.../CurrentPathDestinationLinkResponseFilter.php   |   1 +
 ...urrentPathDestinationLinkResponseFilterTest.php | 127 +++++++++++++++++++++
 2 files changed, 128 insertions(+)

diff --git a/core/lib/Drupal/Core/EventSubscriber/CurrentPathDestinationLinkResponseFilter.php b/core/lib/Drupal/Core/EventSubscriber/CurrentPathDestinationLinkResponseFilter.php
index 8feb9da..2569f1c 100644
--- a/core/lib/Drupal/Core/EventSubscriber/CurrentPathDestinationLinkResponseFilter.php
+++ b/core/lib/Drupal/Core/EventSubscriber/CurrentPathDestinationLinkResponseFilter.php
@@ -127,6 +127,7 @@ public static function setCurrentPathAsDestination($html_markup, $current_path)
       $url = $node->getAttribute('href');
       $glue = (strpos($url, '?') === FALSE) ? '?' : '&';
       $node->setAttribute('href', $url . $glue . $destination);
+      $node->removeAttribute('data-current-path-destination');
 
       // Get the updated tag.
       $updated_tag = $dom->saveXML($node, LIBXML_NOEMPTYTAG);
diff --git a/core/tests/Drupal/Tests/Core/EventSubscriber/CurrentPathDestinationLinkResponseFilterTest.php b/core/tests/Drupal/Tests/Core/EventSubscriber/CurrentPathDestinationLinkResponseFilterTest.php
new file mode 100644
index 0000000..4ecfa4e
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/EventSubscriber/CurrentPathDestinationLinkResponseFilterTest.php
@@ -0,0 +1,127 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\Core\EventSubscriber\CurrentPathDestinationLinkResponseFilterTest.
+ */
+
+namespace Drupal\Tests\Core\EventSubscriber;
+
+use Drupal\Core\EventSubscriber\CurrentPathDestinationLinkResponseFilter;
+use Drupal\Core\Template\Attribute;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\Core\EventSubscriber\CurrentPathDestinationLinkResponseFilter
+ * @group EventSubscriber
+ */
+class CurrentPathDestinationLinkResponseFilterTest extends UnitTestCase {
+
+  /**
+   * Provides test data for setCurrentPathAsDestination().
+   *
+   * @see \Drupal\Core\EventSubscriber\CurrentPathDestinationLinkResponseFilter::setCurrentPathAsDestination()
+   */
+  public function providerTestSetCurrentPathAsDestination() {
+    // Define all the variations that *don't* affect whether or not an
+    // "destination" query string is set, but that should remain unchanged:
+    // - surrounding HTML
+    // - tags for which to test the setting of the "destination" query string
+    // - content of said tags
+    $edge_case_html5 = '<audio src="foo.ogg">
+  <track kind="captions" src="foo.en.vtt" srclang="en" label="English">
+  <track kind="captions" src="foo.sv.vtt" srclang="sv" label="Svenska">
+</audio>';
+    $html = [
+      // Simple HTML.
+      0 => ['prefix' => '<div><p>', 'suffix' => '</p></div>'],
+      // Tricky HTML5 example that's unsupported by PHP <=5.4's DOMDocument:
+      // https://www.drupal.org/comment/7938201#comment-7938201.
+      1 => ['prefix' => '<div><p>', 'suffix' => '</p>' . $edge_case_html5 . '</div>'],
+      // Multi-byte content *before* the HTML that needs the "destination" query
+      // string.
+      2 => ['prefix' => '<div><p>αβγδεζηθικλμνξοσὠ</p><p>', 'suffix' => '</p></div>'],
+    ];
+    $tags = [
+      // Of course, it must work on anchors.
+      'a',
+      // … but it should work, on *any* tag, really.
+      'foo',
+    ];
+    $contents = [
+      // Regular content.
+      'test',
+      // Mix of UTF-8 and HTML entities, both must be retained.
+      '☆ 3 × 4 = €12 and 4 &times; 3 = &euro;12 &#9734',
+      // Multi-byte content.
+      'ΑΒΓΔΕΖΗΘΙΚΛΜΝΞΟΣὨ',
+    ];
+    $situations = [
+      // Without a "data-current-path-destination" attribute present, nothing
+      // happens.
+      0 => ['path' => 'foo', 'attributes' => ['href' => '/some/path'], 'expected href' => '/some/path'],
+      // With a "data-current-path-destination" attribute present, the
+      // "destination" query string is added.
+      1 => ['path' => 'foo', 'attributes' => ['href' => '/some/path', 'data-current-path-destination' => TRUE], 'expected href' => '/some/path?destination=foo'],
+      // With a "data-current-path-destination" attribute present on a link that
+      // already has a "destination" query string, we just append it. We do not
+      // babysit broken code in CurrentPathDestinationLinkResponseFilter.
+      2 => ['path' => 'foo', 'attributes' => ['href' => '/some/path?destination=/already/there', 'data-current-path-destination' => TRUE], 'expected href' => '/some/path?destination=/already/there&destination=foo'],
+    ];
+
+    // Loop over the surrounding HTML variations.
+    $data = [];
+    for ($h = 0; $h < count($html); $h++) {
+      $html_prefix = $html[$h]['prefix'];
+      $html_suffix = $html[$h]['suffix'];
+      // Loop over the tag variations.
+      for ($t = 0; $t < count($tags); $t++) {
+        $tag = $tags[$t];
+        // Loop over the tag contents variations.
+        for ($c = 0; $c < count($contents); $c++) {
+          $tag_content = $contents[$c];
+
+          $create_markup = function (Attribute $attributes) use ($html_prefix, $html_suffix, $tag, $tag_content) {
+            return $html_prefix . '<' . $tag . $attributes . '>' . $tag_content . '</' . $tag . '>' . $html_suffix;
+          };
+
+          // Loop over the situations.
+          for ($s = 0; $s < count($situations); $s++) {
+            $situation = $situations[$s];
+
+            // Build the source markup.
+            $source_markup = $create_markup(new Attribute($situation['attributes']));
+
+            // Build the target markup.
+            $active_attributes = $situation['attributes'];
+            $active_attributes['href'] = $situation['expected href'];
+            unset($active_attributes['data-current-path-destination']);
+            $target_markup = $create_markup(new Attribute($active_attributes));
+
+            $data[] = [$source_markup, $situation['path'], $target_markup];
+          }
+        }
+      }
+    }
+
+    return $data;
+  }
+
+  /**
+   * Tests setCurrentPathAsDestination().
+   *
+   * @param string $html_markup
+   *   The original HTML markup.
+   * @param string $current_path
+   *   The system path of the currently active page.
+   * @param string $expected_html_markup
+   *   The expected updated HTML markup.
+   *
+   * @dataProvider providerTestSetCurrentPathAsDestination
+   * @covers ::setCurrentPathAsDestination
+   */
+  public function testSetCurrentPathAsDestination($html_markup, $current_path, $expected_html_markup) {
+    $this->assertSame($expected_html_markup, CurrentPathDestinationLinkResponseFilter::setCurrentPathAsDestination($html_markup, $current_path));
+  }
+
+}