Pre-generate bindgen file

[Bromeon]

Bindgen not only adds a ton of dependencies that slow down initial compilation, but it is regularly an obstacle for users to get started, because they don't have LLVM installed or correctly configured.

We could generate the bindings Rust file on developer machines and ship it. CI could be used to enforce that bindings are up-to-date.

If it turns out that different platforms have different binding files, conditional compilation is an option. Would add a bit of development of maintenance effort, but probably worth the easier and faster setup process for everyone.

[nikitalita]

you'd need to version them per release version; I've found that even patch number updates can introduce breaking changes (semver not withstanding). This also wouldn't work with custom builds, like Godot versions with Steam integration built in.

[Bromeon]

Yes, there would still need to be an option to generate bindings in godot-ffi, also for CI to verify that the binding is up-to-date.

What I could imagine is something similar to the custom-godot feature in GDNative: by default, we support the latest Godot version out-of-the-box, and allow customization via feature flag (which would pull and run bindgen). We could even verify at build time that the Godot engine version in PATH is the same as the one for which bindgen was run, and throw an error otherwise.

This is a bit a mess during Godot 4 beta, as I'd like to use nightly Godot builds for CI (changing every day), and then every single version is possibly breaking. Maybe a compromise would be to always support latest Godot nightly on master, and issue a warning (but no error) if someone uses an older version. That way, people can decide themselves whether they want to take the risk.

A very involved approach is to maintain a list of all nightly versions since the last time the binding headers changed, and check if Godot in PATH is one of them. This would be quite some effort, and still not work of Godot is newer than godot-rust, or of a version between those that were used for nightly builds.

So many options... 😅 I'm open for input!

[nikitalita]

IMO, it’s not worth the effort to try and support people developing on top of the current master. If they’re doing that, then they likely have LLVM already installed (or know how to do it easily). I’d recommend only keeping the official beta releases as the prebuilt ones and if users have something else, throw an error and tell them they need to use bindgen by compiling with a feature flag or something.

This is a bit a mess during Godot 4 beta, as I'd like to use nightly Godot builds for CI (changing every day), and then every single version is possibly breaking

lord, tell me about it. I developed on top of master for a year and a half, and it was a pain in the ass. What I did was I had the main CI workflow pinned to the last good commit, and I had a separate workflow that ran on a timer that just compiled to see if I had drifted out of sync.

[Bromeon]

I’d recommend only keeping the official beta releases as the prebuilt ones and if users have something else, throw an error and tell them they need to use bindgen by compiling with a feature flag or something.

Yeah, maybe "support latest Beta release out of the box" might be a good policy.

We can still run CI additionally against Godot nightly builds, maybe in a way that allows failing, to learn about potential changes sooner.