look for stdout instead of stderr for plain output

[kasperk81]

make the primary decision based on 'stdout is redictected' instead of stderr; like many software.
e.g. docker build ... | tee should be enough to make it realize term is a nay instead of docker build ... 2>&1 | tee.

[jedevc]

Buildx should already support NO_COLOR - this was added a while back: #1815

[kasperk81]

@jedevc currently it is not behaving as expected? this pr is trying to make NO_COLOR=1 docker build and docker build | tee to have the same effect as BUILDKIT_PROGRESS=plain docker build or docker build 2>&1 | tee.

it helps with some ci systems like appveyor (where currently the output gets cluttered), as NO_COLOR is more widespread than BUILDKIT_PROGRESS.

[jedevc]

https://no-color.org/:

Command-line software which adds ANSI color to its output by default should check for a NO_COLOR environment variable that, when present and not an empty string (regardless of its value), prevents the addition of ANSI color.

This is what the option does today in buildkit.

I don't think that NO_COLOR should change the progress output type to an entirely different format.

[kasperk81]

ok, removed NO_COLOR bit

[crazy-max]

Not sure what you're trying to achieve with this change. This func just checks if provided "file" is a console.

[crazy-max]

If you meant to have progress output to stdout this is not something we are going to do. Progress, diagnostics or logs go to stderr. See also moby/buildkit#1186 (comment)

[kasperk81]

it's not that? currently docker build ... 2>&1 | tee switches to plain text and docker build ... | tee does not. with this change it would in the latter case.

[tonistiigi]

Stdout is used for build result with -o. This change makes it so that buildx -o type=tar does not produce TTY output anymore. Use --progress to control what kind of output you wish to achieve.

[kasperk81]

ok, i've opened appveyor/build-images#152. the issue was with docker-build cluttering the logs in appveyor ci, because unlike github actions, appveyor does not run the job with redirected output and it keeps on printing the whole dockerfile content with every progress line... 60k+ lines in logs from RUN apt install ... alone in debian container.

expecting everyone to specify the progress=plain is bit counter-intuitive. perhaps docker can check for CI=ignorecase(true) and CI=1 well-known environment variable for CI systems in the wild and make the decision for the user? avid users can still optin to (broken) tty logs.