Hint git-fetch-with-cli on git errors

[kornelski]

Our team has struggled with making Cargo git dependencies work in CI, until learning about this setting.

Cargo doesn't have a dedicated system for error hints like rustc, so I've stuffed the hint into the error message.

[alexcrichton]

I'm a bit hesitant to blindly recommend for any and all errors that git-fetch-with-cli is used instead. Would it be possible to catch specifically authentication errors and make that recommendation instead? Additionally could this link to online documentation about this configuration option?

[kornelski]

@alexcrichton I understand your concern. I've tried to narrow it down to specific libgit errors, but in the end it didn't feel like an improvement.

The first problem is that it's not limited to just auth errors. In my case libgit not using our VPN-aware proxy looks like a regular network errors, e.g. DNS error and connection timeouts.

Git errors generally fall into network errors, auth errors, invalid repo state, invalid command. The first two categories would benefit from the hint. The other two are unlikely to happen, because Cargo manages the repo state and commands itself.

Another problem with this is that just getting to the relevant libgit error codes via anyhow's chain takes more code than the rest of the checkout function. I don't know if you'd be OK with such relatively complicated thing for a small check.

[alexcrichton]

Hm so extraction of error codes should be pretty simple, I think it's just calling downcast_ref? (note the outer .chain() isn't necessary there)

I'd personally still prefer to limit this somehow. I think it's ok to be a bit broad, but if there's something like a corrupt db or if a remote branch doesn't exist then you shouldn't get a recommendation to switch git implementations.

[kornelski]

I've expanded it to check libgit's error class

[kornelski]

Tests for my change pass. The failure comes from another test, which seems unrelated:

thread 'rustc_info_cache::rustc_info_cache' panicked at '
Expected: execs
    but: expected not to find:
[..] rustc info cache miss[..]

[alexcrichton]

@bors: r+

Looks great to me, thanks for this! Those test failures should be fixed on master now.

[bors]

📌 Commit 4fd4835 has been approved by alexcrichton

[bors]

⌛ Testing commit 4fd4835 with merge 893db8c...

[bors]

☀️ Test successful - checks-azure
Approved by: alexcrichton
Pushing 893db8c to master...

[ehuss]

This broke on rust-lang/rust CI:

---- git_auth::net_err_suggests_fetch_with_cli stdout ----
running `/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/release/cargo build -v`
running `/checkout/obj/build/x86_64-unknown-linux-gnu/stage2-tools/x86_64-unknown-linux-gnu/release/cargo build -v`
thread 'git_auth::net_err_suggests_fetch_with_cli' panicked at '
Expected: execs
    but: differences:
 16 - |ssh: Could not resolve hostname[..]|
    + |error: cannot run ssh: No such file or directory|

 19 - |Please make sure you have the correct access rights|
    +

 20 - |and the repository exists.|
    +

 21 - |[..]|
    +

I'm a little confused by the error. It almost looks like it is trying to run ssh, but I thought libgit used libssh. This is on an ubuntu 16 docker image. Can you please take a look?

[kornelski]

Ouch. This is a limitation of Cargo's test comparison. The output contains strings that are specific to git and ssh, but the test can't account for varying number of lines :(

I've cut the test down to minimum.