Block with Failed Condition produce PHP Warning

Thank you for that report.

Instead of unset the array, using #access FALSE should prevent it from showing when rendered:

        if (!$visible && $all_must_pass) {
          $build['content']['#access'] = FALSE;
        }

I've updated tests to account for this, and items were not visible to me in manual testing and no logs issues were present. Give the dev release a try.

I checked to see if I could locate how Context handles blocks normally but could not find much. I think template_preprocess_block will be called no matter what since nothing is actually preventing the execution of that code, its tagging the render array as not being displayed. I need to review the preRenderBlock method of the Blocks ContextReaction plugin for some insight.

Previously, the logs were occurring because 'content' was being unset from the array which resulted in "Warning: Undefined array key "content" in template_preprocess_block() ".

Kevin it's a good start! This worked for the blocks but any sections with context do not seem to follow any context rules now.

Messed with Pre_Render

In /src/Utility/Visibility.php, I replaced $build['content']['#access'] = FALSE with $build['#pre_render']['#printed'] = TRUE but elements are still rendering. Maybe something else is in the pre_render array?

Stuff that I've been reading

Render Arrays section of the Render API docs →
Code Blocks.php ContextReaction - Context

I am a little lost. I have put back $build['content'] = [] instead of unset it in the dev branch, the context rules all appear to work for section or block. hook_preprocess_block was only called for visible blocks.

I hope this isn't forgotten. The commit is an improvement but results in a couple of nested empty divs, which were visible in my theme. I'm not sure what a better solution is though. It kind of seems like a core bug to assume the existence of the content key? As a workaround, I added this to the theme's theme_preprocess_block():

  if (isset($variables['content']['#access']) && $variables['content']['#access'] === false) {
    $variables['attributes']['class'][] = 'hidden';
  }

That could be part of it, yes. "content" is typically the property name for render array data, but it could be whatever a developer specifies it as in contrib.

I added this to the theme

What theme?

Sorry that wasn't clear. My site's custom theme. I think with core, it would just result in <div></div>. In my particular case, we have an additional div in the block template which monkeyed with the spacing.