Method parse

datafusion/spark/src/function/string/format_string.rs:285–359

Parses a printf-style format string into a Formatter with validation. This method implements a comprehensive parser for Java `java.util.Formatter` syntax, processing the format string character by character to identify and validate format specifiers against the provided argument types. # Arguments `fmt` - The format string containing literal text and format specifiers `arg_types` - Array of Dat

(fmt: &'a str, arg_types: &[DataType])

    /// Returns a Formatter containing the parsed elements and the maximum argument
    /// index encountered, enabling efficient argument validation during formatting.
    pub fn parse(fmt: &'a str, arg_types: &[DataType]) -> Result<Self> {
        // find the first %
        let mut res = Vec::new();

        let mut rem = fmt;
        let mut argument_index = 0;

        let mut prev: Option<usize> = None;

        while !rem.is_empty() {
            if let Some((verbatim_prefix, rest)) = rem.split_once('%') {
                if !verbatim_prefix.is_empty() {
                    res.push(FormatElement::Verbatim(verbatim_prefix));
                }
                if let Some(rest) = rest.strip_prefix('%') {
                    res.push(FormatElement::Verbatim("%"));
                    rem = rest;
                    continue;
                }
                if let Some(rest) = rest.strip_prefix('n') {
                    res.push(FormatElement::Verbatim("\n"));
                    rem = rest;
                    continue;
                }
                if let Some(rest) = rest.strip_prefix('<') {
                    // %< means reuse the previous argument
                    let Some(p) = prev else {
                        return exec_err!("No previous argument to reference");
                    };
                    let (spec, rest) =
                        take_conversion_specifier(rest, p, &arg_types[p - 1])?;
                    res.push(FormatElement::Format(spec));
                    rem = rest;
                    continue;
                }

                let (current_argument_index, rest2) = take_numeric_param(rest, false);
                let (current_argument_index, rest) =
                    match (current_argument_index, rest2.starts_with('$')) {
                        (NumericParam::Literal(index), true) => {
                            (index as usize, &rest2[1..])
                        }
                        (NumericParam::FromArgument, true) => {
                            return exec_err!("Invalid numeric parameter");
                        }
                        (_, false) => {
                            argument_index += 1;
                            (argument_index, rest)
                        }
                    };
                if current_argument_index == 0 || current_argument_index > arg_types.len()
                {
                    return exec_err!(
                        "Argument index {} is out of bounds",
                        current_argument_index
                    );
                }