Show forms on empty product pages

The current logic for form rendering assumes that a single product page
will trigger the filter `the_content`. This is not always true. In cases
where the product has no description, WooCommerce does not render the
description tab at all, which is where that filter usually fires (in my
testing).

This change ensures that we still give these forms a chance to render on
 such pages.

MAILPOET-5859

mailpoet/lib/Form/DisplayFormInWPContent.php

@@ -130,7 +130,7 @@ class DisplayFormInWPContent {
    * @return void
    */
   public function maybeRenderFormsInFooter(): void {
-    if ($this->wp->isArchive() || $this->wp->isFrontPage() || $this->wp->isHome()) {
+    if ($this->wp->isArchive() || $this->wp->isFrontPage() || $this->wp->isHome() || $this->isWooProductPageWithoutContent()) {
       $formMarkup = $this->getFormMarkup();
       if (!empty($formMarkup)) {
         $this->assetsController->setupFrontEndDependencies();
@@ -141,6 +141,20 @@ class DisplayFormInWPContent {
     }
   }
 
+  /**
+   * @return bool
+   */
+  public function isWooProductPageWithoutContent(): bool {
+    if (
+      !$this->wp->isSingular('product')
+      || !$this->wp->didAction('wp_footer')
+    ) {
+      return false;
+    }
+
+    return !$this->wp->didFilter('the_content');
+  }
+
   private function shouldDisplay(): bool {
     $result = true;
     // This is a fix Yoast plugin and Shapely theme compatibility

mailpoet/lib/WP/Functions.php

@@ -41,6 +41,14 @@ class Functions {
     return did_action($hookName);
   }
 
+  /**
+   * @param string $hookName
+   * @return int
+   */
+  public function didFilter($hookName) {
+    return did_filter($hookName);
+  }
+
   public function trailingslashit(string $url) {
     return trailingslashit($url);
   }

mailpoet/tests/unit/Form/DisplayFormInWPContentTest.php

@@ -894,6 +894,35 @@ class DisplayFormInWPContentTest extends \MailPoetUnitTest {
     verify($result)->stringEndsWith($formHtml);
   }
 
+  public function testFormRendersOnProductPageWithoutContent(): void {
+    $formHtml = '<form id="test-form"></form>';
+    $this->wp->expects($this->any())->method('isSingular')->willReturn(true);
+    $this->wp->expects($this->once())->method('didAction')->with($this->equalTo('wp_footer'))->willReturn(true);
+    $this->wp->expects($this->once())->method('didFilter')->with($this->equalTo('the_content'))->willReturn(false);
+    $this->assetsController->expects($this->once())->method('setupFrontEndDependencies');
+    $this->templateRenderer->expects($this->once())->method('render')->willReturn($formHtml);
+    $this->wp
+      ->expects($this->never())
+      ->method('setTransient');
+    $form = new FormEntity('My Form');
+    $form->setSettings([
+      'segments' => ['3'],
+      'form_placement' => [
+        'below_posts' => ['enabled' => '', 'pages' => ['all' => ''], 'posts' => ['all' => '']],
+        'popup' => ['enabled' => '1', 'pages' => ['all' => ''], 'posts' => ['all' => '']],
+        'fixed_bar' => ['enabled' => '1', 'pages' => ['all' => '1'], 'posts' => ['all' => '1']]],
+      'success_message' => 'Hello',
+    ]);
+    $form->setBody([['type' => 'submit', 'params' => ['label' => 'Subscribe!'], 'id' => 'submit', 'name' => 'Submit']]);
+    $this->repository->expects($this->once())->method('findBy')->willReturn([$form]);
+
+    ob_start();
+    $this->hook->maybeRenderFormsInFooter();
+    $renderedFormHtml = ob_get_clean();
+    verify($renderedFormHtml)->notEquals('content');
+    verify($renderedFormHtml)->stringEndsWith($formHtml);
+  }
+
   public function _after() {
     parent::_after();
     WPFunctions::set(new WPFunctions());