Source generator for Unity 2021

[trondtactile]

Unity 2021 supports Source Generators:

• https://docs.microsoft.com/en-us/dotnet/csharp/roslyn-sdk/source-generators-overview
• https://docs.unity3d.com/Manual/roslyn-analyzers.html

Instead of having to manually click "generate", this would just generate the code when compiling, meaning your assets would always be in sync with your generated code.

[Eastrall]

Rosalina uses an AssetProcessor from Unity to detect when a UIDocument has changed to generate the associated binding script. This process is automatic and triggered when the .uxml is saved.
https://github.com/Eastrall/Rosalina/blob/main/Editor/Scripts/RosalinaAssetProcessor.cs#L12

I don't know much about source generators, but if it's a compile-time (or build) action, this will not fit into the code generation process since the binding script should be always synchronized with the UIDocument. This is why I used an AssetProcessor to do so.

Of course, you can "force" the binding script generation through the Rosalina > Generate UI bindings but this is only useful if there is a problem with the AssetProcessor. Not mandatory to use it everytime 😉

[trondtactile]

It's really nice that this is automatic on asset change! Did not notice that.

One upside with Source Generators is that their output is not actual files in the project, but just compiled classes. And when using frameworks with "code behind" generation, the classes are indeed reflected on asset change.

However, as Unity is a special little snowflake, maybe this approach would not work very well, as one does not "build" Unity in order to compile it.

[Eastrall]

Indeed, if it was a "pure" C# project, this would be a nice solution.
Closing this for now, but keeping the idea in the back of my mind. 😉

[blepmlem]

So I took a stab at running Rosalina as a Source Generator, and... it's really working great. There is no real problem in regards to picking up on changes in the Uxml files, since the changes are picked up as soon as you do anything in your IDE (which you'd want to do anyway if you've added/changed a named VisualElement). It's fantastic to have all bindings up to date in your IDE at all times without the extra recompile! I can supply the code when I've cleaned it up a bit.

[Eastrall]

That's great @blepmlem ! Would love to see how you achieve to implement source generators within Unity. Feel free to open a PR and contribute 😄

Reopening the issue for better tracking.

[blepmlem]

My fork is located at https://github.com/blepmlem/Rosalina/tree/source-generator
I've modified it quite a bit for my own purposes, but the general Source Generator work should be pretty universal! (I look for scripts implementing a specific interface, and don't do anything with MonoBehaviours and UIDocuments since I use this tool for both editor and runtime UI 😄)

[blepmlem]

The gist of it is that I implement an ISyntaxReceiver for finding the relevant scripts to create partial classes for, then pass the information to the RosalinaBindingsGenerator, it does its thing as usual, and the output code is added to the compilation process.

[trondtactile]

Wow, that is awesome! I'll certainly try to get this capability into my fork (unless it can be added to this repo somehow).

[Eastrall]

@blepmlem this is a great Proof Of Concept you made here! I am going checkout your code and see how it works, in order to understand properly what's going on within Unity and the source generator.
Aditionnaly, this would solve the "Pathing support" described in issue #13 by @siglocpp