Add "Disable Add new module page" option to settings page

I have created a simple module called "Disable add new moldule" as a sub-module.

I used a RouteSubscriber to deny access to the "/admin/modules/install" route. I had hoped this would hid the menu, since normally the menu system will hide menus you don't have access to, but I think the admin user has access to all menus.

Instead I used "hook_menu_links_discovered_alter" to remove any menu items with the route.

I also added a functional test to verify access is denied to the Add new module page, and that uninstalling the module restores access.

I considered adding a test that the menu was removed, but I don't think Add new module appears on any menu unless you have Admin Toolbar enabled, and I didn't want to add a test that depends on a contrib module.

One question to consider is should this be a sub-module, or just a setting in the main project browser modules? Or perhaps even just decide that .tar modules are incompatible with PB and disable the page when PB is enabled.

Advantages of merging: Keeps everything self contained.

Advantages of separate module: Module only needs to do one thing. When .tar functionality gets removed from core, easier to remove from PB.

Thoughts?

After discussion with @chrisfromredfin and @timplunkett on Slack, I have moved the functionality into the Project Browser module. I've added an option to the Project browser settings, enabled by default.

TODO:

At present, after changing "Disable add new menu" setting, it is necessary to rebuild cache for the changes to take effect.

Add additional tests to test for changing setting.

I tried various methods of clearing partial cache to make "Add new module" page show after changing the setting. I could get the menu item to appear. However, I was unable to find a cache to clear to make the page accessible. At present, I am using drupal_flush_all_caches();, which is a bit heavy handed, but it does avoid adding new dependency injection, so will make it easier to remove this feature when the "Add new module" page gets removed in Drupal core.

Still need to add some tests for the settings page.

Updated issue title and description to reflect that this is now a setting in the PB module, not a separate module.

Added test to verify that unchecking the "Disable add new module" enables the Add new module page, and that re-checking it disables the page again.

I think this is ready for review.

I tested via drupalpod and the functionality is the expected one.

I made a few comments in the code, mostly about which caches to clear (if any). As they are mostly questions rather than asking for changes (I guess it depends on the answers) I'm leaving the issue status as it is now.

I added some really minor suggestions, just small clean-up and variable renaming, but they are really minor. If you even feel that they're not needed please say so.

I also re-tested things via drupalpod, and found a weird behavior:
* When checking the disable checkbox, things work as expected. The link to install new modules shows before the change, and does not show after the change.
* When unchecking the disable checkbox, things don't change. The links to install new modules does not show before the change, and still does not show after the change.

Obviously, this is due to not clearing all caches now, but I still think it's the way to go, so it seems like we might need to add something more so that both scenarios work as expected.

We still need to address the case where the link won't show back when unticking the checkbox.

We also need to clear the render cache. I've been testing and adding this line fixes the issue, we just need to add the service via dependency injection.
\Drupal::service('cache.render')->invalidateAll();

Thanks! I've added the render cache invalidation.

Great. I've tested multiple times and reviewed the code a few times as well. I'm going to mark it RTBC.
Thanks so much for this feature!

Double-checked, reviewed, and tested in DrupalPod -- and love it!

Automatically closed - issue fixed for 2 weeks with no activity.