When you setup LALRPOP, you create a build.rs file that looks something like this:

extern crate lalrpop;

fn main() {
    lalrpop::process_root().unwrap();
}

This process_root() call simply applies the default configuration: so it will transform .lalrpop files into .rs files in-place (in your src directory), and it will only do so if the .lalrpop file has actually changed. But you can also use the Configuration struct to get more detailed control.

For example, to force the use of colors in the output (ignoring the TTY settings), you might make your build.rs file look like so:

extern crate lalrpop;

fn main() {
    lalrpop::Configuration::new()
        .always_use_colors()
        .process_current_dir();
}