Bricks makes use of deprecated eck 'entity' variable

Of course, I'm happy to help.

There are a number of modules installed, but you should be able to reproduce it using just bricks and and its submodule bricks_default, including the latter's dependencies, which include ECK.

In your theme override eck-entity--brick.html.twig so that it displays {{ content }} instead of {{ entity }}. Bricks_default will have created a demo page with lots of bricks placed, which should be sufficient to observe the behaviour I'm reporting. When you visit the page, to see the content you will scroll past multiple messages like the one below:

User deprecated function: You are using the 'entity' variable in your eck-entity template. You should use 'content' instead. The 'entity' variable will be removed before the release of 8.x-1.0-beta1 in Drupal\eck\ArrayDeprecationWrapper->offsetExists() (line 45 of modules/contrib/eck/src/ArrayDeprecationWrapper.php).
Drupal\eck\ArrayDeprecationWrapper->offsetExists('field_childs') (Line: 89)
bricks_preprocess_eck_entity(Array, 'eck_entity', Array) (Line: 287)
Drupal\Core\Theme\ThemeManager->render('eck_entity', Array) (Line: 437)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 450)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 195)
Drupal\Core\Render\Renderer->render(Array) (Line: 490)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 71)
__TwigTemplate_2f11609e76f1e6417cb76a3e3d2308879e780edce60ab7330a966f0ce210555f->doDisplay(Array, Array) (Line: 432)
Twig_Template->displayWithErrorHandling(Array, Array) (Line: 403)
Twig_Template->display(Array) (Line: 411)
Twig_Template->render(Array) (Line: 64)
twig_render_template('themes/de_theme/templates/field/field.html.twig', Array) (Line: 384)
Drupal\Core\Theme\ThemeManager->render('field', Array) (Line: 437)
Drupal\Core\Render\Renderer->doRender(Array) (Line: 450)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 195)
Drupal\Core\Render\Renderer->render(Array) (Line: 490)
Drupal\Core\Template\TwigExtension->escapeFilter(Object, Array, 'html', NULL, 1) (Line: 114)
__TwigTemplate_e2d948cb564ea7f4f4bd4eeeede1b7611d107b26af421839c88f9a6ae06020bb->doDisplay(Array, Array) (Line: 432)
Twig_Template->displayWithErrorHandling(Array, Array) (Line: 403)
Twig_Template->display(Array) (Line: 411)
Twig_Template->render(Array) (Line: 64)
twig_render_template('themes/de_theme/templates/content/node.html.twig', Array) (Line: 384)
Drupal\Core\Theme\ThemeManager->render('node', Array) (Line: 437)
Drupal\Core\Render\Renderer->doRender(Array, ) (Line: 195)
Drupal\Core\Render\Renderer->render(Array, ) (Line: 226)
Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}() (Line: 582)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 227)
Drupal\Core\Render\MainContent\HtmlRenderer->prepare(Array, Object, Object) (Line: 117)
Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object, Object) (Line: 90)
Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object, 'kernel.view', Object)
call_user_func(Array, Object, 'kernel.view', Object) (Line: 111)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.view', Object) (Line: 156)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 68)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 99)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 78)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 84)
Drupal\shield\ShieldMiddleware->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 665)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

I totally understand the desire to warn the admins of the site, but I have a number of issues with the implementation of the deprecation warning that was added to alpha5 of ECK:

• As stated in the issue description, you get this warning even if you override the offending template.
• The warning is unnecessarily verbose for being displayed as a message. If it's deemed necessary to display all this detail, push it into watchdog, and set a message that says to check the log for details. Personally I don't think showing all this is useful, since the specific templates it cites don't have the defect. In my case, every time it would cite all my template overrides, which were already fixed.
• It would be much better if it were possible to only display this error once. Since it's an issue with a single module, displaying the message over and over again for each entity displayed doesn't provide additional useful information. On the site where I first observed this, I saw saw this message 19 times on the home page. To be honest, when I first saw it I thought the site was broken, not there was a deprecation issue.

I'll add one more thing: If you go into the Bricks module and change eck-entity--brick.html.twig to use {{ content }}, all the warning go away, even though that template was already overridden.