In DemoConsole app, all tagPages are empty without controls displayed

[Olina-Zhang]

.NET version

.Net 9.0: Main branch of Winforms repo

Did it work in .NET Framework?

Not tested/verified

Did it work in any of the earlier releases of .NET Core or .NET 5+?

Yes, it is a regression issue, last week for Winforms repo testing, we can see controls in tabPages of DemoConsole test app

Issue description

In DemoConsole test app of Winforms repo, when running it, all tabPages are empty without controls displayed as following:

DemoConsoleIssue.mp4

Steps to reproduce

Test sample: DemoConsole in Winforms repo

[LeafShi1]

This issue caused by the PR #11081， PR changed null! to String.Empty at

winforms/src/System.Windows.Forms.Design/src/System/ComponentModel/Design/DesignerHost.cs

Line 922 in 32bc644

((IDesignerHost)this).CreateComponent(componentType, string.Empty);

, but name=empty was not judged when create site

winforms/src/System.Windows.Forms.Design/src/System/ComponentModel/Design/DesignerHost.cs

Lines 369 to 386 in 32bc644

	protected override ISite CreateSite(IComponent component, string? name)
	{
	Debug.Assert(component is not null, "Caller should have guarded against a null component");
	// We need to handle the case where a component's ctor adds itself to the container. We don't want to do the
	// work of creating a name, and then immediately renaming. So, DesignerHost's CreateComponent will set
	// _newComponentName to the newly created name before creating the component.
	if (!string.IsNullOrEmpty(_newComponentName))
	{
	name = _newComponentName;
	_newComponentName = null;
	}
	INameCreationService? nameCreate = GetService(typeof(INameCreationService)) as INameCreationService;
	// Fabricate a name if one wasn't provided. We try to use the name creation service, but if it is not available
	// we will just use an empty string.
	if (name is null)

.

[JeremyKuhne]

Thanks @LeafShi1, if you want to change the condition on line 386 to be null or empty that would be great. :)

[Tanya-Solyanik]

I think that the correct fix is to change nullability in Container.CreateSite method, but we don't own it. Null is a valid input and it implies that container (designer host) should try to create a new name for the component. Empty string means that component does not have a name, and we should not attempt to create one. I don't remember what scenario this is.
This issue could be fixed by reverting the change that introdcued it.

[JeremyKuhne]

@Tanya-Solyanik What is the bad in creating a name for string.Empty? Can you provide any context on why not having a name is important?

[Tanya-Solyanik]

@Tanya-Solyanik What is the bad in creating a name for string.Empty?

@JeremyKuhne - potentially we will be attempting to create a name multiple times in the case when the naming service is not available. Not all components are named, some inner ones are not. This is a protected virtual method, we don't know what assumption the overriders make when they call the base method, but it's reasonable to assume that anyone who implements DesignerHost or Container assumes the same behavior as in the InProc designer. We don't have sufficient test base to validate all design time scenarios in this repo, we will not see immediate failures, but this change has a potential to prevent migration.

Can you provide any context on why not having a name is important?

No, I don't remember the specific scenario

[MelonWang1]

Verified this issue on winforms repo from main branch, it was fixed, now all tabPages show the controls.

11095.mp4