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HTML API: Preserve newlines when normalizing special elements.
Ensures normalization preserves content in `PRE`, `LISTING`, and `TEXTAREA` elements. These elements ignore a single leading newline during parsing. Normalization now injects a newline after the tag opener to trigger this behavior, preventing significant newlines from being incorrectly stripped. Developed in #10871. Props jonsurrell, dmsnell, mukesh27. Fixes #64607. git-svn-id: https://develop.svn.wordpress.org/trunk@61747 602fd350-edb4-49c9-b593-d223f7449a82
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‎src/wp-includes/html-api/class-wp-html-processor.php‎

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@@ -1414,6 +1414,32 @@ public function serialize_token(): string {
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$html .= '>';
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/*
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* The HTML parser strips a leading newline immediately after the start
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* tag of TEXTAREA, PRE, and LISTING elements. When serializing, prepend
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* a leading newline to ensure the semantic HTML content is preserved.
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*
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* For example, `<pre>\n\nX</pre>` must not become `<pre>\nX</pre>` because its content
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* has changed. However, `<pre>X</pre>` and `<pre>\nX</pre>` are _equivalent_.
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*
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* > A start tag whose tag name is "textarea"
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* > …
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* > If the next token is a U+000A LINE FEED (LF) character token, then ignore
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* > that token and move on to the next one. (Newlines at the start of textarea
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* > elements are ignored as an authoring convenience.)
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*
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* > A start tag whose tag name is one of: "pre", "listing"
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* > …
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* > If the next token is a U+000A LINE FEED (LF) character token, then ignore
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* > that token and move on to the next one. (Newlines at the start of pre blocks
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* > are ignored as an authoring convenience.)
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*
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* @see https://html.spec.whatwg.org/multipage/parsing.html
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*/
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if ( 'TEXTAREA' === $tag_name || 'PRE' === $tag_name || 'LISTING' === $tag_name ) {
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$html .= "\n";
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}
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// Flush out self-contained elements.
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if ( $in_html && in_array( $tag_name, array( 'IFRAME', 'NOEMBED', 'NOFRAMES', 'SCRIPT', 'STYLE', 'TEXTAREA', 'TITLE', 'XMP' ), true ) ) {
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$text = $this->get_modifiable_text();

‎tests/phpunit/tests/html-api/wpHtmlProcessor-serialize.php‎

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@@ -321,4 +321,72 @@ public static function data_provider_serialize_doctype() {
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'Double quotes in system ID' => array( '<!DOCTYPE html SYSTEM \'"quoted"\'\>', '<!DOCTYPE html SYSTEM \'"quoted"\'>' ),
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);
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}
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/**
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* Ensures that leading newlines in PRE, LISTING, and TEXTAREA elements are preserved upon normalization,
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* and that normalization is idempotent in these cases.
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*
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* @ticket 64607
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*
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* @dataProvider data_provider_normalize_special_leading_newline_cases
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*
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* @param string $input HTML input containing leading newlines in PRE, LISTING, or TEXTAREA elements.
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* @param string $expected Expected output after normalization, which should preserve leading newlines.
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*/
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public function test_normalize_special_leading_newline_handling( string $input, string $expected ) {
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$normalized = WP_HTML_Processor::normalize( $input );
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$this->assertEqualHTML( $expected, $normalized );
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$normalized_twice = WP_HTML_Processor::normalize( $normalized );
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$this->assertEqualHTML( $expected, $normalized_twice );
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}
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/**
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* Data provider.
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*
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* @return array[]
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*/
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public static function data_provider_normalize_special_leading_newline_cases() {
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return array(
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'Leading newline in PRE' => array(
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"<pre>\nline 1\nline 2</pre>",
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"<pre>line 1\nline 2</pre>",
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),
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'Double leading newline in PRE' => array(
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"<pre>\n\nline 2\nline 3</pre>",
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"<pre>\n\nline 2\nline 3</pre>",
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),
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'Multiple text nodes inside PRE' => array(
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"<pre>\nline 1<!--comment--> still line 1</pre>",
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'<pre>line 1<!--comment--> still line 1</pre>',
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),
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'Multiple text nodes inside PRE with leading newlines' => array(
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"<pre>\n\nline 2<!--comment--> still line 2</pre>",
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"<pre>\n\nline 2<!--comment--> still line 2</pre>",
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),
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'Leading newline in LISTING' => array(
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"<listing>\nline 1\nline 2</listing>",
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"<listing>line 1\nline 2</listing>",
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),
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'Double leading newline in LISTING' => array(
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"<listing>\n\nline 2\nline 3</listing>",
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"<listing>\n\nline 2\nline 3</listing>",
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),
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'Multiple text nodes inside LISTING' => array(
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"<listing>\nline 1<!--comment--> still line 1</listing>",
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'<listing>line 1<!--comment--> still line 1</listing>',
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),
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'Multiple text nodes inside LISTING with leading newlines' => array(
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"<listing>\n\nline 2<!--comment--> still line 2</listing>",
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"<listing>\n\nline 2<!--comment--> still line 2</listing>",
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),
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'Leading newline in TEXTAREA' => array(
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"<textarea>\nline 1\nline 2</textarea>",
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"<textarea>line 1\nline 2</textarea>",
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),
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'Double leading newline in TEXTAREA' => array(
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"<textarea>\n\nline 2\nline 3</textarea>",
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"<textarea>\n\nline 2\nline 3</textarea>",
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),
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);
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}
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}

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