I'm developing some components which have lots of common code. I removed code duplication by created abstract base classes which can be inherited in Blazor code behind files. It works fine with non generic components. Code looks like this:

Abstract base class in MyComponentBase.cs:

public abstract class MyComponentBase : ComponentBase
{ ... }

Razor component Code behind file Component1.razor.cs:

public partial class Component1 : MyComponentBase
{ ... }

Razor component file Component1.razor:

@inherits MyComponentBase

However there is a build error with generic @typeparam components. But both class (generated and codebehind) has the same generic base types:

Severity	Code	Description	Project	File	Line	Suppression State
Error	CS0263	Partial declarations of 'TypeaheadInput<TItem>' must not specify different base classes	Blazor.Components.Typeahead	D:\Projects\GitHub\blazor-components\src\Blazor.Components.Typeahead\obj\Debug\net5.0\RazorDeclaration\TypeaheadInput.razor.g.cs	78	Active

Generic code is very similar to the above code:
Abstract generic base class in MyComponentBase.cs :

public abstract class MyComponentBase<TItem>  : ComponentBase
{ ... }

Razor component Code behind file Component1.razor.cs:

public partial class Component1<TItem> : MyComponentBase<TItem>
{ ... }

Razor component file Component1.razor`:

@typeparam TItem
@inherits MyComponentBase<TItem>