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Matcher.php
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Matcher.php
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<?php
/**
* @file
* @license https://opensource.org/licenses/Apache-2.0 Apache-2.0
*/
namespace Wikimedia\CSS\Grammar;
use Iterator;
use Wikimedia\CSS\Objects\ComponentValueList;
use Wikimedia\CSS\Objects\CSSFunction;
use Wikimedia\CSS\Objects\SimpleBlock;
use Wikimedia\CSS\Objects\Token;
/**
* Base class for grammar matchers.
*
* The [CSS Syntax Level 3][SYN3] and [Values Level 3][VAL3] specifications use
* a mostly context-free grammar to define what things like selectors and
* property values look like. The Matcher classes allow for constructing an
* object that will determine whether a ComponentValueList actually matches
* this grammar.
*
* [SYN3]: https://www.w3.org/TR/2019/CR-css-syntax-3-20190716/
* [VAL3]: https://www.w3.org/TR/2019/CR-css-values-3-20190606/
*/
abstract class Matcher {
/** @var string|null Name to set on GrammarMatch objects */
protected $captureName = null;
/**
* @var array Default options for self::matchAgainst()
* - skip-whitespace: (bool) Allow whitespace in between any two tokens
* - nonterminal: (bool) Don't require the whole of $values is matched
* - mark-significance: (bool) On a successful match, replace T_WHITESPACE
* tokens as necessary to indicate significant whitespace.
*/
protected $defaultOptions = [
'skip-whitespace' => true,
'nonterminal' => false,
'mark-significance' => false,
];
/**
* Create an instance.
* @param mixed ...$args See static::__construct()
* @return static
*/
public static function create( ...$args ) {
// @phan-suppress-next-line PhanParamTooManyUnpack,PhanTypeInstantiateAbstractStatic
return new static( ...$args );
}
/**
* Return a copy of this matcher that will capture its matches
*
* A "capturing" Matcher will produce GrammarMatches that return a value from
* the GrammarMatch::getName() method. The GrammarMatch::getCapturedMatches()
* method may be used to retrieve them from the top-level GrammarMatch.
*
* The concept is similar to capturing groups in PCRE and other regex
* languages.
*
* @param string|null $captureName Name to apply to captured GrammarMatch objects
* @return static
*/
public function capture( $captureName ) {
$ret = clone $this;
$ret->captureName = $captureName;
return $ret;
}
/**
* Match against a list of ComponentValues
* @param ComponentValueList $values
* @param array $options Matching options, see self::$defaultOptions
* @return GrammarMatch|null
*/
public function matchAgainst( ComponentValueList $values, array $options = [] ) {
$options += $this->getDefaultOptions();
$start = $this->next( $values, -1, $options );
$l = count( $values );
foreach ( $this->generateMatches( $values, $start, $options ) as $match ) {
if ( $options['nonterminal'] || $match->getNext() === $l ) {
if ( $options['mark-significance'] ) {
$significantWS = self::collectSignificantWhitespace( $match );
self::markSignificantWhitespace( $values, $match, $significantWS, $match->getNext() );
}
return $match;
}
}
return null;
}
/**
* Collect any 'significantWhitespace' matches
* @param GrammarMatch $match
* @param Token[] &$ret
* @return Token[]
*/
private static function collectSignificantWhitespace( GrammarMatch $match, &$ret = [] ) {
if ( $match->getName() === 'significantWhitespace' ) {
$ret = array_merge( $ret, $match->getValues() );
}
foreach ( $match->getCapturedMatches() as $m ) {
self::collectSignificantWhitespace( $m, $ret );
}
return $ret;
}
/**
* Mark whitespace as significant or not
* @param ComponentValueList $list
* @param GrammarMatch $match
* @param Token[] $significantWS
* @param int $end
*/
private static function markSignificantWhitespace( $list, $match, $significantWS, $end ) {
for ( $i = 0; $i < $end; $i++ ) {
$cv = $list[$i];
if ( $cv instanceof Token && $cv->type() === Token::T_WHITESPACE ) {
$significant = in_array( $cv, $significantWS, true );
if ( $significant !== $cv->significant() ) {
$newCv = $cv->copyWithSignificance( $significant );
$match->fixWhitespace( $cv, $newCv );
$list[$i] = $newCv;
}
} elseif ( $cv instanceof CSSFunction || $cv instanceof SimpleBlock ) {
self::markSignificantWhitespace(
$cv->getValue(), $match, $significantWS, count( $cv->getValue() )
);
}
}
}
/**
* Fetch the default options for this Matcher
* @return array See self::$defaultOptions
*/
public function getDefaultOptions() {
return $this->defaultOptions;
}
/**
* Set the default options for this Matcher
* @param array $options See self::$defaultOptions
* @return static $this
*/
public function setDefaultOptions( array $options ) {
$this->defaultOptions = $options + $this->defaultOptions;
return $this;
}
/**
* Find the next ComponentValue in the input, possibly skipping whitespace
* @param ComponentValueList $values Input values
* @param int $start Current position in the input. May be -1, in which
* case the first position in the input should be returned.
