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Sam Smith 84226b41b6 featureManager: Add DynamicConfigRequirement requirement

We expect the vast majority of requirements and features to be defined
in services as possible. However, there are some "complex" requirements
that require additional application/HTTP request state. Unfortunately,
service wiring is done before some of that state is available.

I65702426 attempted to work around this by requiring clients of the
Feature Manager to pass that additional state on every interaction with
the system. Those complex requirements would then select the parts of
the state that they required when it was required. However
implementations of \IContextSource are God objects and their use should
be limited.

Whilst reviewing I65702426, Stephen Niedzielski mentioned that the
application state being available is a requirement. This remarkably
simple solution:

- Keeps the Requirement interface and FeatureManager API free of God
  objects;

- Is true to the nature of the Feature Manager - it makes clear and
  centralizes the various checks for application state being available
  across the codebase; and

- Inject a Requirement implementations' dependencies at construction
  time

It just so happens that the $wgFullyInitialised variable flags whether
the application state is available...

Changes:

- Add the the FeatureManager\Requirements\DynamicConfigRequirement class
  and tests. The DynamicConfigRequirement lazily evaluates a single
  configuration value whenever ::isMet is invoked

- Register an DynamicConfigRequirement instance, configured to evaluate
  $wgFullyInitialised while constructing the Vector.FeatureManager
  service

Bug: T244481
Change-Id: I7a2cdc2dfdf20d78e4548f07cf53994563b234b3

2020-03-18 10:10:42 +00:00

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TODO

Currently the FeatureManager class is a very shallow interpretation of Piotr Miazga's proposed API and associated scaffolding classes (see https://phabricator.wikimedia.org/T244481 and https://gerrit.wikimedia.org/r/#/c/mediawiki/skins/Vector/+/572323/). This document aims to list the steps required to get from this system to something as powerful as Piotr's.

Consider supporing memoization of those requirements (see https://gerrit.wikimedia.org/r/#/c/mediawiki/skins/Vector/+/573626/7/includes/FeatureManagement/FeatureManager.php@68)
Add support for getting all requirements
Add support for getting all features enabled when a requirement is enabled/disabled

687 B Raw Blame History

TODO

687 B

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