Exception in BlazorWasm applications due to NullabilityInfoContext usage

[sebastienros]

Description

This was introduced in #102499. This blocking runtime ingestion in ASP.NET for preview 5.

This exception is thrown when running a BlazorWasm application.

NullabilityInfoContext is not supported in the current application because 'System.Reflection.NullabilityInfoContext.IsSupported' is set to false. Set the MSBuild Property 'NullabilityInfoContextSupport' to true in order to enable it.

The BlazorWebAssembly SDK disabled the feature https://github.com/dotnet/sdk/blob/a304e06708d72c1be0d78e214366a2c7c601b5d8/src/BlazorWasmSdk/Targets/Microsoft.NET.Sdk.BlazorWebAssembly.6_0.targets#L49

This method should check NullabilityInfoContext.IsSupported is true before using calling NullabilityInfoContext.Create.

Reproduction Steps

Run a BlazorWebAssembly application like this one:

https://github.com/dotnet/aspnetcore/blob/release/9.0-preview5/src/Components/WebAssembly/testassets/StandaloneApp/StandaloneApp.csproj

Expected behavior

Application should not throw an exception when the System.Reflection.NullabilityInfoContext.IsSupported flag is false.

Actual behavior

An exception is thrown.

Regression?

Yes

Known Workarounds

Enable the System.Reflection.NullabilityInfoContext.IsSupported switch.

Configuration

No response

Other information

No response

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-text-json, @gregsdennis
See info in area-owners.md if you want to be subscribed.

[jozkee]

System.Reflection.NullabilityInfoContext.IsSupported is used by apps to trim nullability annotations, as @eiriktsarpalis mentioned offline, we could bail when the switch is set to false and process things like they were nullable-oblivious, but it feels odd that NullabilityInfoContext throws here rather than returning new NullabilityInfo { ReadState = NullabilityState.Unknown, WriteState = NullabilityState.Unknown }.

cc @buyaa-n @eerhardt