git clone https://gitlab.com/veloren/veloren-docker-ci/
cd veloren-docker-ci
cd base
# modify Dockerfile and change the RUST_TOOLCHAIN argument in line 3 to `nightly-2020-06-10` 
#   or similar, it also breaks with 06-05. 06-10 is only taken because of 
#   https://rust-lang.github.io/rustup-components-history/
nano Dockerfile
#Wait for BASE IMAGE TO BUILD
time docker build -t registry.gitlab.com/veloren/veloren-docker-ci:base --no-cache .;
# It will build just fine. It just generate a docker image to build veloren and it's macos cross compiltion
# Now we will see that the compilation will fail, start the container
docker run -it <id here, some hex number> bash
#inside the docker container setup the project:
export RUST_TOOLCHAIN=nightly-2020-06-10;
export PROJECTNAME=veloren;
cd /dockercache; \
    mkdir /dockercache/cache-all; \
    mkdir /dockercache/cache-release-linux; \
    mkdir /dockercache/cache-release-windows; \
    mkdir /dockercache/cache-release-macos; \
    mkdir /dockercache/cache-tarpaulin; \
    git lfs clone "https://gitlab.com/veloren/${PROJECTNAME}.git"; \
    cd "/dockercache/${PROJECTNAME}"; \
    git lfs install; \
    git lfs fetch --recent; \
    git checkout master; \
    git lfs pull; \
    sleep 10; \
    echo ${RUST_TOOLCHAIN} > ./rust-toolchain; \
    . /root/.cargo/env; \

    ln -s /dockercache/cache-release-macos /dockercache/veloren/target; \
    VELOREN_ASSETS=assets PATH="/dockercache/osxcross/target/bin:$PATH" COREAUDIO_SDK_PATH=/dockercache/osxcross/target/SDK/MacOSX10.13.sdk CC=o64-clang CXX=o64-clang++ cargo build --target=x86_64-apple-darwin --release; \
# the last command will fail with the error above.
# IF you would try this with old `2020-04-17` toolchain it wouldn't fail.

root@ddc242b44794:/dockercache/veloren# rustc --version --verbose
rustc 1.46.0-nightly (feb3536eb 2020-06-09)
binary: rustc
commit-hash: feb3536eba10c2e4585d066629598f03d5ddc7c6
commit-date: 2020-06-09
host: x86_64-unknown-linux-gnu
release: 1.46.0-nightly
LLVM version: 10.0