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
