Introduction
Laravel Pennant is a simple and light-weight feature flag package - without the cruft. Feature flags enable you to incrementally roll out new application features with confidence, A/B test new interface designs, complement a trunk-based development strategy, and much more.
Installation
First, install Pennant into your project using the Composer package manager:
composer require laravel/pennant
Next, you should publish the Pennant configuration and migration
files using the vendor:publish
Artisan command:
php artisan vendor:publish --provider="Laravel\Pennant\PennantServiceProvider"
Finally, you should run your application's database migrations. This
will create a features
table that Pennant uses to power its
database
driver:
php artisan migrate
Configuration
After publishing Pennant's assets, its configuration file will be
located at config/pennant.php
. This configuration file
allows you to specify the default storage mechanism that will be used by
Pennant to store resolved feature flag values.
Pennant includes support for storing resolved feature flag values in
an in-memory array via the array
driver. Or, Pennant can
store resolved feature flag values persistently in a relational database
via the database
driver, which is the default storage
mechanism used by Pennant.
Defining Features
To define a feature, you may use the define
method
offered by the Feature
facade. You will need to provide a
name for the feature, as well as a closure that will be invoked to
resolve the feature's initial value.
Typically, features are defined in a service provider using the
Feature
facade. The closure will receive the "scope" for
the feature check. Most commonly, the scope is the currently
authenticated user. In this example, we will define a feature for
incrementally rolling out a new API to our application's users:
<?php
namespace App\Providers;
use App\Models\User;
use Illuminate\Support\Lottery;
use Illuminate\Support\ServiceProvider;
use Laravel\Pennant\Feature;
class AppServiceProvider extends ServiceProvider
{
/**
* Bootstrap any application services.
*/
public function boot(): void
{
Feature::define('new-api', fn (User $user) => match (true) {
$user->isInternalTeamMember() => true,
$user->isHighTrafficCustomer() => false,
default => Lottery::odds(1 / 100),
});
}
}
As you can see, we have the following rules for our feature:
- All internal team members should be using the new API.
- Any high traffic customers should not be using the new API.
- Otherwise, the feature should be randomly assigned to users with a 1 in 100 chance of being active.
The first time the new-api
feature is checked for a
given user, the result of the closure will be stored by the storage
driver. The next time the feature is checked against the same user, the
value will be retrieved from storage and the closure will not be
invoked.
For convenience, if a feature definition only returns a lottery, you may omit the closure completely:
Feature::define('site-redesign', Lottery::odds(1, 1000));
Class Based Features
Pennant also allows you to define class based features. Unlike
closure based feature definitions, there is no need to register a class
based feature in a service provider. To create a class based feature,
you may invoke the pennant:feature
Artisan command. By
default the feature class will be placed in your application's
app/Features
directory:
php artisan pennant:feature NewApi
When writing a feature class, you only need to define a
resolve
method, which will be invoked to resolve the
feature's initial value for a given scope. Again, the scope will
typically be the currently authenticated user:
<?php
namespace App\Features;
use Illuminate\Support\Lottery;
class NewApi
{
/**
* Resolve the feature's initial value.
*/
public function resolve(User $user): mixed
{
return match (true) {
$user->isInternalTeamMember() => true,
$user->isHighTrafficCustomer() => false,
default => Lottery::odds(1 / 100),
};
}
}
Note: Feature classes are resolved via the container, so you may inject dependencies into the feature class's constructor when needed.
Checking Features
To determine if a feature is active, you may use the
active
method on the Feature
facade. By
default, features are checked against the currently authenticated
user:
<?php
namespace App\Http\Controllers;
use Illuminate\Http\Request;
use Illuminate\Http\Response;
use Laravel\Pennant\Feature;
class PodcastController
{
/**
* Display a listing of the resource.
*/
public function index(Request $request): Response
{
return Feature::active('new-api')
? $this->resolveNewApiResponse($request)
: $this->resolveLegacyApiResponse($request);
}
// ...
}
Although features are checked against the currently authenticated
user by default, you may easily check the feature against another user
or scope. To accomplish this, use the
for
method offered by the Feature
facade:
return Feature::for($user)->active('new-api')
? $this->resolveNewApiResponse($request)
: $this->resolveLegacyApiResponse($request);
Pennant also offers some additional convenience methods that may prove useful when determining if a feature is active or not:
// Determine if all of the given features are active...
