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Formatting: Improve accuracy of force_balance_tags() and add suppor…
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…t for custom element tags.

This changeset includes a major iteration on the regular expression used to balance tags, with comprehensive test coverage to ensure that all scenarios are supported or unsupported as expected.

Props dmsnell, westonruter, birgire.
Fixes #47014.


git-svn-id: https://develop.svn.wordpress.org/trunk@45929 602fd350-edb4-49c9-b593-d223f7449a82
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@felixarntz
felixarntz committed Sep 2, 2019
1 parent 122cb28 commit ac2df4e
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Showing 2 changed files with 299 additions and 44 deletions.
124 changes: 80 additions & 44 deletions src/wp-includes/formatting.php
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Original file line number Diff line number Diff line change
Expand Up @@ -2429,7 +2429,7 @@ function convert_invalid_entities( $content ) {
* @return string Balanced text
*/
function balanceTags( $text, $force = false ) { // phpcs:ignore WordPress.NamingConventions.ValidFunctionName.FunctionNameInvalid
if ( $force || get_option( 'use_balanceTags' ) == 1 ) {
if ( $force || (int) get_option( 'use_balanceTags' ) === 1 ) {
return force_balance_tags( $text );
} else {
return $text;
Expand All @@ -2440,6 +2440,7 @@ function balanceTags( $text, $force = false ) { // phpcs:ignore WordPress.Namin
* Balances tags of string using a modified stack.
*
* @since 2.0.4
* @since 5.3.0 Improve accuracy and add support for custom element tags.
*
* @author Leonard Lin <leonard@acm.org>
* @license GPL
Expand Down Expand Up @@ -2469,32 +2470,74 @@ function force_balance_tags( $text ) {
// WP bug fix for LOVE <3 (and other situations with '<' before a number)
$text = preg_replace( '#<([0-9]{1})#', '&lt;$1', $text );

while ( preg_match( '/<(\/?[\w:]*)\s*([^>]*)>/', $text, $regex ) ) {
/**
* Matches supported tags.
*
* To get the pattern as a string without the comments paste into a PHP
* REPL like `php -a`.
*
* @see https://html.spec.whatwg.org/#elements-2
* @see https://w3c.github.io/webcomponents/spec/custom/#valid-custom-element-name
*
* @example
* ~# php -a
* php > $s = [paste copied contents of expression below including parentheses];
* php > echo $s;
*/
$tag_pattern = (
'#<' . // Start with an opening bracket.
'(/?)' . // Group 1 - If it's a closing tag it'll have a leading slash.
'(' . // Group 2 - Tag name.
// Custom element tags have more lenient rules than HTML tag names.
'(?:[a-z](?:[a-z0-9._]*)-(?:[a-z0-9._-]+)+)' .
'|' .
// Traditional tag rules approximate HTML tag names.
'(?:[\w:]+)' .
')' .
'(?:' .
// We either immediately close the tag with its '>' and have nothing here.
'\s*' .
'(/?)' . // Group 3 - "attributes" for empty tag.
'|' .
// Or we must start with space characters to separate the tag name from the attributes (or whitespace).
'(\s+)' . // Group 4 - Pre-attribute whitespace.
'([^>]*)' . // Group 5 - Attributes.
')' .
'>#' // End with a closing bracket.
);

while ( preg_match( $tag_pattern, $text, $regex ) ) {
$full_match = $regex[0];
$has_leading_slash = ! empty( $regex[1] );
$tag_name = $regex[2];
$tag = strtolower( $tag_name );
$is_single_tag = in_array( $tag, $single_tags, true );
$pre_attribute_ws = isset( $regex[4] ) ? $regex[4] : '';
$attributes = trim( isset( $regex[5] ) ? $regex[5] : $regex[3] );
$has_self_closer = '/' === substr( $attributes, -1 );

$newtext .= $tagqueue;

$i = strpos( $text, $regex[0] );
$l = strlen( $regex[0] );
$i = strpos( $text, $full_match );
$l = strlen( $full_match );

// clear the shifter
// Clear the shifter.
$tagqueue = '';
// Pop or Push
if ( isset( $regex[1][0] ) && '/' == $regex[1][0] ) { // End Tag
$tag = strtolower( substr( $regex[1], 1 ) );
// if too many closing tags
if ( $has_leading_slash ) { // End Tag.
// If too many closing tags.
if ( $stacksize <= 0 ) {
$tag = '';
// or close to be safe $tag = '/' . $tag;
// Or close to be safe $tag = '/' . $tag.

