PhabricatorApplicationTransactionEditor.php
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Created: Sat, Feb 1, 21:50

PhabricatorApplicationTransactionEditor.php
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	<?php

	/**
	*
	* Publishing and Managing State
	* ======
	*
	* After applying changes, the Editor queues a worker to publish mail, feed,
	* and notifications, and to perform other background work like updating search
	* indexes. This allows it to do this work without impacting performance for
	* users.
	*
	* When work is moved to the daemons, the Editor state is serialized by
	* @{method:getWorkerState}, then reloaded in a daemon process by
	* @{method:loadWorkerState}. This is fragile.
	*
	* State is not persisted into the daemons by default, because we can not send
	* arbitrary objects into the queue. This means the default behavior of any
	* state properties is to reset to their defaults without warning prior to
	* publishing.
	*
	* The easiest way to avoid this is to keep Editors stateless: the overwhelming
	* majority of Editors can be written statelessly. If you need to maintain
	* state, you can either:
	*
	* - not require state to exist during publishing; or
	* - pass state to the daemons by implementing @{method:getCustomWorkerState}
	* and @{method:loadCustomWorkerState}.
	*
	* This architecture isn't ideal, and we may eventually split this class into
	* "Editor" and "Publisher" parts to make it more robust. See T6367 for some
	* discussion and context.
	*
	* @task mail Sending Mail
	* @task feed Publishing Feed Stories
	* @task search Search Index
	* @task files Integration with Files
	* @task workers Managing Workers
	*/
	abstract class PhabricatorApplicationTransactionEditor
	extends PhabricatorEditor {

	private $contentSource;
	private $object;
	private $xactions;

	private $isNewObject;
	private $mentionedPHIDs;
	private $continueOnNoEffect;
	private $continueOnMissingFields;
	private $parentMessageID;
	private $heraldAdapter;
	private $heraldTranscript;
	private $subscribers;
	private $unmentionablePHIDMap = array();
	private $applicationEmail;

	private $isPreview;
	private $isHeraldEditor;
	private $isInverseEdgeEditor;
	private $actingAsPHID;
	private $disableEmail;

	private $heraldEmailPHIDs = array();
	private $heraldForcedEmailPHIDs = array();
	private $heraldHeader;
	private $mailToPHIDs = array();
	private $mailCCPHIDs = array();
	private $feedNotifyPHIDs = array();
	private $feedRelatedPHIDs = array();
	private $modularTypes;

	const STORAGE_ENCODING_BINARY = 'binary';

	/**
	* Get the class name for the application this editor is a part of.
	*
	* Uninstalling the application will disable the editor.
	*
	* @return string Editor's application class name.
	*/
	abstract public function getEditorApplicationClass();


	/**
	* Get a description of the objects this editor edits, like "Differential
	* Revisions".
	*
	* @return string Human readable description of edited objects.
	*/
	abstract public function getEditorObjectsDescription();


	public function setActingAsPHID($acting_as_phid) {
	$this->actingAsPHID = $acting_as_phid;
	return $this;
	}

	public function getActingAsPHID() {
	if ($this->actingAsPHID) {
	return $this->actingAsPHID;
	}
	return $this->getActor()->getPHID();
	}


	/**
	* When the editor tries to apply transactions that have no effect, should
	* it raise an exception (default) or drop them and continue?
	*
	* Generally, you will set this flag for edits coming from "Edit" interfaces,
	* and leave it cleared for edits coming from "Comment" interfaces, so the
	* user will get a useful error if they try to submit a comment that does
	* nothing (e.g., empty comment with a status change that has already been
	* performed by another user).
	*
	* @param bool True to drop transactions without effect and continue.
	* @return this
	*/
	public function setContinueOnNoEffect($continue) {
	$this->continueOnNoEffect = $continue;
	return $this;
	}

	public function getContinueOnNoEffect() {
	return $this->continueOnNoEffect;
	}


	/**
	* When the editor tries to apply transactions which don't populate all of
	* an object's required fields, should it raise an exception (default) or
	* drop them and continue?
	*
	* For example, if a user adds a new required custom field (like "Severity")
	* to a task, all existing tasks won't have it populated. When users
	* manually edit existing tasks, it's usually desirable to have them provide
	* a severity. However, other operations (like batch editing just the
	* owner of a task) will fail by default.
	*
	* By setting this flag for edit operations which apply to specific fields
	* (like the priority, batch, and merge editors in Maniphest), these
	* operations can continue to function even if an object is outdated.
	*
	* @param bool True to continue when transactions don't completely satisfy
	* all required fields.
	* @return this
	*/
	public function setContinueOnMissingFields($continue_on_missing_fields) {
	$this->continueOnMissingFields = $continue_on_missing_fields;
	return $this;
	}

	public function getContinueOnMissingFields() {
	return $this->continueOnMissingFields;
	}


	/**
	* Not strictly necessary, but reply handlers ideally set this value to
	* make email threading work better.
	*/
	public function setParentMessageID($parent_message_id) {
	$this->parentMessageID = $parent_message_id;
	return $this;
	}
	public function getParentMessageID() {
	return $this->parentMessageID;
	}

	public function getIsNewObject() {
	return $this->isNewObject;
	}

	protected function getMentionedPHIDs() {
	return $this->mentionedPHIDs;
	}

	public function setIsPreview($is_preview) {
	$this->isPreview = $is_preview;
	return $this;
	}

	public function getIsPreview() {
	return $this->isPreview;
	}

	public function setIsInverseEdgeEditor($is_inverse_edge_editor) {
	$this->isInverseEdgeEditor = $is_inverse_edge_editor;
	return $this;
	}

	public function getIsInverseEdgeEditor() {
	return $this->isInverseEdgeEditor;
	}

	public function setIsHeraldEditor($is_herald_editor) {
	$this->isHeraldEditor = $is_herald_editor;
	return $this;
	}

	public function getIsHeraldEditor() {
	return $this->isHeraldEditor;
	}

	/**
	* Prevent this editor from generating email when applying transactions.
	*
	* @param bool True to disable email.
	* @return this
	*/
	public function setDisableEmail($disable_email) {
	$this->disableEmail = $disable_email;
	return $this;
	}

	public function getDisableEmail() {
	return $this->disableEmail;
	}

	public function setUnmentionablePHIDMap(array $map) {
	$this->unmentionablePHIDMap = $map;
	return $this;
	}

	public function getUnmentionablePHIDMap() {
	return $this->unmentionablePHIDMap;
	}

	protected function shouldEnableMentions(
	PhabricatorLiskDAO $object,
	array $xactions) {
	return true;
	}

	public function setApplicationEmail(
	PhabricatorMetaMTAApplicationEmail $email) {
	$this->applicationEmail = $email;
	return $this;
	}

	public function getApplicationEmail() {
	return $this->applicationEmail;
	}

	public function getTransactionTypesForObject($object) {
	$old = $this->object;
	try {
	$this->object = $object;
	$result = $this->getTransactionTypes();
	$this->object = $old;
	} catch (Exception $ex) {
	$this->object = $old;
	throw $ex;
	}
	return $result;
	}

	public function getTransactionTypes() {
	$types = array();

	$types[] = PhabricatorTransactions::TYPE_CREATE;

	if ($this->object instanceof PhabricatorSubscribableInterface) {
	$types[] = PhabricatorTransactions::TYPE_SUBSCRIBERS;
	}

	if ($this->object instanceof PhabricatorCustomFieldInterface) {
	$types[] = PhabricatorTransactions::TYPE_CUSTOMFIELD;
	}

	if ($this->object instanceof HarbormasterBuildableInterface) {
	$types[] = PhabricatorTransactions::TYPE_BUILDABLE;
	}

	if ($this->object instanceof PhabricatorTokenReceiverInterface) {
	$types[] = PhabricatorTransactions::TYPE_TOKEN;
	}

	if ($this->object instanceof PhabricatorProjectInterface \|\|
	$this->object instanceof PhabricatorMentionableInterface) {
	$types[] = PhabricatorTransactions::TYPE_EDGE;
	}

	if ($this->object instanceof PhabricatorSpacesInterface) {
	$types[] = PhabricatorTransactions::TYPE_SPACE;
	}

	$template = $this->object->getApplicationTransactionTemplate();
	if ($template instanceof PhabricatorModularTransaction) {
	$xtypes = $template->newModularTransactionTypes();
	foreach ($xtypes as $xtype) {
	$types[] = $xtype->getTransactionTypeConstant();
	}
	}

	return $types;
	}

	private function adjustTransactionValues(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {

	if ($xaction->shouldGenerateOldValue()) {
	$old = $this->getTransactionOldValue($object, $xaction);
	$xaction->setOldValue($old);
	}

	$new = $this->getTransactionNewValue($object, $xaction);
	$xaction->setNewValue($new);
	}

	private function getTransactionOldValue(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {

	$type = $xaction->getTransactionType();

	$xtype = $this->getModularTransactionType($type);
	if ($xtype) {
	return $xtype->generateOldValue($object);
	}

	switch ($type) {
	case PhabricatorTransactions::TYPE_CREATE:
	return null;
	case PhabricatorTransactions::TYPE_SUBSCRIBERS:
	return array_values($this->subscribers);
	case PhabricatorTransactions::TYPE_VIEW_POLICY:
	if ($this->getIsNewObject()) {
	return null;
	}
	return $object->getViewPolicy();
	case PhabricatorTransactions::TYPE_EDIT_POLICY:
	if ($this->getIsNewObject()) {
	return null;
	}
	return $object->getEditPolicy();
	case PhabricatorTransactions::TYPE_JOIN_POLICY:
	if ($this->getIsNewObject()) {
	return null;
	}
	return $object->getJoinPolicy();
	case PhabricatorTransactions::TYPE_SPACE:
	if ($this->getIsNewObject()) {
	return null;
	}

	$space_phid = $object->getSpacePHID();
	if ($space_phid === null) {
	$default_space = PhabricatorSpacesNamespaceQuery::getDefaultSpace();
	if ($default_space) {
	$space_phid = $default_space->getPHID();
	}
	}

	return $space_phid;
	case PhabricatorTransactions::TYPE_EDGE:
	$edge_type = $xaction->getMetadataValue('edge:type');
	if (!$edge_type) {
	throw new Exception(
	pht(
	"Edge transaction has no '%s'!",
	'edge:type'));
	}

	$old_edges = array();
	if ($object->getPHID()) {
	$edge_src = $object->getPHID();

	$old_edges = id(new PhabricatorEdgeQuery())
	->withSourcePHIDs(array($edge_src))
	->withEdgeTypes(array($edge_type))
	->needEdgeData(true)
	->execute();

	$old_edges = $old_edges[$edge_src][$edge_type];
	}
	return $old_edges;
	case PhabricatorTransactions::TYPE_CUSTOMFIELD:
	// NOTE: Custom fields have their old value pre-populated when they are
	// built by PhabricatorCustomFieldList.
	return $xaction->getOldValue();
	case PhabricatorTransactions::TYPE_COMMENT:
	return null;
	default:
	return $this->getCustomTransactionOldValue($object, $xaction);
	}
	}

	private function getTransactionNewValue(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {

	$type = $xaction->getTransactionType();

	$xtype = $this->getModularTransactionType($type);
	if ($xtype) {
	return $xtype->generateNewValue($object, $xaction->getNewValue());
	}

	switch ($type) {
	case PhabricatorTransactions::TYPE_CREATE:
	return null;
	case PhabricatorTransactions::TYPE_SUBSCRIBERS:
	return $this->getPHIDTransactionNewValue($xaction);
	case PhabricatorTransactions::TYPE_VIEW_POLICY:
	case PhabricatorTransactions::TYPE_EDIT_POLICY:
	case PhabricatorTransactions::TYPE_JOIN_POLICY:
	case PhabricatorTransactions::TYPE_BUILDABLE:
	case PhabricatorTransactions::TYPE_TOKEN:
	case PhabricatorTransactions::TYPE_INLINESTATE:
	return $xaction->getNewValue();
	case PhabricatorTransactions::TYPE_SPACE:
	$space_phid = $xaction->getNewValue();
	if (!strlen($space_phid)) {
	// If an install has no Spaces or the Spaces controls are not visible
	// to the viewer, we might end up with the empty string here instead
	// of a strict `null`, because some controller just used `getStr()`
	// to read the space PHID from the request.
	// Just make this work like callers might reasonably expect so we
	// don't need to handle this specially in every EditController.
	return $this->getActor()->getDefaultSpacePHID();
	} else {
	return $space_phid;
	}
	case PhabricatorTransactions::TYPE_EDGE:
	$new_value = $this->getEdgeTransactionNewValue($xaction);