Feature::allAreActive(['new-api', 'site-redesign']);
// Determine if any of the given features are active...
Feature::someAreActive(['new-api', 'site-redesign']);
// Determine if a feature is inactive...
Feature::inactive('new-api');
// Determine if all of the given features are inactive...
Feature::allAreInactive(['new-api', 'site-redesign']);
// Determine if any of the given features are inactive...
Feature::someAreInactive(['new-api', 'site-redesign']);
Note: When using Pennant outside of an HTTP context, such as in an Artisan command or a queued job, you should typically explicitly specify the feature's scope. Alternatively, you may define a default scope that accounts for both authenticated HTTP contexts and unauthenticated contexts.
Checking Class Based Features
For class based features, you should provide the class name when checking the feature:
<?php
namespace App\Http\Controllers;
use App\Features\NewApi;
use Illuminate\Http\Request;
use Illuminate\Http\Response;
use Laravel\Pennant\Feature;
class PodcastController
{
/**
* Display a listing of the resource.
*/
public function index(Request $request): Response
{
return Feature::active(NewApi::class)
? $this->resolveNewApiResponse($request)
: $this->resolveLegacyApiResponse($request);
}
// ...
}
Conditional Execution
The when
method may be used to fluently execute a given
closure if a feature is active. Additionally, a second closure may be
provided and will be executed if the feature is inactive:
<?php
namespace App\Http\Controllers;
use App\Features\NewApi;
use Illuminate\Http\Request;
use Illuminate\Http\Response;
use Laravel\Pennant\Feature;
class PodcastController
{
/**
* Display a listing of the resource.
*/
public function index(Request $request): Response
{
return Feature::when(NewApi::class,
fn () => $this->resolveNewApiResponse($request),
fn () => $this->resolveLegacyApiResponse($request),
);
}
// ...
}
The unless
method serves as the inverse of the
when
method, executing the first closure if the feature is
inactive:
return Feature::unless(NewApi::class,
fn () => $this->resolveLegacyApiResponse($request),
fn () => $this->resolveNewApiResponse($request),
);
The HasFeatures
Trait
Pennant's HasFeatures
trait may be added to your
application's User
model (or any other model that has
features) to provide a fluent, convenient way to check features directly
from the model:
<?php
namespace App\Models;
use Illuminate\Foundation\Auth\User as Authenticatable;
use Laravel\Pennant\Concerns\HasFeatures;
class User extends Authenticatable
{
use HasFeatures;
// ...
}
Once the trait has been added to your model, you may easily check
features by invoking the features
method:
if ($user->features()->active('new-api')) {
// ...
}
Of course, the features
method provides access to many
other convenient methods for interacting with features:
// Values...
$value = $user->features()->value('purchase-button')
$values = $user->features()->values(['new-api', 'purchase-button']);
// State...
$user->features()->active('new-api');
$user->features()->allAreActive(['new-api', 'server-api']);
$user->features()->someAreActive(['new-api', 'server-api']);
$user->features()->inactive('new-api');
$user->features()->allAreInactive(['new-api', 'server-api']);
$user->features()->someAreInactive(['new-api', 'server-api']);
// Conditional execution...
$user->features()->when('new-api',
fn () => /* ... */,
fn () => /* ... */,
);
$user->features()->unless('new-api',
fn () => /* ... */,
fn () => /* ... */,
);
Blade Directive
To make checking features in Blade a seamless experience, Pennant
offers a @feature
directive:
@feature('site-redesign')
<!-- 'site-redesign' is active -->
@else
<!-- 'site-redesign' is inactive -->
@endfeature
Middleware
Pennant also includes a middleware that
may be used to verify the currently authenticated user has access to a
feature before a route is even invoked. You may assign the middleware to
a route and specify the features that are required to access the route.
If any of the specified features are inactive for the currently
authenticated user, a 400 Bad Request
HTTP response will be
returned by the route. Multiple features may be passed to the static
using
method.
use Illuminate\Support\Facades\Route;
use Laravel\Pennant\Middleware\EnsureFeaturesAreActive;
Route::get('/api/servers', function () {
// ...
