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			@title Events User Guide: Installing Event Listeners
			@group userguide

			Using Phabricator event listeners to customize behavior.

			= Overview =

			(WARNING) The event system is an artifact of a bygone era. Use of the event
			system is strongly discouraged. We have been removing events since 2013 and
			will continue to remove events in the future.

			Phabricator and Arcanist allow you to install custom runtime event listeners
			which can react to certain things happening (like a Maniphest Task being edited
			or a user creating a new Differential Revision) and run custom code to perform
			logging, synchronize with other systems, or modify workflows.

			These listeners are PHP classes which you install beside Phabricator or
			Arcanist, and which Phabricator loads at runtime and runs in-process. They
			require somewhat more effort upfront than simple configuration switches, but are
			the most direct and powerful way to respond to events.

			= Installing Event Listeners (Phabricator) =

			To install event listeners in Phabricator, follow these steps:

			- Write a listener class which extends @{class@libphutil:PhutilEventListener}.
			- Add it to a libphutil library, or create a new library (for instructions,
			see @{article@phabcontrib:Adding New Classes}.
			- Configure Phabricator to load the library by adding it to `load-libraries`
			in the Phabricator config.
			- Configure Phabricator to install the event listener by adding the class
			name to `events.listeners` in the Phabricator config.

			You can verify your listener is registered in the "Events" tab of DarkConsole.
			It should appear at the top under "Registered Event Listeners". You can also
			see any events the page emitted there. For details on DarkConsole, see
			@{article:Using DarkConsole}.

			= Installing Event Listeners (Arcanist) =

			To install event listeners in Arcanist, follow these steps:

			- Write a listener class which extends @{class@libphutil:PhutilEventListener}.
			- Add it to a libphutil library, or create a new library (for instructions,
			see @{article@phabcontrib:Adding New Classes}.
			- Configure Phabricator to load the library by adding it to `load`
			in the Arcanist config (e.g., `.arcconfig`, or user/global config).
			- Configure Arcanist to install the event listener by adding the class
			name to `events.listeners` in the Arcanist config.

			You can verify your listener is registered by running any `arc` command with
			`--trace`. You should see output indicating your class was registered as an
			event listener.

			= Example Listener =

			Phabricator includes an example event listener,
			@{class:PhabricatorExampleEventListener}, which may be useful as a starting
			point in developing your own listeners. This listener listens for a test
			event that is emitted by the script `scripts/util/emit_test_event.php`.

			If you run this script normally, it should output something like this:

			$ ./scripts/util/emit_test_event.php
			Emitting event...
			Done.

			This is because there are no listeners for the event, so nothing reacts to it
			when it is emitted. You can add the example listener by either adding it to
			your `events.listeners` configuration or with the `--listen` command-line flag:

			$ ./scripts/util/emit_test_event.php --listen PhabricatorExampleEventListener
			Installing 'PhabricatorExampleEventListener'...
			Emitting event...
			PhabricatorExampleEventListener got test event at 1341344566
			Done.

			This time, the listener was installed and had its callback invoked when the
			test event was emitted.

			= Available Events =

			You can find a list of all Phabricator events in @{class:PhabricatorEventType}.

			== All Events ==

			The special constant `PhutilEventType::TYPE_ALL` will let you listen for all
			events. Normally, you want to listen only to specific events, but if you're
			writing a generic handler you can listen to all events with this constant
			rather than by enumerating each event.

			== Arcanist Events ==

			Arcanist event constants are listed in @{class@arcanist:ArcanistEventType}.

			All Arcanist events have this data available:

			- `workflow` The active @{class@arcanist:ArcanistWorkflow}.

			== Arcanist: Commit: Will Commit SVN ==

			The constant for this event is `ArcanistEventType::TYPE_COMMIT_WILLCOMMITSVN`.

			This event is dispatched before an `svn commit` occurs and allows you to
			modify the commit message. Data available on this event:

			- `message` The text of the message.

			== Arcanist: Diff: Will Build Message ==

			The constant for this event is `ArcanistEventType::TYPE_DIFF_WILLBUILDMESSAGE`.

			This event is dispatched before an editable message is presented to the user,
			and allows you to, e.g., fill in default values for fields. Data available
			on this event:

			- `fields` A map of field values to be compiled into a message.

			== Arcanist: Diff: Was Created ==

			The constant for this event is `ArcanistEventType::TYPE_DIFF_WASCREATED`.

			This event is dispatched after a diff is created. It is currently only useful
			for collecting timing information. No data is available on this event.

			== Arcanist: Revision: Will Create Revision ==

			The constant for this event is
			`ArcanistEventType::TYPE_REVISION_WILLCREATEREVISION`.

			This event is dispatched before a revision is created. It allows you to modify
			fields to, e.g., edit revision titles. Data available on this event:

			- `specification` Parameters that will be used to invoke the
			`differential.createrevision` Conduit call.

			== Differential: Will Mark Generated ==

			The constant for this event is
			`PhabricatorEventType::TYPE_DIFFERENTIAL_WILLMARKGENERATED`.

			This event is dispatched before Differential decides if a file is generated (and
			doesn't need to be reviewed) or not. Data available on this event:

			- `corpus` Body of the file.
			- `is_generated` Boolean indicating if this file should be treated as
			generated.