	$edge_type = $xaction->getMetadataValue('edge:type');
	$type_project = PhabricatorProjectObjectHasProjectEdgeType::EDGECONST;
	if ($edge_type == $type_project) {
	$new_value = $this->applyProjectConflictRules($new_value);
	}

	return $new_value;
	case PhabricatorTransactions::TYPE_CUSTOMFIELD:
	$field = $this->getCustomFieldForTransaction($object, $xaction);
	return $field->getNewValueFromApplicationTransactions($xaction);
	case PhabricatorTransactions::TYPE_COMMENT:
	return null;
	default:
	return $this->getCustomTransactionNewValue($object, $xaction);
	}
	}

	protected function getCustomTransactionOldValue(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {
	throw new Exception(pht('Capability not supported!'));
	}

	protected function getCustomTransactionNewValue(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {
	throw new Exception(pht('Capability not supported!'));
	}

	protected function transactionHasEffect(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {

	switch ($xaction->getTransactionType()) {
	case PhabricatorTransactions::TYPE_CREATE:
	return true;
	case PhabricatorTransactions::TYPE_COMMENT:
	return $xaction->hasComment();
	case PhabricatorTransactions::TYPE_CUSTOMFIELD:
	$field = $this->getCustomFieldForTransaction($object, $xaction);
	return $field->getApplicationTransactionHasEffect($xaction);
	case PhabricatorTransactions::TYPE_EDGE:
	// A straight value comparison here doesn't always get the right
	// result, because newly added edges aren't fully populated. Instead,
	// compare the changes in a more granular way.
	$old = $xaction->getOldValue();
	$new = $xaction->getNewValue();

	$old_dst = array_keys($old);
	$new_dst = array_keys($new);

	// NOTE: For now, we don't consider edge reordering to be a change.
	// We have very few order-dependent edges and effectively no order
	// oriented UI. This might change in the future.
	sort($old_dst);
	sort($new_dst);

	if ($old_dst !== $new_dst) {
	// We've added or removed edges, so this transaction definitely
	// has an effect.
	return true;
	}

	// We haven't added or removed edges, but we might have changed
	// edge data.
	foreach ($old as $key => $old_value) {
	$new_value = $new[$key];
	if ($old_value['data'] !== $new_value['data']) {
	return true;
	}
	}

	return false;
	}

	return ($xaction->getOldValue() !== $xaction->getNewValue());
	}

	protected function shouldApplyInitialEffects(
	PhabricatorLiskDAO $object,
	array $xactions) {
	return false;
	}

	protected function applyInitialEffects(
	PhabricatorLiskDAO $object,
	array $xactions) {
	throw new PhutilMethodNotImplementedException();
	}

	private function applyInternalEffects(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {

	$type = $xaction->getTransactionType();

	$xtype = $this->getModularTransactionType($type);
	if ($xtype) {
	return $xtype->applyInternalEffects($object, $xaction->getNewValue());
	}

	switch ($type) {
	case PhabricatorTransactions::TYPE_CUSTOMFIELD:
	$field = $this->getCustomFieldForTransaction($object, $xaction);
	return $field->applyApplicationTransactionInternalEffects($xaction);
	case PhabricatorTransactions::TYPE_CREATE:
	case PhabricatorTransactions::TYPE_BUILDABLE:
	case PhabricatorTransactions::TYPE_TOKEN:
	case PhabricatorTransactions::TYPE_VIEW_POLICY:
	case PhabricatorTransactions::TYPE_EDIT_POLICY:
	case PhabricatorTransactions::TYPE_JOIN_POLICY:
	case PhabricatorTransactions::TYPE_SUBSCRIBERS:
	case PhabricatorTransactions::TYPE_INLINESTATE:
	case PhabricatorTransactions::TYPE_EDGE:
	case PhabricatorTransactions::TYPE_SPACE:
	case PhabricatorTransactions::TYPE_COMMENT:
	return $this->applyBuiltinInternalTransaction($object, $xaction);
	}

	return $this->applyCustomInternalTransaction($object, $xaction);
	}

	private function applyExternalEffects(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {

	$type = $xaction->getTransactionType();

	$xtype = $this->getModularTransactionType($type);
	if ($xtype) {
	return $xtype->applyExternalEffects($object, $xaction->getNewValue());
	}

	switch ($type) {
	case PhabricatorTransactions::TYPE_SUBSCRIBERS:
	$subeditor = id(new PhabricatorSubscriptionsEditor())
	->setObject($object)
	->setActor($this->requireActor());

	$old_map = array_fuse($xaction->getOldValue());
	$new_map = array_fuse($xaction->getNewValue());

	$subeditor->unsubscribe(
	array_keys(
	array_diff_key($old_map, $new_map)));

	$subeditor->subscribeExplicit(
	array_keys(
	array_diff_key($new_map, $old_map)));

	$subeditor->save();

	// for the rest of these edits, subscribers should include those just
	// added as well as those just removed.
	$subscribers = array_unique(array_merge(
	$this->subscribers,
	$xaction->getOldValue(),
	$xaction->getNewValue()));
	$this->subscribers = $subscribers;
	return $this->applyBuiltinExternalTransaction($object, $xaction);

	case PhabricatorTransactions::TYPE_CUSTOMFIELD:
	$field = $this->getCustomFieldForTransaction($object, $xaction);
	return $field->applyApplicationTransactionExternalEffects($xaction);
	case PhabricatorTransactions::TYPE_CREATE:
	case PhabricatorTransactions::TYPE_EDGE:
	case PhabricatorTransactions::TYPE_BUILDABLE:
	case PhabricatorTransactions::TYPE_TOKEN:
	case PhabricatorTransactions::TYPE_VIEW_POLICY:
	case PhabricatorTransactions::TYPE_EDIT_POLICY:
	case PhabricatorTransactions::TYPE_JOIN_POLICY:
	case PhabricatorTransactions::TYPE_INLINESTATE:
	case PhabricatorTransactions::TYPE_SPACE:
	case PhabricatorTransactions::TYPE_COMMENT:
	return $this->applyBuiltinExternalTransaction($object, $xaction);
	}

	return $this->applyCustomExternalTransaction($object, $xaction);
	}

	protected function applyCustomInternalTransaction(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {
	$type = $xaction->getTransactionType();
	throw new Exception(
	pht(
	"Transaction type '%s' is missing an internal apply implementation!",
	$type));
	}

	protected function applyCustomExternalTransaction(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {
	$type = $xaction->getTransactionType();
	throw new Exception(
	pht(
	"Transaction type '%s' is missing an external apply implementation!",
	$type));
	}

	/**
	* @{class:PhabricatorTransactions} provides many built-in transactions
	* which should not require much - if any - code in specific applications.
	*
	* This method is a hook for the exceedingly-rare cases where you may need
	* to do additional work for built-in transactions. Developers should
	* extend this method, making sure to return the parent implementation
	* regardless of handling any transactions.
	*
	* See also @{method:applyBuiltinExternalTransaction}.
	*/
	protected function applyBuiltinInternalTransaction(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {

	switch ($xaction->getTransactionType()) {
	case PhabricatorTransactions::TYPE_VIEW_POLICY:
	$object->setViewPolicy($xaction->getNewValue());
	break;
	case PhabricatorTransactions::TYPE_EDIT_POLICY:
	$object->setEditPolicy($xaction->getNewValue());
	break;
	case PhabricatorTransactions::TYPE_JOIN_POLICY:
	$object->setJoinPolicy($xaction->getNewValue());
	break;
	case PhabricatorTransactions::TYPE_SPACE:
	$object->setSpacePHID($xaction->getNewValue());
	break;
	}
	}

	/**
	* See @{method::applyBuiltinInternalTransaction}.
	*/
	protected function applyBuiltinExternalTransaction(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {

	switch ($xaction->getTransactionType()) {
	case PhabricatorTransactions::TYPE_EDGE:
	if ($this->getIsInverseEdgeEditor()) {
	// If we're writing an inverse edge transaction, don't actually
	// do anything. The initiating editor on the other side of the
	// transaction will take care of the edge writes.
	break;
	}

	$old = $xaction->getOldValue();
	$new = $xaction->getNewValue();
	$src = $object->getPHID();
	$const = $xaction->getMetadataValue('edge:type');

	$type = PhabricatorEdgeType::getByConstant($const);
	if ($type->shouldWriteInverseTransactions()) {
	$this->applyInverseEdgeTransactions(
	$object,
	$xaction,
	$type->getInverseEdgeConstant());
	}

	foreach ($new as $dst_phid => $edge) {
	$new[$dst_phid]['src'] = $src;
	}

	$editor = new PhabricatorEdgeEditor();

	foreach ($old as $dst_phid => $edge) {
	if (!empty($new[$dst_phid])) {
	if ($old[$dst_phid]['data'] === $new[$dst_phid]['data']) {
	continue;
	}
	}
	$editor->removeEdge($src, $const, $dst_phid);
	}

	foreach ($new as $dst_phid => $edge) {
	if (!empty($old[$dst_phid])) {
	if ($old[$dst_phid]['data'] === $new[$dst_phid]['data']) {
	continue;
	}
	}

	$data = array(
	'data' => $edge['data'],
	);

	$editor->addEdge($src, $const, $dst_phid, $data);
	}

	$editor->save();

	$this->updateWorkboardColumns($object, $const, $old, $new);
	break;
	case PhabricatorTransactions::TYPE_VIEW_POLICY:
	case PhabricatorTransactions::TYPE_SPACE:
	$this->scrambleFileSecrets($object);
	break;
	}
	}

	/**
	* Fill in a transaction's common values, like author and content source.
	*/
	protected function populateTransaction(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {

	$actor = $this->getActor();

	// TODO: This needs to be more sophisticated once we have meta-policies.
	$xaction->setViewPolicy(PhabricatorPolicies::POLICY_PUBLIC);

	if ($actor->isOmnipotent()) {
	$xaction->setEditPolicy(PhabricatorPolicies::POLICY_NOONE);
	} else {
	$xaction->setEditPolicy($this->getActingAsPHID());
	}

	// If the transaction already has an explicit author PHID, allow it to
	// stand. This is used by applications like Owners that hook into the
	// post-apply change pipeline.
	if (!$xaction->getAuthorPHID()) {
	$xaction->setAuthorPHID($this->getActingAsPHID());
	}

	$xaction->setContentSource($this->getContentSource());
	$xaction->attachViewer($actor);
	$xaction->attachObject($object);

	if ($object->getPHID()) {
	$xaction->setObjectPHID($object->getPHID());
	}

	return $xaction;
	}

	protected function didApplyInternalEffects(
	PhabricatorLiskDAO $object,
	array $xactions) {
	return $xactions;
	}

	protected function applyFinalEffects(
	PhabricatorLiskDAO $object,
	array $xactions) {
	return $xactions;
	}

	public function setContentSource(PhabricatorContentSource $content_source) {
	$this->contentSource = $content_source;
	return $this;
	}

	public function setContentSourceFromRequest(AphrontRequest $request) {
	return $this->setContentSource(
	PhabricatorContentSource::newFromRequest($request));
	}

	public function getContentSource() {
	return $this->contentSource;
	}

	final public function applyTransactions(
	PhabricatorLiskDAO $object,
	array $xactions) {

	$this->object = $object;
	$this->xactions = $xactions;
	$this->isNewObject = ($object->getPHID() === null);

	$this->validateEditParameters($object, $xactions);

	$actor = $this->requireActor();

	// NOTE: Some transaction expansion requires that the edited object be
	// attached.
	foreach ($xactions as $xaction) {
	$xaction->attachObject($object);
	$xaction->attachViewer($actor);
	}

	$xactions = $this->expandTransactions($object, $xactions);
	$xactions = $this->expandSupportTransactions($object, $xactions);
	$xactions = $this->combineTransactions($xactions);

	foreach ($xactions as $xaction) {
	$xaction = $this->populateTransaction($object, $xaction);
	}

	$is_preview = $this->getIsPreview();
	$read_locking = false;
	$transaction_open = false;

	if (!$is_preview) {
	$errors = array();
	$type_map = mgroup($xactions, 'getTransactionType');
	foreach ($this->getTransactionTypes() as $type) {
	$type_xactions = idx($type_map, $type, array());
	$errors[] = $this->validateTransaction($object, $type, $type_xactions);
	}

	$errors[] = $this->validateAllTransactions($object, $xactions);
	$errors = array_mergev($errors);

	$continue_on_missing = $this->getContinueOnMissingFields();
	foreach ($errors as $key => $error) {
	if ($continue_on_missing && $error->getIsMissingFieldError()) {
	unset($errors[$key]);
	}
	}

	if ($errors) {
	throw new PhabricatorApplicationTransactionValidationException($errors);
	}

	$this->willApplyTransactions($object, $xactions);

	if ($object->getID()) {
	foreach ($xactions as $xaction) {

	// If any of the transactions require a read lock, hold one and
	// reload the object. We need to do this fairly early so that the
	// call to `adjustTransactionValues()` (which populates old values)
	// is based on the synchronized state of the object, which may differ
	// from the state when it was originally loaded.

	if ($this->shouldReadLock($object, $xaction)) {
	$object->openTransaction();
	$object->beginReadLocking();
	$transaction_open = true;
	$read_locking = true;
	$object->reload();
	break;
	}
	}
	}

	if ($this->shouldApplyInitialEffects($object, $xactions)) {
	if (!$transaction_open) {
	$object->openTransaction();
	$transaction_open = true;
	}
	}
	}

	if ($this->shouldApplyInitialEffects($object, $xactions)) {
	$this->applyInitialEffects($object, $xactions);
	}

	foreach ($xactions as $xaction) {
	$this->adjustTransactionValues($object, $xaction);
	}

	try {
	$xactions = $this->filterTransactions($object, $xactions);
	} catch (Exception $ex) {
	if ($read_locking) {
	$object->endReadLocking();
	}
	if ($transaction_open) {
	$object->killTransaction();
	}
	throw $ex;
	}

