Function to_out_dir 

pub fn to_out_dir(path: impl AsRef<Path>) -> Result<PathBuf, String>

Generates a form into OUT_DIR and tells Cargo to watch it.

The whole of a build.rs:

fn main() {
    denise_forms::codegen::to_out_dir("forms/settings.dform").unwrap();
}

The module lands at $OUT_DIR/<stem>.rs and the struct is named after the stem: settings.dform gives Settings and SettingsMessage.

Errors

Anything generate can say, and anything reading or writing a file can.