[D7 PHP 8.1] system_modules(): Deprecated function: str_replace(): Passing null to parameter #3 ($subject) of type array|string is deprecated

@joelpittet: I've fixed your merge request (you created merge request to 9.4.x) to 7.x.

I've also created patch from your commits to be used while waiting for merge.

@joelpittet Thanks for the info, didn't know about patches from merge requests.

Ideally we'd like one or more tests to accompany all of these PHP 8.1 fixes.

However, both of these changes look like they're buried in long functions that are not well suited to targetted unit testing.

Is there any existing test coverage that could be adapted / built upon to exercise this problem with PHP 8.1?

Wow, the functions we're changing here really don't lend themselves to nice clean unit tests :)

I think this ought to work, but I'm having trouble getting it to fail with PHP 8.1 locally. Let's see what the bot says.

It's actually the module's dependencies that cause a problem if they have a null version, so we need two test modules.

I'm fairly certain this test results in this line getting a null version:

        // Disable this module if it is incompatible with the dependency's version.
        if ($incompatible_version = drupal_check_incompatibility($v, str_replace(DRUPAL_CORE_COMPATIBILITY . '-', '', $files[$requires]->info['version'])))

https://git.drupalcode.org/project/drupal/-/blob/7.87/modules/system/sys...

...so I'm not sure why I'm getting no error locally.

Well that certainly seems to have triggered the exception with PHP 8.1 - strictly speaking I think this is only exercising the code in system.admin.inc and not the .install function that we're also changing. I think that's probably sufficient though.

Here's the test only patch again with a tiny tweak (proper version for the test module that requires the problematic dependency) plus a test + fix patch (latest from the MR).

Thanks everyone!