[API Proposal]: Make IHostEnvironment.ApplicationName non-nullable

[halter73]

Background and motivation

In 7.0-preview3 we made IHostEnvironment.ApplicationName and IHostingEnvironment.ApplicationName nullable because of the following:

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;
	}

https://github.com/dotnet/runtime/pull/65403/files/dabdada197861a1fe343f0c82e6ebf3f87c663b5#r829310348

While this is technically correct, it's not user friendly. Historically, applications have expected this property to be non-nullable like the other properties on the interface like EnvironmentName.

It would be better if, similar to EnvironmentName and "Production", we just pick a default ApplicationName when Assembly.GetEntryAssembly() returns null.

API Proposal

namespace Microsoft.Extensions.Hosting;

 public interface IHostEnvironment {
-    string? ApplicationName { get; set; }
+    string ApplicationName { get; set; }
 }
 public interface IHostingEnvironment {
-    string? ApplicationName { get; set; }
+    string ApplicationName { get; set; }
 }

API Usage

Instead of doing complicated null-checks:

if (env.ApplicationName is not null)
{
    var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));
    if (appAssembly != null)
    {
        config.AddUserSecrets(appAssembly, optional: true);
    }
}

We should be able to assume ApplicationName is non-null:

var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));
if (appAssembly != null)
{
    config.AddUserSecrets(appAssembly, optional: true);
}

See https://github.com/dotnet/aspnetcore/pull/40754/files#diff-ba47e8a57bffee356b71c57b0ac4709dc0eb1329d547a36ee30fea262cf8358c

Alternative Designs

Keeping ApplicationName nullable.

Risks

We cannot come up with a good ApplicationName for when Assembly.GetEntryAssembly() returns null.

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[eerhardt]

we just pick a default ApplicationName when Assembly.GetEntryAssembly() returns null.

Do you have a proposal for what it should be? string.Empty, "Application", ?

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Issue Details

---

Background and motivation

In 7.0-preview3 we made IHostEnvironment.ApplicationName and IHostingEnvironment.ApplicationName nullable because of the following:

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;
	}

https://github.com/dotnet/runtime/pull/65403/files/dabdada197861a1fe343f0c82e6ebf3f87c663b5#r829310348

While this is technically correct, it's not user friendly. Historically, applications have expected this property to be non-nullable like the other properties on the interface like EnvironmentName.

It would be better if, similar to EnvironmentName and "Production", we just pick a default ApplicationName when Assembly.GetEntryAssembly() returns null.

API Proposal

namespace Microsoft.Extensions.Hosting;

 public interface IHostEnvironment {
-    string? ApplicationName { get; set; }
+    string ApplicationName { get; set; }
 }
 public interface IHostingEnvironment {
-    string? ApplicationName { get; set; }
+    string ApplicationName { get; set; }
 }

API Usage

Instead of doing complicated null-checks:

if (env.ApplicationName is not null)
{
    var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));
    if (appAssembly != null)
    {
        config.AddUserSecrets(appAssembly, optional: true);
    }
}

We should be able to assume ApplicationName is non-null:

var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));
if (appAssembly != null)
{
    config.AddUserSecrets(appAssembly, optional: true);
}

See https://github.com/dotnet/aspnetcore/pull/40754/files#diff-ba47e8a57bffee356b71c57b0ac4709dc0eb1329d547a36ee30fea262cf8358c

Alternative Designs

Keeping ApplicationName nullable.

Risks

We cannot come up with a good ApplicationName for when Assembly.GetEntryAssembly() returns null.

Author:	halter73
Assignees:	-
Labels:	api-suggestion, untriaged, area-Extensions-Hosting
Milestone:	-

[halter73]

I like string.Empty or maybe "<Unkown>".

I don't expect this to come up much outside of certain testing and tooling scenarios since Assembly.GetEntryAssembly() is usually non-null. I don't think we should use a nice name like "Application" which would be a valid default when an entry assembly is found. I'd rather make it obvious that a good default couldn't be found.

[eerhardt]

I think I like “<Unknown>”. That would be a good default when we can’t default anything else.

[maryamariyan]

Went over this with @tarekgh and @eerhardt and for this one we could skip api review because we just annotated this in the past few weeks.

Compared to 6.0, we went from having no nullable to now having nullable annotated as being not nullable.

The observable change in behavior: on an app we could get null application name but now you'd get default value.

FYI: https://docs.microsoft.com/en-us/dotnet/api/system.reflection.assembly.getentryassembly?view=net-6.0#:~:text=The%20GetEntryAssembly%20method%20can%20return%20null%20when%20a,was%20unmanaged%20code%20rather%20than%20a%20managed%20assembly.