`docker build` quiet `-q` with output `-o` specified prints empty line

[jonasbadstuebner]

Contributing guidelines

• I've read the contributing guidelines and wholeheartedly agree

I've found a bug and checked that ...

• ... the documentation does not mention anything about my problem
• ... there are no open or closed issues that are related to my problem

Description

I ran docker build -q -t myimage:local -o output-path/ .

I'm aware that -q explicitly states that it prints the Image ID on success.

Expected behaviour

It should print nothing and just put all files to the output directory.

Actual behaviour

I get an empty line in my output.

Buildx version

github.com/docker/buildx 0.25.0 faaea65

Docker info

Builders list

not relevant

Configuration

I could provide, if necessary - but this is probably not related.

Build logs

Additional info

I know it is a nitpick, but I run this command in a make command and it just looks as if there is something missing. I could sed or awk it away, but this just works around the root cause.

I'm happy to open a PR for this small inconvenience, I just need some input, if the output should be skipped if:

1. the image id is empty anyway? (could break scripts that check the last line of the output)
2. only if a special flag is set? (would be explicit, non-breaking and fit my use-case just fine)
3. only local and tar exports are specified? (is the image id always empty then?)

[jonasbadstuebner]

I found an argument against option 1: https://github.com/docker/buildx/pull/740/files#r702071754

I would prefer option 2 and call the flag --suppress-iid-output.
But that would not make it clear, that it is only in quiet mode...

I wish quiet would just mean "no-output on success"...

[tonistiigi]

I think we should just add --progress=none. -q is an old flag with weird behavior, where it controls multiple things and is only meant for build with special conditions. Controlling progress should be done with --progress and getting image ID/metadata with --iidfile or more powerful --metadata-file.

I was actually surprised we didn't support this already. We have --progress=quiet, but unfortunately, that copies the behavior of printing image ID.