Add test for issue-77911

Author: JohnTitor

src/test/ui/mir/issue-77911.rs

@@ -0,0 +1,16 @@
+// compile-flags: -Z mir-opt-level=2
+// ignore-cloudabi no std::fs
+// build-pass
+
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+
+fn file_lines() -> impl Iterator<Item = String> {
+    BufReader::new(File::open("").unwrap())
+        .lines()
+        .map(Result::unwrap)
+}
+
+fn main() {
+    for _ in file_lines() {}
+}