Support array subscript operator in BigQuery

Refs #243

Author: nene

src/languages/bigquery.formatter.ts

@@ -1,6 +1,6 @@
 import Formatter from 'src/core/Formatter';
 import Tokenizer from 'src/core/Tokenizer';
-import { EOF_TOKEN, type Token } from 'src/core/token';
+import { EOF_TOKEN, TokenType, type Token } from 'src/core/token';
 import { dedupe } from 'src/utils';
 
 /**
@@ -858,7 +858,27 @@ export default class BigQueryFormatter extends Formatter {
   }
 }
 
-function preprocess(tokens: Token[]) {
+function preprocess(tokens: Token[]): Token[] {
+  return detectArraySubscripts(combineParameterizedTypes(tokens));
+}
+
+// Converts OFFSET token inside array from RESERVED_COMMAND to RESERVED_KEYWORD
+// See: https://cloud.google.com/bigquery/docs/reference/standard-sql/functions-and-operators#array_subscript_operator
+function detectArraySubscripts(tokens: Token[]) {
+  let prevToken = EOF_TOKEN;
+  return tokens.map(token => {
+    if (token.value === 'OFFSET' && prevToken.value === '[') {
+      prevToken = token;
+      return { ...token, type: TokenType.RESERVED_KEYWORD };
+    } else {
+      prevToken = token;
+      return token;
+    }
+  });
+}
+
+// Combines multiple tokens forming a parameterized type like STRUCT<ARRAY<INT64>> into a single token
+function combineParameterizedTypes(tokens: Token[]) {
   const processed: Token[] = [];
   for (let i = 0; i < tokens.length; i++) {
     const token = tokens[i];

test/bigquery.test.ts

@@ -145,4 +145,25 @@ describe('BigQueryFormatter', () => {
         varBigdecimal BIGDECIMAL(1, 1);
     `);
   });
+
+  // Regression test for issue #243
+  it('supports array subscript operator', () => {
+    expect(
+      format(`
+      SELECT item_array[OFFSET(1)] AS item_offset,
+      item_array[ORDINAL(1)] AS item_ordinal,
+      item_array[SAFE_OFFSET(6)] AS item_safe_offset,
+      item_array[SAFE_ORDINAL(6)] AS item_safe_ordinal
+      FROM Items;
+    `)
+    ).toBe(dedent`
+      SELECT
+        item_array[OFFSET(1)] AS item_offset,
+        item_array[ORDINAL(1)] AS item_ordinal,
+        item_array[SAFE_OFFSET(6)] AS item_safe_offset,
+        item_array[SAFE_ORDINAL(6)] AS item_safe_ordinal
+      FROM
+        Items;
+    `);
+  });
 });