Auto merge of #11492 - GuillaumeGomez:async-fn-returned-closure, r=Centri3

Fix mutaby used async function argument in closure for `needless_pass_by_ref_mut`

Fixes https://github.com/rust-lang/rust-clippy/issues/11380.

The problem was that it needed to go through closures as well in async functions to correctly find the mutable usage of async function arguments.

changelog: Correctly handle mutable usage of async function arguments in closures.

r? `@Centri3`

tests/ui/needless_pass_by_ref_mut.rs

@@ -1,4 +1,4 @@
-#![allow(clippy::if_same_then_else, clippy::no_effect)]
+#![allow(clippy::if_same_then_else, clippy::no_effect, clippy::redundant_closure_call)]
 #![feature(lint_reasons)]
 //@no-rustfix
 use std::ptr::NonNull;
@@ -231,6 +231,32 @@ async fn async_vec2(b: &mut Vec<bool>) {
     b.push(true);
 }
 
+// Should not warn.
+pub async fn closure(n: &mut usize) -> impl '_ + FnMut() {
+    || {
+        *n += 1;
+    }
+}
+
+// Should warn.
+pub fn closure2(n: &mut usize) -> impl '_ + FnMut() -> usize {
+    //~^ ERROR: this argument is a mutable reference, but not used mutably
+    || *n + 1
+}
+
+// Should not warn.
+pub async fn closure3(n: &mut usize) {
+    (|| *n += 1)();
+}
+
+// Should warn.
+pub async fn closure4(n: &mut usize) {
+    //~^ ERROR: this argument is a mutable reference, but not used mutably
+    (|| {
+        let _x = *n + 1;
+    })();
+}
+
 fn main() {
     let mut u = 0;
     let mut v = vec![0];

tests/ui/needless_pass_by_ref_mut.stderr

@@ -107,5 +107,29 @@ error: this argument is a mutable reference, but not used mutably
 LL | async fn inner_async3(x: &mut i32, y: &mut u32) {
    |                          ^^^^^^^^ help: consider changing to: `&i32`
 
-error: aborting due to 17 previous errors
+error: this argument is a mutable reference, but not used mutably
+  --> $DIR/needless_pass_by_ref_mut.rs:235:25
+   |
+LL | pub async fn closure(n: &mut usize) -> impl '_ + FnMut() {
+   |                         ^^^^^^^^^^ help: consider changing to: `&usize`
+   |
+   = warning: changing this function will impact semver compatibility
+
+error: this argument is a mutable reference, but not used mutably
+  --> $DIR/needless_pass_by_ref_mut.rs:242:20
+   |
+LL | pub fn closure2(n: &mut usize) -> impl '_ + FnMut() -> usize {
+   |                    ^^^^^^^^^^ help: consider changing to: `&usize`
+   |
+   = warning: changing this function will impact semver compatibility
+
+error: this argument is a mutable reference, but not used mutably
+  --> $DIR/needless_pass_by_ref_mut.rs:253:26
+   |
+LL | pub async fn closure4(n: &mut usize) {
+   |                          ^^^^^^^^^^ help: consider changing to: `&usize`
+   |
+   = warning: changing this function will impact semver compatibility
+
+error: aborting due to 20 previous errors