nickel-lang-parser 0.2.0

use std::path::{Path, PathBuf};

fn main() {
    let checked_in_grammar_path =
        Path::new(&concat!(env!("CARGO_MANIFEST_DIR"), "/src/grammar.rs"));

    let out_dir = PathBuf::from(std::env::var_os("OUT_DIR").expect("missing OUT_DIR variable"));
    std::fs::create_dir_all(&out_dir).expect("failed to create $OUT_DIR");
    // Running lalrpop can be expensive. When building from git, we generate the parser
    // in this build script, but when publishing the crate we add the generated
    // parser to the published crate at `src/grammar.rs`.
    //
    // In order to have this build script work for both the published crate and the git
    // version, we try to copy `src/grammar.rs` into the same location in $OUT_DIR
    // that lalrpop would generate the grammar. If that copy fails because `src/grammar.rs`
    // doesn't exist, we're probably building from git and so we generate the grammar.
    match std::fs::copy(checked_in_grammar_path, out_dir.join("grammar.rs")) {
        Ok(_) => {
            eprintln!("Found a pre-generated LALRPOP grammar, copying it over");
        }
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
            eprintln!("Generating a fresh LALRPOP grammar");
            lalrpop::Configuration::new()
                .use_cargo_dir_conventions()
                .process_file("src/grammar.lalrpop")
                .unwrap();
        }
        Err(e) => panic!("{e}"),
    }
    println!("cargo:rerun-if-changed=src/grammar.lalrpop");
}