BREAKING! PostgreSQL array[] type now uses Empty

Instead of using empty ListExpr we now use a more concrete Empty
node. Similarly for array[3] we now use just NumberLiteral not
ListExpr<NumberLiteral>.

This should make more sense as there can never be more than one
number inside the bounds specifier, so ListExpr was a bad choice.

Author: nene

src/cst/DataType.ts

@@ -1,4 +1,4 @@
-import { BaseNode, Keyword } from "./Base";
+import { BaseNode, Empty, Keyword } from "./Base";
 import { ColumnConstraint } from "./Constraint";
 import { Identifier, ListExpr, ParenExpr } from "./Expr";
 import { Literal, NumberLiteral } from "./Literal";
@@ -28,9 +28,7 @@ export interface ArrayDataType extends BaseNode {
 // PostgreSQL
 export interface ArrayBounds extends BaseNode {
   type: "array_bounds";
-  // This can only contain one or zero items.
-  // We use a list because we want to store whitespace and comments inside empty [] brackets.
-  bounds: ListExpr<NumberLiteral>; // TODO: use Empty node instead of empty ListExpr
+  bounds: NumberLiteral | Empty;
 }
 
 // PostgreSQL

src/parser.pegjs

@@ -3585,10 +3585,10 @@ data_type
   / named_data_type
 
 array_bounds
-  = "[" bounds:(__ empty_list __) "]" {
+  = "[" bounds:(__ empty __) "]" {
     return loc({ type: "array_bounds", bounds: read(bounds) });
   }
-  / "[" bounds:(__ list$number_literal __) "]" {
+  / "[" bounds:(__ number_literal __) "]" {
     return loc({ type: "array_bounds", bounds: read(bounds) });
   }