I think this could become the default value of tag. We could set tag ? null, if tag is null then the tag is the output hash otherwise, the user can explicitly set a tag value, such as latest. This also reduces the number of arguments and simplifies documentation.

@nlewo I was thinking about the same, but this would be a breaking change for everyone who currently relies on the default value "latest".

If a breaking API change is not a problem then I’m happy to implement the suggestions from @nlewo.

I don't think a API breaking change is a problem if it is an improvement and if we mention it in the release changelog.

@Profpatsch @zimbatm WDYT about the default tag value?

Referring to the output hash by string splitting in bash seems kind of wrong. I could have sworn there was a builtin or library function that already does that, but I couldn’t find anything.

I don't mind if we break backward-compatibility so it could happen if tag is null

I’d prefer that, combined with good function docs.

I could have sworn there was a builtin or library function that already does that, but I couldn’t find anything.

I built a pure nix function to do that in the past but it wouldn't work in that case as it depends on the derivation output to calculate the hash.

Thanks for all the feedback.
I’ve implemented the proposed changed and adapted the documentation and release notes.

A nix builtin function would be nice indeed. I’ve experimented a little bit with placeholder "out", but that doesn’t work because I can’t manipulate its return value by passing it to other nix functions because placeholder only returns a magic string which will be substituted with the real value later at build-time.

I think it’s the best we can do at the moment, and it shouldn’t be a problem.

Thanks, merged.

hmm, maybe tests are failing because they are expecting the tag latest

@GrahamcOfBorg test docker-tools

Success on aarch64-linux

Attempted: tests.docker-tools

No partial log is available.

Failure on x86_64-linux (full log)

Attempted: tests.docker-tools

docker: exit status 125
docker: output:
error: command `docker run --rm bash bash --version' did not succeed (exit code 125)
command `docker run --rm bash bash --version' did not succeed (exit code 125)
cleaning up
killing docker (pid 593)
vde_switch: EOF on stdin, cleaning up and exiting
vde_switch: Could not remove ctl dir '/build/vde1.ctl': Directory not empty
builder for '/nix/store/8bbqsj6w1wsznx8a59h4vyhca1qdizal-vm-test-run-docker-tools.drv' failed with exit code 255
error: build of '/nix/store/8bbqsj6w1wsznx8a59h4vyhca1qdizal-vm-test-run-docker-tools.drv' failed

Failure on x86_64-linux (full log)

Attempted: tests.docker-tools

docker: exit status 125
docker: output:
error: command `docker run --rm bash bash --version' did not succeed (exit code 125)
command `docker run --rm bash bash --version' did not succeed (exit code 125)
cleaning up
killing docker (pid 593)
vde_switch: EOF on stdin, cleaning up and exiting
vde_switch: Could not remove ctl dir '/build/vde1.ctl': Directory not empty
builder for '/nix/store/053v805qmah6p6027awrc4yg0n489dzl-vm-test-run-docker-tools.drv' failed with exit code 255
error: build of '/nix/store/053v805qmah6p6027awrc4yg0n489dzl-vm-test-run-docker-tools.drv' failed

Fixed by #43119

Ah, I missed querying ofborg. Thanks!