Improve error message when unable to initialize git index repo

[nipunn1313]

With this - it'll be more obvious which git repo
couldn't be initialized.

Looks like this

➜  cargo RUST_BACKTRACE=1 target/debug/cargo build
error: failed to get `anyhow` as a dependency of package `cargo v0.57.0 (/Users/nipunn/src/cargo)`

Caused by:
  failed to initialize index git repository (in "/Users/nipunn/.cargo/registry/index/github.com-1ecc6299db9ec823")

Caused by:
  failed to parse config file: invalid configuration key (in /Users/nipunn/.config/git/config:1); class=Config (7)

Does the best we can with #9854 - since I don't think it can actually be fixed.
Fixes #9854

[rust-highfive]

r? @alexcrichton

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[alexcrichton]

@bors: r+

Thanks! I'm a bit uncertain on whether this closes the issue, but I'm ok doing that for now. I think that Cargo relies on enough git things that it wouldn't be great to ignore the errors here and I'm hoping that it's something that's either easily fixable in the gitconfig itself or is something that can be fixed in libgit2.

[bors]

📌 Commit 168fac4 has been approved by alexcrichton

[bors]

⌛ Testing commit 168fac4 with merge d405d73...

[nipunn1313]

The specific gitconfig issue (incorrectly assuming it's malformed) #9853 should be fixed - via a fix to libgit2

However, I don't think #9854 can be fixed - it's asking for cargo to work despite a malformed gitconfig. AFAICT cargo can't initialize the registry in this kind of case and has to fail.

This is my understanding - what do you think?

[alexcrichton]

I think it sort of depends on the error. While giving a better error is certainly better than the status quo I also don't think that this is something that users should be running into regularly. For example I wouldn't want to hide bugs in libgit2 but if users frequently hit the same bug in libgit2 then that helps us prioritize fixing it and/or reporting it upstream.

Basically this shouldn't happen, but there's no way really to predict why it will happen to preemptively cover it up. There may be some situations though where it's reasonable to ignore the global config, but I don't know them off the top of my head, so just having a better error for now I think is fine.

[bors]

☀️ Test successful - checks-actions
Approved by: alexcrichton
Pushing d405d73 to master...