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@lina As a MacPorts maintainer and a FreeBSD sysadmin, I run into two problems with rust:
1) It is unwieldy to maintain rust and cargo, so both are often out of date on MacPorts.
2) On FreeBSD some random library (e.g. librsvg) that depends on rust/cargo causes Poudriere to rebuild rust every time some build dependency is updated. This usually takes several hours on my build machine. For this reason, and that it adds a lot of extra packages, MacPorts still doesn't use librsvg built using rust.