Function parse_select_distinct_option

crates/gitql-parser/src/parser.rs:643–723

(
    context: &mut ParserContext,
    tokens: &[Token],
    position: &mut usize,
)

}

fn parse_select_distinct_option(
    context: &mut ParserContext,
    tokens: &[Token],
    position: &mut usize,
) -> Result<Distinct, Box<Diagnostic>> {
    if is_current_token(tokens, position, TokenKind::Distinct) {
        // Consume `DISTINCT` keyword
        *position += 1;

        if is_current_token(tokens, position, TokenKind::On) {
            // Consume `ON` keyword
            *position += 1;

            if !is_current_token(tokens, position, TokenKind::LeftParen) {
                return Err(Diagnostic::error("Expect `(` after `DISTINCT ON`")
                    .add_help("Try to add `(` after ON and before fields")
                    .with_location(calculate_safe_location(tokens, *position))
                    .as_boxed());
            }

            // Consume `(` Left Parenthesis
            *position += 1;

            let mut distinct_fields: Vec<String> = vec![];
            while !is_current_token(tokens, position, TokenKind::RightParen) {
                let field_token = &tokens[*position];
                let literal = &field_token.to_string();
                let location = field_token.location;

                distinct_fields.push(literal.to_string());

                context.hidden_selections.push(literal.to_string());
                context.projection_names.push(literal.to_string());
                context.projection_locations.push(location);

                // Consume field name
                *position += 1;

                if is_current_token(tokens, position, TokenKind::Comma) {
                    // Consume `,`
                    *position += 1;
                } else {
                    break;
                }
            }

            // Consume `)` Right Parenthesis
            consume_token_or_error(
                tokens,
                position,
                TokenKind::RightParen,
                "Expect `)` after `DISTINCT ON fields`",
            )?;

            // Prevent passing empty fields
            if distinct_fields.is_empty() {
                return Err(Diagnostic::error(
                    "DISTINCT ON(...) must be used with one of more column",