Add nullable annotations

[maxkoshevoi]

Please, add support for nullable reference types to these packages.

Microsoft.Extensions.* dependencies should be annotated in .Net 7 (not all of them are annotated so far)

[zhiyuanliang-ms]

@maxkoshevoi Where do you want to have nullable reference types?

Is there any use case/scenario where nullable reference would be very helpful for you? Could you provide a code snippet?

[maxkoshevoi]

@zhiyuanliang-ms Here's an example where they would be helpful. This is the example code from this repository. If I launch it and don't have a connection_string in appsettings.json file, I get a NRE. With nullable reference types there would be a warning that options.Connect() doesn't allow nulls, and settings["connection_string"] might be null

var builder = WebApplication.CreateBuilder(args);
builder.Host.ConfigureAppConfiguration((hostingContext, config) =>
{
    var settings = config.AddJsonFile("appsettings.json").Build();
    config.AddAzureAppConfiguration(options =>
    {
        options.Connect(settings["connection_string"]);
    });
});
builder.Services.AddAzureAppConfiguration();

var app = builder.Build();
app.UseAzureAppConfiguration();

app.Run();

[zhiyuanliang-ms]

Hi, @maxkoshevoi Thank you for the response.

If I launch it and don't have a connection_string in appsettings.json file, I get a NRE.

This is expected, isn't it? Are you suggesting that we should not throw exception when connection string is null/empty, instead, we should just log warning and do nothing?

BTW, could you make your code like this by having null check for connection string before call AddAzureAppConfiguration.

[maxkoshevoi]

Are you suggesting that we should not throw exception

Not at all, exception is what I would expect in this situation. No behavioral changes are needed.
I'm suggesting that there should be a warning telling the user that there's a possible NRE since IConfigurations indexer is already telling the compiler that it might return null

The only thing left is to tell compiler that options.Connect() doesn't expect null as a first argument.

All nullable reference types do is give the compiler additional information, so that it can warn users of potential NREs at compile time. Like so:

BTW, could you make your code like this by having null check for connection string before call AddAzureAppConfiguration.

In this case there won't be an NRE (and if nullable reference types were to be enabled in this package the compiler also wouldn't show the warning, where in the previous example it would which would encourage the user to add the if you mentioned to check connection string for null beforehand)

[maxkoshevoi]

I can create the PR for this issue if it's okay

[zhiyuanliang-ms]

Hi, @maxkoshevoi

I can create the PR for this issue if it's okay

That will be great! Thank you so much.

[maxkoshevoi]

@zhiyuanliang-ms could you take a look at the PR please?

[zhiyuanliang-ms]

@maxkoshevoi Sure. I was distracted by some other tasks. I didn't put my main focus on .NET provider. I will take a look this RP once I finish my current tasks.