From ba3f8e0befea74429430b1ae988ab4d573883ed8 Mon Sep 17 00:00:00 2001
From: Lucas Werkmeister <lucas.werkmeister@wikimedia.de>
Date: Fri, 6 Jun 2025 15:15:12 +0200
Subject: [PATCH] Throw errors from HTML parsing
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Replace some TODOs with actual exception throwing. The exceptions aren’t
great, but at least they’re better than just ignoring the errors.

The first case doesn’t have a test because, as far as I can tell, it’s
basically impossible to trigger. There are apparently very few
situations where loadHTML() will return false [1] rather than trying to
fix up the markup somehow, and we’re already guaranteeing that the HTML
isn’t empty and that the options are valid.

The second case can raise a variety of errors; just test one of them.
Turning the array of LibXMLError instances (which aren’t Throwable) into
a “tree” / “stack” of Exception instances isn’t super nice, but better
than doing nothing or only throwing an Exception for the first error.

Note that we have to ignore / skip one error: libxml may complain about
“invalid” <template> tags, but we need those for SFC handling.

[1]: https://stackoverflow.com/a/79055330/1420237
---
 src/HtmlParser.php           | 12 +++++++++---
 tests/php/HtmlParserTest.php |  7 +++++++
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/HtmlParser.php b/src/HtmlParser.php
index acd9e89..4a88634 100644
--- a/src/HtmlParser.php
+++ b/src/HtmlParser.php
@@ -28,7 +28,7 @@ public function parseHtml( string $html ): DOMDocument {
 		// LIBXML_NOBLANKS Constant excludes "ghost nodes" to avoid violating
 		// vue's single root node constraint
 		if ( !$document->loadHTML( '<?xml encoding="utf-8" ?>' . $html, LIBXML_NOBLANKS ) ) {
-			//TODO Test failure
+			throw new Exception( 'Failed to parse HTML' );
 		}
 
 		/** @var LibXMLError[] $errors */
@@ -41,9 +41,15 @@ public function parseHtml( string $html ): DOMDocument {
 			libxml_disable_entity_loader( $entityLoaderDisabled );
 		}
 
+		$exception = null;
 		foreach ( $errors as $error ) {
-			//TODO html5 tags can fail parsing
-			//TODO Throw an exception
+			if ( strpos( $error->message, 'Tag template invalid' ) === 0 ) {
+				continue;
+			}
+			$exception = new Exception( $error->message, $error->code, $exception );
+		}
+		if ( $exception !== null ) {
+			throw $exception;
 		}
 
 		return $document;
diff --git a/tests/php/HtmlParserTest.php b/tests/php/HtmlParserTest.php
index af824b4..02e43a1 100644
--- a/tests/php/HtmlParserTest.php
+++ b/tests/php/HtmlParserTest.php
@@ -63,4 +63,11 @@ public function testTwoRootNodes() {
 		$this->parseAndGetRootNode( '<p></p><p></p>' );
 	}
 
+	public function testMalformedHtml(): void {
+		$htmlParser = new HtmlParser();
+		$this->expectException( Exception::class );
+		$this->expectExceptionMessage( 'Unexpected end tag' );
+		$htmlParser->parseHtml( '</p>' );
+	}
+
 }