[Bug]: Legacy MSBuild projects sometimes fail to build

[timothylcooke]

Describe the bug 🐞

By adding a Window with a namespace definition in an SDK-style .NET Framework WPF application, we can essentially prevent SourceGenerators from generating code. The IDE makes it look like everything is fine: you can navigate to the generated source file for properties generated by the [ReactiveUI.SourceGenerators.ReactiveAttribute], but the project fails to compile:

error CS0234: The type or namespace name 'SourceGenerators' does not exist in the namespace 'ReactiveUI' (are you missing an assembly reference?)

Step to reproduce

This project is a minimal reproduction. Initial commit b27e435 builds just fine in both a legacy and sdk-style project. a845b4a adds an xmlns:local definition to XAML. Once that namespace is added, the legacy application no longer compiles (though the SDK-style project continues to compile).

Reproduction repository

https://github.com/timothylcooke/SourceGeneratorIssue

Expected behavior

The project should compile

Screenshots 🖼️

No response

IDE

No response

Operating system

Windows 11 23H2

Version

Visual Studio 17.12.3

Device

No response

ReactiveUI Version

2.0.17

Additional information ℹ️

It's unclear if this is even your bug, or if it's an issue in msbuild.

I have a legacy WPF application deployed with ClickOnce, so I can't switch to an SDK-style project without a whole lot of headache. While ReactiveUI.Fody works fine, I'd like to start using ReactiveUI.SourceGenerators.

Adding local namespaces in XAML is a very common thing in WPF that I can't just avoid doing. The best workaround I have is to move any VM classes to a library.

If you remove all references to ReactiveAttribute to get the project to compile, you can access the type via reflection: var reactiveAttributeTypeViaReflection = GetType().Assembly.GetType("ReactiveUI.SourceGenerators.ReactiveAttribute"); So, it seems like it's an issue with the order of build events: it seems that the generated files are being added after the static files are built, so any references from static files to generated types fail to compile because the types haven't been generated yet.

[timothylcooke]

I just saw in the README that for net481, you're supposed to use Polyfill or PolySharp -- not sure how I missed that before. I added a polysharp branch to the repro where I use PolySharp instead of my own hack. The behavior is unchanged.

Polyfill does not support legacy csproj files.

[glennawatson]

I'm a bit behind on a lot of maintenance stuff in regards to this project and @ChrisPulman is out til christmas.

There can be issues with source generator relying on source generators. I know they moved some of the xaml into a generated based context, not sure if they are using source generators to do.

[glennawatson]

Usually the way I've solved source generator relying on source generator issues is to move into separate projects the source code so only one generator happens at any one time.

[ChrisPulman]

From the looks of things, the ReactiveUI Source Generator is generating the files correctly, therefore my guess is that it is an issue with MS-Build and the way it works with source generators, Fody injects IL modifications after the build is complete hence this will work. The most viable work around may be to use a netstandard2.0 library project for ViewModels and Source Generated elements and then keep the Views and ViewModels separated. I have tested this option and it does work; but I guess it depends on your individual project.

[timothylcooke]

Yeah, @ChrisPulman. That's exactly what I've been doing. Thanks for looking into this. I gather that there's nothing to do here except close this issue and possibly open an issue with msbuild (I'm assuming that's not worth it)?

[timothylcooke]

From the looks of things, the ReactiveUI Source Generator is generating the files correctly

The Source Generator is definitely working. Generated types exist at runtime. It's just that they can only be referenced via reflection. Static references cause build failures. Very strange behavior.

[glennawatson]

Probably try the latest source gen we just published, see if it working, then chase up with msbuild if that fails.

[ChrisPulman]

Version 2.1.8 has been released, there may have been some issues with a version of Visual Studio, if you still feel that there is something wrong with the ReactiveUI Source Generators please reopen this or create a new issue with any updates, thank you.

[timothylcooke]

Many thanks to both of you! Sorry for not getting back to you sooner.

The behavior remains unchanged with ReactiveUI.SourceGenerators 2.1.8 and VS 17.13.0. Presumably it's msbuild's issue, not yours. The workaround of using a library is working just fine, and some day I'll migrate my legacy project and the issue won't even affect me.

[github-actions]

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.