AddFeatureManagement doesn't Register a Custom Configuration

[daniell-reeco]

Nuget version affected: 4.2.0 (worked in 4.0.0 until nuget updated)

In my Program.cs:
builder.Services.AddFeatureManagement(builder.Configuration.GetSection("FeatureFlags"));

GetSection confirmed to retrieve the configuration from appsettings.json which is:
"FeatureFlags": { "UseReecoUsers": true }

but when calling IsEnabledAsync with the manager I received the following log:
"The feature definition for the feature 'UseReecoUsers' was not found"

When changing the feature flag section to:
"FeatureManagement": { "UseReecoUsers": true }

and changing the line in Program.cs to:
builder.Services.AddFeatureManagement(/*builder.Configuration.GetSection("FeatureFlags")*/);

it identifed the feature flag.

[micheltol]

I can confirm this issue. It worked with version 4.1.0

[zhiyuanliang-ms]

Hi, @micheltol @daniell-reeco
I am sorry about this issue. This is an oversight. It is a bug introduced in 4.2.0.

In 4.2.0, we added an enhancement #536 that we will merge Microsoft feature flags from different configuration sources.

This enhancement will make the operation to GetMicrosoftFeatureDefinitionSections becomes more time-consuming.
Before 4.2.0, we will get all configuration sections for feature definitions and find the feature flags among them each time when there is no cache. code
In 4.2.0, to improve the performance, we will cache all configuration sections for feature definitions when constructing the ConfigurationFeatureDefinitionProvider. code. So, until the configuration is changed, we only get all configuration sections for feature definitions for once and it happens in the constructor of the ConfigurationFeatureDefinitionProvide.

However,

builder.Services.AddFeatureManagement(builder.Configuration.GetSection("FeatureFlags"));

the above the usage is something we called RootConfigurationFallback. It will only be set to true when you provide an IConfiguration when calling AddFeatureManagement. The RootConfigurationFallbackEnabled property of ConfigurationFeatureDefinitionProvider is set to true after the constructor of the ConfigurationFeatureDefinitionProvider. code So, for the first time we call GetDotnetFeatureDefinitionSections in the constructor, the RootConfigurationFallbackEnabled will not be respected. This caused the issue.

I have sent out a bug fix PR: #547

Put more backgrounds here:
We have some back and forth on this feature. we even removed this feature in 3.0.0 and added it back in 3.1.0. #308 #312

You might have question: why we don't use init key word. Here is the reason.

[jimmyca15]

Thanks for reporting this issue. Package version 4.2.0 has been unlisted

[zhiyuanliang-ms]

@daniell-reeco @micheltol 4.2.1 is released. It should fix the issue.