fix(query-interface): allow sequelize.fn and sequelize.literal in fields of IndexesOptions (#12224)

types/lib/query-interface.d.ts

@@ -4,6 +4,7 @@ import QueryTypes = require('./query-types');
 import { Sequelize, RetryOptions } from './sequelize';
 import { Transaction } from './transaction';
 import { SetRequired } from './../type-helpers/set-required';
+import { Fn, Literal } from './utils';
 
 type BindOrReplacements = { [key: string]: unknown } | unknown[];
 type FieldMap = { [key: string]: string };
@@ -172,7 +173,7 @@ export interface IndexesOptions {
    * (field name), `length` (create a prefix index of length chars), `order` (the direction the column
    * should be sorted in), `collate` (the collation (sort order) for the column), `operator` (likes IndexesOptions['operator'])
    */
-  fields?: (string | { name: string; length?: number; order?: 'ASC' | 'DESC'; collate?: string; operator?: string })[];
+  fields?: (string | { name: string; length?: number; order?: 'ASC' | 'DESC'; collate?: string; operator?: string } | Fn | Literal)[];
 
   /**
    * The method to create the index by (`USING` statement in SQL). BTREE and HASH are supported by mysql and

types/test/query-interface.ts

-import { DataTypes, Model } from 'sequelize';
+import { DataTypes, Model, fn, literal, col } from 'sequelize';
 // tslint:disable-next-line:no-submodule-imports
 import { QueryInterface } from 'sequelize/lib/query-interface';
 
@@ -154,6 +154,20 @@ queryInterface.addIndex('Foo', {
   ],
 });
 
+queryInterface.addIndex('Foo', {
+  name: 'foo_b_lower',
+  fields: [
+    fn('lower', col('foo_b'))
+  ],
+});
+
+queryInterface.addIndex('Foo', {
+  name: 'foo_c_lower',
+  fields: [
+    literal('LOWER(foo_c)')
+  ]
+})
+
 queryInterface.removeIndex('Person', 'SuperDuperIndex');
 
 // or