Improve error message for invalid path dependencies within git dependencies

[NickeZ]

Problem
I add a git dependency on "noise-rust-crypto" which is part of the "noise-rust" repository and cargo doesn't find it.

$ cargo update
    Updating git repository `https://github.com/sopium/noise-rust`
error: failed to load source for a dependency on `noise-rust-crypto`

Caused by:
  Unable to update https://github.com/sopium/noise-rust

Caused by:
  Could not find `Cargo.toml` in `/home/niklas/.cargo/git/checkouts/noise-rust-6131949caf0d2152/dad7f8b/noise`

Steps

1. echo "noise-rust-crypto = {git = "https://github.com/sopium/noise-rust"}" >> Cargo.toml
2. cargo update

Possible Solution(s)

Notes

Output of cargo version:

$ cargo --version
cargo 1.40.0 (bc8e4c8be 2019-11-22)

[ehuss]

It's a poor error message. The issue is that this line references a directory that doesn't exist.

[NickeZ]

Ok so it actually breaks when it fails instead of continue to search. That sounds brittle. I'll make a pr to the repo. Thanks

[ehuss]

Yea, it is supposed to ignore errors like this. It's just an oversight that it doesn't in this particular case (path dependencies require a special code path).

[NickeZ]

I tried to update the issue name to something actionable. Thanks!

[ehuss]

I think this is now resolved by #7784. Bad paths in the git repo are now ignored (unless the package itself is missing).