Update to Drupal 8.1.5. For more information, see https://www.drupal.org/project/drupal/releases/8.1.5

core/modules/big_pipe/src/Render/BigPipe.php

@@ -226,6 +226,13 @@ class BigPipe implements BigPipeInterface {
     $preg_placeholder_strings = array_map($prepare_for_preg_split, array_keys($no_js_placeholders));
     $fragments = preg_split('/' . implode('|', $preg_placeholder_strings) . '/', $html, NULL, PREG_SPLIT_NO_EMPTY | PREG_SPLIT_DELIM_CAPTURE);
 
+    // Determine how many occurrences there are of each no-JS placeholder.
+    $placeholder_occurrences = array_count_values(array_intersect($fragments, array_keys($no_js_placeholders)));
+
+    // Set up a variable to store the content of placeholders that have multiple
+    // occurrences.
+    $multi_occurrence_placeholders_content = [];
+
     foreach ($fragments as $fragment) {
       // If the fragment isn't one of the no-JS placeholders, it is the HTML in
       // between placeholders and it must be printed & flushed immediately. The
@@ -236,6 +243,15 @@ class BigPipe implements BigPipeInterface {
         continue;
       }
 
+      // If there are multiple occurrences of this particular placeholder, and
+      // this is the second occurrence, we can skip all calculations and just
+      // send the same content.
+      if ($placeholder_occurrences[$fragment] > 1 && isset($multi_occurrence_placeholders_content[$fragment])) {
+        print $multi_occurrence_placeholders_content[$fragment];
+        flush();
+        continue;
+      }
+
       $placeholder = $fragment;
       assert('isset($no_js_placeholders[$placeholder])');
       $token = Crypt::randomBytesBase64(55);
@@ -310,6 +326,13 @@ class BigPipe implements BigPipeInterface {
       // they can be sent in ::sendPreBody().
       $cumulative_assets->setAlreadyLoadedLibraries(array_merge($cumulative_assets->getAlreadyLoadedLibraries(), $html_response->getAttachments()['library']));
       $cumulative_assets->setSettings($html_response->getAttachments()['drupalSettings']);
+
+      // If there are multiple occurrences of this particular placeholder, track
+      // the content that was sent, so we can skip all calculations for the next
+      // occurrence.
+      if ($placeholder_occurrences[$fragment] > 1) {
+        $multi_occurrence_placeholders_content[$fragment] = $html_response->getContent();
+      }
     }
   }
 
@@ -508,7 +531,9 @@ EOF;
    *
    * @return array
    *   Indexed array; the order in which the BigPipe placeholders must be sent.
-   *   Values are the BigPipe placeholder IDs.
+   *   Values are the BigPipe placeholder IDs. Note that only unique
+   *   placeholders are kept: if the same placeholder occurs multiple times, we
+   *   only keep the first occurrence.
    */
   protected function getPlaceholderOrder($html) {
     $fragments = explode('<div data-big-pipe-placeholder-id="', $html);
@@ -521,7 +546,7 @@ EOF;
       $order[] = $placeholder;
     }
 
-    return $order;
+    return array_unique($order);
   }
 
 }

core/modules/big_pipe/src/Tests/BigPipeTest.php

@@ -269,6 +269,42 @@ class BigPipeTest extends WebTestBase {
     unlink(\Drupal::root() . '/' . $this->siteDirectory . '/error.log');
   }
 
+  /**
+   * Tests BigPipe with a multi-occurrence placeholder.
+   */
+  public function testBigPipeMultiOccurrencePlaceholders() {
+    $this->drupalLogin($this->rootUser);
+    $this->assertSessionCookieExists(TRUE);
+    $this->assertBigPipeNoJsCookieExists(FALSE);
+
+    // By not calling performMetaRefresh() here, we simulate JavaScript being
+    // enabled, because as far as the BigPipe module is concerned, JavaScript is
+    // enabled in the browser as long as the BigPipe no-JS cookie is *not* set.
+    // @see setUp()
+    // @see performMetaRefresh()
+
+    $this->drupalGet(Url::fromRoute('big_pipe_test_multi_occurrence'));
+    $big_pipe_placeholder_id = 'callback=Drupal%5CCore%5CRender%5CElement%5CStatusMessages%3A%3ArenderMessages&args[0]&token=a8c34b5e';
+    $expected_placeholder_replacement = '<script type="application/vnd.drupal-ajax" data-big-pipe-replacement-for-placeholder-with-id="' . $big_pipe_placeholder_id . '">';
+    $this->assertRaw('The count is 1.');
+    $this->assertNoRaw('The count is 2.');
+    $this->assertNoRaw('The count is 3.');
+    $raw_content = $this->getRawContent();
+    $this->assertTrue(substr_count($raw_content, $expected_placeholder_replacement) == 1, 'Only one placeholder replacement was found for the duplicate #lazy_builder arrays.');
+
+    // By calling performMetaRefresh() here, we simulate JavaScript being
+    // disabled, because as far as the BigPipe module is concerned, it is
+    // enabled in the browser when the BigPipe no-JS cookie is set.
+    // @see setUp()
+    // @see performMetaRefresh()
+    $this->performMetaRefresh();
+    $this->assertBigPipeNoJsCookieExists(TRUE);
+    $this->drupalGet(Url::fromRoute('big_pipe_test_multi_occurrence'));
+    $this->assertRaw('The count is 1.');
+    $this->assertNoRaw('The count is 2.');
+    $this->assertNoRaw('The count is 3.');
+  }
+
   protected function assertBigPipeResponseHeadersPresent() {
     $this->pass('Verifying BigPipe response headers…', 'Debug');
     $this->assertTrue(FALSE !== strpos($this->drupalGetHeader('Cache-Control'), 'private'), 'Cache-Control header set to "private".');