Port of #35768

Customer impact

This is a feature that we added in 6.0 to support customers that are prerendering their Blazor applications and that allows them to save state and then access it the next time the app starts after it has been prerendered.

Most changes are renaming for APIs that a customer doesn't ever interact with (because he can't extend the type nor call methods on it in a way that is useful; the APIs are public because of layering constraints between Blazor Server/Wasm and Mvc.)

This is not a core feature of the framework, so we are changing somethign that only a few folks will use (say 10% to put a number on it).

Of the APIs, the ones a customer will interact 99% of the time are below and the updates are very straighforward:

Here is a sample of the 99% use case for the feature:

-@inject ComponentApplicationState ApplicationState
+@inject PersistentComponentState ApplicationState

-        ApplicationState.OnPersisting += () +> PersistForecasts;
-        if(!ApplicationState.TryTakeAsJson<WeatherForecast[]>("fetchdata", out var restored))
+        _persistingSubscription = ApplicationState.RegisterOnPersisting(PersistForecasts);
+        if(!ApplicationState.TryTakeFromJson<WeatherForecast[]>("fetchdata", out var restored))
         {
             forecasts = await WeatherForecastService.GetForecastAsync(DateTime.Now);
         }
@@ -11,7 +11,8 @@
             forecasts = restored!;
         }
         void Dispose()
         {

-            ApplicationState.OnPersisting -= PersistForecasts;
+            _persistingSubscription.Dispose();
         }

Other renames/changes are for types that are public that customers don't directly use.

Testing

Automated. We have unit tests and E2E test coverage for all the changed APIs.

Risk

Low

• Its a new feature included in 6.0, so it won't break existing customers on previous releases.
• The change renames APIs.
• Changes for customers are straighforward.
• Its an enhancement feature used by a subset of our customers.
• No other features build on top of this feature.