phorge-phorge/src/docs/user/userguide/herald.diviner

@title Herald User Guide
@group userguide

Use Herald to get notified of changes you care about.

= Overview =

Herald allows you to write processing rules that take effect when objects (such
as Differential revisions and commits) are created or updated. For instance, you
might want to get notified every time someone sends out a revision that affects
some file you're interested in, even if they didn't add you as a reviewer.

Herald is less useful for small organizations (where everyone will generally
know most of what's going on) but the usefulness of the application increases
as an organization scales. Once there is too much activity to keep track of it
all, Herald allows you to filter it down so you're only notified of things you
are interested in.

= Global and Personal Rules =

You can create two kinds of Herald rules, //global// and //personal//:

  - **Personal Rules** are rules you own, but they can only affect you. Only
    you can edit or delete personal rules, but their actions are limited to
    adding you to CC, subscribing you, etc.
  - **Global Rules** are rules everyone owns, and they can affect anything.
    Anyone can edit or delete a global rule, and they can take any action,
    including affecting projects and mailing lists.

The general idea is to prevent individuals from controlling rules that affect
shared resources, so if a rule needs to be updated it's not a big deal if the
person who created it is on vacation.

= Rules, Conditions and Actions =

The best way to think of Herald is as a system similar to the mail rules you can
set up in most email clients, to organize mail based on "To", "Subject", etc.
Herald works very similarly, but operates on Phabricator objects (like revisions
and commits) instead of emails.

Every time an object is created or updated, Herald rules are run on it and
the actions for any matching rules are taken.

To create a new Herald rule, choose which type of event you want to act on
(e.g., changes to Differential Revisions, or Commits), and then set a list of
conditions. For example, you might add the condition `Author is alincoln
(Abraham Lincoln)` to keep track of everything alincoln does. Finally, set
a list of actions to take when the conditions match, like adding yourself to the
CC list.

Now you'll automatically be added to CC any time alincoln creates a revision,
and can keep an eye on what he's up to.

= Available Actions =

Herald rules can take a number of actions. Note that some actions are only
available from Global rules, and others only from Personal rules. Additionally,
not every action is available for every object type (for instance, you can not
trigger an audit based on a Differential revision).

  - **Add CC**: Add a user or mailing list to the CC list for the object. For
    personal rules, you can only add yourself.
  - **Remove CC**: Remove a user or mailing list from the CC list for the
    object. For personal rules, you can only remove yourself.
  - **Send an Email to**: Send one email, but don't subscribe to other updates.
    For personal rules, you can only email yourself.
  - **Trigger an Audit**: For commits, trigger an audit request for a project
    or user. For personal rules, you can only trigger an audit request to
    yourself.
  - **Mark with flag**: Flag the object for later review. This action is only
    available on personal rules. If an object already has a flag, this action
    will not add another flag.
  - **Do Nothing**: Don't do anything. This can be used to disable a rule
    temporarily, or to create a rule for an "Another Herald rule" condition.

= Testing Rules =

When you've created a rule, use the "Test Console" to test it out. Enter a
revision or commit and Herald will do a dry run against that object, showing
you which rules //would// match had it actually been updated. Dry runs executed
via the test console don't take any actions.

= Advanced Herald =

A few features in Herald are particularly complicated:

  - **matches regexp pair**: for Differential revisions, you can set a condition
  like "Any changed file content matches regexp pair...". This allows you to
  specify two regexes in JSON format. The first will be used to match the
  filename of the changed file; the second will be used to match the content.
  For example, if you want to match revisions which add or remove calls to
  a "muffinize" function, //but only in JS files//, you can set the value
  to `["/\\.js$/", "/muffinize/"]` or similar.
  - **Another Herald rule**: you can create Herald rules which depend on other
  rules. This can be useful if you need to express a more complicated predicate
  than "all" vs "any" allows, or have a common set of conditions which you want
  to share between several rules. If a rule is only being used as a group of
  conditions, you can set the action to "Do Nothing".