})->middleware(EnsureFeaturesAreActive::using('new-api', 'servers-api'));
Customizing The Response
If you would like to customize the response that is returned by the
middleware when one of the listed features is inactive, you may use the
whenInactive
method provided by the
EnsureFeaturesAreActive
middleware. Typically, this method
should be invoked within the boot
method of one of your
application's service providers:
use Illuminate\Http\Request;
use Illuminate\Http\Response;
use Laravel\Pennant\Middleware\EnsureFeaturesAreActive;
/**
* Bootstrap any application services.
*/
public function boot(): void
{
EnsureFeaturesAreActive::whenInactive(
function (Request $request, array $features) {
return new Response(status: 403);
}
);
// ...
}
In-Memory Cache
When checking a feature, Pennant will create an in-memory cache of
the result. If you are using the database
driver, this
means that re-checking the same feature flag within a single request
will not trigger additional database queries. This also ensures that the
feature has a consistent result for the duration of the request.
If you need to manually flush the in-memory cache, you may use the
flushCache
method offered by the Feature
facade:
Feature::flushCache();
Scope
Specifying The Scope
As discussed, features are typically checked against the currently
authenticated user. However, this may not always suit your needs.
Therefore, it is possible to specify the scope you would like to check a
given feature against via the Feature
facade's
for
method:
return Feature::for($user)->active('new-api')
? $this->resolveNewApiResponse($request)
: $this->resolveLegacyApiResponse($request);
Of course, feature scopes are not limited to "users". Imagine you have built a new billing experience that you are rolling out to entire teams rather than individual users. Perhaps you would like the oldest teams to have a slower rollout than the newer teams. Your feature resolution closure might look something like the following:
use App\Models\Team;
use Carbon\Carbon;
use Illuminate\Support\Lottery;
use Laravel\Pennant\Feature;
Feature::define('billing-v2', function (Team $team) {
if ($team->created_at->isAfter(new Carbon('1st Jan, 2023'))) {
return true;
}
if ($team->created_at->isAfter(new Carbon('1st Jan, 2019'))) {
return Lottery::odds(1 / 100);
}
return Lottery::odds(1 / 1000);
});
You will notice that the closure we have defined is not expecting a
User
, but is instead expecting a Team
model.
To determine if this feature is active for a user's team, you should
pass the team to the for
method offered by the
Feature
facade:
if (Feature::for($user->team)->active('billing-v2')) {
return redirect()->to('/billing/v2');
}
// ...
Default Scope
It is also possible to customize the default scope Pennant uses to
check features. For example, maybe all of your features are checked
against the currently authenticated user's team instead of the user.
Instead of having to call Feature::for($user->team)
every time you check a feature, you may instead specify the team as the
default scope. Typically, this should be done in one of your
application's service providers:
<?php
namespace App\Providers;
use Illuminate\Support\Facades\Auth;
use Illuminate\Support\ServiceProvider;
use Laravel\Pennant\Feature;
class AppServiceProvider extends ServiceProvider
{
/**
* Bootstrap any application services.
*/
public function boot(): void
{
Feature::resolveScopeUsing(fn ($driver) => Auth::user()?->team);
// ...
}
}
If no scope is explicitly provided via the for
method,
the feature check will now use the currently authenticated user's team
as the default scope:
Feature::active('billing-v2');
// Is now equivalent to...
Feature::for($user->team)->active('billing-v2');
Nullable Scope
If the scope you provide when checking a feature is null
and the feature's definition does not support null
via a
nullable type or by including null
in a union type, Pennant
will automatically return false
as the feature's result
value.
So, if the scope you are passing to a feature is potentially
null
and you want the feature's value resolver to be
invoked, you should account for that in your feature's definition. A
null
scope may occur if you check a feature within an
Artisan command, queued job, or unauthenticated route. Since there is
usually not an authenticated user in these contexts, the default scope
will be null
.
If you do not always explicitly
specify your feature scope then you should ensure the scope's type
is "nullable" and handle the null
scope value within your
feature definition logic:
use App\Models\User;
use Illuminate\Support\Lottery;
use Laravel\Pennant\Feature;
Feature::define('new-api', fn (User $user) => match (true) {// [tl! remove]
Feature::define('new-api', fn (User|null $user) => match (true) {// [tl! add]
$user === null => true,// [tl! add]
$user->isInternalTeamMember() => true,
$user->isHighTrafficCustomer() => false,
default => Lottery::odds(1 / 100),
});
Identifying Scope
Pennant's built-in array
and database
storage drivers know how to properly store scope identifiers for all PHP
data types as well as Eloquent models. However, if your application
utilizes a third-party Pennant driver, that driver may not know how to
properly store an identifier for an Eloquent model or other custom types
in your application.