	// TODO: Once everything is on EditEngine, just use getIsNewObject() to
	// figure this out instead.
	$mark_as_create = false;
	$create_type = PhabricatorTransactions::TYPE_CREATE;
	foreach ($xactions as $xaction) {
	if ($xaction->getTransactionType() == $create_type) {
	$mark_as_create = true;
	}
	}

	if ($mark_as_create) {
	foreach ($xactions as $xaction) {
	$xaction->setIsCreateTransaction(true);
	}
	}

	// Now that we've merged, filtered, and combined transactions, check for
	// required capabilities.
	foreach ($xactions as $xaction) {
	$this->requireCapabilities($object, $xaction);
	}

	$xactions = $this->sortTransactions($xactions);
	$file_phids = $this->extractFilePHIDs($object, $xactions);

	if ($is_preview) {
	$this->loadHandles($xactions);
	return $xactions;
	}

	$comment_editor = id(new PhabricatorApplicationTransactionCommentEditor())
	->setActor($actor)
	->setActingAsPHID($this->getActingAsPHID())
	->setContentSource($this->getContentSource());

	if (!$transaction_open) {
	$object->openTransaction();
	}

	foreach ($xactions as $xaction) {
	$this->applyInternalEffects($object, $xaction);
	}

	$xactions = $this->didApplyInternalEffects($object, $xactions);

	try {
	$object->save();
	} catch (AphrontDuplicateKeyQueryException $ex) {
	$object->killTransaction();

	// This callback has an opportunity to throw a better exception,
	// so execution may end here.
	$this->didCatchDuplicateKeyException($object, $xactions, $ex);

	throw $ex;
	}

	foreach ($xactions as $xaction) {
	$xaction->setObjectPHID($object->getPHID());
	if ($xaction->getComment()) {
	$xaction->setPHID($xaction->generatePHID());
	$comment_editor->applyEdit($xaction, $xaction->getComment());
	} else {
	$xaction->save();
	}
	}

	if ($file_phids) {
	$this->attachFiles($object, $file_phids);
	}

	foreach ($xactions as $xaction) {
	$this->applyExternalEffects($object, $xaction);
	}

	$xactions = $this->applyFinalEffects($object, $xactions);
	if ($read_locking) {
	$object->endReadLocking();
	$read_locking = false;
	}

	$object->saveTransaction();

	// Now that we've completely applied the core transaction set, try to apply
	// Herald rules. Herald rules are allowed to either take direct actions on
	// the database (like writing flags), or take indirect actions (like saving
	// some targets for CC when we generate mail a little later), or return
	// transactions which we'll apply normally using another Editor.

	// First, check if this is a sub-editor which is itself applying Herald
	// rules: if it is, stop working and return so we don't descend into
	// madness.

	// Otherwise, we're not a Herald editor, so process Herald rules (possibly
	// using a Herald editor to apply resulting transactions) and then send out
	// mail, notifications, and feed updates about everything.

	if ($this->getIsHeraldEditor()) {
	// We are the Herald editor, so stop work here and return the updated
	// transactions.
	return $xactions;
	} else if ($this->getIsInverseEdgeEditor()) {
	// If we're applying inverse edge transactions, don't trigger Herald.
	// From a product perspective, the current set of inverse edges (most
	// often, mentions) aren't things users would expect to trigger Herald.
	// From a technical perspective, objects loaded by the inverse editor may
	// not have enough data to execute rules. At least for now, just stop
	// Herald from executing when applying inverse edges.
	} else if ($this->shouldApplyHeraldRules($object, $xactions)) {
	// We are not the Herald editor, so try to apply Herald rules.
	$herald_xactions = $this->applyHeraldRules($object, $xactions);

	if ($herald_xactions) {
	$xscript_id = $this->getHeraldTranscript()->getID();
	foreach ($herald_xactions as $herald_xaction) {
	// Don't set a transcript ID if this is a transaction from another
	// application or source, like Owners.
	if ($herald_xaction->getAuthorPHID()) {
	continue;
	}

	$herald_xaction->setMetadataValue('herald:transcriptID', $xscript_id);
	}

	// NOTE: We're acting as the omnipotent user because rules deal with
	// their own policy issues. We use a synthetic author PHID (the
	// Herald application) as the author of record, so that transactions
	// will render in a reasonable way ("Herald assigned this task ...").
	$herald_actor = PhabricatorUser::getOmnipotentUser();
	$herald_phid = id(new PhabricatorHeraldApplication())->getPHID();

	// TODO: It would be nice to give transactions a more specific source
	// which points at the rule which generated them. You can figure this
	// out from transcripts, but it would be cleaner if you didn't have to.

	$herald_source = PhabricatorContentSource::newForSource(
	PhabricatorHeraldContentSource::SOURCECONST);

	$herald_editor = newv(get_class($this), array())
	->setContinueOnNoEffect(true)
	->setContinueOnMissingFields(true)
	->setParentMessageID($this->getParentMessageID())
	->setIsHeraldEditor(true)
	->setActor($herald_actor)
	->setActingAsPHID($herald_phid)
	->setContentSource($herald_source);

	$herald_xactions = $herald_editor->applyTransactions(
	$object,
	$herald_xactions);

	// Merge the new transactions into the transaction list: we want to
	// send email and publish feed stories about them, too.
	$xactions = array_merge($xactions, $herald_xactions);
	}

	// If Herald did not generate transactions, we may still need to handle
	// "Send an Email" rules.
	$adapter = $this->getHeraldAdapter();
	$this->heraldEmailPHIDs = $adapter->getEmailPHIDs();
	$this->heraldForcedEmailPHIDs = $adapter->getForcedEmailPHIDs();
	}

	$this->didApplyTransactions($xactions);

	if ($object instanceof PhabricatorCustomFieldInterface) {
	// Maybe this makes more sense to move into the search index itself? For
	// now I'm putting it here since I think we might end up with things that
	// need it to be up to date once the next page loads, but if we don't go
	// there we could move it into search once search moves to the daemons.

	// It now happens in the search indexer as well, but the search indexer is
	// always daemonized, so the logic above still potentially holds. We could
	// possibly get rid of this. The major motivation for putting it in the
	// indexer was to enable reindexing to work.

	$fields = PhabricatorCustomField::getObjectFields(
	$object,
	PhabricatorCustomField::ROLE_APPLICATIONSEARCH);
	$fields->readFieldsFromStorage($object);
	$fields->rebuildIndexes($object);
	}

	$herald_xscript = $this->getHeraldTranscript();
	if ($herald_xscript) {
	$herald_header = $herald_xscript->getXHeraldRulesHeader();
	$herald_header = HeraldTranscript::saveXHeraldRulesHeader(
	$object->getPHID(),
	$herald_header);
	} else {
	$herald_header = HeraldTranscript::loadXHeraldRulesHeader(
	$object->getPHID());
	}
	$this->heraldHeader = $herald_header;

	// We're going to compute some of the data we'll use to publish these
	// transactions here, before queueing a worker.
	//
	// Primarily, this is more correct: we want to publish the object as it
	// exists right now. The worker may not execute for some time, and we want
	// to use the current To/CC list, not respect any changes which may occur
	// between now and when the worker executes.
	//
	// As a secondary benefit, this tends to reduce the amount of state that
	// Editors need to pass into workers.
	$object = $this->willPublish($object, $xactions);

	if (!$this->getDisableEmail()) {
	if ($this->shouldSendMail($object, $xactions)) {
	$this->mailToPHIDs = $this->getMailTo($object);
	$this->mailCCPHIDs = $this->getMailCC($object);
	}
	}

	if ($this->shouldPublishFeedStory($object, $xactions)) {
	$this->feedRelatedPHIDs = $this->getFeedRelatedPHIDs($object, $xactions);
	$this->feedNotifyPHIDs = $this->getFeedNotifyPHIDs($object, $xactions);
	}

	PhabricatorWorker::scheduleTask(
	'PhabricatorApplicationTransactionPublishWorker',
	array(
	'objectPHID' => $object->getPHID(),
	'actorPHID' => $this->getActingAsPHID(),
	'xactionPHIDs' => mpull($xactions, 'getPHID'),
	'state' => $this->getWorkerState(),
	),
	array(
	'objectPHID' => $object->getPHID(),
	'priority' => PhabricatorWorker::PRIORITY_ALERTS,
	));

	return $xactions;
	}

	protected function didCatchDuplicateKeyException(
	PhabricatorLiskDAO $object,
	array $xactions,
	Exception $ex) {
	return;
	}

	public function publishTransactions(
	PhabricatorLiskDAO $object,
	array $xactions) {

	// Hook for edges or other properties that may need (re-)loading
	$object = $this->willPublish($object, $xactions);

	$messages = array();
	if (!$this->getDisableEmail()) {
	if ($this->shouldSendMail($object, $xactions)) {
	$messages = $this->buildMail($object, $xactions);
	}
	}

	if ($this->supportsSearch()) {
	PhabricatorSearchWorker::queueDocumentForIndexing(
	$object->getPHID(),
	array(
	'transactionPHIDs' => mpull($xactions, 'getPHID'),
	));
	}

	if ($this->shouldPublishFeedStory($object, $xactions)) {

	$mailed = array();
	foreach ($messages as $mail) {
	foreach ($mail->buildRecipientList() as $phid) {
	$mailed[$phid] = $phid;
	}
	}

	$this->publishFeedStory($object, $xactions, $mailed);
	}

	// NOTE: This actually sends the mail. We do this last to reduce the chance
	// that we send some mail, hit an exception, then send the mail again when
	// retrying.
	foreach ($messages as $mail) {
	$mail->save();
	}

	return $xactions;
	}

	protected function didApplyTransactions(array $xactions) {
	// Hook for subclasses.
	return;
	}


	/**
	* Determine if the editor should hold a read lock on the object while
	* applying a transaction.
	*
	* If the editor does not hold a lock, two editors may read an object at the
	* same time, then apply their changes without any synchronization. For most
	* transactions, this does not matter much. However, it is important for some
	* transactions. For example, if an object has a transaction count on it, both
	* editors may read the object with `count = 23`, then independently update it
	* and save the object with `count = 24` twice. This will produce the wrong
	* state: the object really has 25 transactions, but the count is only 24.
	*
	* Generally, transactions fall into one of four buckets:
	*
	* - Append operations: Actions like adding a comment to an object purely
	* add information to its state, and do not depend on the current object
	* state in any way. These transactions never need to hold locks.
	* - Overwrite operations: Actions like changing the title or description
	* of an object replace the current value with a new value, so the end
	* state is consistent without a lock. We currently do not lock these
	* transactions, although we may in the future.
	* - Edge operations: Edge and subscription operations have internal
	* synchronization which limits the damage race conditions can cause.
	* We do not currently lock these transactions, although we may in the
	* future.
	* - Update operations: Actions like incrementing a count on an object.
	* These operations generally should use locks, unless it is not
	* important that the state remain consistent in the presence of races.
	*
	* @param PhabricatorLiskDAO Object being updated.
	* @param PhabricatorApplicationTransaction Transaction being applied.
	* @return bool True to synchronize the edit with a lock.
	*/
	protected function shouldReadLock(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {
	return false;
	}

	private function loadHandles(array $xactions) {
	$phids = array();
	foreach ($xactions as $key => $xaction) {
	$phids[$key] = $xaction->getRequiredHandlePHIDs();
	}
	$handles = array();
	$merged = array_mergev($phids);
	if ($merged) {
	$handles = id(new PhabricatorHandleQuery())
	->setViewer($this->requireActor())
	->withPHIDs($merged)
	->execute();
	}
	foreach ($xactions as $key => $xaction) {
	$xaction->setHandles(array_select_keys($handles, $phids[$key]));
	}
	}

	private function loadSubscribers(PhabricatorLiskDAO $object) {
	if ($object->getPHID() &&
	($object instanceof PhabricatorSubscribableInterface)) {
	$subs = PhabricatorSubscribersQuery::loadSubscribersForPHID(
	$object->getPHID());
	$this->subscribers = array_fuse($subs);
	} else {
	$this->subscribers = array();
	}
	}

	private function validateEditParameters(
	PhabricatorLiskDAO $object,
	array $xactions) {

	if (!$this->getContentSource()) {
	throw new PhutilInvalidStateException('setContentSource');
	}

	// Do a bunch of sanity checks that the incoming transactions are fresh.
	// They should be unsaved and have only "transactionType" and "newValue"
	// set.

