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libphutil/src/lexer/PhutilLexer.php
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PhutilLexer.php
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<?php
/**
* Slow, inefficient regexp-based lexer. Define rules like this:
*
* array(
* 'start' => array(...),
* 'state1' => array(...),
* 'state2' => array(...),
* )
*
* Lexers start at the state named 'start'. Each state should have a list of
* rules which can match in that state. A list of rules looks like this:
*
* array(
* array('\s+', 'space'),
* array('\d+', 'digit'),
* array('\w+', 'word'),
* )
*
* The lexer operates by processing each rule in the current state in order.
* When one matches, it produces a token. For example, the lexer above would
* lex this text:
*
* 3 asdf
*
* ...to produce these tokens (assuming the rules are for the 'start' state):
*
* array('digit', '3', null),
* array('space', ' ', null),
* array('word', 'asdf', null),
*
* A rule can also cause a state transition:
*
* array('zebra', 'animal', 'saw_zebra'),
*
* This would match the text "zebra", emit a token of type "animal", and change
* the parser state to "saw_zebra", causing the lexer to start using the rules
* from that state.
*
* To pop the lexer's state, you can use the special state '!pop'.
*
* Finally, you can provide additional options in the fourth parameter.
* Supported options are `case-insensitive` and `context`.
*
* Possible values for `context` are `push` (push the token value onto the
* context stack), `pop` (pop the context stack and use it to provide context
* for the token), and `discard` (pop the context stack and throw away the
* value).
*
* For example, to lex text like this:
*
* Class::CONSTANT
*
* You can use a rule set like this:
*
* 'start' => array(
* array('\w+(?=::)', 'class', 'saw_class', array('context' => 'push')),
* ),
* 'saw_class' => array(
* array('::', 'operator'),
* array('\w+', 'constant, '!pop', array('context' => 'pop')),
* ),
*
* This would parse the above text into this token stream:
*
* array('class', 'Class', null),
* array('operator', '::', null),
* array('constant', 'CONSTANT', 'Class'),
*
* For a concrete implementation, see @{class:PhutilPHPFragmentLexer}.
*
* @task lexerimpl Lexer Implementation
* @task rule Lexer Rules
* @task tokens Lexer Tokens
*
* @group lexer
*/
abstract class PhutilLexer {
private $processedRules;
private $lastState;
/* -( Lexer Rules )-------------------------------------------------------- */
/**
* Return a set of rules for this lexer. See description in
* @{class:PhutilLexer}.
*
* @return dict Lexer rules.
* @task lexerimpl
*/
abstract protected function getRawRules();
/* -( Lexer Rules )-------------------------------------------------------- */
/**
* Process, normalize, and validate the raw lexer rules.
*
* @task rule
*/
protected function getRules() {
$class = get_class($this);
$raw_rules = $this->getRawRules();
if (!is_array($raw_rules)) {
$type = gettype($raw_rules);
throw new UnexpectedValueException(
"Expected {$class}->getRawRules() to return array, got {$type}.");
}
if (empty($raw_rules['start'])) {
throw new UnexpectedValueException(
"Expected {$class} rules to define rules for state 'start'.");
}
$processed_rules = array();
foreach ($raw_rules as $state => $rules) {
if (!is_array($rules)) {
$type = gettype($rules);
throw new UnexpectedValueException(
"Expected list of rules for state '{$state}' in {$class}, got ".
"{$type}.");
}
foreach ($rules as $key => $rule) {
$n = count($rule);
if ($n < 2 || $n > 4) {
throw new UnexpectedValueException(
"Expected rule '{$key}' in state '{$state}' in {$class} to have ".
"2-4 elements (regex, token, [next state], [options]), got {$n}.");
}
$rule = array_values($rule);
if (count($rule) == 2) {
$rule[] = null;
}
if (count($rule) == 3) {
$rule[] = array();
}
foreach ($rule[3] as $option => $value) {
switch ($option) {
case 'context':
if ($value !== 'push' &&
$value !== 'pop' &&
$value !== 'discard' &&
$value !== null) {
throw new UnexpectedValueException(
"Rule '{$key}' in state '{$state}' in {$class} has unknown ".
