Arrow-avro Writer Dense Union support

[nathaniel-d-ef]

Which issue does this PR close?

Relates to:
#8348
#4886

Rationale for this change

This PR completes the efforts of @jecsand838, adding dense union support to the encoder side of the crate, along with four other minor extensions of existing time-related encoding.

Note: currently this PR is stacked behind #8546. Once that's merged this will be updated and will not include those changes.

What changes are included in this PR?

• Dense union support for the writer
• Tests

Are these changes tested?

• A full round-trip test, reading in an existing union avro file and asserting that the output matches expectations
• Unit tests covering new encoders.

Are there any user-facing changes?

Crate not yet public

[mbrobbel]

Thanks @nathaniel-d-ef and @jecsand838

[jecsand838]

@mbrobbel Just a heads up that @nathaniel-d-ef is out of office until early next week.

[alamb]

@mbrobbel Just a heads up that @nathaniel-d-ef is out of office until early next week.

Thanks @jecsand838 -- to keep things moving do you think you would be able to implement the PR suggestions? I would normally do it myself, but I don't have the permissions to push to the elastiflow fork: https://github.com/elastiflow/arrow-rs

[nathaniel-d-ef]

Thanks @mbrobbel and @alamb - I’m fully AFK until next week. I’ll pass this thread to my team to see if someone can tackle it before then.

…

On Tue, Oct 7, 2025 at 20:27 Andrew Lamb ***@***.***> wrote: *alamb* left a comment (apache/arrow-rs#8550) <#8550 (comment)> @mbrobbel <https://github.com/mbrobbel> Just a heads up that @nathaniel-d-ef <https://github.com/nathaniel-d-ef> is out of office until early next week. Thanks @nathaniel-d-ef <https://github.com/nathaniel-d-ef> -- to keep things moving do you think you would be able to implement the PR suggestions? I would normally do it myself, but I don't have the permissions to push to the elastiflow fork: https://github.com/elastiflow/arrow-rs — Reply to this email directly, view it on GitHub <#8550 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BJ7GZK5BSIPPEOEV2CRNA5L3WQAZBAVCNFSM6AAAAACIHQMRT2VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTGNZYGA3TONZTGM> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[jecsand838]

@mbrobbel Just a heads up that @nathaniel-d-ef is out of office until early next week.

Thanks @jecsand838 -- to keep things moving do you think you would be able to implement the PR suggestions? I would normally do it myself, but I don't have the permissions to push to the elastiflow fork: https://github.com/elastiflow/arrow-rs

Absolutely! Just pushed up those PR suggestions.

[mbrobbel]

Thanks @jecsand838!

[alamb]

woohoo!