take_until equivalent combinator

[rushmorem]

What's synom's equivalent combinator for take_until, if any? If none, how can it be achieved? I want a way to grab everything in a token stream until I reach a comma.

[rushmorem]

Here is what I have so far:-

impl Synom for ToComma {
    fn parse(mut rest: Cursor) -> PResult<Self> {
        let mut tokens = Vec::new();
        while let Some((tree, cursor)) = rest.token_tree() {
            rest = cursor;
            if let TokenTree::Punct(p) = tree.clone() {
                if p.as_char() == ',' {
                    break;
                }
            }
            tokens.push(tree);
        }
        let stream = TokenStream::from_iter(tokens);
        Ok((ToComma(stream), rest))
    }
    
    fn description() -> Option<&'static str> {
        Some("token stream to comma")
    }
}

However, for any input that has more tokens after a comma, this gives "failed to parse token stream to comma: failed to parse all tokens". Where am I going wrong?

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EDIT: Never mind. This parser is actually working as expected. The final parser used in tests has to consume all tokens, otherwise it will be seen as a failure.

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Now I simply need to know if there is already a way to do this in synom besides manually implementing the trait like this.

[rushmorem]

Here is the final version (in case someone is interested):-

impl Synom for ToComma {
    fn parse(mut rest: Cursor) -> PResult<Self> {
        let mut tokens = Vec::new();
        while let Some((tree, cursor)) = rest.token_tree() {
            if let TokenTree::Punct(p) = tree.clone() {
                if p.as_char() == ',' {
                    if !tokens.is_empty() {
                        break;
                    }
                }
            }
            rest = cursor;
            tokens.push(tree);
        }
        let stream = TokenStream::from_iter(tokens);
        Ok((ToComma(stream), rest))
    }
    
    fn description() -> Option<&'static str> {
        Some("token stream to comma")
    }
}