[redundant_closure_call]: avoid duplicated async keyword when triggering on closure that returns async block

clippy_lints/src/redundant_closure_call.rs

@@ -4,8 +4,8 @@ use clippy_utils::get_parent_expr;
 use clippy_utils::sugg::Sugg;
 use rustc_errors::Applicability;
 use rustc_hir as hir;
-use rustc_hir::intravisit as hir_visit;
 use rustc_hir::intravisit::{Visitor as HirVisitor, Visitor};
+use rustc_hir::{intravisit as hir_visit, CoroutineKind, CoroutineSource, Node};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::hir::nested_filter;
 use rustc_middle::lint::in_external_macro;
@@ -60,11 +60,14 @@ impl<'tcx> Visitor<'tcx> for ReturnVisitor {
     }
 }
 
-/// Checks if the body is owned by an async closure
-fn is_async_closure(body: &hir::Body<'_>) -> bool {
-    if let hir::ExprKind::Closure(closure) = body.value.kind
-        && let [resume_ty] = closure.fn_decl.inputs
-        && let hir::TyKind::Path(hir::QPath::LangItem(hir::LangItem::ResumeTy, ..)) = resume_ty.kind
+/// Checks if the body is owned by an async closure.
+/// Returns true for `async || whatever_expression`, but false for `|| async { whatever_expression
+/// }`.
+fn is_async_closure(cx: &LateContext<'_>, body: &hir::Body<'_>) -> bool {
+    if let hir::ExprKind::Closure(innermost_closure_generated_by_desugar) = body.value.kind
+        && let desugared_inner_closure_body = cx.tcx.hir().body(innermost_closure_generated_by_desugar.body)
+        // checks whether it is `async || whatever_expression`
+        && let Some(CoroutineKind::Async(CoroutineSource::Closure)) = desugared_inner_closure_body.coroutine_kind
     {
         true
     } else {
@@ -100,7 +103,7 @@ fn find_innermost_closure<'tcx>(
         data = Some((
             body.value,
             closure.fn_decl,
-            if is_async_closure(body) {
+            if is_async_closure(cx, body) {
                 ty::Asyncness::Yes
             } else {
                 ty::Asyncness::No
@@ -173,12 +176,18 @@ impl<'tcx> LateLintPass<'tcx> for RedundantClosureCall {
                             hint = hint.asyncify();
                         }
 
-                        diag.span_suggestion(
-                            full_expr.span,
-                            "try doing something like",
-                            hint.maybe_par(),
-                            applicability,
-                        );
+                        let is_in_fn_call_arg =
+                            clippy_utils::get_parent_node(cx.tcx, expr.hir_id).is_some_and(|x| match x {
+                                Node::Expr(expr) => matches!(expr.kind, hir::ExprKind::Call(_, _)),
+                                _ => false,
+                            });
+
+                        // avoid clippy::double_parens
+                        if !is_in_fn_call_arg {
+                            hint = hint.maybe_par();
+                        };
+
+                        diag.span_suggestion(full_expr.span, "try doing something like", hint, applicability);
                     }
                 },
             );

tests/ui/redundant_closure_call_fixable.fixed

@@ -84,3 +84,21 @@ fn issue9956() {
     bar()(42, 5);
     foo(42, 5);
 }
+
+async fn issue11357() {
+    async {}.await;
+}
+
+mod issue11707 {
+    use core::future::Future;
+
+    fn spawn_on(fut: impl Future<Output = ()>) {}
+
+    fn demo() {
+        spawn_on(async move {});
+    }
+}
+
+fn avoid_double_parens() {
+    std::convert::identity(13_i32 + 36_i32).leading_zeros();
+}

tests/ui/redundant_closure_call_fixable.rs

@@ -84,3 +84,21 @@ fn issue9956() {
     bar()((|| || 42)()(), 5);
     foo((|| || 42)()(), 5);
 }
+
+async fn issue11357() {
+    (|| async {})().await;
+}
+
+mod issue11707 {
+    use core::future::Future;
+
+    fn spawn_on(fut: impl Future<Output = ()>) {}
+
+    fn demo() {
+        spawn_on((|| async move {})());
+    }
+}
+
+fn avoid_double_parens() {
+    std::convert::identity((|| 13_i32 + 36_i32)()).leading_zeros();
+}

tests/ui/redundant_closure_call_fixable.stderr

@@ -123,5 +123,23 @@ error: try not to call a closure in the expression where it is declared
 LL |     foo((|| || 42)()(), 5);
    |         ^^^^^^^^^^^^^^ help: try doing something like: `42`
 
-error: aborting due to 14 previous errors
+error: try not to call a closure in the expression where it is declared
+  --> $DIR/redundant_closure_call_fixable.rs:89:5
+   |
+LL |     (|| async {})().await;
+   |     ^^^^^^^^^^^^^^^ help: try doing something like: `async {}`
+
+error: try not to call a closure in the expression where it is declared
+  --> $DIR/redundant_closure_call_fixable.rs:98:18
+   |
+LL |         spawn_on((|| async move {})());
+   |                  ^^^^^^^^^^^^^^^^^^^^ help: try doing something like: `async move {}`
+
+error: try not to call a closure in the expression where it is declared
+  --> $DIR/redundant_closure_call_fixable.rs:103:28
+   |
+LL |     std::convert::identity((|| 13_i32 + 36_i32)()).leading_zeros();
+   |                            ^^^^^^^^^^^^^^^^^^^^^^ help: try doing something like: `13_i32 + 36_i32`
+
+error: aborting due to 17 previous errors