	$types = array_fill_keys($this->getTransactionTypes(), true);

	assert_instances_of($xactions, 'PhabricatorApplicationTransaction');
	foreach ($xactions as $xaction) {
	if ($xaction->getPHID() \|\| $xaction->getID()) {
	throw new PhabricatorApplicationTransactionStructureException(
	$xaction,
	pht('You can not apply transactions which already have IDs/PHIDs!'));
	}

	if ($xaction->getObjectPHID()) {
	throw new PhabricatorApplicationTransactionStructureException(
	$xaction,
	pht(
	'You can not apply transactions which already have %s!',
	'objectPHIDs'));
	}

	if ($xaction->getCommentPHID()) {
	throw new PhabricatorApplicationTransactionStructureException(
	$xaction,
	pht(
	'You can not apply transactions which already have %s!',
	'commentPHIDs'));
	}

	if ($xaction->getCommentVersion() !== 0) {
	throw new PhabricatorApplicationTransactionStructureException(
	$xaction,
	pht(
	'You can not apply transactions which already have '.
	'commentVersions!'));
	}

	$expect_value = !$xaction->shouldGenerateOldValue();
	$has_value = $xaction->hasOldValue();

	if ($expect_value && !$has_value) {
	throw new PhabricatorApplicationTransactionStructureException(
	$xaction,
	pht(
	'This transaction is supposed to have an %s set, but it does not!',
	'oldValue'));
	}

	if ($has_value && !$expect_value) {
	throw new PhabricatorApplicationTransactionStructureException(
	$xaction,
	pht(
	'This transaction should generate its %s automatically, '.
	'but has already had one set!',
	'oldValue'));
	}

	$type = $xaction->getTransactionType();
	if (empty($types[$type])) {
	throw new PhabricatorApplicationTransactionStructureException(
	$xaction,
	pht(
	'Transaction has type "%s", but that transaction type is not '.
	'supported by this editor (%s).',
	$type,
	get_class($this)));
	}
	}
	}

	protected function requireCapabilities(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {

	if ($this->getIsNewObject()) {
	return;
	}

	$actor = $this->requireActor();
	switch ($xaction->getTransactionType()) {
	case PhabricatorTransactions::TYPE_COMMENT:
	PhabricatorPolicyFilter::requireCapability(
	$actor,
	$object,
	PhabricatorPolicyCapability::CAN_VIEW);
	break;
	case PhabricatorTransactions::TYPE_VIEW_POLICY:
	case PhabricatorTransactions::TYPE_EDIT_POLICY:
	case PhabricatorTransactions::TYPE_JOIN_POLICY:
	case PhabricatorTransactions::TYPE_SPACE:
	PhabricatorPolicyFilter::requireCapability(
	$actor,
	$object,
	PhabricatorPolicyCapability::CAN_EDIT);
	break;
	}
	}

	private function buildSubscribeTransaction(
	PhabricatorLiskDAO $object,
	array $xactions,
	array $changes) {

	if (!($object instanceof PhabricatorSubscribableInterface)) {
	return null;
	}

	if ($this->shouldEnableMentions($object, $xactions)) {
	// Identify newly mentioned users. We ignore users who were previously
	// mentioned so that we don't re-subscribe users after an edit of text
	// which mentions them.
	$old_texts = mpull($changes, 'getOldValue');
	$new_texts = mpull($changes, 'getNewValue');

	$old_phids = PhabricatorMarkupEngine::extractPHIDsFromMentions(
	$this->getActor(),
	$old_texts);

	$new_phids = PhabricatorMarkupEngine::extractPHIDsFromMentions(
	$this->getActor(),
	$new_texts);

	$phids = array_diff($new_phids, $old_phids);
	} else {
	$phids = array();
	}

	$this->mentionedPHIDs = $phids;

	if ($object->getPHID()) {
	// Don't try to subscribe already-subscribed mentions: we want to generate
	// a dialog about an action having no effect if the user explicitly adds
	// existing CCs, but not if they merely mention existing subscribers.
	$phids = array_diff($phids, $this->subscribers);
	}

	if ($phids) {
	$users = id(new PhabricatorPeopleQuery())
	->setViewer($this->getActor())
	->withPHIDs($phids)
	->execute();
	$users = mpull($users, null, 'getPHID');

	foreach ($phids as $key => $phid) {
	// Do not subscribe mentioned users
	// who do not have VIEW Permissions
	if ($object instanceof PhabricatorPolicyInterface
	&& !PhabricatorPolicyFilter::hasCapability(
	$users[$phid],
	$object,
	PhabricatorPolicyCapability::CAN_VIEW)
	) {
	unset($phids[$key]);
	} else {
	if ($object->isAutomaticallySubscribed($phid)) {
	unset($phids[$key]);
	}
	}
	}
	$phids = array_values($phids);
	}
	// No else here to properly return null should we unset all subscriber
	if (!$phids) {
	return null;
	}

	$xaction = newv(get_class(head($xactions)), array());
	$xaction->setTransactionType(PhabricatorTransactions::TYPE_SUBSCRIBERS);
	$xaction->setNewValue(array('+' => $phids));

	return $xaction;
	}

	protected function mergeTransactions(
	PhabricatorApplicationTransaction $u,
	PhabricatorApplicationTransaction $v) {

	$type = $u->getTransactionType();

	switch ($type) {
	case PhabricatorTransactions::TYPE_SUBSCRIBERS:
	return $this->mergePHIDOrEdgeTransactions($u, $v);
	case PhabricatorTransactions::TYPE_EDGE:
	$u_type = $u->getMetadataValue('edge:type');
	$v_type = $v->getMetadataValue('edge:type');
	if ($u_type == $v_type) {
	return $this->mergePHIDOrEdgeTransactions($u, $v);
	}
	return null;
	}

	// By default, do not merge the transactions.
	return null;
	}

	/**
	* Optionally expand transactions which imply other effects. For example,
	* resigning from a revision in Differential implies removing yourself as
	* a reviewer.
	*/
	protected function expandTransactions(
	PhabricatorLiskDAO $object,
	array $xactions) {

	$results = array();
	foreach ($xactions as $xaction) {
	foreach ($this->expandTransaction($object, $xaction) as $expanded) {
	$results[] = $expanded;
	}
	}

	return $results;
	}

	protected function expandTransaction(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {
	return array($xaction);
	}


	public function getExpandedSupportTransactions(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {

	$xactions = array($xaction);
	$xactions = $this->expandSupportTransactions(
	$object,
	$xactions);

	if (count($xactions) == 1) {
	return array();
	}

	foreach ($xactions as $index => $cxaction) {
	if ($cxaction === $xaction) {
	unset($xactions[$index]);
	break;
	}
	}

	return $xactions;
	}

	private function expandSupportTransactions(
	PhabricatorLiskDAO $object,
	array $xactions) {
	$this->loadSubscribers($object);

	$xactions = $this->applyImplicitCC($object, $xactions);

	$changes = $this->getRemarkupChanges($xactions);

	$subscribe_xaction = $this->buildSubscribeTransaction(
	$object,
	$xactions,
	$changes);
	if ($subscribe_xaction) {
	$xactions[] = $subscribe_xaction;
	}

	// TODO: For now, this is just a placeholder.
	$engine = PhabricatorMarkupEngine::getEngine('extract');
	$engine->setConfig('viewer', $this->requireActor());

	$block_xactions = $this->expandRemarkupBlockTransactions(
	$object,
	$xactions,
	$changes,
	$engine);

	foreach ($block_xactions as $xaction) {
	$xactions[] = $xaction;
	}

	return $xactions;
	}

	private function getRemarkupChanges(array $xactions) {
	$changes = array();

	foreach ($xactions as $key => $xaction) {
	foreach ($this->getRemarkupChangesFromTransaction($xaction) as $change) {
	$changes[] = $change;
	}
	}

	return $changes;
	}

	private function getRemarkupChangesFromTransaction(
	PhabricatorApplicationTransaction $transaction) {
	return $transaction->getRemarkupChanges();
	}

	private function expandRemarkupBlockTransactions(
	PhabricatorLiskDAO $object,
	array $xactions,
	array $changes,
	PhutilMarkupEngine $engine) {

	$block_xactions = $this->expandCustomRemarkupBlockTransactions(
	$object,
	$xactions,
	$changes,
	$engine);

	$mentioned_phids = array();
	if ($this->shouldEnableMentions($object, $xactions)) {
	foreach ($changes as $change) {
	// Here, we don't care about processing only new mentions after an edit
	// because there is no way for an object to ever "unmention" itself on
	// another object, so we can ignore the old value.
	$engine->markupText($change->getNewValue());

	$mentioned_phids += $engine->getTextMetadata(
	PhabricatorObjectRemarkupRule::KEY_MENTIONED_OBJECTS,
	array());
	}
	}

	if (!$mentioned_phids) {
	return $block_xactions;
	}

	$mentioned_objects = id(new PhabricatorObjectQuery())
	->setViewer($this->getActor())
	->withPHIDs($mentioned_phids)
	->execute();

	$mentionable_phids = array();
	if ($this->shouldEnableMentions($object, $xactions)) {
	foreach ($mentioned_objects as $mentioned_object) {
	if ($mentioned_object instanceof PhabricatorMentionableInterface) {
	$mentioned_phid = $mentioned_object->getPHID();
	if (idx($this->getUnmentionablePHIDMap(), $mentioned_phid)) {
	continue;
	}
	// don't let objects mention themselves
	if ($object->getPHID() && $mentioned_phid == $object->getPHID()) {
	continue;
	}
	$mentionable_phids[$mentioned_phid] = $mentioned_phid;
	}
	}
	}

	if ($mentionable_phids) {
	$edge_type = PhabricatorObjectMentionsObjectEdgeType::EDGECONST;
	$block_xactions[] = newv(get_class(head($xactions)), array())
	->setIgnoreOnNoEffect(true)
	->setTransactionType(PhabricatorTransactions::TYPE_EDGE)
	->setMetadataValue('edge:type', $edge_type)
	->setNewValue(array('+' => $mentionable_phids));
	}

	return $block_xactions;
	}

	protected function expandCustomRemarkupBlockTransactions(
	PhabricatorLiskDAO $object,
	array $xactions,
	array $changes,
	PhutilMarkupEngine $engine) {
	return array();
	}


	/**
	* Attempt to combine similar transactions into a smaller number of total
	* transactions. For example, two transactions which edit the title of an
	* object can be merged into a single edit.
	*/
	private function combineTransactions(array $xactions) {
	$stray_comments = array();

	$result = array();
	$types = array();
	foreach ($xactions as $key => $xaction) {
	$type = $xaction->getTransactionType();
	if (isset($types[$type])) {
	foreach ($types[$type] as $other_key) {
	$other_xaction = $result[$other_key];

	// Don't merge transactions with different authors. For example,
	// don't merge Herald transactions and owners transactions.
	if ($other_xaction->getAuthorPHID() != $xaction->getAuthorPHID()) {
	continue;
	}

	$merged = $this->mergeTransactions($result[$other_key], $xaction);
	if ($merged) {
	$result[$other_key] = $merged;

	if ($xaction->getComment() &&
	($xaction->getComment() !== $merged->getComment())) {
	$stray_comments[] = $xaction->getComment();
	}

	if ($result[$other_key]->getComment() &&
	($result[$other_key]->getComment() !== $merged->getComment())) {
	$stray_comments[] = $result[$other_key]->getComment();
	}

	// Move on to the next transaction.
	continue 2;
	}
	}
	}
	$result[$key] = $xaction;
	$types[$type][] = $key;
	}

	// If we merged any comments away, restore them.
	foreach ($stray_comments as $comment) {
	$xaction = newv(get_class(head($result)), array());
	$xaction->setTransactionType(PhabricatorTransactions::TYPE_COMMENT);
	$xaction->setComment($comment);
	$result[] = $xaction;
	}

	return array_values($result);
	}

	protected function mergePHIDOrEdgeTransactions(
	PhabricatorApplicationTransaction $u,
	PhabricatorApplicationTransaction $v) {

	$result = $u->getNewValue();
	foreach ($v->getNewValue() as $key => $value) {
	if ($u->getTransactionType() == PhabricatorTransactions::TYPE_EDGE) {
	if (empty($result[$key])) {
	$result[$key] = $value;
	} else {
	// We're merging two lists of edge adds, sets, or removes. Merge
	// them by merging individual PHIDs within them.
	$merged = $result[$key];

	foreach ($value as $dst => $v_spec) {
	if (empty($merged[$dst])) {
	$merged[$dst] = $v_spec;
	} else {
	// Two transactions are trying to perform the same operation on
	// the same edge. Normalize the edge data and then merge it. This
	// allows transactions to specify how data merges execute in a
	// precise way.

