implicit_return: do not suggest adding return into desugared code

Blocks created by desugaring will not contain an explicit `return`. Do not
suggest to add it when the user has no control over the desugared code.

Author: samueltardieu

clippy_lints/src/implicit_return.rs

@@ -5,7 +5,7 @@ use clippy_utils::{get_async_fn_body, is_async_fn, is_from_proc_macro};
 use core::ops::ControlFlow;
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::FnKind;
-use rustc_hir::{Block, Body, Expr, ExprKind, FnDecl, FnRetTy, HirId};
+use rustc_hir::{Block, Body, Closure, ClosureKind, CoroutineKind, Expr, ExprKind, FnDecl, FnRetTy, HirId};
 use rustc_lint::{LateContext, LateLintPass, LintContext};
 use rustc_session::declare_lint_pass;
 use rustc_span::def_id::LocalDefId;
@@ -200,6 +200,12 @@ fn lint_implicit_returns(
             LintLocation::Inner
         },
 
+        // Closures issues from desugaring don't need a return statement.
+        ExprKind::Closure(Closure {
+            kind: ClosureKind::Coroutine(CoroutineKind::Desugared(..)),
+            ..
+        }) => LintLocation::Inner,
+
         _ =>
         {
             #[expect(clippy::option_if_let_else)]

tests/ui/implicit_return.fixed

@@ -165,3 +165,7 @@ with_span!(
         x
     }
 );
+
+fn block_in_closure() {
+    let _ = async || return 0;
+}

tests/ui/implicit_return.rs

@@ -165,3 +165,7 @@ with_span!(
         x
     }
 );
+
+fn block_in_closure() {
+    let _ = async || return 0;
+}