Issue #3410126 by kim.pepper, catch, larowlan, DamienMcKenna, alexpott: File validation logic from #3221793 broke backwards compatibility

core/modules/file/src/Validation/FileValidator.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\file\Validation;
 
+use Drupal\Component\Plugin\Exception\PluginNotFoundException;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Validation\ConstraintManager;
 use Drupal\Core\Validation\DrupalTranslator;
@@ -53,7 +54,12 @@ class FileValidator implements FileValidatorInterface {
       else {
         // Create the constraint.
         // Options are an associative array of constraint properties and values.
-        $constraints[] = $this->constraintManager->create($validator, $options);
+        try {
+          $constraints[] = $this->constraintManager->create($validator, $options);
+        }
+        catch (PluginNotFoundException) {
+          @trigger_error(sprintf('Passing invalid constraint plugin ID "%s" in the list of $validators to Drupal\file\Validation\FileValidator::validate() is deprecated in drupal:10.2.0 and will throw an exception in drupal:11.0.0. See https://www.drupal.org/node/3363700', $validator), E_USER_DEPRECATED);
+        }
       }
     }
 

core/modules/file/tests/src/Kernel/Validation/FileValidatorTest.php

@@ -31,9 +31,11 @@ class FileValidatorTest extends FileValidatorTestBase {
     // Use a mix of legacy functions and plugin IDs to test both work.
     // Each Constraint has its own tests under
     // core/modules/file/tests/src/Kernel/Plugin/Validation/Constraint.
+    // Also check that arbitrary strings can be used.
     $validators = [
       'file_validate_name_length' => [],
       'FileNameLength' => [],
+      'foo' => [],
     ];
     file_test_reset();
 
@@ -42,6 +44,7 @@ class FileValidatorTest extends FileValidatorTestBase {
     $this->assertCount(0, $violations);
     $this->assertCount(1, file_test_get_calls('validate'));
 
+    $this->expectDeprecation('Passing invalid constraint plugin ID "foo" in the list of $validators to Drupal\file\Validation\FileValidator::validate() is deprecated in drupal:10.2.0 and will throw an exception in drupal:11.0.0. See https://www.drupal.org/node/3363700');
     file_test_reset();
     $this->file->set('filename', '');
     $violations = $this->validator->validate($this->file, $validators);