	$u_spec = $merged[$dst];

	if (!is_array($u_spec)) {
	$u_spec = array('dst' => $u_spec);
	}
	if (!is_array($v_spec)) {
	$v_spec = array('dst' => $v_spec);
	}

	$ux_data = idx($u_spec, 'data', array());
	$vx_data = idx($v_spec, 'data', array());

	$merged_data = $this->mergeEdgeData(
	$u->getMetadataValue('edge:type'),
	$ux_data,
	$vx_data);

	$u_spec['data'] = $merged_data;
	$merged[$dst] = $u_spec;
	}
	}

	$result[$key] = $merged;
	}
	} else {
	$result[$key] = array_merge($value, idx($result, $key, array()));
	}
	}
	$u->setNewValue($result);

	// When combining an "ignore" transaction with a normal transaction, make
	// sure we don't propagate the "ignore" flag.
	if (!$v->getIgnoreOnNoEffect()) {
	$u->setIgnoreOnNoEffect(false);
	}

	return $u;
	}

	protected function mergeEdgeData($type, array $u, array $v) {
	return $v + $u;
	}

	protected function getPHIDTransactionNewValue(
	PhabricatorApplicationTransaction $xaction,
	$old = null) {

	if ($old !== null) {
	$old = array_fuse($old);
	} else {
	$old = array_fuse($xaction->getOldValue());
	}

	$new = $xaction->getNewValue();
	$new_add = idx($new, '+', array());
	unset($new['+']);
	$new_rem = idx($new, '-', array());
	unset($new['-']);
	$new_set = idx($new, '=', null);
	if ($new_set !== null) {
	$new_set = array_fuse($new_set);
	}
	unset($new['=']);

	if ($new) {
	throw new Exception(
	pht(
	"Invalid '%s' value for PHID transaction. Value should contain only ".
	"keys '%s' (add PHIDs), '%s' (remove PHIDs) and '%s' (set PHIDS).",
	'new',
	'+',
	'-',
	'='));
	}

	$result = array();

	foreach ($old as $phid) {
	if ($new_set !== null && empty($new_set[$phid])) {
	continue;
	}
	$result[$phid] = $phid;
	}

	if ($new_set !== null) {
	foreach ($new_set as $phid) {
	$result[$phid] = $phid;
	}
	}

	foreach ($new_add as $phid) {
	$result[$phid] = $phid;
	}

	foreach ($new_rem as $phid) {
	unset($result[$phid]);
	}

	return array_values($result);
	}

	protected function getEdgeTransactionNewValue(
	PhabricatorApplicationTransaction $xaction) {

	$new = $xaction->getNewValue();
	$new_add = idx($new, '+', array());
	unset($new['+']);
	$new_rem = idx($new, '-', array());
	unset($new['-']);
	$new_set = idx($new, '=', null);
	unset($new['=']);

	if ($new) {
	throw new Exception(
	pht(
	"Invalid '%s' value for Edge transaction. Value should contain only ".
	"keys '%s' (add edges), '%s' (remove edges) and '%s' (set edges).",
	'new',
	'+',
	'-',
	'='));
	}

	$old = $xaction->getOldValue();

	$lists = array($new_set, $new_add, $new_rem);
	foreach ($lists as $list) {
	$this->checkEdgeList($list, $xaction->getMetadataValue('edge:type'));
	}

	$result = array();
	foreach ($old as $dst_phid => $edge) {
	if ($new_set !== null && empty($new_set[$dst_phid])) {
	continue;
	}
	$result[$dst_phid] = $this->normalizeEdgeTransactionValue(
	$xaction,
	$edge,
	$dst_phid);
	}

	if ($new_set !== null) {
	foreach ($new_set as $dst_phid => $edge) {
	$result[$dst_phid] = $this->normalizeEdgeTransactionValue(
	$xaction,
	$edge,
	$dst_phid);
	}
	}

	foreach ($new_add as $dst_phid => $edge) {
	$result[$dst_phid] = $this->normalizeEdgeTransactionValue(
	$xaction,
	$edge,
	$dst_phid);
	}

	foreach ($new_rem as $dst_phid => $edge) {
	unset($result[$dst_phid]);
	}

	return $result;
	}

	private function checkEdgeList($list, $edge_type) {
	if (!$list) {
	return;
	}
	foreach ($list as $key => $item) {
	if (phid_get_type($key) === PhabricatorPHIDConstants::PHID_TYPE_UNKNOWN) {
	throw new Exception(
	pht(
	'Edge transactions must have destination PHIDs as in edge '.
	'lists (found key "%s" on transaction of type "%s").',
	$key,
	$edge_type));
	}
	if (!is_array($item) && $item !== $key) {
	throw new Exception(
	pht(
	'Edge transactions must have PHIDs or edge specs as values '.
	'(found value "%s" on transaction of type "%s").',
	$item,
	$edge_type));
	}
	}
	}

	private function normalizeEdgeTransactionValue(
	PhabricatorApplicationTransaction $xaction,
	$edge,
	$dst_phid) {

	if (!is_array($edge)) {
	if ($edge != $dst_phid) {
	throw new Exception(
	pht(
	'Transaction edge data must either be the edge PHID or an edge '.
	'specification dictionary.'));
	}
	$edge = array();
	} else {
	foreach ($edge as $key => $value) {
	switch ($key) {
	case 'src':
	case 'dst':
	case 'type':
	case 'data':
	case 'dateCreated':
	case 'dateModified':
	case 'seq':
	case 'dataID':
	break;
	default:
	throw new Exception(
	pht(
	'Transaction edge specification contains unexpected key "%s".',
	$key));
	}
	}
	}

	$edge['dst'] = $dst_phid;

	$edge_type = $xaction->getMetadataValue('edge:type');
	if (empty($edge['type'])) {
	$edge['type'] = $edge_type;
	} else {
	if ($edge['type'] != $edge_type) {
	$this_type = $edge['type'];
	throw new Exception(
	pht(
	"Edge transaction includes edge of type '%s', but ".
	"transaction is of type '%s'. Each edge transaction ".
	"must alter edges of only one type.",
	$this_type,
	$edge_type));
	}
	}

	if (!isset($edge['data'])) {
	$edge['data'] = array();
	}

	return $edge;
	}

	protected function sortTransactions(array $xactions) {
	$head = array();
	$tail = array();

	// Move bare comments to the end, so the actions precede them.
	foreach ($xactions as $xaction) {
	$type = $xaction->getTransactionType();
	if ($type == PhabricatorTransactions::TYPE_COMMENT) {
	$tail[] = $xaction;
	} else {
	$head[] = $xaction;
	}
	}

	return array_values(array_merge($head, $tail));
	}


	protected function filterTransactions(
	PhabricatorLiskDAO $object,
	array $xactions) {

	$type_comment = PhabricatorTransactions::TYPE_COMMENT;

	$no_effect = array();
	$has_comment = false;
	$any_effect = false;
	foreach ($xactions as $key => $xaction) {
	if ($this->transactionHasEffect($object, $xaction)) {
	if ($xaction->getTransactionType() != $type_comment) {
	$any_effect = true;
	}
	} else if ($xaction->getIgnoreOnNoEffect()) {
	unset($xactions[$key]);
	} else {
	$no_effect[$key] = $xaction;
	}
	if ($xaction->hasComment()) {
	$has_comment = true;
	}
	}

	if (!$no_effect) {
	return $xactions;
	}

	if (!$this->getContinueOnNoEffect() && !$this->getIsPreview()) {
	throw new PhabricatorApplicationTransactionNoEffectException(
	$no_effect,
	$any_effect,
	$has_comment);
	}

	if (!$any_effect && !$has_comment) {
	// If we only have empty comment transactions, just drop them all.
	return array();
	}

	foreach ($no_effect as $key => $xaction) {
	if ($xaction->hasComment()) {
	$xaction->setTransactionType($type_comment);
	$xaction->setOldValue(null);
	$xaction->setNewValue(null);
	} else {
	unset($xactions[$key]);
	}
	}

	return $xactions;
	}


	/**
	* Hook for validating transactions. This callback will be invoked for each
	* available transaction type, even if an edit does not apply any transactions
	* of that type. This allows you to raise exceptions when required fields are
	* missing, by detecting that the object has no field value and there is no
	* transaction which sets one.
	*
	* @param PhabricatorLiskDAO Object being edited.
	* @param string Transaction type to validate.
	* @param list<PhabricatorApplicationTransaction> Transactions of given type,
	* which may be empty if the edit does not apply any transactions of the
	* given type.
	* @return list<PhabricatorApplicationTransactionValidationError> List of
	* validation errors.
	*/
	protected function validateTransaction(
	PhabricatorLiskDAO $object,
	$type,
	array $xactions) {

	$errors = array();

	$xtype = $this->getModularTransactionType($type);
	if ($xtype) {
	$errors[] = $xtype->validateTransactions($object, $xactions);
	}

	switch ($type) {
	case PhabricatorTransactions::TYPE_VIEW_POLICY:
	$errors[] = $this->validatePolicyTransaction(
	$object,
	$xactions,
	$type,
	PhabricatorPolicyCapability::CAN_VIEW);
	break;
	case PhabricatorTransactions::TYPE_EDIT_POLICY:
	$errors[] = $this->validatePolicyTransaction(
	$object,
	$xactions,
	$type,
	PhabricatorPolicyCapability::CAN_EDIT);
	break;
	case PhabricatorTransactions::TYPE_SPACE:
	$errors[] = $this->validateSpaceTransactions(
	$object,
	$xactions,
	$type);
	break;
	case PhabricatorTransactions::TYPE_CUSTOMFIELD:
	$groups = array();
	foreach ($xactions as $xaction) {
	$groups[$xaction->getMetadataValue('customfield:key')][] = $xaction;
	}

	$field_list = PhabricatorCustomField::getObjectFields(
	$object,
	PhabricatorCustomField::ROLE_EDIT);
	$field_list->setViewer($this->getActor());

	$role_xactions = PhabricatorCustomField::ROLE_APPLICATIONTRANSACTIONS;
	foreach ($field_list->getFields() as $field) {
	if (!$field->shouldEnableForRole($role_xactions)) {
	continue;
	}
	$errors[] = $field->validateApplicationTransactions(
	$this,
	$type,
	idx($groups, $field->getFieldKey(), array()));
	}
	break;
	}

	return array_mergev($errors);
	}

	private function validatePolicyTransaction(
	PhabricatorLiskDAO $object,
	array $xactions,
	$transaction_type,
	$capability) {

	$actor = $this->requireActor();
	$errors = array();
	// Note $this->xactions is necessary; $xactions is $this->xactions of
	// $transaction_type
	$policy_object = $this->adjustObjectForPolicyChecks(
	$object,
	$this->xactions);

	// Make sure the user isn't editing away their ability to $capability this
	// object.
	foreach ($xactions as $xaction) {
	try {
	PhabricatorPolicyFilter::requireCapabilityWithForcedPolicy(
	$actor,
	$policy_object,
	$capability,
	$xaction->getNewValue());
	} catch (PhabricatorPolicyException $ex) {
	$errors[] = new PhabricatorApplicationTransactionValidationError(
	$transaction_type,
	pht('Invalid'),
	pht(
	'You can not select this %s policy, because you would no longer '.
	'be able to %s the object.',
	$capability,
	$capability),
	$xaction);
	}
	}

	if ($this->getIsNewObject()) {
	if (!$xactions) {
	$has_capability = PhabricatorPolicyFilter::hasCapability(
	$actor,
	$policy_object,
	$capability);
	if (!$has_capability) {
	$errors[] = new PhabricatorApplicationTransactionValidationError(
	$transaction_type,
	pht('Invalid'),
	pht(
	'The selected %s policy excludes you. Choose a %s policy '.
	'which allows you to %s the object.',
	$capability,
	$capability,
	$capability));
	}
	}
	}

	return $errors;
	}


	private function validateSpaceTransactions(
	PhabricatorLiskDAO $object,
	array $xactions,
	$transaction_type) {
	$errors = array();

	$actor = $this->getActor();

	$has_spaces = PhabricatorSpacesNamespaceQuery::getViewerSpacesExist($actor);
	$actor_spaces = PhabricatorSpacesNamespaceQuery::getViewerSpaces($actor);
	$active_spaces = PhabricatorSpacesNamespaceQuery::getViewerActiveSpaces(
	$actor);
	foreach ($xactions as $xaction) {
	$space_phid = $xaction->getNewValue();

	if ($space_phid === null) {
	if (!$has_spaces) {
	// The install doesn't have any spaces, so this is fine.
	continue;
	}

	// The install has some spaces, so every object needs to be put
	// in a valid space.
	$errors[] = new PhabricatorApplicationTransactionValidationError(
	$transaction_type,
	pht('Invalid'),
	pht('You must choose a space for this object.'),
	$xaction);
	continue;
	}

	// If the PHID isn't `null`, it needs to be a valid space that the
	// viewer can see.
	if (empty($actor_spaces[$space_phid])) {
	$errors[] = new PhabricatorApplicationTransactionValidationError(
	$transaction_type,
	pht('Invalid'),
	pht(
	'You can not shift this object in the selected space, because '.
	'the space does not exist or you do not have access to it.'),
	$xaction);
	} else if (empty($active_spaces[$space_phid])) {

	// It's OK to edit objects in an archived space, so just move on if
	// we aren't adjusting the value.
	$old_space_phid = $this->getTransactionOldValue($object, $xaction);
	if ($space_phid == $old_space_phid) {
	continue;
	}

	$errors[] = new PhabricatorApplicationTransactionValidationError(
	$transaction_type,
	pht('Archived'),
	pht(
	'You can not shift this object into the selected space, because '.
	'the space is archived. Objects can not be created inside (or '.
	'moved into) archived spaces.'),
	$xaction);
	}
	}

	return $errors;
	}


	protected function adjustObjectForPolicyChecks(
	PhabricatorLiskDAO $object,
	array $xactions) {

	$copy = clone $object;

	foreach ($xactions as $xaction) {
	switch ($xaction->getTransactionType()) {
	case PhabricatorTransactions::TYPE_SUBSCRIBERS:
	$clone_xaction = clone $xaction;
	$clone_xaction->setOldValue(array_values($this->subscribers));
	$clone_xaction->setNewValue(
	$this->getPHIDTransactionNewValue(
	$clone_xaction));

	PhabricatorPolicyRule::passTransactionHintToRule(
	$copy,
	new PhabricatorSubscriptionsSubscribersPolicyRule(),
	array_fuse($clone_xaction->getNewValue()));

	break;
	case PhabricatorTransactions::TYPE_SPACE:
	$space_phid = $this->getTransactionNewValue($object, $xaction);
	$copy->setSpacePHID($space_phid);
	break;
	}
	}

	return $copy;
	}

	protected function validateAllTransactions(
	PhabricatorLiskDAO $object,
	array $xactions) {
	return array();
	}

