Print a space between adjacent prefix unary operators

src/ast/mod.rs

@@ -1963,7 +1963,8 @@ impl fmt::Display for Expr {
                         | UnaryOperator::DoubleAt
                         | UnaryOperator::QuestionDash
                         | UnaryOperator::QuestionPipe
-                ) {
+                ) || matches!(expr.as_ref(), Expr::UnaryOp { .. })
+                {
                     write!(f, "{op} {expr}")
                 } else {
                     write!(f, "{op}{expr}")

tests/sqlparser_common.rs

@@ -19679,3 +19679,11 @@ fn parse_function_arg_call_chain_no_exponential_blowup() {
     rx.recv_timeout(Duration::from_secs(5))
         .expect("parser should reject this quickly, not loop exponentially");
 }
+
+#[test]
+fn parse_nested_unary_ops() {
+    all_dialects().verified_stmt("SELECT - -1");
+    all_dialects().verified_stmt("SELECT ~ ~1");
+    all_dialects().verified_stmt("SELECT NOT NOT a");
+    all_dialects().one_statement_parses_to("SELECT ~ ~ 1", "SELECT ~ ~1");
+}

tests/sqlparser_postgres.rs

@@ -9663,3 +9663,29 @@ fn parse_right_deep_join_chain() {
     // NATURAL JOIN followed by a constrained join must stay left-associative.
     pg().verified_stmt("SELECT * FROM t0 NATURAL JOIN t1 INNER JOIN t2 ON true");
 }
+
+#[test]
+fn parse_nested_pg_unary_ops() {
+    let select = pg().verified_only_select("SELECT @ @1");
+    assert_eq!(
+        SelectItem::UnnamedExpr(Expr::UnaryOp {
+            op: UnaryOperator::PGAbs,
+            expr: Box::new(Expr::UnaryOp {
+                op: UnaryOperator::PGAbs,
+                expr: Box::new(Expr::value(number("1"))),
+            }),
+        }),
+        select.projection[0]
+    );
+
+    let select = pg().verified_only_select("SELECT @@ 1");
+    assert_eq!(
+        SelectItem::UnnamedExpr(Expr::UnaryOp {
+            op: UnaryOperator::DoubleAt,
+            expr: Box::new(Expr::value(number("1"))),
+        }),
+        select.projection[0]
+    );
+
+    pg().verified_stmt("SELECT |/ |/1");
+}