There is NOT at least X GiB RAM

Recently while compiling latest Rust version I came across a problem on my very old Macbook, where emerge complained about not enough RAM to compile Rust.

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...
pre_build_checks() {
    CHECKREQS_DISK_BUILD="7G"
    CHECKREQS_MEMORY="4G"
...
    check-reqs_pkg_setup
}

check-reqs_pkg_setup from check-reqs.eclass takes care of the check and looks if ${I_KNOW_WHAT_I_AM_DOING} is set, if it is then the checks will succeed even if the space constraints are not met.

tl;dr Solution

Some packages require X ammount of disk space and RAM to build and Rust is one of them. Add enough Swap space and run emerge again with ${I_KNOW_WHAT_I_AM_DOING} set.

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# fallocate -l 8G /mnt/swap.swap
# mkswap /mnt/swap.swap
# swapon /mnt/swap.swap
# chmod 600 /mnt/swap.swap
# I_KNOW_WHAT_I_AM_DOING=1 emerge -1 rust