	/**
	* Check for a missing text field.
	*
	* A text field is missing if the object has no value and there are no
	* transactions which set a value, or if the transactions remove the value.
	* This method is intended to make implementing @{method:validateTransaction}
	* more convenient:
	*
	* $missing = $this->validateIsEmptyTextField(
	* $object->getName(),
	* $xactions);
	*
	* This will return `true` if the net effect of the object and transactions
	* is an empty field.
	*
	* @param wild Current field value.
	* @param list<PhabricatorApplicationTransaction> Transactions editing the
	* field.
	* @return bool True if the field will be an empty text field after edits.
	*/
	protected function validateIsEmptyTextField($field_value, array $xactions) {
	if (strlen($field_value) && empty($xactions)) {
	return false;
	}

	if ($xactions && strlen(last($xactions)->getNewValue())) {
	return false;
	}

	return true;
	}

	/**
	* Check that text field input isn't longer than a specified length.
	*
	* A text field input is invalid if the length of the input is longer than a
	* specified length. This length can be determined by the space allotted in
	* the database, or given arbitrarily.
	* This method is intended to make implementing @{method:validateTransaction}
	* more convenient:
	*
	* $overdrawn = $this->validateIsTextFieldTooLong(
	* $object->getName(),
	* $xactions,
	* $field_length);
	*
	* This will return `true` if the net effect of the object and transactions
	* is a field that is too long.
	*
	* @param wild Current field value.
	* @param list<PhabricatorApplicationTransaction> Transactions editing the
	* field.
	* @param integer for maximum field length.
	* @return bool True if the field will be too long after edits.
	*/
	protected function validateIsTextFieldTooLong(
	$field_value,
	array $xactions,
	$length) {

	if ($xactions) {
	$new_value_length = phutil_utf8_strlen(last($xactions)->getNewValue());
	if ($new_value_length <= $length) {
	return false;
	} else {
	return true;
	}
	}

	$old_value_length = phutil_utf8_strlen($field_value);
	if ($old_value_length <= $length) {
	return false;
	}

	return true;
	}


	/* -( Implicit CCs )------------------------------------------------------- */


	/**
	* When a user interacts with an object, we might want to add them to CC.
	*/
	final public function applyImplicitCC(
	PhabricatorLiskDAO $object,
	array $xactions) {

	if (!($object instanceof PhabricatorSubscribableInterface)) {
	// If the object isn't subscribable, we can't CC them.
	return $xactions;
	}

	$actor_phid = $this->getActingAsPHID();

	$type_user = PhabricatorPeopleUserPHIDType::TYPECONST;
	if (phid_get_type($actor_phid) != $type_user) {
	// Transactions by application actors like Herald, Harbormaster and
	// Diffusion should not CC the applications.
	return $xactions;
	}

	if ($object->isAutomaticallySubscribed($actor_phid)) {
	// If they're auto-subscribed, don't CC them.
	return $xactions;
	}

	$should_cc = false;
	foreach ($xactions as $xaction) {
	if ($this->shouldImplyCC($object, $xaction)) {
	$should_cc = true;
	break;
	}
	}

	if (!$should_cc) {
	// Only some types of actions imply a CC (like adding a comment).
	return $xactions;
	}

	if ($object->getPHID()) {
	if (isset($this->subscribers[$actor_phid])) {
	// If the user is already subscribed, don't implicitly CC them.
	return $xactions;
	}

	$unsub = PhabricatorEdgeQuery::loadDestinationPHIDs(
	$object->getPHID(),
	PhabricatorObjectHasUnsubscriberEdgeType::EDGECONST);
	$unsub = array_fuse($unsub);
	if (isset($unsub[$actor_phid])) {
	// If the user has previously unsubscribed from this object explicitly,
	// don't implicitly CC them.
	return $xactions;
	}
	}

	$xaction = newv(get_class(head($xactions)), array());
	$xaction->setTransactionType(PhabricatorTransactions::TYPE_SUBSCRIBERS);
	$xaction->setNewValue(array('+' => array($actor_phid)));

	array_unshift($xactions, $xaction);

	return $xactions;
	}

	protected function shouldImplyCC(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {

	return $xaction->isCommentTransaction();
	}


	/* -( Sending Mail )------------------------------------------------------- */


	/**
	* @task mail
	*/
	protected function shouldSendMail(
	PhabricatorLiskDAO $object,
	array $xactions) {
	return false;
	}


	/**
	* @task mail
	*/
	private function buildMail(
	PhabricatorLiskDAO $object,
	array $xactions) {

	$email_to = $this->mailToPHIDs;
	$email_cc = $this->mailCCPHIDs;
	$email_cc = array_merge($email_cc, $this->heraldEmailPHIDs);

	$targets = $this->buildReplyHandler($object)
	->getMailTargets($email_to, $email_cc);

	// Set this explicitly before we start swapping out the effective actor.
	$this->setActingAsPHID($this->getActingAsPHID());

	$messages = array();
	foreach ($targets as $target) {
	$original_actor = $this->getActor();

	$viewer = $target->getViewer();
	$this->setActor($viewer);
	$locale = PhabricatorEnv::beginScopedLocale($viewer->getTranslation());

	$caught = null;
	$mail = null;
	try {
	// Reload handles for the new viewer.
	$this->loadHandles($xactions);

	$mail = $this->buildMailForTarget($object, $xactions, $target);
	} catch (Exception $ex) {
	$caught = $ex;
	}

	$this->setActor($original_actor);
	unset($locale);

	if ($caught) {
	throw $ex;
	}

	if ($mail) {
	$messages[] = $mail;
	}
	}

	$this->runHeraldMailRules($messages);

	return $messages;
	}

	private function buildMailForTarget(
	PhabricatorLiskDAO $object,
	array $xactions,
	PhabricatorMailTarget $target) {

	// Check if any of the transactions are visible for this viewer. If we
	// don't have any visible transactions, don't send the mail.

	$any_visible = false;
	foreach ($xactions as $xaction) {
	if (!$xaction->shouldHideForMail($xactions)) {
	$any_visible = true;
	break;
	}
	}

	if (!$any_visible) {
	return null;
	}

	$mail = $this->buildMailTemplate($object);
	$body = $this->buildMailBody($object, $xactions);

	$mail_tags = $this->getMailTags($object, $xactions);
	$action = $this->getMailAction($object, $xactions);

	if (PhabricatorEnv::getEnvConfig('metamta.email-preferences')) {
	$this->addEmailPreferenceSectionToMailBody(
	$body,
	$object,
	$xactions);
	}

	$mail
	->setSensitiveContent(false)
	->setFrom($this->getActingAsPHID())
	->setSubjectPrefix($this->getMailSubjectPrefix())
	->setVarySubjectPrefix('['.$action.']')
	->setThreadID($this->getMailThreadID($object), $this->getIsNewObject())
	->setRelatedPHID($object->getPHID())
	->setExcludeMailRecipientPHIDs($this->getExcludeMailRecipientPHIDs())
	->setForceHeraldMailRecipientPHIDs($this->heraldForcedEmailPHIDs)
	->setMailTags($mail_tags)
	->setIsBulk(true)
	->setBody($body->render())
	->setHTMLBody($body->renderHTML());

	foreach ($body->getAttachments() as $attachment) {
	$mail->addAttachment($attachment);
	}

	if ($this->heraldHeader) {
	$mail->addHeader('X-Herald-Rules', $this->heraldHeader);
	}

	if ($object instanceof PhabricatorProjectInterface) {
	$this->addMailProjectMetadata($object, $mail);
	}

	if ($this->getParentMessageID()) {
	$mail->setParentMessageID($this->getParentMessageID());
	}

	return $target->willSendMail($mail);
	}

	private function addMailProjectMetadata(
	PhabricatorLiskDAO $object,
	PhabricatorMetaMTAMail $template) {

	$project_phids = PhabricatorEdgeQuery::loadDestinationPHIDs(
	$object->getPHID(),
	PhabricatorProjectObjectHasProjectEdgeType::EDGECONST);

	if (!$project_phids) {
	return;
	}

	// TODO: This viewer isn't quite right. It would be slightly better to use
	// the mail recipient, but that's not very easy given the way rendering
	// works today.

	$handles = id(new PhabricatorHandleQuery())
	->setViewer($this->requireActor())
	->withPHIDs($project_phids)
	->execute();

	$project_tags = array();
	foreach ($handles as $handle) {
	if (!$handle->isComplete()) {
	continue;
	}
	$project_tags[] = '<'.$handle->getObjectName().'>';
	}

	if (!$project_tags) {
	return;
	}

	$project_tags = implode(', ', $project_tags);
	$template->addHeader('X-Phabricator-Projects', $project_tags);
	}


	protected function getMailThreadID(PhabricatorLiskDAO $object) {
	return $object->getPHID();
	}


	/**
	* @task mail
	*/
	protected function getStrongestAction(
	PhabricatorLiskDAO $object,
	array $xactions) {
	return last(msort($xactions, 'getActionStrength'));
	}


	/**
	* @task mail
	*/
	protected function buildReplyHandler(PhabricatorLiskDAO $object) {
	throw new Exception(pht('Capability not supported.'));
	}

	/**
	* @task mail
	*/
	protected function getMailSubjectPrefix() {
	throw new Exception(pht('Capability not supported.'));
	}


	/**
	* @task mail
	*/
	protected function getMailTags(
	PhabricatorLiskDAO $object,
	array $xactions) {
	$tags = array();

	foreach ($xactions as $xaction) {
	$tags[] = $xaction->getMailTags();
	}

	return array_mergev($tags);
	}

	/**
	* @task mail
	*/
	public function getMailTagsMap() {
	// TODO: We should move shared mail tags, like "comment", here.
	return array();
	}


	/**
	* @task mail
	*/
	protected function getMailAction(
	PhabricatorLiskDAO $object,
	array $xactions) {
	return $this->getStrongestAction($object, $xactions)->getActionName();
	}


	/**
	* @task mail
	*/
	protected function buildMailTemplate(PhabricatorLiskDAO $object) {
	throw new Exception(pht('Capability not supported.'));
	}


	/**
	* @task mail
	*/
	protected function getMailTo(PhabricatorLiskDAO $object) {
	throw new Exception(pht('Capability not supported.'));
	}


	/**
	* @task mail
	*/
	protected function getMailCC(PhabricatorLiskDAO $object) {
	$phids = array();
	$has_support = false;

	if ($object instanceof PhabricatorSubscribableInterface) {
	$phid = $object->getPHID();
	$phids[] = PhabricatorSubscribersQuery::loadSubscribersForPHID($phid);
	$has_support = true;
	}

	if ($object instanceof PhabricatorProjectInterface) {
	$project_phids = PhabricatorEdgeQuery::loadDestinationPHIDs(
	$object->getPHID(),
	PhabricatorProjectObjectHasProjectEdgeType::EDGECONST);

	if ($project_phids) {
	$projects = id(new PhabricatorProjectQuery())
	->setViewer(PhabricatorUser::getOmnipotentUser())
	->withPHIDs($project_phids)
	->needWatchers(true)
	->execute();

	$watcher_phids = array();
	foreach ($projects as $project) {
	foreach ($project->getAllAncestorWatcherPHIDs() as $phid) {
	$watcher_phids[$phid] = $phid;
	}
	}

	if ($watcher_phids) {
	// We need to do a visibility check for all the watchers, as
	// watching a project is not a guarantee that you can see objects
	// associated with it.
	$users = id(new PhabricatorPeopleQuery())
	->setViewer($this->requireActor())
	->withPHIDs($watcher_phids)
	->execute();

	$watchers = array();
	foreach ($users as $user) {
	$can_see = PhabricatorPolicyFilter::hasCapability(
	$user,
	$object,
	PhabricatorPolicyCapability::CAN_VIEW);
	if ($can_see) {
	$watchers[] = $user->getPHID();
	}
	}
	$phids[] = $watchers;
	}
	}

	$has_support = true;
	}

	if (!$has_support) {
	throw new Exception(pht('Capability not supported.'));
	}

	return array_mergev($phids);
	}


	/**
	* @task mail
	*/
	protected function buildMailBody(
	PhabricatorLiskDAO $object,
	array $xactions) {

	$body = new PhabricatorMetaMTAMailBody();
	$body->setViewer($this->requireActor());

	$this->addHeadersAndCommentsToMailBody($body, $xactions);
	$this->addCustomFieldsToMailBody($body, $object, $xactions);
	return $body;
	}


	/**
	* @task mail
	*/
	protected function addEmailPreferenceSectionToMailBody(
	PhabricatorMetaMTAMailBody $body,
	PhabricatorLiskDAO $object,
	array $xactions) {

	$href = PhabricatorEnv::getProductionURI(
	'/settings/panel/emailpreferences/');
	$body->addLinkSection(pht('EMAIL PREFERENCES'), $href);
	}


	/**
	* @task mail
	*/
	protected function addHeadersAndCommentsToMailBody(
	PhabricatorMetaMTAMailBody $body,
	array $xactions,
	$object_label = null,
	$object_href = null) {