* @param array $options See self::$defaultOptions
* @return int Next token index
*/
protected function next( ComponentValueList $values, $start, array $options ) {
$skipWS = $options['skip-whitespace'];
$i = $start;
$l = count( $values );
do {
$i++;
} while ( $skipWS && $i < $l &&
// @phan-suppress-next-line PhanNonClassMethodCall False positive
$values[$i] instanceof Token && $values[$i]->type() === Token::T_WHITESPACE
);
return $i;
}
/**
* Create a GrammarMatch
* @param ComponentValueList $list
* @param int $start
* @param int $end First position after the match
* @param GrammarMatch|null $submatch Sub-match, for capturing. If $submatch
* itself named it will be kept as a capture in the returned GrammarMatch,
* otherwise its captured matches (if any) as returned by getCapturedMatches()
* will be kept as captures in the returned GrammarMatch.
* @param array $stack Stack from which to fetch more submatches for
* capturing (see $submatch). The stack is expected to be an array of
* arrays, with the first element of each subarray being a GrammarMatch.
* @return GrammarMatch
*/
protected function makeMatch(
ComponentValueList $list, $start, $end, ?GrammarMatch $submatch = null, array $stack = []
) {
$matches = array_column( $stack, 0 );
$matches[] = $submatch;
$keptMatches = [];
while ( $matches ) {
$m = array_shift( $matches );
if ( !$m instanceof GrammarMatch ) {
// skip it, probably null
} elseif ( $m->getName() !== null ) {
$keptMatches[] = $m;
} elseif ( $m->getCapturedMatches() ) {
$matches = array_merge( $m->getCapturedMatches(), $matches );
}
}
return new GrammarMatch( $list, $start, $end - $start, $this->captureName, $keptMatches );
}
/**
* Match against a list of ComponentValues
*
* The job of a Matcher is to determine all the ways its particular grammar
* fragment can consume ComponentValues starting at a particular location
* in the ComponentValueList, represented by returning GrammarMatch objects.
* For example, a matcher implementing `IDENT*` at a starting position where
* there are three IDENT tokens in a row would be able to match 0, 1, 2, or
* all 3 of those IDENT tokens, and therefore should return an iterator
* over that set of GrammarMatch objects.
*
* Some matchers take other matchers as input, for example `IDENT*` is
* probably going to be implemented as a matcher for `*` that repeatedly
* applies a matcher for `IDENT`. The `*` matcher would call the `IDENT`
* matcher's generateMatches() method directly.
*
* Most Matchers implement this method as a generator to not build up
* the full set of results when it's reasonably likely the caller is going
* to terminate early.
*
* @param ComponentValueList $values
* @param int $start Starting position in $values
* @param array $options See self::$defaultOptions.
* Always use the options passed in, don't use $this->defaultOptions yourself.
* @return Iterator<GrammarMatch> Iterates over the set of GrammarMatch
* objects defining all the ways this matcher can match.
*/
abstract protected function generateMatches( ComponentValueList $values, $start, array $options );
}

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