Unrealistic error description on developer mode

Question

I m running Magento2.3 and getting below error.

How can I find where exactly error in file. which XML is causing the issue?

Please, can anyone guide me on this? This is very confusing to solve

    1 exception(s):
Exception #0 (Magento\Framework\Config\Dom\ValidationException): Element 'referenceBlock', attribute 'class': The attribute 'class' is not allowed.
Line: 972


Exception #0 (Magento\Framework\Config\Dom\ValidationException): Element 'referenceBlock', attribute 'class': The attribute 'class' is not allowed.
Line: 972

#0 /home/ukprinting/public_html/vendor/magento/framework/Config/Dom.php(117): Magento\Framework\Config\Dom->_initDom('<layout xmlns:x...')
#1 /home/ukprinting/public_html/vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php(116): Magento\Framework\Config\Dom->__construct('<layout xmlns:x...', Object(Magento\Framework\App\Arguments\ValidationState), Array, NULL, '/home/ukprintin...', '%message%\nLine:...')
#2 /home/ukprinting/public_html/vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php(66): Magento\Framework\ObjectManager\Factory\AbstractFactory->createObject('Magento\\Framewo...', Array)
#3 /home/ukprinting/public_html/vendor/magento/framework/ObjectManager/ObjectManager.php(56): Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create('Magento\\Framewo...', Array)
#4 /home/ukprinting/public_html/vendor/magento/framework/Config/DomFactory.php(43): Magento\Framework\ObjectManager\ObjectManager->create('Magento\\Framewo...', Array)
#5 /home/ukprinting/public_html/vendor/magento/framework/View/Model/Layout/Update/Validator.php(141): Magento\Framework\Config\DomFactory->createDom(Array)
#6 /home/ukprinting/public_html/vendor/magento/framework/View/Model/Layout/Merge.php(476): Magento\Framework\View\Model\Layout\Update\Validator->isValid('<layout xmlns:x...', 'layout_merged', false)
#7 /home/ukprinting/public_html/vendor/magento/framework/View/Model/Layout/Merge.php(457): Magento\Framework\View\Model\Layout\Merge->_validateMergedLayout('LAYOUT_frontend...', '<!--\r\n    <refe...')
#8 /home/ukprinting/public_html/generated/code/Magento/Framework/View/Model/Layout/Merge/Interceptor.php(193): Magento\Framework\View\Model\Layout\Merge->load(Array)
#9 /home/ukprinting/public_html/vendor/magento/framework/View/Layout/Builder.php(86): Magento\Framework\View\Model\Layout\Merge\Interceptor->load()
#10 /home/ukprinting/public_html/vendor/magento/framework/View/Layout/Builder.php(63): Magento\Framework\View\Layout\Builder->loadLayoutUpdates()
#11 /home/ukprinting/public_html/vendor/magento/framework/View/Layout.php(253): Magento\Framework\View\Layout\Builder->build()
#12 /home/ukprinting/public_html/vendor/magento/framework/View/Layout.php(875): Magento\Framework\View\Layout->build()
#13 /home/ukprinting/public_html/generated/code/Magento/Framework/View/Layout/Interceptor.php(414): Magento\Framework\View\Layout->getBlock('page_content_he...')
#14 /home/ukprinting/public_html/vendor/magento/module-cms/Helper/Page.php(171): Magento\Framework\View\Layout\Interceptor->getBlock('page_content_he...')
#15 /home/ukprinting/public_html/vendor/magento/module-cms/Controller/Index/Index.php(74): Magento\Cms\Helper\Page->prepareResultPage(Object(Magento\Cms\Controller\Index\Index\Interceptor), 'home')
#16 /home/ukprinting/public_html/generated/code/Magento/Cms/Controller/Index/Index/Interceptor.php(24): Magento\Cms\Controller\Index\Index->execute(NULL)
#17 /home/ukprinting/public_html/vendor/magento/framework/App/Action/Action.php(108): Magento\Cms\Controller\Index\Index\Interceptor->execute()
#18 /home/ukprinting/public_html/vendor/magento/framework/Interception/Interceptor.php(58): Magento\Framework\App\Action\Action->dispatch(Object(Magento\Framework\App\Request\Http))
#19 /home/ukprinting/public_html/vendor/magento/framework/Interception/Interceptor.php(138): Magento\Cms\Controller\Index\Index\Interceptor->___callParent('dispatch', Array)
