latest cargo update broke cargo install command in my ci

[matthiaskrgr]

Hi, it looks like the latest cargo submodule bump in the rustc repo
rust-lang/rust@f23db01
broke my cargo-cache ci.

I was running the command cargo install --force --git https://github.com/matthiaskrgr/cargo-cache --no-default-features --features ci-autoclean cargo-cache
which worked prior to the submodule update and now fails with

    Updating git repository `https://github.com/matthiaskrgr/cargo-cache`
  Installing cargo-cache v0.4.2 (https://github.com/matthiaskrgr/cargo-cache#379c40c2)
    Updating crates.io index
error: failed to compile `cargo-cache v0.4.2 (https://github.com/matthiaskrgr/cargo-cache#379c40c2)`, intermediate artifacts can be found at `/tmp/cargo-installDT5PxT`

Caused by:
  failed to determine package fingerprint for build script for cargo-cache v0.4.2 (/home/runner/.cargo/git/checkouts/cargo-cache-16826c8e13331adc/379c40c)

Caused by:
  failed to determine the most recently modified file in /home/runner/.cargo/git/checkouts/cargo-cache-16826c8e13331adc/379c40c

Caused by:
  failed to determine list of files in /home/runner/.cargo/git/checkouts/cargo-cache-16826c8e13331adc/379c40c

Caused by:
  expected git repo /usr/share/rust/.cargo/git/checkouts/cargo-cache-16826c8e13331adc/379c40c/.git/ to be parent of package /home/runner/.cargo/git/checkouts/cargo-cache-16826c8e13331adc/379c40c

Caused by:
  prefix not found
##[error]Process completed with exit code 101.

I have never seen this error before and was not able to reproduce locally yet with rustc 1.45.0-nightly (fa51f810e 2020-04-29 / cargo 1.45.0-nightly (90931d9b3 2020-04-28)

Do you have any ideas what could be happening here?

[ehuss]

Thanks for the report. It looks like if CARGO_HOME is a symlink causes the problem. Part of the fallout from #8095. I'll take a look.