only focus on `double_must_use` + Add `Result<(), ()>` test

2 files changed, 14 insertions, 8 deletions

diff --git a/clippy_lints/src/functions/must_use.rs b/clippy_lints/src/functions/must_use.rs
index 56acd31b1d2..ab68d7a3726 100644
--- a/clippy_lints/src/functions/must_use.rs
+++ b/clippy_lints/src/functions/must_use.rs
@@ -1,3 +1,4 @@
+use hir::FnSig;
 use rustc_ast::ast::Attribute;
 use rustc_errors::Applicability;
 use rustc_hir::def_id::DefIdSet;
@@ -23,12 +24,11 @@ use super::{DOUBLE_MUST_USE, MUST_USE_CANDIDATE, MUST_USE_UNIT};
 pub(super) fn check_item<'tcx>(cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
     let attrs = cx.tcx.hir().attrs(item.hir_id());
     let attr = cx.tcx.get_attr(item.owner_id, sym::must_use);
-    if let hir::ItemKind::Fn(ref sig, _generics, ref body_id) = item.kind && !sig.header.is_async() /* (#10486) */ {
-
+    if let hir::ItemKind::Fn(ref sig, _generics, ref body_id) = item.kind {
         let is_public = cx.effective_visibilities.is_exported(item.owner_id.def_id);
         let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
         if let Some(attr) = attr {
-            check_needless_must_use(cx, sig.decl, item.owner_id, item.span, fn_header_span, attr);
+            check_needless_must_use(cx, sig.decl, item.owner_id, item.span, fn_header_span, attr, sig);
         } else if is_public && !is_proc_macro(attrs) && !attrs.iter().any(|a| a.has_name(sym::no_mangle)) {
             check_must_use_candidate(
                 cx,
@@ -44,13 +44,13 @@ pub(super) fn check_item<'tcx>(cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>
 }
 
 pub(super) fn check_impl_item<'tcx>(cx: &LateContext<'tcx>, item: &'tcx hir::ImplItem<'_>) {
-    if let hir::ImplItemKind::Fn(ref sig, ref body_id) = item.kind && !sig.header.is_async() /* (#10486) */ {
+    if let hir::ImplItemKind::Fn(ref sig, ref body_id) = item.kind {
         let is_public = cx.effective_visibilities.is_exported(item.owner_id.def_id);
         let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
         let attrs = cx.tcx.hir().attrs(item.hir_id());
         let attr = cx.tcx.get_attr(item.owner_id, sym::must_use);
         if let Some(attr) = attr {
-            check_needless_must_use(cx, sig.decl, item.owner_id, item.span, fn_header_span, attr);
+            check_needless_must_use(cx, sig.decl, item.owner_id, item.span, fn_header_span, attr, sig);
         } else if is_public && !is_proc_macro(attrs) && trait_ref_of_method(cx, item.owner_id.def_id).is_none() {
             check_must_use_candidate(
                 cx,
@@ -66,14 +66,14 @@ pub(super) fn check_impl_item<'tcx>(cx: &LateContext<'tcx>, item: &'tcx hir::Imp
 }
 
 pub(super) fn check_trait_item<'tcx>(cx: &LateContext<'tcx>, item: &'tcx hir::TraitItem<'_>) {
-    if let hir::TraitItemKind::Fn(ref sig, ref eid) = item.kind && !sig.header.is_async() /* (#10486) */ {
+    if let hir::TraitItemKind::Fn(ref sig, ref eid) = item.kind {
         let is_public = cx.effective_visibilities.is_exported(item.owner_id.def_id);
         let fn_header_span = item.span.with_hi(sig.decl.output.span().hi());
 
         let attrs = cx.tcx.hir().attrs(item.hir_id());
         let attr = cx.tcx.get_attr(item.owner_id, sym::must_use);
         if let Some(attr) = attr {
-            check_needless_must_use(cx, sig.decl, item.owner_id, item.span, fn_header_span, attr);
+            check_needless_must_use(cx, sig.decl, item.owner_id, item.span, fn_header_span, attr, sig);
         } else if let hir::TraitFn::Provided(eid) = *eid {
             let body = cx.tcx.hir().body(eid);
             if attr.is_none() && is_public && !is_proc_macro(attrs) {
@@ -98,6 +98,7 @@ fn check_needless_must_use(
     item_span: Span,
     fn_header_span: Span,
     attr: &Attribute,
+    sig: &FnSig<'_>,
 ) {
     if in_external_macro(cx.sess(), item_span) {
         return;
@@ -112,7 +113,7 @@ fn check_needless_must_use(
                 diag.span_suggestion(attr.span, "remove the attribute", "", Applicability::MachineApplicable);
             },
         );
-    } else if attr.value_str().is_none() && is_must_use_ty(cx, return_ty(cx, item_id)) {
+    } else if attr.value_str().is_none() && is_must_use_ty(cx, return_ty(cx, item_id)) && !sig.header.is_async() {
         span_lint_and_help(
             cx,
             DOUBLE_MUST_USE,
diff --git a/tests/ui/double_must_use.rs b/tests/ui/double_must_use.rs
index a4cd8630de5..26a387b3cf0 100644
--- a/tests/ui/double_must_use.rs
+++ b/tests/ui/double_must_use.rs
@@ -27,6 +27,11 @@ async fn async_must_use() -> usize {
     unimplemented!();
 }
 
+#[must_use]
+async fn async_must_use_result() -> Result<(), ()> {
+    Ok(())
+}
+
 fn main() {
     must_use_result();
     must_use_tuple();