ArcanistReusedIteratorReferenceXHPASTLinterRule.php
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	<?php

	/**
	* Find cases where a `foreach` loop is being iterated using a variable
	* reference and the same variable is used outside of the loop without calling
	* `unset()` or reassigning the variable to another variable reference.
	*
	* COUNTEREXAMPLE
	* foreach ($ar as &$a) {
	* // ...
	* }
	* $a = 1; // <-- Raises an error for using $a
	*/
	final class ArcanistReusedIteratorReferenceXHPASTLinterRule
	extends ArcanistXHPASTLinterRule {

	const ID = 39;

	public function getLintName() {
	return pht('Reuse of Iterator References');
	}

	public function getLintSeverity() {
	return ArcanistLintSeverity::SEVERITY_WARNING;
	}

	public function process(XHPASTNode $root) {
	$defs = $root->selectDescendantsOfTypes(array(
	'n_FUNCTION_DECLARATION',
	'n_METHOD_DECLARATION',
	));

	foreach ($defs as $def) {
	$body = $def->getChildByIndex(5);
	if ($body->getTypeName() === 'n_EMPTY') {
	// Abstract method declaration.
	continue;
	}

	$exclude = array();

	// Exclude uses of variables, unsets, and foreach loops
	// within closures - they are checked on their own
	$func_defs = $body->selectDescendantsOfType('n_FUNCTION_DECLARATION');
	foreach ($func_defs as $func_def) {
	$vars = $func_def->selectDescendantsOfType('n_VARIABLE');
	foreach ($vars as $var) {
	$exclude[$var->getID()] = true;
	}

	$unset_lists = $func_def->selectDescendantsOfType('n_UNSET_LIST');
	foreach ($unset_lists as $unset_list) {
	$exclude[$unset_list->getID()] = true;
	}

	$foreaches = $func_def->selectDescendantsOfType('n_FOREACH');
	foreach ($foreaches as $foreach) {
	$exclude[$foreach->getID()] = true;
	}
	}

	// Find all variables that are unset within the scope
	$unset_vars = array();
	$unset_lists = $body->selectDescendantsOfType('n_UNSET_LIST');
	foreach ($unset_lists as $unset_list) {
	if (isset($exclude[$unset_list->getID()])) {
	continue;
	}

	$unset_list_vars = $unset_list->selectDescendantsOfType('n_VARIABLE');
	foreach ($unset_list_vars as $var) {
	$concrete = $this->getConcreteVariableString($var);
	$unset_vars[$concrete][] = $var->getOffset();
	$exclude[$var->getID()] = true;
	}
	}

	// Find all reference variables in foreach expressions
	$reference_vars = array();
	$foreaches = $body->selectDescendantsOfType('n_FOREACH');
	foreach ($foreaches as $foreach) {
	if (isset($exclude[$foreach->getID()])) {
	continue;
	}

	$foreach_expr = $foreach->getChildOfType(0, 'n_FOREACH_EXPRESSION');
	$var = $foreach_expr->getChildByIndex(2);
	if ($var->getTypeName() !== 'n_VARIABLE_REFERENCE') {
	continue;
	}

	$reference = $var->getChildByIndex(0);
	if ($reference->getTypeName() !== 'n_VARIABLE') {
	continue;
	}

	$reference_name = $this->getConcreteVariableString($reference);
	$reference_vars[$reference_name][] = $reference->getOffset();
	$exclude[$reference->getID()] = true;

	// Exclude uses of the reference variable within the foreach loop
	$foreach_vars = $foreach->selectDescendantsOfType('n_VARIABLE');
	foreach ($foreach_vars as $var) {
	$name = $this->getConcreteVariableString($var);
	if ($name === $reference_name) {
	$exclude[$var->getID()] = true;
	}
	}
	}

	// Allow usage if the reference variable is assigned to another
	// reference variable
	$binary = $body->selectDescendantsOfType('n_BINARY_EXPRESSION');
	foreach ($binary as $expr) {
	if ($expr->getChildByIndex(1)->getConcreteString() !== '=') {
	continue;
	}
	$lval = $expr->getChildByIndex(0);
	if ($lval->getTypeName() !== 'n_VARIABLE') {
	continue;
	}
	$rval = $expr->getChildByIndex(2);
	if ($rval->getTypeName() !== 'n_VARIABLE_REFERENCE') {
	continue;
	}

	// Counts as unsetting a variable
	$concrete = $this->getConcreteVariableString($lval);
	$unset_vars[$concrete][] = $lval->getOffset();
	$exclude[$lval->getID()] = true;
	}

	$all_vars = array();
	$all = $body->selectDescendantsOfType('n_VARIABLE');
	foreach ($all as $var) {
	if (isset($exclude[$var->getID()])) {
	continue;
	}

	$name = $this->getConcreteVariableString($var);

	if (!isset($reference_vars[$name])) {
	continue;
	}

	// Find the closest reference offset to this variable
	$reference_offset = null;
	foreach ($reference_vars[$name] as $offset) {
	if ($offset < $var->getOffset()) {
	$reference_offset = $offset;
	} else {
	break;
	}
	}
	if (!$reference_offset) {
	continue;
	}

	// Check if an unset exists between reference and usage of this
	// variable
	$warn = true;
	if (isset($unset_vars[$name])) {
	foreach ($unset_vars[$name] as $unset_offset) {
	if ($unset_offset > $reference_offset &&
	$unset_offset < $var->getOffset()) {
	$warn = false;
	break;
	}
	}
	}
	if ($warn) {
	$this->raiseLintAtNode(
	$var,
	pht(
	'This variable was used already as a by-reference iterator '.
	'variable. Such variables survive outside the `%s` loop, '.
	'do not reuse.',
	'foreach'));
	}
	}

	}
	}

	}

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