#20 /home/ukprinting/public_html/vendor/magento/framework/Interception/Interceptor.php(153): Magento\Cms\Controller\Index\Index\Interceptor->Magento\Framework\Interception\{closure}(Object(Magento\Framework\App\Request\Http))
#21 /home/ukprinting/public_html/generated/code/Magento/Cms/Controller/Index/Index/Interceptor.php(39): Magento\Cms\Controller\Index\Index\Interceptor->___callPlugins('dispatch', Array, Array)
#22 /home/ukprinting/public_html/vendor/magento/framework/App/FrontController.php(159): Magento\Cms\Controller\Index\Index\Interceptor->dispatch(Object(Magento\Framework\App\Request\Http))
#23 /home/ukprinting/public_html/vendor/magento/framework/App/FrontController.php(99): Magento\Framework\App\FrontController->processRequest(Object(Magento\Framework\App\Request\Http), Object(Magento\Cms\Controller\Index\Index\Interceptor))
#24 /home/ukprinting/public_html/vendor/magento/framework/Interception/Interceptor.php(58): Magento\Framework\App\FrontController->dispatch(Object(Magento\Framework\App\Request\Http))
#25 /home/ukprinting/public_html/vendor/magento/framework/Interception/Interceptor.php(138): Magento\Framework\App\FrontController\Interceptor->___callParent('dispatch', Array)
#26 /home/ukprinting/public_html/vendor/magento/module-store/App/FrontController/Plugin/RequestPreprocessor.php(94): Magento\Framework\App\FrontController\Interceptor->Magento\Framework\Interception\{closure}(Object(Magento\Framework\App\Request\Http))
#27 /home/ukprinting/public_html/vendor/magento/framework/Interception/Interceptor.php(135): Magento\Store\App\FrontController\Plugin\RequestPreprocessor->aroundDispatch(Object(Magento\Framework\App\FrontController\Interceptor), Object(Closure), Object(Magento\Framework\App\Request\Http))
#28 /home/ukprinting/public_html/vendor/magento/module-page-cache/Model/App/FrontController/BuiltinPlugin.php(69): Magento\Framework\App\FrontController\Interceptor->Magento\Framework\Interception\{closure}(Object(Magento\Framework\App\Request\Http))
#29 /home/ukprinting/public_html/vendor/magento/framework/Interception/Interceptor.php(135): Magento\PageCache\Model\App\FrontController\BuiltinPlugin->aroundDispatch(Object(Magento\Framework\App\FrontController\Interceptor), Object(Closure), Object(Magento\Framework\App\Request\Http))
#30 /home/ukprinting/public_html/vendor/magento/framework/Interception/Interceptor.php(153): Magento\Framework\App\FrontController\Interceptor->Magento\Framework\Interception\{closure}(Object(Magento\Framework\App\Request\Http))
#31 /home/ukprinting/public_html/generated/code/Magento/Framework/App/FrontController/Interceptor.php(26): Magento\Framework\App\FrontController\Interceptor->___callPlugins('dispatch', Array, NULL)
#32 /home/ukprinting/public_html/vendor/magento/framework/App/Http.php(135): Magento\Framework\App\FrontController\Interceptor->dispatch(Object(Magento\Framework\App\Request\Http))
#33 /home/ukprinting/public_html/generated/code/Magento/Framework/App/Http/Interceptor.php(24): Magento\Framework\App\Http->launch()
#34 /home/ukprinting/public_html/vendor/magento/framework/App/Bootstrap.php(258): Magento\Framework\App\Http\Interceptor->launch()
#35 /home/ukprinting/public_html/index.php(39): Magento\Framework\App\Bootstrap->run(Object(Magento\Framework\App\Http\Interceptor))
#36 {main}

Answer 1

In case you are using the PhpStorm you can build a custom inspection which can find this and another xml errors almost automatically.

1) Generate urn for PHPStorm using Magento's built-in command bin/magento dev:urn-catalog:generate. Note: if you generate it on the deployment server you should copy the .idea/misc.xml file manually to your local project.

2) Create new code inspection in PHPStorm:

• Open context menu

  

• Open inspection preferences

  

• Create new xml inspection using the gear icon

  

• Hit the Ok to run inspection

• Check result

  

PS: you can run this inspection to the overall project or to the selected directories/files.

Answer 2

It will be an extension or theme you have added. Does the store have many extensions installed?

Search for referenceBlock

Then you've got to work through the results and see where class= has been used