`cargo report future-incompatibilities` doesn't check for color support correctly

[ehuss]

Problem
cargo report future-incompatibilities does not check for color support correctly. If you pipe the output to a file or something like less, it is not stripping the colors. This wasn't quite the intended behavior in #9606. The issue is here where it only checks if stderr supports color.

Steps

1. cargo report future-incompatibilities > some_file

Notice that some_file contains lots of escape characters

Possible Solution(s)

I'm not entirely sure of the best approach to fix this. Perhaps just check if both stdout and stderr support color at the line noted above? I can't imagine a scenario where that would matter. I'd be reluctant to make this too fussy or complicated, though worst case the check to call strip_ansi_escapes::strip could be moved to the callers, but I think I'd rather avoid that.

Notes

Output of cargo version:

cargo 1.57.0-nightly (d56b42c 2021-09-27)

[dswij]

I might be missing something here, but since cargo report future-incompatibilities command prints to stdout, what's the reason behind checking stderr only?

[ehuss]

That code is shared for two different places. When displaying as part of a regular build (here) it is sent to stderr (since all build errors/warnings go to stderr). When displayed as part of the cargo report subcommand, it is displayed to stdout as it is intended to be a human-readable text report, and it seemed more natural to send that to stdout (and more convenient to pipe the output).

[dswij]

I'd say that additionally checking stdout would probably be a good enough approach since this should not be too complicated.

I'll try to have a look at it 🙂 @rustbot claim

[ehuss]

@dswij Just checking if you've had a chance to look at this, or had any questions.

[dswij]

I've had a look, but got distracted along the way. I'll continue working on it once I have the chance to.