Issue #2285311 by joelpittet, tomatkins, susannecoates: Theme's "Path to custom logo" always validated even if "Use the default logo" is set

core/modules/system/src/Form/ThemeSettingsForm.php

@@ -379,6 +379,16 @@ class ThemeSettingsForm extends ConfigFormBase {
         }
       }
 
+      // When intending to use the default logo, unset the logo_path.
+      if ($form_state->getValue('default_logo')) {
+        $form_state->unsetValue('logo_path');
+      }
+
+      // When intending to use the default favicon, unset the favicon_path.
+      if ($form_state->getValue('default_favicon')) {
+        $form_state->unsetValue('favicon_path');
+      }
+
       // If the user provided a path for a logo or favicon file, make sure a file
       // exists at that path.
       if ($form_state->getValue('logo_path')) {

core/modules/system/src/Tests/System/ThemeTest.php

@@ -201,6 +201,18 @@ class ThemeTest extends WebTestBase {
     $this->assertLink($theme_handler->getName('stable'));
     $this->drupalGet('admin/appearance/settings/stable');
     $this->assertResponse(200, 'The theme settings form URL for a hidden theme that is the admin theme is available.');
+
+    // Ensure default logo and favicons are not triggering custom path
+    // validation errors if their custom paths are set on the form.
+    $edit = [
+      'default_logo' => TRUE,
+      'logo_path' => 'public://whatever.png',
+      'default_favicon' => TRUE,
+      'favicon_path' => 'public://whatever.ico',
+    ];
+    $this->drupalPostForm('admin/appearance/settings', $edit, 'Save configuration');
+    $this->assertNoText('The custom logo path is invalid.');
+    $this->assertNoText('The custom favicon path is invalid.');
   }
 
   /**