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Herald User Guide Article

Use Herald to get notified of changes you care about.


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".