add test for rust-lang#99975

Author: dingxiangfei2009

src/test/ui/let-else/issue-99975.rs

@@ -0,0 +1,20 @@
+// run-pass
+// compile-flags: -C opt-level=3 -Zvalidate-mir
+
+#![feature(let_else)]
+
+fn return_result() -> Option<String> {
+    Some("ok".to_string())
+}
+
+fn start() -> String {
+    let Some(content) = return_result() else {
+        return "none".to_string()
+    };
+
+    content
+}
+
+fn main() {
+    start();
+}