New doc explaining vcs_version.

[benjyw]

[ci skip-rust]

[ci skip-build-wheels]

[benjyw]

It'll be an adventure to see if we can sync a new doc up to readme.com this way. From my perusal of the rdme docs it should work, but we'll see.

[benjyw]

@kaos Can you think of a way to use this to generate docker image tags? I couldn't find a way to tag an image based on a string in a file, but you'll know better than I.

[kaos]

I think we would want a generic way to load target field values from files on disk in a generic way, akin to the http_source object.

target(
  tags=file_source("path/to/my-tags.yaml"),
  description=file_source("path/to/description.txt"),
)

[kaos]

Can you think of a way to use this to generate docker image tags? I couldn't find a way to tag an image based on a string in a file, but you'll know better than I.

No, I think the better way would be the file_source suggestion mentioned above, otherwise it would be leveraging the #16077 feature but that would still require a custom plugin if we don't add something to it for this particular case (which I think would be inferior to the file_source alternative).

[Eric-Arellano]

Thanks!

[benjyw]

I think we would want a generic way to load target field values from files on disk in a generic way, akin to the http_source object.

Trouble is, these aren't "files on disk" - these get generated long after BUILD files have been parsed. So it might not be that simple.

[da-tubi]

How can I use the version produced by vcs_version for packaging and publishing purpose?

[benjyw]

@da-tubi what is your current packaging/publishing process? Which language are we talking about?

Currently this generates a file that other Pants rules can read and act on, but it really depends on the details.