Source

File: wp-includes/formatting.php

function shortcode_unautop( $pee ) {
	global $shortcode_tags;

	if ( empty( $shortcode_tags ) || ! is_array( $shortcode_tags ) ) {
		return $pee;
	}

	$tagregexp = join( '|', array_map( 'preg_quote', array_keys( $shortcode_tags ) ) );
	$spaces    = wp_spaces_regexp();

	// phpcs:disable Squiz.Strings.ConcatenationSpacing.PaddingFound,WordPress.WhiteSpace.PrecisionAlignment.Found -- don't remove regex indentation
	$pattern =
		'/'
		. '<p>'                              // Opening paragraph.
		. '(?:' . $spaces . ')*+'            // Optional leading whitespace.
		. '('                                // 1: The shortcode.
		.     '\\['                          // Opening bracket.
		.     "($tagregexp)"                 // 2: Shortcode name.
		.     '(?![\\w-])'                   // Not followed by word character or hyphen.
											 // Unroll the loop: Inside the opening shortcode tag.
		.     '[^\\]\\/]*'                   // Not a closing bracket or forward slash.
		.     '(?:'
		.         '\\/(?!\\])'               // A forward slash not followed by a closing bracket.
		.         '[^\\]\\/]*'               // Not a closing bracket or forward slash.
		.     ')*?'
		.     '(?:'
		.         '\\/\\]'                   // Self closing tag and closing bracket.
		.     '|'
		.         '\\]'                      // Closing bracket.
		.         '(?:'                      // Unroll the loop: Optionally, anything between the opening and closing shortcode tags.
		.             '[^\\[]*+'             // Not an opening bracket.
		.             '(?:'
		.                 '\\[(?!\\/\\2\\])' // An opening bracket not followed by the closing shortcode tag.
		.                 '[^\\[]*+'         // Not an opening bracket.
		.             ')*+'
		.             '\\[\\/\\2\\]'         // Closing shortcode tag.
		.         ')?'
		.     ')'
		. ')'
		. '(?:' . $spaces . ')*+'            // Optional trailing whitespace.
		. '<\\/p>'                           // Closing paragraph.
		. '/';
	// phpcs:enable

	return preg_replace( $pattern, '$1', $pee );
}