--color=always still checks for a terminal before printing colors

[durka]

rustc --color=always foo.rs 2>&1 | cat

This produces colored output on 1.6.0, but not 1.7.0 or 1.8.0. Related to rust-lang/rust-playpen#174, cc @nrc.

[durka]

Also related to #29999, @Stebalien do you have any thoughts?

[TimNN]

I also commented on the playpen issue and think that some change (maybe #29999) changed term::stderr() so that it no longer returns Some(_) if stderr is not a tty or something like that.

[nrc]

A fix for this should get uplifted to Beta (not sure how to signal that with the available labels).

[Stebalien]

Ignoring windows...

The term library doesn't care if it's writing to a TTY, only if (1) the TERM environment variable is set and (2) it can find/parse the terminfo database.

This appears to have been introduced in #30711. Adding -Z unstable-options --error-format=human brings the color back. I've submitted a pull-request.