Does your rust ebuild depend on llvm installed with -system-llvm? I didn't run into this on my main system because it has llvm installed anyway, but as I created a clean chroot the emerge throws out an error:
* rustc-1.20.0-src.tar.gz SHA256 SHA512 WHIRLPOOL size ;-) ... [ ok ]
* rust-1.19.0-x86_64-unknown-linux-musl.tar.xz SHA256 SHA512 WHIRLPOOL size ;-) ... [ ok ]
* ERROR: dev-lang/rust-1.20.0::smaeul failed (setup phase):
* No LLVM slot <= 4 found installed!
*
* Call stack:
* ebuild.sh, line 115: Called pkg_setup
* rust-1.20.0.ebuild, line 89: Called llvm_pkg_setup
* llvm.eclass, line 162: Called get_llvm_prefix '4'
* llvm.eclass, line 141: Called die
* The specific snippet of code:
* die "No LLVM slot${1:+ <= ${1}} found installed!"
*
* If you need support, post the output of `emerge --info '=dev-lang/rust-1.20.0::smaeul'`,
* the complete build log and the output of `emerge -pqv '=dev-lang/rust-1.20.0::smaeul'`.
* The complete build log is located at '/var/tmp/portage/dev-lang/rust-1.20.0/temp/build.log'.
* The ebuild environment file is located at '/var/tmp/portage/dev-lang/rust-1.20.0/temp/environment'.
* Working directory: '/var/tmp/portage/dev-lang/rust-1.20.0/homedir'
* S: '/var/tmp/portage/dev-lang/rust-1.20.0/work/rustc-1.20.0-src'
So I installed llvm (and GCC 6) via emerge and got rust-1.20.0 up and working on amd64 :) If you need llvm for dev-lang/rust please consider to add it to the dependencies of the ebuild so that it will get pulled in.
Does your rust ebuild depend on llvm installed with -system-llvm? I didn't run into this on my main system because it has llvm installed anyway, but as I created a clean chroot the emerge throws out an error:
Calculating dependencies... done! [ebuild R ~] dev-lang/rust-1.20.0:stable/1.20::smaeul USE="-debug -doc -jemalloc -system-llvm" 0 KiB
So I installed llvm (and GCC 6) via emerge and got rust-1.20.0 up and working on amd64 :) If you need llvm for dev-lang/rust please consider to add it to the dependencies of the ebuild so that it will get pulled in.