Andrey Postnikov
--- a/core/lib/Drupal/Component/Utility/ToStringTrait.php
+++ b/core/lib/Drupal/Component/Utility/ToStringTrait.php

 namespace Drupal\Component\Utility;

+@trigger_error('The ' . __NAMESPACE__ . '\ToStringTrait is deprecated in drupal:11.1.0 and is removed from drupal:12.0.0. Use to implement the __toString() method instead. See https://www.drupal.org/node/3466031', E_USER_DEPRECATED);
+
 /**
 * Wraps __toString in a trait to avoid some fatal errors.
+ *
+ * @deprecated in drupal:11.1.0 and is removed from drupal:12.0.0. Use to
+ *   implement the __toString() method instead.
--- a/core/tests/Drupal/Tests/Core/StringTranslation/TranslatableMarkupTest.php
+++ b/core/tests/Drupal/Tests/Core/StringTranslation/TranslatableMarkupTest.php
    $string = 'May I have an exception?';
    $text = $this->getMockBuilder(TranslatableMarkup::class)
      ->setConstructorArgs([$string, [], [], $translation])
-      ->onlyMethods(['_die'])
      ->getMock();
-    $text
-      ->expects($this->once())
-      ->method('_die')
-      ->willReturn('');
--- a/core/tests/Drupal/Tests/Core/StringTranslation/TranslatableMarkupTest.php
+++ b/core/tests/Drupal/Tests/Core/StringTranslation/TranslatableMarkupTest.php
-        throw new \Exception('Yes you may.');
-      });
-
-    // We set a custom error handler because of https://github.com/sebastianbergmann/phpunit/issues/487
-    set_error_handler([$this, 'errorHandler']);
-    // We want this to trigger an error.
-    (string) $text;
-    restore_error_handler();
+      ->method('render')
+      ->willThrowException($exception);

-    $this->assertEquals(E_USER_ERROR, $this->lastErrorNumber);
-    $this->assertMatchesRegularExpression('/Exception thrown while calling __toString on a .*MockObject_TranslatableMarkup_.* object in .*TranslatableMarkupTest.php on line [0-9]+: Yes you may./', $this->lastErrorMessage);
+    $this->expectException(\Exception::class);
+    $this->expectExceptionMessage($exception->getMessage());
+    $this->assertTrue('' === (string) $text);
--- a/core/modules/big_pipe/src/Render/BigPipe.php
+++ b/core/modules/big_pipe/src/Render/BigPipe.php
          throw $e;
        }
        else {
-          trigger_error($e, E_USER_ERROR);
+          $this->logger->error($e->getMessage(), [
+            'exception' => $e,
+            'backtrace' => $e->getTraceAsString(),
+          ]);
--- a/core/modules/big_pipe/src/Render/BigPipe.php
+++ b/core/modules/big_pipe/src/Render/BigPipe.php
            throw $e;
          }
          else {
-            trigger_error($e, E_USER_ERROR);
+            $this->logger->error($e->getMessage(), [
+              '@message' => $e->getMessage(),