cannot install rust-src component for nightly-2020-07-21

[ehuss]

Not sure if this is due to the packaging, or if it is a rustup bug, but I cannot install the rust-src component for the latest nightly-2020-07-21.

> rustup toolchain install nightly-2020-07-21 --profile=minimal -c rust-src
info: syncing channel updates for 'nightly-2020-07-21-x86_64-unknown-linux-gnu'
info: latest update on 2020-07-21, rust version 1.47.0-nightly (f9a308636 2020-07-20)
info: downloading component 'cargo'
  5.2 MiB /   5.2 MiB (100 %)   1.7 MiB/s in  3s ETA:  0s
info: downloading component 'rust-src'
  2.1 MiB /   2.1 MiB (100 %)   1.7 MiB/s in  1s ETA:  0s
info: downloading component 'rust-std'
 19.7 MiB /  19.7 MiB (100 %)   1.5 MiB/s in 13s ETA:  0s
info: downloading component 'rustc'
 51.0 MiB /  51.0 MiB (100 %) 896.0 KiB/s in 59s ETA:  0s
info: installing component 'cargo'
info: Defaulting to 500.0 MiB unpack ram
info: installing component 'rust-src'
info: rolling back changes
error: tar entry kind 'Symlink' is not supported

Fails on macOS and Linux with the same error.

I'll try to dig in some tonight, but figured I'd file this to see if anyone has any ideas. If I had to take a wild guess, I would say it may be related to #74520.

rustup 1.22.1 (b01adbbc3 2020-07-08)

[tesuji]

Rustup doesn't support symlink entry in tar file: https://github.com/rust-lang/rustup/blob/ac1a8c415b5c2886275ca92a3a8f3a4cd0587711/src/dist/component/package.rs#L397-L407
There are two symlinks in backtrace:

% fd --type l . src/backtrace 
src/backtrace/crates/backtrace-sys/LICENSE-APACHE
src/backtrace/crates/backtrace-sys/LICENSE-MIT

[Mark-Simulacrum]

cc @alexcrichton

[Mark-Simulacrum]

Once this is fixed we should look into checking that we're not creating these tarballs on the dist builders (rather than failing "late" when rustup fails to install)

[matthiaskrgr]

Getting the same with rust-toolchain-installer-master (this might break ci of clippy/rustfmt/rls etc):
error: unsupported tar entry: Symlink

[ehuss]

Posted a fix at #74578.