rustup/rustc etc proxy for distro installs

rustup

#!/bin/sh

SYSRUST_DIR=/usr/lib/rust
SYSRUSTUP_DIR=/usr/lib/rustup

exename=$(basename "$0")

have_sysrustup=no
[ -x "$SYSRUSTUP_DIR/rustup" ] && have_sysrustup=yes

have_mrsetup=no
mrhome="$HOME/.multirust"
[ -n "$RUSTUP_HOME" ] && mrhome="$RUSTUP_HOME"
while [ -d "$mrhome" ]; do
    [ -f "$mrhome/settings.toml" ] || break
    [ -d "$mrhome/toolchains" ] || break
    n_toolch=$(find "$mrhome/toolchains" -mindepth 1 -maxdepth 1 \! -type f | wc -l)
    [ $n_toolch -gt 0 ] || break
    have_mrsetup=yes
    break
done

want_sysrust=no
[ -n "$USE_SYSTEM_RUST" ] && want_sysrust=yes

is_rustup=no
[ "$exename" = rustup ] && is_rustup=yes

[ $is_rustup = yes -a $have_mrsetup = no ] && {
    [ "$1" = "init" ] && {
        set -e
        "$SYSRUSTUP_DIR/rustup" toolchain link system "$SYSRUST_DIR"
        exec "$SYSRUSTUP_DIR/rustup" toolchain default system
    }
    echo >&2 "rustup(system): no user configuration found, run \`rustup init' to create one"
    exit 1
}
[ $is_rustup = yes ] && exec "$SYSRUSTUP_DIR/rustup" "$@"

unset nextexe
if [ $want_sysrust = yes -o $have_sysrustup = no -o $have_mrsetup = no ]; then
    nextexe="$SYSRUST_DIR/bin/$exename"
else
    nextexe="$SYSRUSTUP_DIR/$exename"
fi

exec "$nextexe" "$@"