FR: add --check-only flag to pip sync command

[ofek]

We have a need to check whether environments are synchronized without performing action so it would be nice to have such a flag that would produce JSON output like:

{
    "in-sync": false
}

[charliermarsh]

Can we resolve this by adding --dry-run to uv pip sync (which already exists on uv pip install)?

[ofek]

Probably! What would the output be if everything is synchronized already?

[charliermarsh]

Right now it ends with "Would make no changes" but we could consider using separate exit codes.

[ofek]

I think it would be preferable to have an additional --json flag to not be reliant upon exit codes.

[charliermarsh]

Can consider it but will take a lot more time and work given that it's committing to a public API that we'll need to build and maintain in perpetuity.

[ofek]

Then I'm definitely fine with the quicker solution 🙂

[charliermarsh]

I do think we want JSON output: #411. At least for resolution. But we haven't figured it out yet :) \cc @konstin

[Rogdham]

This feature seems related to the recurring usecase of the CI checking that the committed requirements.in and requirements.txt files match each other. In that case, we are only interested in the exit code (the output does not matter much). This would be similar to the --check parameter of ruff format.

A workaround looks like the following:

uv pip compile requirements.in -o requirements.txt && git diff --exit-code requirements.txt

For reference, the feature has been asked for pip-tools in jazzband/pip-tools#882, which might provide more context.

[FlorianKoegler]

Right now it ends with "Would make no changes" but we could consider using separate exit codes.

Hi,
i found this issue, because I'm trying to use uv pip sync --dry-run to test if a virtual environment matches it's lock file.

It would be great if it would have a non-zero return code, in case there are deviations.
This would make parsing much more reliable than evaluating the output message. :)

For comparison, pip-sync --dry-run also returns an non-zero return code.