MDL-82359 Install: Allow install to succeed with missing default blocks

lib/blocklib.php

@@ -945,6 +945,28 @@ public function add_blocks($blocks, $pagetypepattern = NULL, $subpagepattern = N
         }
     }
 
+    /**
+     * Given an array of blocks in the format used by {@see add_blocks}, removes any blocks from
+     * the list if they are not installed in the system.
+     *
+     * @param array $blocks Array keyed by region
+     * @return array Updated array
+     */
+    public function filter_nonexistent_blocks(array $blocks): array {
+        $installed = array_fill_keys(
+            array_map(fn($block) => $block->name, $this->get_installed_blocks()), true);
+        $result = [];
+        foreach ($blocks as $region => $regionblocks) {
+            $result[$region] = [];
+            foreach ($regionblocks as $blockname) {
+                if (array_key_exists($blockname, $installed)) {
+                    $result[$region][] = $blockname;
+                }
+            }
+        }
+        return $result;
+    }
+
     /**
      * Move a block to a new position on this page.
      *
@@ -2684,6 +2706,9 @@ function blocks_get_default_site_course_blocks() {
 /**
  * Add the default blocks to a course.
  *
+ * Because this function is used on install, we skip over any default blocks that do not exist
+ * so that install can complete successfully even if blocks are removed.
+ *
  * @param object $course a course object.
  */
 function blocks_add_default_course_blocks($course) {
@@ -2711,19 +2736,26 @@ function blocks_add_default_course_blocks($course) {
     }
     $page = new moodle_page();
     $page->set_course($course);
-    $page->blocks->add_blocks($blocknames, $pagetypepattern);
+    $page->blocks->add_blocks($page->blocks->filter_nonexistent_blocks($blocknames),
+        $pagetypepattern);
 }
 
 /**
  * Add the default system-context blocks. E.g. the admin tree.
+ *
+ * Because this function is used on install, we skip over any default blocks that do not exist
+ * so that install can complete successfully even if blocks are removed.
  */
 function blocks_add_default_system_blocks() {
     global $DB;
 
     $page = new moodle_page();
     $page->set_context(context_system::instance());
     // We don't add blocks required by the theme, they will be auto-created.
-    $page->blocks->add_blocks(array(BLOCK_POS_LEFT => array('admin_bookmarks')), 'admin-*', null, null, 2);
+    $page->blocks->add_blocks($page->blocks->filter_nonexistent_blocks([
+        BLOCK_POS_LEFT => [
+            'admin_bookmarks',
+        ]]), 'admin-*', null, null, 2);
 
     if ($defaultmypage = $DB->get_record('my_pages', array('userid' => null, 'name' => '__default', 'private' => 1))) {
         $subpagepattern = $defaultmypage->id;
@@ -2737,22 +2769,22 @@ function blocks_add_default_system_blocks() {
         $mycoursesubpagepattern = null;
     }
 
-    $page->blocks->add_blocks([
+    $page->blocks->add_blocks($page->blocks->filter_nonexistent_blocks([
         BLOCK_POS_RIGHT => [
             'recentlyaccesseditems',
         ],
         'content' => [
             'timeline',
             'calendar_month',
-        ]],
+        ]]),
         'my-index',
         $subpagepattern
     );
 
-    $page->blocks->add_blocks([
+    $page->blocks->add_blocks($page->blocks->filter_nonexistent_blocks([
         'content' => [
             'myoverview'
-        ]],
+        ]]),
         'my-index',
         $mycoursesubpagepattern
     );