[Bug]: Inconsistend code generation for ObservableAsProperty attribute when using it at a field or partial property

[DarkCloud14]

Describe the bug 🐞

When creating a partial property with ObservableAsProperty attribute in a class which is subclass of ReactiveObject the generated code is different from the code that gets generated when applying the ObservableAsProperty to a field.

Applying the ObservableAsProperty to a field will generate code that gives you a CS8618 warning in the classes custom constructors that the generated helper field must contain a non-null value when exiting constructor.

Applying the ObservableAsProperty to a partial property it will generate code that doesn't give you the CS8618 warning.

Step to reproduce

1. Create a new .NET9 class library project (with Nullable enabled)
2. Install the ReactiveUI and ReactiveUI.SourceGenerators packages
3. Write a simple partial class which is a subclass of ReactiveObject
4. Add a partial get-only property with [ObservableAsProperty] attribute and a field [ObservableAsProperty] attribute
5. Add one or more constructors

public partial class TestClass : ReactiveObject
{
    [ObservableAsProperty]
    private bool _observableTestField;

    public TestClass()
    {
    }

    [ObservableAsProperty]
    public partial bool ObservableTestProperty { get; }
}

6. See that a CS8618 warning is generated for the generated _observableTestFieldHelper field but not for the generated _observableTestPropertyHelper field.

Reproduction repository

https://github.com/DarkCloud14/ReactiveUI_SourceGen_ObservableAsProperty_Issue

Expected behavior

I would expect that in both cases code is generated which would result in a CS8618 warning if the helper field doesn't contain a non-null value when exiting the constructor.

Screenshots 🖼️

No response

IDE

Rider macOS

Operating system

macOS Sequoia 15.3.1

Version

No response

Device

No response

ReactiveUI Version

ReactiveUI 20.1.63, ReactiveUI.SourceGenerators 2.1.1

Additional information ℹ️

No response

[DarkCloud14]

Hmm I just had a look at the generated code and if ObservableAsProperty attribute is used at a field the source generator creates a readonly helper field if ReadOnly parameter isn't set to true.

Using ObservableAsProperty attribute at a partial property will not result in a readonly helper field, even if you set the ReadOnly parameter to true.

Also the GeneratedCode attribute is missing at the helper fields as soon as you set the ReadOnly parameter explicitly to true or false. In case of partial property it is always missing at the helper fields (even without ReadOnly parameter) and at the generated backing fields if ReadOnly parameter is added and set to true/false.

Regarding GeneratedCode attribute I didn't check any other combination, just saw that this is also different...

Should I create another bug report for this?

[glennawatson]

Another bug would be great.

[DarkCloud14]

Ok just created another bug for the ReadOnly issue.

The missing GeneratedCode attribute might not be that important but I may create another bug report for that too if you want.

[github-actions]

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