signal-desktop/js/modules/migrations/get_placeholder_migrations.js

const Migrations0DatabaseWithAttachmentData = require('./migrations_0_database_with_attachment_data');
const Migrations1DatabaseWithoutAttachmentData = require('./migrations_1_database_without_attachment_data');

exports.getPlaceholderMigrations = () => {
  const last0MigrationVersion = Migrations0DatabaseWithAttachmentData.getLatestVersion();
  const last1MigrationVersion = Migrations1DatabaseWithoutAttachmentData.getLatestVersion();

  const lastMigrationVersion = last1MigrationVersion || last0MigrationVersion;

  return [
    {
      version: lastMigrationVersion,
      migrate() {
        throw new Error(
          'Unexpected invocation of placeholder migration!' +
            '\n\nMigrations must explicitly be run upon application startup instead' +
            ' of implicitly via Backbone IndexedDB adapter at any time.'
        );
      },
    },
  ];
};