GH-51100: [C++] Deprecate IPC tensor/sparse tensor messages

[pitrou]

Rationale for this change

Deprecate IPC APIs for reading and writing Tensor / SparseTensor messages.

Deprecating IPC support for Tensor and SparseTensor was discussed in https://lists.apache.org/thread/z2kl4g1353mbtgpt3qo7j3bzohq0q7fv.

Are these changes tested?

By existing CI tests.

Are there any user-facing changes?

No.

• GitHub Issue: [C++] Deprecate IPC tensor/sparse tensor messages #51100

[github-actions]

⚠️ GitHub issue #51100has been automatically assigned in GitHub to PR creator.

[pitrou]

Let's keep this PR draft until final consensus is reached on the ML.

[rok]

@pitrou I'm very much on board with the sparse tensors. I so wonder about tensors, are we sure this is not being used? I'm ok to add a deprecation and wait for a release to see if we hear back. But my expectation is there would be some users out there.

[pitrou]

I'm ok to add a deprecation and wait for a release to see if we hear back. But my expectation is there would be some users out there.

Hopefully the deprecation will have them chime in? But my attempt at code-searching this on GH did not lead to many recent relevant results.

[rok]

I'm ok to add a deprecation and wait for a release to see if we hear back. But my expectation is there would be some users out there.

Hopefully the deprecation will have them chime in? But my attempt at code-searching this on GH did not lead to many recent relevant results.

Agreed. I'll take a look myself and report back.

[rok]

I've checked and found some projects using Tensor (1, 2, 3, ..), but I think they can all easily switch to tensor array. I agree with deprecating Tensor.