Function parse_kleene_op

fn parse_kleene_op<'a>(
    input: &mut impl Iterator<Item = &'a TokenTree>,
    span: Span,
) -> Result<Result<(KleeneOp, Span), Token>, Span>

Parse the next token tree of the input looking for a KleeneOp. Returns

• Ok(Ok((op, span))) if the next token tree is a KleeneOp
• Ok(Err(tok, span)) if the next token tree is a token but not a KleeneOp
• Err(span) if the next token tree is not a token