Block Module: Fix documentation that refers to enabling/disabling of modules

Attaching the patch from #2318813-5: Comment module: Fix documentation that refers to enabling/disabling of modules which was for block.module but was posted in the issue for comment.module.

Credit goes to @Lowell.

Just a reroll. I think the patch is still incomplete though. For example, there are tests that say "Modules to enable." that need to be fixed.

Added the missing fixes to #6.

Looks good. I searched core/modules/block for enabl and disabl and there are none that relate to modules. RTBC.

+++ b/core/modules/block/block.module

@@ -34,7 +34,7 @@ function block_help($route_name, RouteMatchInterface $route_match) {
...
-      $output .= '<dd>' . t('You can add custom blocks, if the the <em>Custom Block</em> module is enabled on the <a href="!extend">Extend page</a>. For more information, see the <a href="!blockcontent-help">Custom Block help page</a>.', array('!extend' => \Drupal::url('system.modules_list'), '!blockcontent-help' => \Drupal::url('help.page', array('name' => 'block_content')))) . '</dd>';
+      $output .= '<dd>' . t('You can add custom blocks, if the the <em>Custom Block</em> module is installed on the <a href="!extend">Extend page</a>. For more information, see the <a href="!blockcontent-help">Custom Block help page</a>.', array('!extend' => \Drupal::url('system.modules_list'), '!blockcontent-help' => \Drupal::url('help.page', array('name' => 'block_content')))) . '</dd>';

Not related to this issue, but as we are changing the line anyway, I wonder if we can change "the the" to "the" here? If not, I'll file a separate issue.

Great to see these sub-issues.

Couple of comments:

1. +++ b/core/modules/block/block.module
   @@ -108,8 +108,9 @@ function _block_rehash($theme = NULL) {
        }
   

   I don't think this can be right. If a module is uninstalled the block will disappear altogether. However isn't this talking about block being disabled anyway?

2. +++ b/core/modules/block/src/BlockPluginCollection.php
   @@ -64,8 +64,9 @@ protected function initializePlugin($instance_id) {
   +      // Ignore blocks belonging to uninstalled modules, but re-throw valid
   

   We should open a follow-up to review this. It shouldn't be possible to get into this state by uninstalling a module - all the blocks should be removed then.

We already have an issue open for updating hook_help for the Block module but yes let's remove "the the" here. I mentioned it on #2349907: Review and fix block hook_help text in case it doesn't get fixed here.

I also agree with the block rehash assessment -- the code comment is really talking about disabled blocks, not disabled modules.

Rerolled. I changed the block rehash comment and also deleted the extra "the".

Opened the follow-up for that exception #2385517: Block initialization eats exceptions if a module is missing.

Changes look good so moving back to RTBC.

This has been properly beta-evaluated, and is purely docs fixes. Looks good to me too. Committed to 8.0.x.