Regarding the perf concern, why would customResolver be slower than JS alias plugin? customResolver function will be only called if the id matches the alias, while the resolveId hook of the JS alias plugin will be called for every id resolution (unless Vite wraps it with withFilter). For that reason, I guess customResolver has less overhead.

Regarding the perf concern, why would customResolver be slower than JS alias plugin? customResolver function will be only called if the id matches the alias, while the resolveId hook of the JS alias plugin will be called for every id resolution (unless Vite wraps it with withFilter). For that reason, I guess customResolver has less overhead.

Yes, the performance difference may not be significant. I actually tried implementing it a few days ago. The main challenge right now is that Rolldown wraps all plugin hooks with a JS-side context. There's currently no good solution for standalone plugins — we might need to implement something like an applyToEnvironment function to handle this.