The bin/magento setup:upgrade Command will Enable Non-Enabled modules

[magento-engcom-team]

Preconditions

1. Magento installed via composer --create-project method, confirmed 2.1.3, 2.1.5, 2.1.6

Steps to reproduce

1. Create a new module in app/code ($ pestle.phar magento2:generate:module AbcCorp Testbed 0.0.1
2. Run php bin/magento setup:upgrade
3. Examine app/etc/config.php

Expected result

1. AbcCorp_Testbed should not appear in app/etc/config.php

Actual result

1. AbcCorp_Testbed appears in app/etc/config.php, and is enabled

It's a reasonable developer expectation that setup:update should not enable modules that were not previously enabled. This bug came from real world interactions with working developers who hit this bug. This bug caused unexpected Setup Upgrade code to run, and resulted in lost real world working billable hours.

Original Report: magento/magento2#9516 by @astorm

[orlangur]

@magento-engcom-team note that according to a conversion in Slack maintainers channels it was agreed that new behavior must be introduced as an option and default behavior must remain unchanged.

[korostii]

as an option and default behavior must remain unchanged

In which case, documentation should also be updated in order to reflect this current\default behavior (as well as the new option).