	$headers = array();
	$headers_html = array();
	$comments = array();
	$details = array();

	foreach ($xactions as $xaction) {
	if ($xaction->shouldHideForMail($xactions)) {
	continue;
	}

	$header = $xaction->getTitleForMail();
	if ($header !== null) {
	$headers[] = $header;
	}

	$header_html = $xaction->getTitleForHTMLMail();
	if ($header_html !== null) {
	$headers_html[] = $header_html;
	}

	$comment = $xaction->getBodyForMail();
	if ($comment !== null) {
	$comments[] = $comment;
	}

	if ($xaction->hasChangeDetailsForMail()) {
	$details[] = $xaction;
	}
	}

	$headers_text = implode("\n", $headers);
	$body->addRawPlaintextSection($headers_text);

	$headers_html = phutil_implode_html(phutil_tag('br'), $headers_html);

	$header_button = null;
	if ($object_label !== null) {
	$button_style = array(
	'text-decoration: none;',
	'padding: 4px 8px;',
	'margin: 0 8px 8px;',
	'float: right;',
	'color: #464C5C;',
	'font-weight: bold;',
	'border-radius: 3px;',
	'background-color: #F7F7F9;',
	'background-image: linear-gradient(to bottom,#fff,#f1f0f1);',
	'display: inline-block;',
	'border: 1px solid rgba(71,87,120,.2);',
	);

	$header_button = phutil_tag(
	'a',
	array(
	'style' => implode(' ', $button_style),
	'href' => $object_href,
	),
	$object_label);
	}

	$xactions_style = array(
	);

	$header_action = phutil_tag(
	'td',
	array(),
	$header_button);

	$header_action = phutil_tag(
	'td',
	array(
	'style' => implode(' ', $xactions_style),
	),
	array(
	$headers_html,
	// Add an extra newline to prevent the "View Object" button from
	// running into the transaction text in Mail.app text snippet
	// previews.
	"\n",
	));

	$headers_html = phutil_tag(
	'table',
	array(),
	phutil_tag('tr', array(), array($header_action, $header_button)));

	$body->addRawHTMLSection($headers_html);

	foreach ($comments as $comment) {
	$body->addRemarkupSection(null, $comment);
	}

	foreach ($details as $xaction) {
	$details = $xaction->renderChangeDetailsForMail($body->getViewer());
	if ($details !== null) {
	$body->addHTMLSection(pht('EDIT DETAILS'), $details);
	}
	}

	}

	/**
	* @task mail
	*/
	protected function addCustomFieldsToMailBody(
	PhabricatorMetaMTAMailBody $body,
	PhabricatorLiskDAO $object,
	array $xactions) {

	if ($object instanceof PhabricatorCustomFieldInterface) {
	$field_list = PhabricatorCustomField::getObjectFields(
	$object,
	PhabricatorCustomField::ROLE_TRANSACTIONMAIL);
	$field_list->setViewer($this->getActor());
	$field_list->readFieldsFromStorage($object);

	foreach ($field_list->getFields() as $field) {
	$field->updateTransactionMailBody(
	$body,
	$this,
	$xactions);
	}
	}
	}


	/**
	* @task mail
	*/
	private function runHeraldMailRules(array $messages) {
	foreach ($messages as $message) {
	$engine = new HeraldEngine();
	$adapter = id(new PhabricatorMailOutboundMailHeraldAdapter())
	->setObject($message);

	$rules = $engine->loadRulesForAdapter($adapter);
	$effects = $engine->applyRules($rules, $adapter);
	$engine->applyEffects($effects, $adapter, $rules);
	}
	}


	/* -( Publishing Feed Stories )-------------------------------------------- */


	/**
	* @task feed
	*/
	protected function shouldPublishFeedStory(
	PhabricatorLiskDAO $object,
	array $xactions) {
	return false;
	}


	/**
	* @task feed
	*/
	protected function getFeedStoryType() {
	return 'PhabricatorApplicationTransactionFeedStory';
	}


	/**
	* @task feed
	*/
	protected function getFeedRelatedPHIDs(
	PhabricatorLiskDAO $object,
	array $xactions) {

	$phids = array(
	$object->getPHID(),
	$this->getActingAsPHID(),
	);

	if ($object instanceof PhabricatorProjectInterface) {
	$project_phids = PhabricatorEdgeQuery::loadDestinationPHIDs(
	$object->getPHID(),
	PhabricatorProjectObjectHasProjectEdgeType::EDGECONST);
	foreach ($project_phids as $project_phid) {
	$phids[] = $project_phid;
	}
	}

	return $phids;
	}


	/**
	* @task feed
	*/
	protected function getFeedNotifyPHIDs(
	PhabricatorLiskDAO $object,
	array $xactions) {

	return array_unique(array_merge(
	$this->getMailTo($object),
	$this->getMailCC($object)));
	}


	/**
	* @task feed
	*/
	protected function getFeedStoryData(
	PhabricatorLiskDAO $object,
	array $xactions) {

	$xactions = msort($xactions, 'getActionStrength');
	$xactions = array_reverse($xactions);

	return array(
	'objectPHID' => $object->getPHID(),
	'transactionPHIDs' => mpull($xactions, 'getPHID'),
	);
	}


	/**
	* @task feed
	*/
	protected function publishFeedStory(
	PhabricatorLiskDAO $object,
	array $xactions,
	array $mailed_phids) {

	$xactions = mfilter($xactions, 'shouldHideForFeed', true);

	if (!$xactions) {
	return;
	}

	$related_phids = $this->feedRelatedPHIDs;
	$subscribed_phids = $this->feedNotifyPHIDs;

	$story_type = $this->getFeedStoryType();
	$story_data = $this->getFeedStoryData($object, $xactions);

	id(new PhabricatorFeedStoryPublisher())
	->setStoryType($story_type)
	->setStoryData($story_data)
	->setStoryTime(time())
	->setStoryAuthorPHID($this->getActingAsPHID())
	->setRelatedPHIDs($related_phids)
	->setPrimaryObjectPHID($object->getPHID())
	->setSubscribedPHIDs($subscribed_phids)
	->setMailRecipientPHIDs($mailed_phids)
	->setMailTags($this->getMailTags($object, $xactions))
	->publish();
	}


	/* -( Search Index )------------------------------------------------------- */


	/**
	* @task search
	*/
	protected function supportsSearch() {
	return false;
	}


	/* -( Herald Integration )-------------------------------------------------- */


	protected function shouldApplyHeraldRules(
	PhabricatorLiskDAO $object,
	array $xactions) {
	return false;
	}

	protected function buildHeraldAdapter(
	PhabricatorLiskDAO $object,
	array $xactions) {
	throw new Exception(pht('No herald adapter specified.'));
	}

	private function setHeraldAdapter(HeraldAdapter $adapter) {
	$this->heraldAdapter = $adapter;
	return $this;
	}

	protected function getHeraldAdapter() {
	return $this->heraldAdapter;
	}

	private function setHeraldTranscript(HeraldTranscript $transcript) {
	$this->heraldTranscript = $transcript;
	return $this;
	}

	protected function getHeraldTranscript() {
	return $this->heraldTranscript;
	}

	private function applyHeraldRules(
	PhabricatorLiskDAO $object,
	array $xactions) {

	$adapter = $this->buildHeraldAdapter($object, $xactions)
	->setContentSource($this->getContentSource())
	->setIsNewObject($this->getIsNewObject())
	->setAppliedTransactions($xactions);

	if ($this->getApplicationEmail()) {
	$adapter->setApplicationEmail($this->getApplicationEmail());
	}

	$xscript = HeraldEngine::loadAndApplyRules($adapter);

	$this->setHeraldAdapter($adapter);
	$this->setHeraldTranscript($xscript);

	if ($adapter instanceof HarbormasterBuildableAdapterInterface) {
	HarbormasterBuildable::applyBuildPlans(
	$adapter->getHarbormasterBuildablePHID(),
	$adapter->getHarbormasterContainerPHID(),
	$adapter->getQueuedHarbormasterBuildRequests());
	}

	return array_merge(
	$this->didApplyHeraldRules($object, $adapter, $xscript),
	$adapter->getQueuedTransactions());
	}

	protected function didApplyHeraldRules(
	PhabricatorLiskDAO $object,
	HeraldAdapter $adapter,
	HeraldTranscript $transcript) {
	return array();
	}


	/* -( Custom Fields )------------------------------------------------------ */


	/**
	* @task customfield
	*/
	private function getCustomFieldForTransaction(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {

	$field_key = $xaction->getMetadataValue('customfield:key');
	if (!$field_key) {
	throw new Exception(
	pht(
	"Custom field transaction has no '%s'!",
	'customfield:key'));
	}

	$field = PhabricatorCustomField::getObjectField(
	$object,
	PhabricatorCustomField::ROLE_APPLICATIONTRANSACTIONS,
	$field_key);

	if (!$field) {
	throw new Exception(
	pht(
	"Custom field transaction has invalid '%s'; field '%s' ".
	"is disabled or does not exist.",
	'customfield:key',
	$field_key));
	}

	if (!$field->shouldAppearInApplicationTransactions()) {
	throw new Exception(
	pht(
	"Custom field transaction '%s' does not implement ".
	"integration for %s.",
	$field_key,
	'ApplicationTransactions'));
	}

	$field->setViewer($this->getActor());

	return $field;
	}


	/* -( Files )-------------------------------------------------------------- */


	/**
	* Extract the PHIDs of any files which these transactions attach.
	*
	* @task files
	*/
	private function extractFilePHIDs(
	PhabricatorLiskDAO $object,
	array $xactions) {

	$changes = $this->getRemarkupChanges($xactions);
	$blocks = mpull($changes, 'getNewValue');

	$phids = array();
	if ($blocks) {
	$phids[] = PhabricatorMarkupEngine::extractFilePHIDsFromEmbeddedFiles(
	$this->getActor(),
	$blocks);
	}

	foreach ($xactions as $xaction) {
	$type = $xaction->getTransactionType();

	$xtype = $this->getModularTransactionType($type);
	if ($xtype) {
	$phids[] = $xtype->extractFilePHIDs($object, $xaction->getNewValue());
	} else {
	$phids[] = $this->extractFilePHIDsFromCustomTransaction(
	$object,
	$xaction);
	}
	}

	$phids = array_unique(array_filter(array_mergev($phids)));
	if (!$phids) {
	return array();
	}

	// Only let a user attach files they can actually see, since this would
	// otherwise let you access any file by attaching it to an object you have
	// view permission on.

	$files = id(new PhabricatorFileQuery())
	->setViewer($this->getActor())
	->withPHIDs($phids)
	->execute();

	return mpull($files, 'getPHID');
	}

	/**
	* @task files
	*/
	protected function extractFilePHIDsFromCustomTransaction(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction) {
	return array();
	}


	/**
	* @task files
	*/
	private function attachFiles(
	PhabricatorLiskDAO $object,
	array $file_phids) {

	if (!$file_phids) {
	return;
	}

	$editor = new PhabricatorEdgeEditor();

	$src = $object->getPHID();
	$type = PhabricatorObjectHasFileEdgeType::EDGECONST;
	foreach ($file_phids as $dst) {
	$editor->addEdge($src, $type, $dst);
	}

	$editor->save();
	}

	private function applyInverseEdgeTransactions(
	PhabricatorLiskDAO $object,
	PhabricatorApplicationTransaction $xaction,
	$inverse_type) {

	$old = $xaction->getOldValue();
	$new = $xaction->getNewValue();

	$add = array_keys(array_diff_key($new, $old));
	$rem = array_keys(array_diff_key($old, $new));

	$add = array_fuse($add);
	$rem = array_fuse($rem);
	$all = $add + $rem;

	$nodes = id(new PhabricatorObjectQuery())
	->setViewer($this->requireActor())
	->withPHIDs($all)
	->execute();

	foreach ($nodes as $node) {
	if (!($node instanceof PhabricatorApplicationTransactionInterface)) {
	continue;
	}

	if ($node instanceof PhabricatorUser) {
	// TODO: At least for now, don't record inverse edge transactions
	// for users (for example, "alincoln joined project X"): Feed fills
	// this role instead.
	continue;
	}

	$editor = $node->getApplicationTransactionEditor();
	$template = $node->getApplicationTransactionTemplate();
	$target = $node->getApplicationTransactionObject();

	if (isset($add[$node->getPHID()])) {
	$edge_edit_type = '+';
	} else {
	$edge_edit_type = '-';
	}

	$template
	->setTransactionType($xaction->getTransactionType())
	->setMetadataValue('edge:type', $inverse_type)
	->setNewValue(
	array(
	$edge_edit_type => array($object->getPHID() => $object->getPHID()),
	));

	$editor
	->setContinueOnNoEffect(true)
	->setContinueOnMissingFields(true)
	->setParentMessageID($this->getParentMessageID())
	->setIsInverseEdgeEditor(true)
	->setActor($this->requireActor())
	->setActingAsPHID($this->getActingAsPHID())
	->setContentSource($this->getContentSource());

	$editor->applyTransactions($target, array($template));
	}
	}


	/* -( Workers )------------------------------------------------------------ */


	/**
	* Load any object state which is required to publish transactions.
	*
	* This hook is invoked in the main process before we compute data related
	* to publishing transactions (like email "To" and "CC" lists), and again in
	* the worker before publishing occurs.
	*
	* @return object Publishable object.
	* @task workers
	*/
	protected function willPublish(PhabricatorLiskDAO $object, array $xactions) {
	return $object;
	}


