The release team is hoping to reduce the size of std installs/tarballs for most users, but the last time we tried to enable this we ran into some bugs in the implementation. We'd like to ask users to test via this command:
RUSTUP_DIST_SERVER=https://dev-static.rust-lang.org rustup toolchain install nightly-2019-10-16 (only that specific nightly will work) and report back on this thread if you run into any problems. We're not quite sure what might break so the "expected" testing is hard to define, but just using that nightly in the daily workflow for a single 'build' is likely to expose any bugs.
Testing can likely look something like
cargo +nightly-2019-10-16 ... or
rustup default nightly-2019-10-16 (can be reverted with e.g.
rustup default stable).