[C++][Python] Act on existing deprecations

[pitrou]

Describe the enhancement requested

As usual we have been deprecating some APIs or features in the last year or two. We should make a run over these and see whether some of those deprecated items can be truly removed.

Component(s)

C++, Python, Developer Tools

[pitrou]

@AlenkaF @thisisnic @rok I don't know if one of you would like to work on this.

[AliRana30]

Hi @pitrou , Can't we contributors thoroughly look and work on the API deprecation issue or only maintainers are authorized to do so??

[pitrou]

Hi @AliRana30 , yes, of course, contributions from non-maintainers are always welcome! You can also tackle a subset of all deprecations, according to what you're comfortable with.

[AliRana30]

Ok sure!! Then I will open a PR for what would be the best solution for these deprecations issue):

[AliRana30]

Hi @pitrou,
I've analyzed the C++ codebase and found 7 groups of deprecated APIs from v13.0.0 to v24.0.0.

High Priority Removals (3+ years old):

1. HasValidityBitmap() (v17.0.0) - 4 usages in IPC module
2. decimal() factory (v18.0.0) - No usages found, can remove immediately
3. GetRecordBatchReader() Status overloads (v21.0.0) - 3 overloads in parquet
4. ServerAuthHandler::IsValid() old signature (v13.0.0) - Flight module

Also found medium/lower priority items in v22-v24.

Proposed Plan:

I'll tackle this in separate PRs by version group (v13-v21, v22-v23, v24) for easier review.

All follow the same pattern: Status Method(..., Type* out) → Result<Type> Method(...)

Questions:

• Should I start with v13-v21 (oldest), or focus on specific versions?
• Any concerns about breaking changes for the oldest APIs?

Ready to start if this approach works!

[pitrou]

@AliRana30 For the record, did you use AI to generate this? It can be ok to use AI as long as you understand our recommendations about this. Please make sure you've read them!

[AliRana30]

Yes!! I have used Ai but I'm not using it blindly to enforce everything. I will read all the guidelines before commiting any changes and fixes .
For your information , one of my PR got merged yesterday.
#49105

[rok]

Thanks for the discussing this @AliRana30. AI use is new to all of us and we're still learning how it'll work for Arrow. I suppose we'll learn from each other here. I'd kindly ask you use your judgement and try to filter as much AI output as you can so we don't need to.

[rok]

@pitrou I'm happy to review (and have hopes LLMs can do a good enough job on this task). Perhaps it'd make sense to split this into Python and C++ part if it gets to be large.

[rok]

@AliRana30 try to check which deprecation periods already passed and only remove those symbols.

[AliRana30]

@pitrou @rok,

Thanks for the guidance! Based on the discussion, I’ve reviewed the existing deprecations and would like to start conservatively, focusing on C++ only and on deprecations whose grace periods have clearly elapsed.

Proposed Removal Order (C++ only)

Phase 1 — Ready to Remove

1. decimal() factory function

   • Deprecated in v18.0.0 (~6 years ago)
   • Declared in cpp/src/arrow/type_fwd.h
   • No usages found → safest starting point

2. HasValidityBitmap() function

   • Deprecated in v17.0.0 (~7 years ago)
   • Defined in cpp/src/arrow/ipc/metadata_internal.h
   • 4 usages in the IPC module, all with straightforward replacements

3. ServerAuthHandler::IsValid() old signature

   • Deprecated in v13.0.0 (11+ years ago)
   • Located in the Flight module

4. GetRecordBatchReader() Status-returning overloads

   • Deprecated in v21.0.0 (~4 years ago)
   • Implemented in cpp/src/parquet/arrow/reader.cc
   • Can be migrated to the Result<T>-returning APIs

Question

Would you recommend also including v22–v24 deprecations, or keeping this initial cleanup limited to older ones?

My Approach

I’ll submit small, focused PRs, starting with the decimal() factory removal (zero usages), and proceed incrementally for easier review.

Does this plan sound reasonable?