	/**
	* Convert the editor state to a serializable dictionary which can be passed
	* to a worker.
	*
	* This data will be loaded with @{method:loadWorkerState} in the worker.
	*
	* @return dict<string, wild> Serializable editor state.
	* @task workers
	*/
	final private function getWorkerState() {
	$state = array();
	foreach ($this->getAutomaticStateProperties() as $property) {
	$state[$property] = $this->$property;
	}

	$custom_state = $this->getCustomWorkerState();
	$custom_encoding = $this->getCustomWorkerStateEncoding();

	$state += array(
	'excludeMailRecipientPHIDs' => $this->getExcludeMailRecipientPHIDs(),
	'custom' => $this->encodeStateForStorage($custom_state, $custom_encoding),
	'custom.encoding' => $custom_encoding,
	);

	return $state;
	}


	/**
	* Hook; return custom properties which need to be passed to workers.
	*
	* @return dict<string, wild> Custom properties.
	* @task workers
	*/
	protected function getCustomWorkerState() {
	return array();
	}


	/**
	* Hook; return storage encoding for custom properties which need to be
	* passed to workers.
	*
	* This primarily allows binary data to be passed to workers and survive
	* JSON encoding.
	*
	* @return dict<string, string> Property encodings.
	* @task workers
	*/
	protected function getCustomWorkerStateEncoding() {
	return array();
	}


	/**
	* Load editor state using a dictionary emitted by @{method:getWorkerState}.
	*
	* This method is used to load state when running worker operations.
	*
	* @param dict<string, wild> Editor state, from @{method:getWorkerState}.
	* @return this
	* @task workers
	*/
	final public function loadWorkerState(array $state) {
	foreach ($this->getAutomaticStateProperties() as $property) {
	$this->$property = idx($state, $property);
	}

	$exclude = idx($state, 'excludeMailRecipientPHIDs', array());
	$this->setExcludeMailRecipientPHIDs($exclude);

	$custom_state = idx($state, 'custom', array());
	$custom_encodings = idx($state, 'custom.encoding', array());
	$custom = $this->decodeStateFromStorage($custom_state, $custom_encodings);

	$this->loadCustomWorkerState($custom);

	return $this;
	}


	/**
	* Hook; set custom properties on the editor from data emitted by
	* @{method:getCustomWorkerState}.
	*
	* @param dict<string, wild> Custom state,
	* from @{method:getCustomWorkerState}.
	* @return this
	* @task workers
	*/
	protected function loadCustomWorkerState(array $state) {
	return $this;
	}


	/**
	* Get a list of object properties which should be automatically sent to
	* workers in the state data.
	*
	* These properties will be automatically stored and loaded by the editor in
	* the worker.
	*
	* @return list<string> List of properties.
	* @task workers
	*/
	private function getAutomaticStateProperties() {
	return array(
	'parentMessageID',
	'disableEmail',
	'isNewObject',
	'heraldEmailPHIDs',
	'heraldForcedEmailPHIDs',
	'heraldHeader',
	'mailToPHIDs',
	'mailCCPHIDs',
	'feedNotifyPHIDs',
	'feedRelatedPHIDs',
	);
	}

	/**
	* Apply encodings prior to storage.
	*
	* See @{method:getCustomWorkerStateEncoding}.
	*
	* @param map<string, wild> Map of values to encode.
	* @param map<string, string> Map of encodings to apply.
	* @return map<string, wild> Map of encoded values.
	* @task workers
	*/
	final private function encodeStateForStorage(
	array $state,
	array $encodings) {

	foreach ($state as $key => $value) {
	$encoding = idx($encodings, $key);
	switch ($encoding) {
	case self::STORAGE_ENCODING_BINARY:
	// The mechanics of this encoding (serialize + base64) are a little
	// awkward, but it allows us encode arrays and still be JSON-safe
	// with binary data.

	$value = @serialize($value);
	if ($value === false) {
	throw new Exception(
	pht(
	'Failed to serialize() value for key "%s".',
	$key));
	}

	$value = base64_encode($value);
	if ($value === false) {
	throw new Exception(
	pht(
	'Failed to base64 encode value for key "%s".',
	$key));
	}
	break;
	}
	$state[$key] = $value;
	}

	return $state;
	}


	/**
	* Undo storage encoding applied when storing state.
	*
	* See @{method:getCustomWorkerStateEncoding}.
	*
	* @param map<string, wild> Map of encoded values.
	* @param map<string, string> Map of encodings.
	* @return map<string, wild> Map of decoded values.
	* @task workers
	*/
	final private function decodeStateFromStorage(
	array $state,
	array $encodings) {

	foreach ($state as $key => $value) {
	$encoding = idx($encodings, $key);
	switch ($encoding) {
	case self::STORAGE_ENCODING_BINARY:
	$value = base64_decode($value);
	if ($value === false) {
	throw new Exception(
	pht(
	'Failed to base64_decode() value for key "%s".',
	$key));
	}

	$value = unserialize($value);
	break;
	}
	$state[$key] = $value;
	}

	return $state;
	}


	/**
	* Remove conflicts from a list of projects.
	*
	* Objects aren't allowed to be tagged with multiple milestones in the same
	* group, nor projects such that one tag is the ancestor of any other tag.
	* If the list of PHIDs include mutually exclusive projects, remove the
	* conflicting projects.
	*
	* @param list<phid> List of project PHIDs.
	* @return list<phid> List with conflicts removed.
	*/
	private function applyProjectConflictRules(array $phids) {
	if (!$phids) {
	return array();
	}

	// Overall, the last project in the list wins in cases of conflict (so when
	// you add something, the thing you just added sticks and removes older
	// values).

	// Beyond that, there are two basic cases:

	// Milestones: An object can't be in "A > Sprint 3" and "A > Sprint 4".
	// If multiple projects are milestones of the same parent, we only keep the
	// last one.

	// Ancestor: You can't be in "A" and "A > B". If "A > B" comes later
	// in the list, we remove "A" and keep "A > B". If "A" comes later, we
	// remove "A > B" and keep "A".

	// Note that it's OK to be in "A > B" and "A > C". There's only a conflict
	// if one project is an ancestor of another. It's OK to have something
	// tagged with multiple projects which share a common ancestor, so long as
	// they are not mutual ancestors.

	$viewer = PhabricatorUser::getOmnipotentUser();

	$projects = id(new PhabricatorProjectQuery())
	->setViewer($viewer)
	->withPHIDs(array_keys($phids))
	->execute();
	$projects = mpull($projects, null, 'getPHID');

	// We're going to build a map from each project with milestones to the last
	// milestone in the list. This last milestone is the milestone we'll keep.
	$milestone_map = array();

	// We're going to build a set of the projects which have no descendants
	// later in the list. This allows us to apply both ancestor rules.
	$ancestor_map = array();

	foreach ($phids as $phid => $ignored) {
	$project = idx($projects, $phid);
	if (!$project) {
	continue;
	}

	// This is the last milestone we've seen, so set it as the selection for
	// the project's parent. This might be setting a new value or overwriting
	// an earlier value.
	if ($project->isMilestone()) {
	$parent_phid = $project->getParentProjectPHID();
	$milestone_map[$parent_phid] = $phid;
	}

	// Since this is the last item in the list we've examined so far, add it
	// to the set of projects with no later descendants.
	$ancestor_map[$phid] = $phid;

	// Remove any ancestors from the set, since this is a later descendant.
	foreach ($project->getAncestorProjects() as $ancestor) {
	$ancestor_phid = $ancestor->getPHID();
	unset($ancestor_map[$ancestor_phid]);
	}
	}

	// Now that we've built the maps, we can throw away all the projects which
	// have conflicts.
	foreach ($phids as $phid => $ignored) {
	$project = idx($projects, $phid);

	if (!$project) {
	// If a PHID is invalid, we just leave it as-is. We could clean it up,
	// but leaving it untouched is less likely to cause collateral damage.
	continue;
	}

	// If this was a milestone, check if it was the last milestone from its
	// group in the list. If not, remove it from the list.
	if ($project->isMilestone()) {
	$parent_phid = $project->getParentProjectPHID();
	if ($milestone_map[$parent_phid] !== $phid) {
	unset($phids[$phid]);
	continue;
	}
	}

	// If a later project in the list is a subproject of this one, it will
	// have removed ancestors from the map. If this project does not point
	// at itself in the ancestor map, it should be discarded in favor of a
	// subproject that comes later.
	if (idx($ancestor_map, $phid) !== $phid) {
	unset($phids[$phid]);
	continue;
	}

	// If a later project in the list is an ancestor of this one, it will
	// have added itself to the map. If any ancestor of this project points
	// at itself in the map, this project should be dicarded in favor of
	// that later ancestor.
	foreach ($project->getAncestorProjects() as $ancestor) {
	$ancestor_phid = $ancestor->getPHID();
	if (isset($ancestor_map[$ancestor_phid])) {
	unset($phids[$phid]);
	continue 2;
	}
	}
	}

	return $phids;
	}

	/**
	* When the view policy for an object is changed, scramble the secret keys
	* for attached files to invalidate existing URIs.
	*/
	private function scrambleFileSecrets($object) {
	// If this is a newly created object, we don't need to scramble anything
	// since it couldn't have been previously published.
	if ($this->getIsNewObject()) {
	return;
	}

	// If the object is a file itself, scramble it.
	if ($object instanceof PhabricatorFile) {
	if ($this->shouldScramblePolicy($object->getViewPolicy())) {
	$object->scrambleSecret();
	$object->save();
	}
	}

	$phid = $object->getPHID();

	$attached_phids = PhabricatorEdgeQuery::loadDestinationPHIDs(
	$phid,
	PhabricatorObjectHasFileEdgeType::EDGECONST);
	if (!$attached_phids) {
	return;
	}

	$omnipotent_viewer = PhabricatorUser::getOmnipotentUser();

	$files = id(new PhabricatorFileQuery())
	->setViewer($omnipotent_viewer)
	->withPHIDs($attached_phids)
	->execute();
	foreach ($files as $file) {
	$view_policy = $file->getViewPolicy();
	if ($this->shouldScramblePolicy($view_policy)) {
	$file->scrambleSecret();
	$file->save();
	}
	}
	}


	/**
	* Check if a policy is strong enough to justify scrambling. Objects which
	* are set to very open policies don't need to scramble their files, and
	* files with very open policies don't need to be scrambled when associated
	* objects change.
	*/
	private function shouldScramblePolicy($policy) {
	switch ($policy) {
	case PhabricatorPolicies::POLICY_PUBLIC:
	case PhabricatorPolicies::POLICY_USER:
	return false;
	}

	return true;
	}

	private function updateWorkboardColumns($object, $const, $old, $new) {
	// If an object is removed from a project, remove it from any proxy
	// columns for that project. This allows a task which is moved up from a
	// milestone to the parent to move back into the "Backlog" column on the
	// parent workboard.

	if ($const != PhabricatorProjectObjectHasProjectEdgeType::EDGECONST) {
	return;
	}

	// TODO: This should likely be some future WorkboardInterface.
	$appears_on_workboards = ($object instanceof ManiphestTask);
	if (!$appears_on_workboards) {
	return;
	}

	$removed_phids = array_keys(array_diff_key($old, $new));
	if (!$removed_phids) {
	return;
	}

	// Find any proxy columns for the removed projects.
	$proxy_columns = id(new PhabricatorProjectColumnQuery())
	->setViewer(PhabricatorUser::getOmnipotentUser())
	->withProxyPHIDs($removed_phids)
	->execute();
	if (!$proxy_columns) {
	return array();
	}

	$proxy_phids = mpull($proxy_columns, 'getPHID');

	$position_table = new PhabricatorProjectColumnPosition();
	$conn_w = $position_table->establishConnection('w');

	queryfx(
	$conn_w,
	'DELETE FROM %T WHERE objectPHID = %s AND columnPHID IN (%Ls)',
	$position_table->getTableName(),
	$object->getPHID(),
	$proxy_phids);
	}

	private function getModularTransactionTypes() {
	if ($this->modularTypes === null) {
	$template = $this->object->getApplicationTransactionTemplate();
	if ($template instanceof PhabricatorModularTransaction) {
	$xtypes = $template->newModularTransactionTypes();
	foreach ($xtypes as $key => $xtype) {
	$xtype = clone $xtype;
	$xtype->setEditor($this);
	$xtypes[$key] = $xtype;
	}
	} else {
	$xtypes = array();
	}

	$this->modularTypes = $xtypes;
	}

	return $this->modularTypes;
	}

	private function getModularTransactionType($type) {
	$types = $this->getModularTransactionTypes();
	return idx($types, $type);
	}

	private function willApplyTransactions($object, array $xactions) {
	foreach ($xactions as $xaction) {
	$type = $xaction->getTransactionType();

	$xtype = $this->getModularTransactionType($type);
	if (!$xtype) {
	continue;
	}

	$xtype->willApplyTransactions($object, $xactions);
	}
	}

	public function getCreateObjectTitle($author, $object) {
	return pht('%s created this object.', $author);
	}

	public function getCreateObjectTitleForFeed($author, $object) {
	return pht('%s created an object: %s.', $author, $object);
	}

	}

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