[Group 3] Enable nullable annotations for Microsoft.Extensions.Hosting.Abstractions

[maxkoshevoi]

Related to #43605

This one is a bit tricky. A lot of abstractions, and hard to know what's null, and what isn't.

Questions:

• This seem like it should be GetRequiredService, since null is not expected here. Yes, I know it's a behavioral change, but it will NRE anyway, this just provides a more crear exception

  runtime/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/HostingAbstractionsHostExtensions.cs

  Line 89 in 6b3ec8e

  IHostApplicationLifetime applicationLifetime = host.Services.GetService<IHostApplicationLifetime>();

• Can this dictionary contain null values?

  runtime/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/HostBuilderContext.cs

  Line 32 in 6b3ec8e

  public IDictionary<object, object> Properties { get; }

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Issue Details

---

Related to #43605

This one is a bit tricky. A lot of abstractions, and hard to know what's null, and what isn't.

Questions:

• This seem like it should be GetRequiredService, since null is not expected here. Yes, I know it's a behavioral change, but it will NRE anyway, this just provides a more crear exception

  runtime/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/HostingAbstractionsHostExtensions.cs

  Line 89 in 6b3ec8e

  IHostApplicationLifetime applicationLifetime = host.Services.GetService<IHostApplicationLifetime>();

• Can this dictionary contain null values?

  runtime/src/libraries/Microsoft.Extensions.Hosting.Abstractions/src/HostBuilderContext.cs

  Line 32 in 6b3ec8e

  public IDictionary<object, object> Properties { get; }

Author:	maxkoshevoi
Assignees:	-
Labels:	new-api-needs-documentation, area-Extensions-Hosting, community-contribution
Milestone:	-

[eerhardt]

These two properties are always set (when we create the object):

runtime/src/libraries/Microsoft.Extensions.Hosting/src/HostBuilder.cs

Lines 213 to 217 in 385fc88

	_hostBuilderContext = new HostBuilderContext(Properties)
	{
	HostingEnvironment = _hostingEnvironment,
	Configuration = _hostConfiguration
	};

It feels wrong to have consumers need to check these for null, when they won't be.

[maxkoshevoi]

Updated PR.

Hm, why they are not part of constructor then?

[eerhardt]

We will probably have problems with these two in the Hosting PR, but we can deal with it then. I think the intention here is that these two properties are not null.

[maxkoshevoi]

@eerhardt Hi, I'm in Ukraine (currently relatively safe in Lviv), so cannot be as active. I'll try to address the comments when I can, but if I don't respond for tool long or disappear altogether, feel free to commit to my branches.

[eerhardt]

Ok - no problem at all, @maxkoshevoi. I'm glad to hear you are safe, as that is the most important thing.

We can definitely take over the PR if you don't have time. Thanks again for all your contributions.

[maxkoshevoi]

We can definitely take over the PR if you don't have time.

For now, I do have time. It's just a heads up that I will be slower to respond, and may not be able to respond for some periods of time. Libraries that left are not that big, so it should be fine.

[eerhardt]

LGTM. Thanks for the work here @maxkoshevoi!

[BrennanConroy]

@eerhardt This one seems odd to be nullable, similar to EnvironmentName above, this is set automatically by the host

[eerhardt]

Given the current code, this annotation is correct as there are scenarios where it can be null:

runtime/src/libraries/Microsoft.Extensions.Hosting/src/HostBuilder.cs

Lines 202 to 213 in 05cb7f5

	var hostingEnvironment = new HostingEnvironment()
	{
	ApplicationName = hostConfiguration[HostDefaults.ApplicationKey],
	EnvironmentName = hostConfiguration[HostDefaults.EnvironmentKey] ?? Environments.Production,
	ContentRootPath = ResolveContentRootPath(hostConfiguration[HostDefaults.ContentRootKey], AppContext.BaseDirectory),
	};
	if (string.IsNullOrEmpty(hostingEnvironment.ApplicationName))
	{
	// Note GetEntryAssembly returns null for the net4x console test runner.
	hostingEnvironment.ApplicationName = Assembly.GetEntryAssembly()?.GetName().Name;
	}