Cargo: Cargo should use progress bar only on terminals that support it

[gnzlbg]

Currently cargo seems to always use a progress bar, but for example the terminal that travis uses does not support it, such that every update to the progress bar creates _a lot_ of noise: https://api.travis-ci.org/v3/job/403149958/log.txt

Cargo should detect whether the terminal allows modifying a line in place, and if it doesn't, it shouldn't really use a progress bar.

Also, there should be an environment variable that allows disabling the progress bar, but I couldn't find one in the cargo book. So maybe the docs need updating, or if there isn't one, we maybe should add one.

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Also, kudos to whoever added the progress bar, been using it all day, and its really nice, so thanks for doing that!

[ehuss]

I think that Travis intentionally sets TERM to xterm because the build output on the website (https://travis-ci.org/rust-lang/rust/) is colorized. Adding TERM=dumb should disable the progress bar.

Note: The progress bar has been placed behind an unstable option in #5716, so it will go away the next time cargo is updated in nightly.

Edit: Also, Travis sets up scripts with a tty.

[gnzlbg]

I think that Travis intentionally sets TERM to xterm because the build output on the website

Oh crap, then cargo cannot really detect this. If there was an environment variable, one could disable the progress bar without having to change the TERM.

The progress bar has been placed behind an unstable option in #5716, so it will go away the next time cargo is updated in nightly.

Sad to hear this, i've enjoyed it a lot today :/

[RalfJung]

So one could argue that the bug is really on the Travis side for setting TERM=xterm without actually supporting xterm properly? Is there an issue on their side to track that?

[gnzlbg]

So one could argue that the bug is really on the Travis side for setting TERM=xterm without actually supporting xterm properly?

Yes, but this is no excuse for cargo to break travis-CI for every Rust project using it: I'm getting notifications that builds are failing because now they are writing N-times more logs due to the progress bar, exceeding the log limit.

A workaround could be for cargo to detect whether it is running in a travis instance (e.g. checking if the TRAVIS environment variables is true - https://docs.travis-ci.com/user/environment-variables#default-environment-variables), and disabling the progress bar if this is the case.

cargo should add some integration test to its CI to make sure that future changes do not break Travis-CI - it is the second time that this particular change breaks it in the last couple of months and it appears to have gone completely unnoticed. Who's fault is it (cargo or travis-ci) is not really relevant IMO.

[ehuss]

I agree there probably should be some way to disable it.

Does anyone at @rust-lang/cargo have any opinions about this, and how to approach it?

• It could check for TRAVIS env var. That seems a little odd, though.
• It could check for CI env var. It looks like the majority of CI systems will set this.
• It could check for some custom var (CARGO_PROGRESS_BAR?). However, if this is the only option, that means everyone who uses travis would need to set it, which most probably won't. (EDIT: another idea is to use some config var which would have an env var for free)

[gnzlbg]

It could check for some custom var (CARGO_PROGRESS_BAR?). However, if this is the only option, that means everyone who uses travis would need to set it, which most probably won't.

I think that having such an environment variable would be useful irrespectively of what's done about the other options.

[nrc]

It could check for CI env var.

This seems good to me, like the most general option and already an established 'standard'.

It could check for some custom var

I have a bad opinion of env vars in general (they are global mutable state) and I'd much prefer to use a command line option (if the CI env var is not good enough).

[dwijnand]

:+1: for the CI env var, seems like a reasonable thing to hinge off of.

If push comes to shove we could _also_ have a CARGO_PROGRESS_BAR env var, that overrides CI.

[alexcrichton]

Oh one thing I should mention on the cli/env/config var debate is that one thing I've intended we should do for a long time is to add a --config flag to Cargo for all subcommands. Just like .cargo/config already has env vars to configure it I'd ideally like to have a --config flag as well, that way whatever's easiest for the use at hand can be used without us having to dictate which is the best

[dwijnand]

one thing I've intended we should do for a long time is to add a --config flag to Cargo for all subcommands

(there's now a proposal for that in https://github.com/rust-lang/cargo/issues/6699)