			== Diffusion: Did Discover Commit ==

			The constant for this event is
			`PhabricatorEventType::TYPE_DIFFUSION_DIDDISCOVERCOMMIT`.

			This event is dispatched when the daemons discover a commit for the first time.
			This event happens very early in the pipeline, and not all commit information
			will be available yet. Data available on this event:

			- `commit` The @{class:PhabricatorRepositoryCommit} that was discovered.
			- `repository` The @{class:PhabricatorRepository} the commit was discovered
			in.

			== Diffusion: Lookup User ==

			The constant for this event is
			`PhabricatorEventType::TYPE_DIFFUSION_LOOKUPUSER`.

			This event is dispatched when the daemons are trying to link a commit to a
			Phabricator user account. You can listen for it to improve the accuracy of
			associating users with their commits.

			By default, Phabricator will try to find matches based on usernames, real names,
			or email addresses, but this can result in incorrect matches (e.g., if you have
			several employees with the same name) or failures to match (e.g., if someone
			changed their email address). Listening for this event allows you to intercept
			the lookup and supplement the results from another datasource.

			Data available on this event:

			- `commit` The @{class:PhabricatorRepositoryCommit} that data is being looked
			up for.
			- `query` The author or committer string being looked up. This will usually
			be something like "Abraham Lincoln <alincoln@logcabin.example.com>", but
			comes from the commit metadata so it may not be well-formatted.
			- `result` The current result from the lookup (Phabricator's best guess at
			the user PHID of the user named in the "query"). To substitute the result
			with a different result, replace this with the correct PHID in your event
			listener.

			Using @{class@libphutil:PhutilEmailAddress} may be helpful in parsing the query.

			== Search: Did Update Index ==

			The constant for this event is
			`PhabricatorEventType::TYPE_SEARCH_DIDUPDATEINDEX`.

			This event is dispatched from the Search application's indexing engine, after
			it indexes a document. It allows you to publish search-like indexes into other
			systems.

			Note that this event happens after the update is fully complete: you can not
			prevent or modify the update. Further, the event may fire significantly later
			in real time than the update, as indexing may occur in the background. You
			should use other events if you need guarantees about when the event executes.

			Finally, this event may fire more than once for a single update. For example,
			if the search indexes are rebuilt, this event will fire on objects which have
			not actually changed.

			So, good use cases for event listeners are:

			- Updating secondary search indexes.

			Bad use cases are:

			- Editing the object or document.
			- Anything with side effects, like sending email.

			Data available on this event:

			- `phid` The PHID of the updated object.
			- `object` The object which was updated (like a @{class:ManiphesTask}).
			- `document` The @{class:PhabricatorSearchAbstractDocument} which was indexed.
			This contains an abstract representation of the object, and may be useful
			in populating secondary indexes because it provides a uniform API.

			== Test: Did Run Test ==

			The constant for this event is
			`PhabricatorEventType::TYPE_TEST_DIDRUNTEST`.

			This is a test event for testing event listeners. See above for details.

			== UI: Did Render Actions ==

			The constant for this event is
			`PhabricatorEventType::TYPE_UI_DIDRENDERACTIONS`.

			This event is dispatched after a @{class:PhabricatorActionListView} is built by
			the UI. It allows you to add new actions that your application may provide, like
			"Fax this Object". Data available on this event:

			- `object` The object which actions are being rendered for.
			- `actions` The current list of available actions.

			NOTE: This event is unstable and subject to change.

			= Debugging Listeners =

			If you're having problems with your listener, try these steps:

			- If you're getting an error about Phabricator being unable to find the
			listener class, make sure you've added it to a libphutil library and
			configured Phabricator to load the library with `load-libraries`.
			- Make sure the listener is registered. It should appear in the "Events" tab
			of DarkConsole. If it's not there, you may have forgotten to add it to
			`events.listeners`.
			- Make sure it calls `listen()` on the right events in its `register()`
			method. If you don't listen for the events you're interested in, you
			won't get a callback.
			- Make sure the events you're listening for are actually happening. If they
			occur on a normal page they should appear in the "Events" tab of
			DarkConsole. If they occur on a POST, you could add a `phlog()`
			to the source code near the event and check your error log to make sure the
			code ran.
			- You can check if your callback is getting invoked by adding `phlog()` with
			a message and checking the error log.
			- You can try listening to `PhutilEventType::TYPE_ALL` instead of a specific
			event type to get all events, to narrow down whether problems are caused
			by the types of events you're listening to.
			- You can edit the `emit_test_event.php` script to emit other types of
			events instead, to test that your listener reacts to them properly. You
			might have to use fake data, but this gives you an easy way to test the
			at least the basics.
			- For scripts, you can run under `--trace` to see which events are emitted
			and how many handlers are listening to each event.

			= Next Steps =

			Continue by:

			- taking a look at @{class:PhabricatorExampleEventListener}; or
			- building a library with @{article:libphutil Libraries User Guide}.

phab/src/docs/user/userguide/events.divinerfb3c18349ec1feature/better-testing

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phab/src/docs/user/userguide/events.diviner
fb3c18349ec1feature/better-testing

events.diviner
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