"context rule '{$value}', expected 'push', 'pop' or ".
"'discard'.");
}
break;
default:
throw new UnexpectedValueException(
"Rule '{$key}' in state '{$state}' in {$class} has unknown ".
"option '{$option}'.");
}
}
$flags = 'sS';
// NOTE: The "\G" assertion is an offset-aware version of "^".
$rule[0] = '(\\G'.$rule[0].')'.$flags;
if (@preg_match($rule[0], '') === false) {
$error = error_get_last();
throw new UnexpectedValueException(
"Rule '{$key}' in state '{$state}' in {$class} defines an ".
"invalid regular expression ('{$rule[0]}'): ".
idx($error, 'message'));
}
$next_state = $rule[2];
if ($next_state !== null && $next_state !== '!pop') {
if (empty($raw_rules[$next_state])) {
throw new UnexpectedValueException(
"Rule '{$key}' in state '{$state}' in {$class} transitions to ".
"state '{$next_state}', but there are no rules for that state.");
}
}
$processed_rules[$state][] = $rule;
}
}
return $processed_rules;
}
/* -( Lexer Tokens )------------------------------------------------------- */
/**
* Lex an input string into tokens.
*
* @param string Input string.
* @param string Initial lexer state.
* @return list List of lexer tokens.
* @task tokens
*/
public function getTokens($input, $initial_state = 'start') {
if (empty($this->processedRules)) {
$this->processedRules = $this->getRules();
}
$rules = $this->processedRules;
$this->lastState = null;
$position = 0;
$length = strlen($input);
$tokens = array();
$states = array();
$states[] = 'start';
if ($initial_state != 'start') {
$states[] = $initial_state;
}
$context = array();
while ($position < $length) {
$state_rules = idx($rules, end($states), array());
foreach ($state_rules as $rule) {
$matches = null;
if (!preg_match($rule[0], $input, $matches, 0, $position)) {
continue;
}
list($regexp, $token_type, $next_state, $options) = $rule;
$match_length = strlen($matches[0]);
if (!$match_length) {
if ($next_state === null) {
throw new UnexpectedValueException(
"Rule '{$regexp}' matched a zero-length token and causes no ".
"state transition.");
}
} else {
$position += $match_length;
$token = array($token_type, $matches[0]);
$copt = idx($options, 'context');
if ($copt == 'push') {
$context[] = $matches[0];
$token[] = null;
} else if ($copt == 'pop') {
if (empty($context)) {
throw new UnexpectedValueException(
"Rule '{$regexp}' popped empty context!");
}
$token[] = array_pop($context);
} else if ($copt == 'discard') {
if (empty($context)) {
throw new UnexpectedValueException(
"Rule '{$regexp}' discarded empty context!");
}
array_pop($context);
$token[] = null;
} else {
$token[] = null;
}
$tokens[] = $token;
}
if ($next_state !== null) {
if ($next_state == '!pop') {
array_pop($states);
if (empty($states)) {
throw new UnexpectedValueException(
"Rule '{$regexp}' popped off the last state.");
}
} else {
$states[] = $next_state;
}
}
continue 2;
}
throw new UnexpectedValueException(
"No lexer rule matched input at char {$position}.");
}
$this->lastState = $states;
return $tokens;
}
/**
* Merge adjacent tokens of the same type. For example, if a comment is
* tokenized as <"//", "comment">, this method will merge the two tokens into
* a single combined token.
*/
public function mergeTokens(array $tokens) {
$last = null;
$result = array();
foreach ($tokens as $token) {
if ($last === null) {
$last = $token;
continue;
}
if (($token[0] == $last[0]) && ($token[2] == $last[2])) {
$last[1] .= $token[1];
} else {
$result[] = $last;
$last = $token;
}
}
if ($last !== null) {
$result[] = $last;
}
return $result;
}
public function getLexerState() {
return $this->lastState;
}
}
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