Preserving original token location throughout tokenization phase

[declard]

I've split out the lexer phase to avoid dealing with whitespaces and comments at the grammar level, so now there is a Pidgin parser for String->[Token] and a Pidgin parser for [Token]->AST.

How do I wire the original token locations correctly?

So far I found the SourcePosDelta/SourcePos types with CurrentSourcePosDelta/CurrentPos parsers, and the WithPosCalculator ext method. My hope was that I could plug SourcePosDelta in it using WithPosCalculator(token => token.Position), but the implementation treats it as the delta between the tokens (something like a token length, but not quite), not the delta from the beginning of the stream/enumerable/whatever-the-source-is.

Is my only option to compute token "lengths"?

If I make a PR that adds WithPosProvider ext method and

if (_sourcePosProvider is not null)
{
    var current = (int)(location - _bufferStartLocation);
    return _sourcePosProvider(_span[current]);
}

may I hope that it's accepted?