nushell/crates/nu-parser/src/deparse.rs

fn string_should_be_quoted(input: &str) -> bool {
    input.starts_with('$')
        || input
            .chars()
            .any(|c| c == ' ' || c == '(' || c == '\'' || c == '`' || c == '"' || c == '\\')
}

pub fn escape_quote_string(input: &str) -> String {
    let mut output = String::with_capacity(input.len() + 2);
    output.push('"');

    for c in input.chars() {
        if c == '"' || c == '\\' {
            output.push('\\');
        }
        output.push(c);
    }

    output.push('"');
    output
}

// Escape rules:
// input argument is not a flag, does not start with $ and doesn't contain special characters, it is passed as it is (foo -> foo)
// input argument is not a flag and either starts with $ or contains special characters, quotes are added, " and \ are escaped (two \words -> "two \\words")
// input argument is a flag without =, it's passed as it is (--foo -> --foo)
// input argument is a flag with =, the first two points apply to the value (--foo=bar -> --foo=bar; --foo=bar' -> --foo="bar'")
//
// special characters are white space, (, ', `, ",and \
pub fn escape_for_script_arg(input: &str) -> String {
    // handle for flag, maybe we need to escape the value.
    if input.starts_with("--") {
        if let Some((arg_name, arg_val)) = input.split_once('=') {
            // only want to escape arg_val.
            let arg_val = if string_should_be_quoted(arg_val) {
                escape_quote_string(arg_val)
            } else {
                arg_val.into()
            };

            return format!("{arg_name}={arg_val}");
        } else {
            return input.into();
        }
    }
    if string_should_be_quoted(input) {
        escape_quote_string(input)
    } else {
        input.into()
    }
}

#[cfg(test)]
mod test {
    use super::escape_for_script_arg;

    #[test]
    fn test_not_extra_quote() {
        // check for input arg like this:
        // nu b.nu word 8
        assert_eq!(escape_for_script_arg("word"), "word".to_string());
        assert_eq!(escape_for_script_arg("8"), "8".to_string());
    }

    #[test]
    fn test_quote_special() {
        // check for input arg like this:
        // nu b.nu "two words" $nake "`123"
        assert_eq!(
            escape_for_script_arg("two words"),
            r#""two words""#.to_string()
        );
        assert_eq!(escape_for_script_arg("$nake"), r#""$nake""#.to_string());
        assert_eq!(escape_for_script_arg("`123"), r#""`123""#.to_string());
    }

    #[test]
    fn test_arg_with_flag() {
        // check for input arg like this:
        // nu b.nu --linux --version=v5.2
        assert_eq!(escape_for_script_arg("--linux"), "--linux".to_string());
        assert_eq!(
            escape_for_script_arg("--version=v5.2"),
            "--version=v5.2".to_string()
        );

        // check for input arg like this:
        // nu b.nu linux --version v5.2
        assert_eq!(escape_for_script_arg("--version"), "--version".to_string());
        assert_eq!(escape_for_script_arg("v5.2"), "v5.2".to_string());
    }

    #[test]
    fn test_flag_arg_with_values_contains_special() {
        // check for input arg like this:
        // nu b.nu test_ver --version='xx yy' --separator="`"
        assert_eq!(
            escape_for_script_arg("--version='xx yy'"),
            r#"--version="'xx yy'""#.to_string()
        );
        assert_eq!(
            escape_for_script_arg("--separator=`"),
            r#"--separator="`""#.to_string()
        );
    }

    #[test]
    fn test_escape() {
        // check for input arg like this:
        // nu b.nu \ --arg='"'
        assert_eq!(escape_for_script_arg(r"\"), r#""\\""#.to_string());
        assert_eq!(
            escape_for_script_arg(r#"--arg=""#),
            r#"--arg="\"""#.to_string()
        );
    }
}