Get more descriptive error when DOM validation fails in Magento

README.md

Get a more debugable error message when DOM validation fails in Magento.

Original Error Message

1 exception(s):
Exception #0 (Magento\Framework\Config\Dom\ValidationException): Element 'arguments': This element is not expected.
Line: 1471

Error Message With Patch

1 exception(s):
Exception #0 (Magento\Framework\Config\Dom\ValidationException): Element 'arguments': This element is not expected.
Line: 1471
The xml was: 
1466:            <argument name="show_category" xsi:type="boolean">true</argument>
1467:         </arguments>
1468:      </block>
1469:      <referenceBlock name="product_view_detail" remove="true"/>
1470:      <block name="abc.gtm.product_view_detail" class="ABC\GoogleTagManager\Block\Detail" template="ABC_GoogleTagManager::detailproduct.phtml"/>
1471:      <arguments>
1472:         <argument name="show_category" xsi:type="boolean">true</argument>
1473:      </arguments>
1474:   </referenceContainer>
1475:</body>

This patch is NOT intended for production use, it is intended to help debug an issue, after the issue has been resolved it should be removed.

Installing & Applying the patch

wget https://gist.githubusercontent.com/adamzero1/2c25dbcf1caec0ad9b55e7f6fd7972d8/raw/b19f6779625aa29122c0bc500ae213ab0b6bb212/nice_dom_error_message.patch
patch -p0 < nice_dom_error_message.patch

Reverting and uninstalling patch

patch -p0 -R < nice_dom_error_message.patch
rm nice_dom_error_message.patch

nice_dom_error_message.patch

--- vendor/magento/framework/Config/Dom.php	2023-01-03 14:33:27.739851841 +0000
+++ "vendor/magento/framework/Config/Dom.php"	2023-01-03 14:33:35.580142053 +0000
@@ -123,13 +123,13 @@
      * @param string $errorFormat
      * @return string[]
      */
-    private static function getXmlErrors($errorFormat)
+    private static function getXmlErrors($errorFormat, $dom = null)
     {
         $errors = [];
         $validationErrors = libxml_get_errors();
         if (count($validationErrors)) {
             foreach ($validationErrors as $error) {
-                $errors[] = self::_renderErrorMessage($error, $errorFormat);
+                $errors[] = self::_renderErrorMessage($error, $errorFormat, $dom);
             }
         } else {
             $errors[] = 'Unknown validation error';
@@ -380,7 +380,7 @@
         try {
             $result = $dom->schemaValidate($schema);
             if (!$result) {
-                $errors = self::getXmlErrors($errorFormat);
+                $errors = self::getXmlErrors($errorFormat, $dom);
             }
         } catch (\Exception $exception) {
             $errors = self::getXmlErrors($errorFormat);
@@ -401,7 +401,7 @@
      * @return string
      * @throws \InvalidArgumentException
      */
-    private static function _renderErrorMessage(\LibXMLError $errorInfo, $format)
+    private static function _renderErrorMessage(\LibXMLError $errorInfo, $format, $dom = null)
     {
         $result = $format;
         foreach ($errorInfo as $field => $value) {
@@ -424,6 +424,15 @@
                 }
             }
         }
+        if($dom){
+            $xml = explode(PHP_EOL, $dom->saveXml());
+            $lines = array_slice($xml, max(0, $errorInfo->line - 5), 10, true);
+            $result .= 'The xml was: '.PHP_EOL;
+            foreach($lines as $lineNumber => $line){
+                $result .= $lineNumber.':'.$line.PHP_EOL;
+            }
+        }
+
         return $result;
     }