Move extension logic to the block plugin, and allow templates to render the logo the same way.

core/modules/system/src/Plugin/Block/SystemBrandingBlock.php

@@ -167,20 +167,29 @@ public function build() {
     if ($logo_uri !== NULL) {
       $extension = pathinfo($logo_uri, PATHINFO_EXTENSION);
     }
-    $build['site_logo'] = [
-      '#theme' => 'image',
-      '#uri' => $logo_uri,
-      '#alt' => $this->t('Home'),
-      '#attributes' => ['loading' => 'eager', 'fetchpriority' => 'high'],
-      '#access' => $this->configuration['use_site_logo'],
-    ];
 
-    // Add width and height attributes. SVGs are printed inline in the template.
-    if (isset($extension) && $extension !== 'svg') {
-      $image = $this->imageFactory->get(ltrim($logo_uri, '/'));
-      if ($image->isValid()) {
-        $build['site_logo']['#attributes']['width'] = $image->getWidth();
-        $build['site_logo']['#attributes']['height'] = $image->getHeight();
+    if (isset($extension)) {
+      $logo_uri = ltrim($logo_uri, '/');
+      $build['site_logo'] = [
+        '#access' => $this->configuration['use_site_logo'],
+      ];
+      // SVG uses an inline template. Otherwise, use the image factory.
+      if ($extension === 'svg') {
+        $build['site_logo']['#type'] = 'inline_template';
+        $build['site_logo']['#template'] = file_get_contents($logo_uri);
+      }
+      else {
+        $image = $this->imageFactory->get($logo_uri);
+        if ($image->isValid()) {
+          $build['site_logo']['#theme'] = 'image';
+          $build['site_logo']['#uri'] = $logo_uri;
+          $build['site_logo']['#alt'] = $this->t('Home');
+          $build['site_logo']['#attributes'] = ['loading' => 'eager',
+            'fetchpriority' => 'high',
+            'width' => $image->getWidth(),
+            'height' => $image->getHeight(),
+          ];
+        }
       }
     }
 

core/modules/system/system.module

@@ -313,9 +313,8 @@ function system_preprocess_block(&$variables): void {
   switch ($variables['base_plugin_id']) {
     case 'system_branding_block':
       $variables['site_logo'] = '';
-      if ($variables['content']['site_logo']['#access'] && $variables['content']['site_logo']['#uri']) {
-        $variables['site_logo'] = $variables['content']['site_logo']['#uri'];
-        $variables['site_logo_rendered'] = $variables['content']['site_logo'];
+      if ($variables['content']['site_logo']['#access']) {
+        $variables['site_logo'] = $variables['content']['site_logo'];
       }
       $variables['site_name'] = '';
       if ($variables['content']['site_name']['#access'] && $variables['content']['site_name']['#markup']) {

core/modules/system/templates/block--system-branding-block.html.twig

@@ -19,11 +19,7 @@
 {% block content %}
   {% if site_logo %}
     <a href="{{ path('<front>') }}" rel="home">
-      {% if site_logo|split('.')|last == "svg" %}
-        {% include site_logo %}
-      {% else %}
-        {{ site_logo_rendered }}
-      {% endif %}
+      {{ site_logo }}
     </a>
   {% endif %}
   {% if site_name %}

core/themes/olivero/templates/block/block--system-branding-block.html.twig

@@ -19,11 +19,7 @@
   <div class="site-branding__inner">
     {% if site_logo %}
       <a href="{{ path('<front>') }}" rel="home" class="site-branding__logo">
-        {% if site_logo|split('.')|last == "svg" %}
-          {% include site_logo %}
-        {% else %}
-          {{ site_logo_rendered }}
-        {% endif %}
+          {{ site_logo }}
       </a>
     {% endif %}
     {% if site_name %}

core/themes/starterkit_theme/templates/block/block--system-branding-block.html.twig

@@ -17,11 +17,7 @@
 {% block content %}
   {% if site_logo %}
     <a href="{{ path('<front>') }}" rel="home" class="site-logo">
-      {% if site_logo|split('.')|last == "svg" %}
-        {% include site_logo %}
-      {% else %}
-        {{ site_logo_rendered }}
-      {% endif %}
+      {{ site_logo }}
     </a>
   {% endif %}
   {% if site_name %}