Mixing @code blocks and partial code-behind classes in a Razor component?

[svick]

The documentation says this about partial code-behind classes in Razor components of a Blazor app:

Components are generated as C# partial classes and are authored using either of the following approaches:

• A single file contains C# code defined in one or more @code blocks, HTML markup, and Razor markup. Blazor project templates define their components using this single-file approach.
• HTML and Razor markup are placed in a Razor file (.razor). C# code is placed in a code-behind file defined as a partial class (.cs).

My question is: can I mix these two approaches in the same component? For example, using the Counter example code, is the following supported?

Counter.razor:

@page "/counter"

<PageTitle>Counter</PageTitle>

<h1>Counter</h1>

<p role="status">Current count: @currentCount</p>

<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>

@code {
    private int currentCount = 0;
}

Counter.cs:

namespace BlazorApp.Pages;

partial class Counter
{
    private void IncrementCount()
    {
        currentCount++;
    }
}

The confusing thing is that this produces an error in VS (CS0103 The name 'currentCount' does not exist in the current context), but then compiles and works fine. This seems to happen, because at design-time, the Microsoft.CodeAnalysis.Razor.Compiler source generator does not generate any code.

If this is not currently supported, should it be?

[svick]

Note that if you have code like this:

@code {
    private int currentCount = 0;
}

@code {
    private void IncrementCount()
    {
        currentCount++;
    }
}

Then applying the Extract code block to code behind refactoring ends up with code like the one above.