I don't think vendoring code is inherently bad, per se, but I do find it more emotionally satisfying to file issues and feature requests upstream and work with other developers on making things better for everyone.
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RE: https://wandering.shop/@xgranade/115855950109692559
It's fascinating that we're in a world where vendoring code and "making things better for everyone" are apparently contradictory acts.
(Tooling!)