Thanks for the precision, it makes sense!This is, unfortunately, not the case. I added this specific recommendation to the Rust package guidelines because there have been quite a few cases where the nightly toolchain will fail to build packages that depend on the stable one. The guideline is *only* applicable to local host builds and irrelevant in a chroot build, so when migrating things to [community] it can and should be dropped, but for the AUR it does help make more packages buildable for more people. It also helps given them useful errors when they have only non-stable toolchains enabled by default. It is actually quite common for people to default to something other than the stable toolchain because quite a number of upstream project give people instructions for how to reset the defaults to nightly in order to build themselves from source, but rarely also include instructions for how to do it while keeping stable as default.
Since the related packages I currently maintain in the AUR does not depend on a specific toolchain to be built (as seen with upstream), is it safe for me to drop the toolchain definition in the PKGBUILD or you're suggesting putting it back to "stable" anyway?
Regarding malachite:You export 'RUSTUP_TOOLCHAIN=stable'. I think you should just let it use the default toolchain because the stable toolchain might not be installed and using a newer toolchain shouldn't break the build. (In general, I would expect the stable toolchain to be the default, to match the rust package.)
-- Regards, Robin Candau