MDL-73339 core_blocks: New method can_block_be_added

A new method, can_block_be_added, has been added to
let blocks override it to decide whether it should
be added to a page or not.

blocks/moodleblock.class.php

@@ -747,6 +747,18 @@ EOD;
     public function get_aria_role() {
         return 'complementary';
     }
+
+    /**
+     * This method can be overriden to add some extra checks to decide whether the block can be added or not to a page.
+     * It doesn't need to do the standard capability checks as they will be performed by has_add_block_capability().
+     * This method is user agnostic. If you want to check if a user can add a block or not, you should use user_can_addto().
+     *
+     * @param moodle_page $page The page where this block will be added.
+     * @return bool Whether the block can be added or not to the given page.
+     */
+    public function can_block_be_added(moodle_page $page): bool {
+        return true;
+    }
 }
 
 /**

blocks/upgrade.txt

@@ -8,6 +8,8 @@ The Quiz results block is hidden by default since Moodle 2.9. It is recommended
 * External function core_block::get_dashboard_blocks has a new parameter to indicate if you want to receive the block on the my/courses page.
 * The `core_block_fetch_addable_blocks` external method accepts an optional `subpage` parameter, in order to correctly
   calculate available blocks for pages that use this property (e.g. the user dashboard)
+* A new method, can_block_be_added(), has been added to let blocks override it when they want to include some extra checks
+to decide whether the block can be added to a page or not.
 
 === 3.8 ===
 * Block block_community is no longer a part of core.
@@ -108,4 +110,3 @@ required changes in code:
 * use 'pluginname' lang pack identifier instead of 'blockname'
 * move cron and version number into standard version.php
 * removed support for old config_global.html, use settings.php
-

lib/blocklib.php

@@ -223,6 +223,7 @@ class block_manager {
             }
             if ($block->visible && !in_array($block->name, $unaddableblocks) &&
                     !in_array($block->name, $requiredbythemeblocks) &&
+                    $bi->can_block_be_added($this->page) &&
                     ($bi->instance_allow_multiple() || !$this->is_block_present($block->name)) &&
                     blocks_name_allowed_in_format($block->name, $pageformat) &&
                     $bi->user_can_addto($this->page)) {