Non-zero status codes should better differentiate why (at which stage) the command failed

[jchlapinski]

At the moment, cargo only seem to support three values for status code (gathered from https://github.com/rust-lang/cargo/tree/master/tests):

• 0 - success
• 1 - returned when cargo verify-project is run with incorrect --manifest-path
• 101 - failure

TL;DR:
I would like for cargo to return different non-zero status codes for at least:

• compilation errors
• test failures

Optionally:

• invalid arguments, syntax errors

Reasoning:
My problem is that I need a fix for this issue: kennytm/cargo-kcov#16, where cargo kcov should generate coverage report regardless of whether the tests failed or not. This issue would be much simpler to fix if cargo returned different status code for failures during compilation stage (in which case cargo kcov needs to fail as well) and different status code if the tests failed (in which case it might continue with preparing coverage report).

I can prepare PR for cargo myself, but I would like to know if this would be acceptable change for cargo beforehand.

Regards

[alexcrichton]

Seems plausible to me!

[epage]

Personally, I think I'd prefer for us to focus on json messages for our errors as that would be a lot more specific and more fine grained than we could get with error codes. Unsure if that makes this worth closing or not.

If someone were to move this forward, they'd need to figure out

• What operations deserve a dedicated error code (the biggest risk being that an operation with a more specific error code can't be split up further)
• How we can avoid holes in this "API"
• How we avoid breaking compatibility on this "API"

[weihanglo]

I understand that it's pretty convenient to just parse the exit code then go. Another use case is a exit code for retryable errors.

However, as previously stated out, JSON or other machine-readable format could be better for programming use cases. We do need to figure out questions above to move on. Currently it doesn't seem a high priority.