In light of this, Pennant allows you to format scope values for
storage by implementing the FeatureScopeable
contract on
the objects in your application that are used as Pennant scopes.
For example, imagine you are using two different feature drivers in a
single application: the built-in database
driver and a
third-party "Flag Rocket" driver. The "Flag Rocket" driver does not know
how to properly store an Eloquent model. Instead, it requires a
FlagRocketUser
instance. By implementing the
toFeatureIdentifier
defined by the
FeatureScopeable
contract, we can customize the storable
scope value provided to each driver used by our application:
<?php
namespace App\Models;
use FlagRocket\FlagRocketUser;
use Illuminate\Database\Eloquent\Model;
use Laravel\Pennant\Contracts\FeatureScopeable;
class User extends Model implements FeatureScopeable
{
/**
* Cast the object to a feature scope identifier for the given driver.
*/
public function toFeatureIdentifier(string $driver): mixed
{
return match($driver) {
'database' => $this,
'flag-rocket' => FlagRocketUser::fromId($this->flag_rocket_id),
};
}
}
Serializing Scope
By default, Pennant will use a fully qualified class name when storing a feature associated with an Eloquent model. If you are already using an Eloquent morph map, you may choose to have Pennant also use the morph map to decouple the stored feature from your application structure.
To achieve this, after defining your Eloquent morph map in a service
provider, you may invoke the Feature
facade's
useMorphMap
method:
use Illuminate\Database\Eloquent\Relations\Relation;
use Laravel\Pennant\Feature;
Relation::enforceMorphMap([
'post' => 'App\Models\Post',
'video' => 'App\Models\Video',
]);
Feature::useMorphMap();
Rich Feature Values
Until now, we have primarily shown features as being in a binary state, meaning they are either "active" or "inactive", but Pennant also allows you to store rich values as well.
For example, imagine you are testing three new colors for the "Buy
now" button of your application. Instead of returning true
or false
from the feature definition, you may instead
return a string:
use Illuminate\Support\Arr;
use Laravel\Pennant\Feature;
Feature::define('purchase-button', fn (User $user) => Arr::random([
'blue-sapphire',
'seafoam-green',
'tart-orange',
]));
You may retrieve the value of the purchase-button
feature using the value
method:
$color = Feature::value('purchase-button');
Pennant's included Blade directive also makes it easy to conditionally render content based on the current value of the feature:
@feature('purchase-button', 'blue-sapphire')
<!-- 'blue-sapphire' is active -->
@elsefeature('purchase-button', 'seafoam-green')
<!-- 'seafoam-green' is active -->
@elsefeature('purchase-button', 'tart-orange')
<!-- 'tart-orange' is active -->
@endfeature
Note: When using rich values, it is important to know that a feature is considered "active" when it has any value other than
false
.
When calling the conditional
when
method, the feature's rich value will be provided
to the first closure:
Feature::when('purchase-button',
fn ($color) => /* ... */,
fn () => /* ... */,
);
Likewise, when calling the conditional unless
method,
the feature's rich value will be provided to the optional second
closure:
Feature::unless('purchase-button',
fn () => /* ... */,
fn ($color) => /* ... */,
);
Retrieving Multiple Features
The values
method allows the retrieval of multiple
features for a given scope:
Feature::values(['billing-v2', 'purchase-button']);
// [
// 'billing-v2' => false,
// 'purchase-button' => 'blue-sapphire',
// ]
Or, you may use the all
method to retrieve the values of
all defined features for a given scope:
Feature::all();
// [
// 'billing-v2' => false,
// 'purchase-button' => 'blue-sapphire',
// 'site-redesign' => true,
// ]
However, class based features are dynamically registered and are not
known by Pennant until they are explicitly checked. This means your
application's class based features may not appear in the results
returned by the all
method if they have not already been
checked during the current request.
If you would like to ensure that feature classes are always included
when using the all
method, you may use Pennant's feature
discovery capabilities. To get started, invoke the discover
method in one of your application's service providers:
<?php
namespace App\Providers;
use Illuminate\Support\ServiceProvider;
use Laravel\Pennant\Feature;
class AppServiceProvider extends ServiceProvider
{
/**
* Bootstrap any application services.
