Throw more specific exception if an svg file's contents is invalid svg code

src/Exception/InvalidSvgException.php

@@ -0,0 +1,7 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pcm\IconBundle\Exception;
+
+class InvalidSvgException extends \Exception {};

src/Twig/Runtime/IconRuntime.php

@@ -7,6 +7,7 @@ namespace Pcm\IconBundle\Twig\Runtime;
 use Pcm\IconBundle\Exception\ColourNotFound;
 use Pcm\IconBundle\Exception\EmptyFileException;
 use Pcm\IconBundle\Exception\IconNotFound;
+use Pcm\IconBundle\Exception\InvalidSvgException;
 use Twig\Extension\RuntimeExtensionInterface;
 
 final class IconRuntime implements RuntimeExtensionInterface
@@ -49,6 +50,10 @@ final class IconRuntime implements RuntimeExtensionInterface
             throw new EmptyFileException(\sprintf("The file %s.svg was found, but it was empty!", $options['icon']));
         }
 
+        if (!$this->isValidXml($svg)) {
+            throw new InvalidSvgException(\sprintf("The file %s.svg was found, but it does not contain valid SVG code!", $options['icon']));
+        }
+
         $this->sanitiseSvg($svg);
 
         $colourClasses = $this->getColourClasses($options['colour'], $options['hover']);
@@ -211,4 +216,15 @@ final class IconRuntime implements RuntimeExtensionInterface
 
         $svg = $this->removeXMLDeclaration($svgAsXml->saveXML());
     }
+
+    private function isValidXml(string $input): bool
+    {
+        try {
+            new \SimpleXMLElement($input);
+        } catch (\Exception) {
+            return false;
+        }
+
+        return true;
+    }
 }

tests/Twig/Runtime/IconRuntimeTest.php

@@ -8,6 +8,7 @@ use Pcm\IconBundle\DependencyInjection\Configuration;
 use Pcm\IconBundle\Exception\ColourNotFound;
 use Pcm\IconBundle\Exception\EmptyFileException;
 use Pcm\IconBundle\Exception\IconNotFound;
+use Pcm\IconBundle\Exception\InvalidSvgException;
 use Pcm\IconBundle\Twig\Runtime\IconRuntime;
 use PHPUnit\Framework\TestCase;
 
@@ -57,6 +58,12 @@ class IconRuntimeTest extends TestCase
         $this->icon->renderIcon(['icon' => 'empty']);
     }
 
+    public function testThrowsIfContentsIsNotValidSvg(): void
+    {
+        $this->expectException(InvalidSvgException::class);
+        $this->icon->renderIcon(['icon' => 'invalid']);
+    }
+
     public function testNoTitleExistsIfNotPassedIn(): void
     {
         $content = $this->icon->renderIcon(['icon' => self::ICON]);

tests/icons/invalid.svg

@@ -0,0 +1 @@
+<svg><svg>