feat(variant-group): support left-side-group

[Simon-He95]

close: #2869

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[antfu]

Thanks for taking time working on it - but I am not sure if it's worth it to support this in tradeoff of Complexity, performance, as well as more surfaces to conflicts/false-positive with other syntaxes in the user code.

[antfu]

Oh, btw, the reason it's called variant group is that it applies to variants.

I still feel this is too risky for a little gain. In the linked issue, I guess it's probably better to improve the DX via shortcuts or variants.

[Simon-He95]

Oh, btw, the reason it's called variant group is that it applies to variants.

I still feel this is too risky for a little gain. In the linked issue, I guess it's probably better to improve the DX via shortcuts or variants.

It is indeed very risky. I did not consider very complex scenarios, such as c2:(d1 d2):d3:a:(a b)
If we provide a base version, such as only processing (?:\s|^)\([\w\s-]+\)[:-]([\w-]+|\[[^\]]+\]), we point at (first second):xx and (first second):[] temporary

There will be better ways to support more complex situations in the future.