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HTML API: Preserve leading newlines in PRE, TEXTAREA #24

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HTML API: Preserve leading newlines in PRE, TEXTAREA #24

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d130c92
Fix newlines disappearing inside PRE,TEXTAREA elements
sirreal Feb 5, 2026
21b48ea
Ticket number, data provider
sirreal Feb 5, 2026
03fb7f0
YODA
sirreal Feb 5, 2026
0acab11
Apply suggestion from @mukeshpanchal27
sirreal Feb 6, 2026
2319b94
Merge branch 'trunk' into html-api/normalization-special-newlines
sirreal Feb 6, 2026
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26 changes: 26 additions & 0 deletions src/wp-includes/html-api/class-wp-html-processor.php
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Original file line number Diff line number Diff line change
Expand Up @@ -1412,6 +1412,32 @@ public function serialize_token(): string {

$html .= '>';

/*
* The HTML parser strips a leading newline immediately after the start
* tag of TEXTAREA, PRE, and LISTING elements. When serializing, prepend
* a leading newline to ensure the semantic HTML content is preserved.
*
* For example, `<pre>\n\nX</pre>` must not become `<pre>\nX</pre>` because its content
* has changed. However, `<pre>X</pre>` and `<pre>\nX</pre>` are _equivalent_.
*
* > A start tag whose tag name is "textarea"
* > …
* > If the next token is a U+000A LINE FEED (LF) character token, then ignore
* > that token and move on to the next one. (Newlines at the start of textarea
* > elements are ignored as an authoring convenience.)
*
* > A start tag whose tag name is one of: "pre", "listing"
* > …
* > If the next token is a U+000A LINE FEED (LF) character token, then ignore
* > that token and move on to the next one. (Newlines at the start of pre blocks
* > are ignored as an authoring convenience.)
*
* @see https://html.spec.whatwg.org/multipage/parsing.html
*/
if ( 'TEXTAREA' === $tag_name || 'PRE' === $tag_name || 'LISTING' === $tag_name ) {
$html .= "\n";
}

// Flush out self-contained elements.
if ( $in_html && in_array( $tag_name, array( 'IFRAME', 'NOEMBED', 'NOFRAMES', 'SCRIPT', 'STYLE', 'TEXTAREA', 'TITLE', 'XMP' ), true ) ) {
$text = $this->get_modifiable_text();
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68 changes: 68 additions & 0 deletions tests/phpunit/tests/html-api/wpHtmlProcessor-serialize.php
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Expand Up @@ -321,4 +321,72 @@ public static function data_provider_serialize_doctype() {
'Double quotes in system ID' => array( '<!DOCTYPE html SYSTEM \'"quoted"\'\>', '<!DOCTYPE html SYSTEM \'"quoted"\'>' ),
);
}

/**
* Ensures that leading newlines in PRE, LISTING, and TEXTAREA elements are preserved upon normalization,
* and that normalization is idempotent in these cases.
*
* @ticket 64607
*
* @dataProvider data_provider_normalize_special_leading_newline_cases
*
* @param string $input HTML input containing leading newlines in PRE, LISTING, or TEXTAREA elements.
* @param string $expected Expected output after normalization, which should preserve leading newlines.
*/
public function test_normalize_special_leading_newline_handling( string $input, string $expected ) {
$normalized = WP_HTML_Processor::normalize( $input );
$this->assertEqualHTML( $expected, $normalized );
$normalized_twice = WP_HTML_Processor::normalize( $normalized );
$this->assertEqualHTML( $expected, $normalized_twice );
}

/**
* Data provider.
*
* @return array[]
*/
public static function data_provider_normalize_special_leading_newline_cases() {
return array(
'Leading newline in PRE' => array(
"<pre>\nline 1\nline 2</pre>",
"<pre>line 1\nline 2</pre>",
),
'Double leading newline in PRE' => array(
"<pre>\n\nline 2\nline 3</pre>",
"<pre>\n\nline 2\nline 3</pre>",
),
'Multiple text nodes inside PRE' => array(
"<pre>\nline 1<!--comment--> still line 1</pre>",
'<pre>line 1<!--comment--> still line 1</pre>',
),
'Multiple text nodes inside PRE with leading newlines' => array(
"<pre>\n\nline 2<!--comment--> still line 2</pre>",
"<pre>\n\nline 2<!--comment--> still line 2</pre>",
),
'Leading newline in LISTING' => array(
"<listing>\nline 1\nline 2</listing>",
"<listing>line 1\nline 2</listing>",
),
'Double leading newline in LISTING' => array(
"<listing>\n\nline 2\nline 3</listing>",
"<listing>\n\nline 2\nline 3</listing>",
),
'Multiple text nodes inside LISTING' => array(
"<listing>\nline 1<!--comment--> still line 1</listing>",
'<listing>line 1<!--comment--> still line 1</listing>',
),
'Multiple text nodes inside LISTING with leading newlines' => array(
"<listing>\n\nline 2<!--comment--> still line 2</listing>",
"<listing>\n\nline 2<!--comment--> still line 2</listing>",
),
'Leading newline in TEXTAREA' => array(
"<textarea>\nline 1\nline 2</textarea>",
"<textarea>line 1\nline 2</textarea>",
),
'Double leading newline in TEXTAREA' => array(
"<textarea>\n\nline 2\nline 3</textarea>",
"<textarea>\n\nline 2\nline 3</textarea>",
),
);
}
}
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