*/
public function boot(): void
{
Feature::discover();
// ...
}
}
The discover
method will register all of the feature
classes in your application's app/Features
directory. The
all
method will now include these classes in its results,
regardless of whether they have been checked during the current
request:
Feature::all();
// [
// 'App\Features\NewApi' => true,
// 'billing-v2' => false,
// 'purchase-button' => 'blue-sapphire',
// 'site-redesign' => true,
// ]
Eager Loading
Although Pennant keeps an in-memory cache of all resolved features for a single request, it is still possible to encounter performance issues. To alleviate this, Pennant offers the ability to eager load feature values.
To illustrate this, imagine that we are checking if a feature is active within a loop:
use Laravel\Pennant\Feature;
foreach ($users as $user) {
if (Feature::for($user)->active('notifications-beta')) {
$user->notify(new RegistrationSuccess);
}
}
Assuming we are using the database driver, this code will execute a
database query for every user in the loop - executing potentially
hundreds of queries. However, using Pennant's load
method,
we can remove this potential performance bottleneck by eager loading the
feature values for a collection of users or scopes:
Feature::for($users)->load(['notifications-beta']);
foreach ($users as $user) {
if (Feature::for($user)->active('notifications-beta')) {
$user->notify(new RegistrationSuccess);
}
}
To load feature values only when they have not already been loaded,
you may use the loadMissing
method:
Feature::for($users)->loadMissing([
'new-api',
'purchase-button',
'notifications-beta',
]);
Updating Values
When a feature's value is resolved for the first time, the underlying driver will store the result in storage. This is often necessary to ensure a consistent experience for your users across requests. However, at times, you may want to manually update the feature's stored value.
To accomplish this, you may use the activate
and
deactivate
methods to toggle a feature "on" or "off":
use Laravel\Pennant\Feature;
// Activate the feature for the default scope...
Feature::activate('new-api');
// Deactivate the feature for the given scope...
Feature::for($user->team)->deactivate('billing-v2');
It is also possible to manually set a rich value for a feature by
providing a second argument to the activate
method:
Feature::activate('purchase-button', 'seafoam-green');
To instruct Pennant to forget the stored value for a feature, you may
use the forget
method. When the feature is checked again,
Pennant will resolve the feature's value from its feature
definition:
Feature::forget('purchase-button');
Bulk Updates
To update stored feature values in bulk, you may use the
activateForEveryone
and deactivateForEveryone
methods.
For example, imagine you are now confident in the
new-api
feature's stability and have landed on the best
'purchase-button'
color for your checkout flow - you can
update the stored value for all users accordingly:
use Laravel\Pennant\Feature;
Feature::activateForEveryone('new-api');
Feature::activateForEveryone('purchase-button', 'seafoam-green');
Alternatively, you may deactivate the feature for all users:
Feature::deactivateForEveryone('new-api');
Note: This will only update the resolved feature values that have been stored by Pennant's storage driver. You will also need to update the feature definition in your application.
Purging Features
Sometimes, it can be useful to purge an entire feature from storage. This is typically necessary if you have removed the feature from your application or you have made adjustments to the feature's definition that you would like to rollout to all users.
You may remove all stored values for a feature using the
purge
method:
// Purging a single feature...
Feature::purge('new-api');
// Purging multiple features...
Feature::purge(['new-api', 'purchase-button']);
If you would like to purge all features from storage, you
may invoke the purge
method without any arguments:
Feature::purge();
As it can be useful to purge features as part of your application's
deployment pipeline, Pennant includes a pennant:purge
Artisan command:
php artisan pennant:purge new-api
php artisan pennant:purge new-api purchase-button
Testing
When testing code that interacts with feature flags, the easiest way to control the feature flag's returned value in your tests is to simply re-define the feature. For example, imagine you have the following feature defined in one of your application's service provider:
use Illuminate\Support\Arr;
use Laravel\Pennant\Feature;
Feature::define('purchase-button', fn () => Arr::random([
'blue-sapphire',
'seafoam-green',
'tart-orange',
]));
To modify the feature's returned value in your tests, you may
re-define the feature at the beginning of the test. The following test
will always pass, even though the Arr::random()
implementation is still present in the service provider:
use Laravel\Pennant\Feature;
public function test_it_can_control_feature_values()
{
Feature::define('purchase-button', 'seafoam-green');
$this->assertSame('seafoam-green', Feature::value('purchase-button'));
}
The same approach may be used for class based features:
use App\Features\NewApi;
use Laravel\Pennant\Feature;
public function test_it_can_control_feature_values()
{
Feature::define(NewApi::class, true);
$this->assertTrue(Feature::value(NewApi::class));
}
If your feature is returning a Lottery
instance, there
are a handful of useful testing
helpers available.