// if stacktop value = tag close value then pop
} elseif ( $tagstack[ $stacksize - 1 ] == $tag ) { // found closing tag
$tag = '</' . $tag . '>'; // Close Tag
// Pop
// If stacktop value = tag close value, then pop.
} elseif ( $tagstack[ $stacksize - 1 ] === $tag ) { // Found closing tag.
$tag = '</' . $tag . '>'; // Close Tag.
array_pop( $tagstack );
$stacksize--;
} else { // closing tag not at top, search for it
} else { // Closing tag not at top, search for it.
for ( $j = $stacksize - 1; $j >= 0; $j-- ) {
if ( $tagstack[ $j ] == $tag ) {
// add tag to tagqueue
if ( $tagstack[ $j ] === $tag ) {
// Add tag to tagqueue.
for ( $k = $stacksize - 1; $k >= $j; $k-- ) {
$tagqueue .= '</' . array_pop( $tagstack ) . '>';
$stacksize--;
Expand All @@ -2504,39 +2547,33 @@ function force_balance_tags( $text ) {
}
$tag = '';
}
} else { // Begin Tag
$tag = strtolower( $regex[1] );

// Tag Cleaning

// If it's an empty tag "< >", do nothing
if ( '' == $tag ) {
// do nothing
} elseif ( substr( $regex[2], -1 ) == '/' ) { // ElseIf it presents itself as a self-closing tag...
} else { // Begin Tag.
if ( $has_self_closer ) { // If it presents itself as a self-closing tag...
// ...but it isn't a known single-entity self-closing tag, then don't let it be treated as such and
// immediately close it with a closing tag (the tag will encapsulate no text as a result)
if ( ! in_array( $tag, $single_tags ) ) {
$regex[2] = trim( substr( $regex[2], 0, -1 ) ) . "></$tag";
if ( ! $is_single_tag ) {
$attributes = trim( substr( $attributes, 0, -1 ) ) . "></$tag";
}
} elseif ( in_array( $tag, $single_tags ) ) { // ElseIf it's a known single-entity tag but it doesn't close itself, do so
$regex[2] .= '/';
} else { // Else it's not a single-entity tag
// If the top of the stack is the same as the tag we want to push, close previous tag
if ( $stacksize > 0 && ! in_array( $tag, $nestable_tags ) && $tagstack[ $stacksize - 1 ] == $tag ) {
} elseif ( $is_single_tag ) { // ElseIf it's a known single-entity tag but it doesn't close itself, do so
$pre_attribute_ws = ' ';
$attributes .= '/';
} else { // It's not a single-entity tag.
// If the top of the stack is the same as the tag we want to push, close previous tag.
if ( $stacksize > 0 && ! in_array( $tag, $nestable_tags, true ) && $tagstack[ $stacksize - 1 ] === $tag ) {
$tagqueue = '</' . array_pop( $tagstack ) . '>';
$stacksize--;
}
$stacksize = array_push( $tagstack, $tag );
}

// Attributes
$attributes = $regex[2];
if ( ! empty( $attributes ) && $attributes[0] != '>' ) {
$attributes = ' ' . $attributes;
// Attributes.
if ( $has_self_closer && $is_single_tag ) {
// We need some space - avoid <br/> and prefer <br />.
$pre_attribute_ws = ' ';
}

$tag = '<' . $tag . $attributes . '>';
//If already queuing a close tag, then put this tag on, too
$tag = '<' . $tag . $pre_attribute_ws . $attributes . '>';
// If already queuing a close tag, then put this tag on too.
if ( ! empty( $tagqueue ) ) {
$tagqueue .= $tag;
$tag = '';
Expand All @@ -2546,18 +2583,17 @@ function force_balance_tags( $text ) {
$text = substr( $text, $i + $l );
}

// Clear Tag Queue
// Clear Tag Queue.
$newtext .= $tagqueue;

// Add Remaining text
// Add remaining text.
$newtext .= $text;

// Empty Stack
while ( $x = array_pop( $tagstack ) ) {
$newtext .= '</' . $x . '>'; // Add remaining tags to close
$newtext .= '</' . $x . '>'; // Add remaining tags to close.
}

// WP fix for the bug with HTML comments
// WP fix for the bug with HTML comments.
$newtext = str_replace( '< !--', '<!--', $newtext );
$newtext = str_replace( '< !--', '< !--', $newtext );

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