Deparser: Add parenthesis around AT LOCAL / AT TIMEZONE if needed

This fixes a correctness issue where the deparsed SQL is not parsable,
since the table DEFAULT expression is a b_expr, not an a_expr.

src/postgres_deparse.c

@@ -2723,6 +2723,11 @@ static void deparseFuncCall(StringInfo str, FuncCall *func_call, DeparseNodeCont
 		else
 			e = lsecond(func_call->args);
 
+		// If we're not inside an a_expr context, we must add wrapping parenthesis around the AT ... syntax
+		if (context != DEPARSE_NODE_CONTEXT_A_EXPR) {
+			appendStringInfoChar(str, '(');
+		}
+
 		if (IsA(e, A_Expr)) {
 			appendStringInfoChar(str, '(');
 		}
@@ -2739,6 +2744,11 @@ static void deparseFuncCall(StringInfo str, FuncCall *func_call, DeparseNodeCont
 			appendStringInfoString(str, " AT TIME ZONE ");
 			deparseExpr(str, linitial(func_call->args), DEPARSE_NODE_CONTEXT_A_EXPR);
 		}
+
+		if (context != DEPARSE_NODE_CONTEXT_A_EXPR) {
+			appendStringInfoChar(str, ')');
+		}
+
 		return;
 	} else if (func_call->funcformat == COERCE_SQL_SYNTAX &&
 		list_length(func_call->funcname) == 2 &&

test/deparse_tests.c

@@ -409,7 +409,11 @@ const char* tests[] = {
   "CREATE INDEX myindex ON public.mytable USING btree (col1, (col2::varchar) varchar_pattern_ops)",
   "SELECT * FROM CAST(1 AS text)",
   "DECLARE \"Foo1\" SCROLL CURSOR FOR SELECT * FROM tenk1 ORDER BY unique2",
-  "FETCH BACKWARD 23 \"Foo1\""
+  "FETCH BACKWARD 23 \"Foo1\"",
+  "CREATE TABLE my_table (created_at timestamptz NOT NULL DEFAULT (now() AT TIME ZONE 'UTC'))",
+  "CREATE TABLE my_table (created_at timestamptz NOT NULL DEFAULT (now() AT LOCAL))",
+  "CREATE TABLE my_table (created_at timestamptz NOT NULL DEFAULT '1 hour'::interval + (current_timestamp AT TIME ZONE 'UTC'))",
+  "CREATE TABLE my_table (created_at int NOT NULL DEFAULT 1 + 2)"
 };
 
 size_t testsLength = __LINE__ - 4;