MDL-86541 blocks: validate allowing block title to be '0' (zero).

public/lib/classes/output/core_renderer.php

@@ -1495,7 +1495,8 @@ class core_renderer extends renderer_base {
         $context->ariarole = !empty($bc->attributes['role']) ? $bc->attributes['role'] : '';
         $context->class = $bc->attributes['class'];
         $context->type = $bc->attributes['data-block'];
-        $context->title = $bc->title;
+        $context->title = (string) $bc->title;
+        $context->showtitle = $context->title !== '';
         $context->content = $bc->content;
         $context->annotation = $bc->annotation;
         $context->footer = $bc->footer;

public/lib/templates/block.mustache

@@ -1,3 +1,16 @@
+{{!
+    This file is part of Moodle - http://moodle.org/
+    Moodle is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+    Moodle is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+    You should have received a copy of the GNU General Public License
+    along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+}}
 {{!
     @template core/block
 
@@ -8,6 +21,7 @@
         "showskiplink": true,
         "type": "html",
         "ariarole": "",
+        "showtitle": true,
         "title": "Test block",
         "blockinstanceid": 1,
         "content": "<p>Hello block world!</p>"
@@ -29,18 +43,18 @@
         aria-label="{{arialabel}}"
      {{/arialabel}}
      {{^arialabel}}
-        {{#title}}
+        {{#showtitle}}
           aria-labelledby="instance-{{blockinstanceid}}-header"
-        {{/title}}
+        {{/showtitle}}
      {{/arialabel}}>
 
     {{! Block contents }}
     <div class="card-body p-3">
 
         {{! Block header }}
-        {{#title}}
+        {{#showtitle}}
             <h3 id="instance-{{blockinstanceid}}-header" class="h5 card-title d-inline">{{{title}}}</h3>
-        {{/title}}
+        {{/showtitle}}
 
         {{#hascontrols}}
             <div class="block-controls float-end header">