused_async_trait_impl.rs:98:9
    |
 LL | /         async fn do_something() -> vec_ty!(u32) {
 LL | |
@@ -74,7 +74,7 @@ LL ~             std::future::ready(Vec::new())
    |
 
 error: unused `async` for async trait impl function with no `.await` statements
-  --> tests/ui/unused_async_trait_impl.rs:104:9
+  --> tests/ui/unused_async_trait_impl.rs:105:9
    |
 LL | /         async fn do_something() -> Vec<u32> {
 LL | |