rustup update fails with no errors reported.

Hi,

When rustup update fails in No space left on device, no errors reported.

nunuqn@nunuqn-house:~$ rustup update
info: syncing channel updates for 'stable-x86_64-unknown-linux-gnu'
info: latest update on 2018-07-10, rust version 1.27.1 (5f2b325f6 2018-07-07)
info: downloading component 'rustc'
info: downloading component 'rust-std'
info: downloading component 'cargo'
info: downloading component 'rust-docs'
info: removing component 'rustc'
info: removing component 'rust-std'
info: removing component 'cargo'
info: removing component 'rust-docs'
info: installing component 'rustc'
info: installing component 'rust-std'
info: installing component 'cargo'
info: installing component 'rust-docs'
info: rolling back changes
error: could not rename component file from '/home/nunuqn/.rustup/tmp/6jfxmhgh0gi8h6fo_dir/bk' to '/home/nunuqn/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/share'
error: could not rename component file from '/home/nunuqn/.rustup/tmp/46hvvd5vcyvrbx4f_dir/bk' to '/home/nunuqn/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/share/doc'
error: could not rename component file from '/home/nunuqn/.rustup/tmp/hwlervja8wvuc3me_dir/bk' to '/home/nunuqn/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/share/doc/rust'
error: could not rename component file from '/home/nunuqn/.rustup/tmp/ew2x1wp1vwm60i_i_dir/bk' to '/home/nunuqn/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/share/doc/rust/html'
error: could not rename component file from '/home/nunuqn/.rustup/tmp/edxe1acnvqjz4tu1_dir/bk' to '/home/nunuqn/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/etc'
error: could not rename component file from '/home/nunuqn/.rustup/tmp/shbes8wlyb1azdlq_dir/bk' to '/home/nunuqn/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/share/zsh'
error: could not rename component file from '/home/nunuqn/.rustup/tmp/lufm4mjte11qmxyl_dir/bk' to '/home/nunuqn/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/share/man'
error: could not rename component file from '/home/nunuqn/.rustup/tmp/rikwiro3ji5i94ab_dir/bk' to '/home/nunuqn/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu'
error: could not copy directory from '/home/nunuqn/.rustup/tmp/_t5jzfij5n_u_u1b_dir/rust-docs/share/doc/rust/html' to '/home/nunuqn/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/share/doc/rust/html'
info: checking for self-updates

  stable-x86_64-unknown-linux-gnu update failed - rustc 1.27.0 (3eda71b00 2018-06-19)

Thank you.

Start by reproducing the failure through rustup update with insufficient disk space and trace the rollback and component-installation paths shown by the error output. Done means the update reports the underlying no-space failure clearly instead of only reporting rename or copy errors.