Function parse_list_inner

src/repr/src/strconv.rs:1076–1151

`parse_list_inner`'s separation from `parse_list` simplifies error handling by allowing subprocedures to return `String` errors.

(
    s: &'a str,
    is_element_type_list: bool,
    mut make_null: impl FnMut() -> T,
    mut gen_elem: impl FnMut(Cow<'a, str>) -> Result<T, E>,
)

// `parse_list_inner`'s separation from `parse_list` simplifies error handling
// by allowing subprocedures to return `String` errors.
fn parse_list_inner<'a, T, E>(
    s: &'a str,
    is_element_type_list: bool,
    mut make_null: impl FnMut() -> T,
    mut gen_elem: impl FnMut(Cow<'a, str>) -> Result<T, E>,
) -> Result<Vec<T>, String>
where
    E: ToString,
{
    let mut elems = vec![];
    let buf = &mut LexBuf::new(s);

    // Consume opening paren.
    if !buf.consume('{') {
        bail!(
            "expected '{{', found {}",
            match buf.next() {
                Some(c) => format!("{}", c),
                None => "empty string".to_string(),
            }
        )
    }

    // Simplifies calls to `gen_elem` by handling errors
    let mut generated = |elem| gen_elem(elem).map_err(|e| e.to_string());
    let is_special_char = |c| matches!(c, '{' | '}' | ',' | '\\' | '"');
    let is_end_of_literal = |c| matches!(c, ',' | '}');

    // Consume elements.
    loop {
        buf.take_while(|ch| ch.is_ascii_whitespace());
        // Check for terminals.
        match buf.next() {
            Some('}') => {
                break;
            }
            _ if elems.len() == 0 => {
                buf.prev();
            }
            Some(',') => {}
            Some(c) => bail!("expected ',' or '}}', got '{}'", c),
            None => bail!("unexpected end of input"),
        }

        buf.take_while(|ch| ch.is_ascii_whitespace());
        // Get elements.
        let elem = match buf.peek() {
            Some('"') => generated(lex_quoted_element(buf)?)?,
            Some('{') => {
                if !is_element_type_list {
                    bail!(
                        "unescaped '{{' at beginning of element; perhaps you \
                        want a nested list, e.g. '{{a}}'::text list list"
                    )
                }
                generated(lex_embedded_element(buf)?)?
            }
            Some(_) => match lex_unquoted_element(buf, is_special_char, is_end_of_literal)? {