Store Configuration
You may configure the store that Pennant will use during testing by
defining the PENNANT_STORE
environment variable in your
application's phpunit.xml
file:
<?xml version="1.0" encoding="UTF-8"?>
<phpunit colors="true">
<!-- ... -->
<php>
<env name="PENNANT_STORE" value="array"/>
<!-- ... -->
</php>
</phpunit>
Adding Custom Pennant Drivers
Implementing The Driver
If none of Pennant's existing storage drivers fit your application's
needs, you may write your own storage driver. Your custom driver should
implement the Laravel\Pennant\Contracts\Driver
interface:
<?php
namespace App\Extensions;
use Laravel\Pennant\Contracts\Driver;
class RedisFeatureDriver implements Driver
{
public function define(string $feature, callable $resolver): void {}
public function defined(): array {}
public function getAll(array $features): array {}
public function get(string $feature, mixed $scope): mixed {}
public function set(string $feature, mixed $scope, mixed $value): void {}
public function setForAllScopes(string $feature, mixed $value): void {}
public function delete(string $feature, mixed $scope): void {}
public function purge(array|null $features): void {}
}
Now, we just need to implement each of these methods using a Redis
connection. For an example of how to implement each of these methods,
take a look at the Laravel\Pennant\Drivers\DatabaseDriver
in the Pennant
source code
Note: Laravel does not ship with a directory to contain your extensions. You are free to place them anywhere you like. In this example, we have created an
Extensions
directory to house theRedisFeatureDriver
.
Registering The Driver
Once your driver has been implemented, you are ready to register it
with Laravel. To add additional drivers to Pennant, you may use the
extend
method provided by the Feature
facade.
You should call the extend
method from the
boot
method of one of your application's service provider:
<?php
namespace App\Providers;
use App\Extensions\RedisFeatureDriver;
use Illuminate\Contracts\Foundation\Application;
use Illuminate\Support\ServiceProvider;
use Laravel\Pennant\Feature;
class AppServiceProvider extends ServiceProvider
{
/**
* Register any application services.
*/
public function register(): void
{
// ...
}
/**
* Bootstrap any application services.
*/
public function boot(): void
{
Feature::extend('redis', function (Application $app) {
return new RedisFeatureDriver($app->make('redis'), $app->make('events'), []);
});
}
}
Once the driver has been registered, you may use the
redis
driver in your application's
config/pennant.php
configuration file:
'stores' => [
'redis' => [
'driver' => 'redis',
'connection' => null,
],
// ...
],
Events
Pennant dispatches a variety of events that can be useful when tracking feature flags throughout your application.
Laravel\Pennant\Events\RetrievingKnownFeature
This event is dispatched the first time a known feature is retrieved during a request for a specific scope. This event can be useful to create and track metrics against the feature flags that are being used throughout your application.
Laravel\Pennant\Events\RetrievingUnknownFeature
This event is dispatched the first time an unknown feature is retrieved during a request for a specific scope. This event can be useful if you have intended to remove a feature flag, but may have accidentally left some stray references to it throughout your application.
For example, you may find it useful to listen for this event and
report
or throw an exception when it occurs:
<?php
namespace App\Providers;
use Illuminate\Foundation\Support\Providers\EventServiceProvider as ServiceProvider;
use Illuminate\Support\Facades\Event;
use Laravel\Pennant\Events\RetrievingUnknownFeature;
class EventServiceProvider extends ServiceProvider
{
/**
* Register any other events for your application.
*/
public function boot(): void
{
Event::listen(function (RetrievingUnknownFeature $event) {
report("Resolving unknown feature [{$event->feature}].");
});
}
}
Laravel\Pennant\Events\DynamicallyDefiningFeature
This event is dispatched when a class based feature is being dynamically checked for the first time during a request.