Function parse_python_shebang

src/cli.rs:245–284

https://en.m.wikipedia.org/wiki/Shebang_(Unix)

(reader: &mut impl Read)

// https://en.m.wikipedia.org/wiki/Shebang_(Unix)
fn parse_python_shebang(reader: &mut impl Read) -> Option<RequestedVersion> {
    let mut shebang_buffer = [0; 2];
    log::info!("Looking for a Python-related shebang");
    if reader.read(&mut shebang_buffer).is_err() || shebang_buffer != [0x23, 0x21] {
        // Doesn't start w/ `#!` in ASCII/UTF-8.
        log::debug!("No '#!' at the start of the first line of the file");
        return None;
    }

    let mut buffered_reader = BufReader::new(reader);
    let mut first_line = String::new();

    if buffered_reader.read_line(&mut first_line).is_err() {
        log::debug!("Can't read first line of the file");
        return None;
    };

    // Whitespace between `#!` and the path is allowed.
    let line = first_line.trim();

    let accepted_paths = [
        "python",
        "/usr/bin/python",
        "/usr/local/bin/python",
        "/usr/bin/env python",
    ];

    for acceptable_path in &accepted_paths {
        if !line.starts_with(acceptable_path) {
            continue;
        }

        log::debug!("Found shebang: {acceptable_path}");
        let version = line[acceptable_path.len()..].to_string();
        log::debug!("Found version: {version}");
        return RequestedVersion::from_str(&version).ok();
    }

    None
}

fn find_executable(version: RequestedVersion, args: &[String]) -> crate::Result<PathBuf> {
    let mut requested_version = version;