PHP Warning when ModulesListConfirmForm::buildMessageList() relies on module that has been unset within ModulesListForm::buildModuleList()

Problem/Motivation

When implementing hook_requirements() using 'severity' => REQUIREMENT_ERROR during install phase within a module and drupal_check_module() fails and the module is unset from installed modules within ModulesListForm::buildModuleList(), a PHP Warning occurs b/c ModulesListConfirmForm::buildMessageList() relies on the installed modules array item here.

I suppose the underlying issue is that a module's dependencies continue to be installed regardless if the selected module can not be installed.

Steps to reproduce

• Implement hook_requirements() using install phase ensuring the condition results in REQUIREMENT_ERROR severity.
• Ensure the module where the implementing the hook_requirements() has a dependency that has yet to be installed.
• Go to /admin/modules and attempt to install the module with the hook_requirements() implementation
• Observe PHP Warning

Proposed resolution

TBD -

• Perform the drupal_check_module() before adding dependencies
• unset $modules['dependencies'][$module] and remove $module's dependencies from $module['install] to prevent them from being installed as well.

Remaining tasks

• Create a failing test to illustrate the issue
• Get consensus on the underlying issue
• Get consensus on on the resolution
• Fix and add/update test(s) as needed

User interface changes

If drupal_check_module() is performed before adding dependencies, there is a UI change in that a user will not see the confirmation form and messaging related to installing module dependencies.

API changes

N/A

Data model changes

N/A

Release notes snippet

TBD