PostgreSQL: regression test for compound-chain blowup

Author: LucaCappelletti94

tests/sqlparser_postgres.rs

@@ -9243,3 +9243,27 @@ fn parse_lock_table() {
         }
     }
 }
+
+/// `parse_compound_expr` used to do 2^N work on `IF a.b.c...x.#` because every
+/// `.` re-entered `parse_subexpr` over the rest of the chain.
+#[test]
+fn parse_compound_chain_no_exponential_blowup() {
+    use std::sync::mpsc;
+    use std::thread;
+    use std::time::Duration;
+
+    let chain: String = (0..30)
+        .map(|i| format!("a{i}"))
+        .collect::<Vec<_>>()
+        .join(".");
+    let sql = format!("IF {chain}.#");
+
+    let (tx, rx) = mpsc::channel();
+    thread::spawn(move || {
+        let _ = sqlparser::parser::Parser::parse_sql(&PostgreSqlDialect {}, &sql);
+        let _ = tx.send(());
+    });
+
+    rx.recv_timeout(Duration::from_secs(5))
+        .expect("parser should reject this quickly, not loop exponentially");
+}