Godot version check + workaround for API generation bug

[Bromeon]

As mentioned in #833, Godot versions < 3.3.1 were subject to a bug that caused non-deterministic crashes during the command:

godot --gdnative-generate-json-api api.json

For users working with affected Godot versions (e.g. 3.2), this makes the feature flag custom-godot annoying to use, since they can't rely on the API generation to succeed -- let alone use it for automation/CI. This PR works around that by retrying the command up to 10 times (magic number). I changed the minimum supported Godot version in our own CI again to 3.2, meaning that if it doesn't work, we have to suffer, too 😬

Additionally, this PR parses the Godot version and emits a meaningful error message if an unsupported version is detected (3.1 or 4.0).

[Bromeon]

Where I was unsure: the whole version logic is in a separate file, to prevent build.rs from growing too much. The problem is, there seems to be no agreed-upon best practice regarding build script separation.

Current approach is this (in build.rs):

#[cfg(feature = "custom-godot")]
mod godot_version {
    include!("src/godot_version.rs");
}

I also tried the following, but my build step got stuck in an endless loop:

#[path = "src/godot_version.rs"]
mod godot_version;

Ideas?

Would also be nice if the tests in godot_version.rs would be run during cargo test. I don't want the version logic to be part of the compiled gdnative-bindings crate, so adding the module in lib.rs is not really an option...

bors try

[bors]

try

Build succeeded!

And happy new year! 🎉

• full-ci

[chitoyuu]

Where I was unsure: the whole version logic is in a separate file, to prevent build.rs from growing too much. The problem is, there seems to be no agreed-upon best practice regarding build script separation.

Perhaps the logic can be put into bindings_generator? It's true that version parsing isn't directly related to code generation, but it is the crate that contains "the rest of build.rs".

[Bromeon]

@chitoyuu Great idea, I moved it to bindings_generator.

I also set up a mass CI test for all 3.x versions: https://github.com/Bromeon/godot-rust/actions/runs/1646049051
This shows two things:

• it rejects versions < 3.2 with a helpful error message
• it works for versions >= 3.2 and < 3.3.1 on first attempt

Godot 4 is not available for download, but I tested it locally, also rejected.

[Bromeon]

bors r+

[bors]

Build failed:

• full-ci

[Bromeon]

bors r+

[bors]

Build succeeded:

• full-ci