Refactor Parquet synthetic column helpers

[mhaseeb123]

Description

Refactor only, no new code. This PR moves Parquet column synthesizer functions into a standalone reusable TU. Parquet readers include and call the helpers directly.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[copy-pr-bot]

Auto-sync is disabled for draft pull requests in this repository. Workflows must be run manually.

Contributors can view more details about this message here.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 56356ec4-9556-47f8-b4d6-3e13a5cd089b

📥 Commits

Reviewing files that changed from the base of the PR and between 7ae8669 and 6811f91.

📒 Files selected for processing (9)

• cpp/CMakeLists.txt
• cpp/src/io/parquet/experimental/hybrid_scan_impl.cpp
• cpp/src/io/parquet/reader_impl.cpp
• cpp/src/io/parquet/reader_impl.hpp
• cpp/src/io/parquet/reader_impl_helpers.cpp
• cpp/src/io/parquet/reader_impl_helpers.hpp
• cpp/src/io/parquet/reader_impl_preprocess.cu
• cpp/src/io/parquet/synthetic_column_helpers.cu
• cpp/src/io/parquet/synthetic_column_helpers.hpp

💤 Files with no reviewable changes (3)

• cpp/src/io/parquet/reader_impl_helpers.hpp
• cpp/src/io/parquet/reader_impl.hpp
• cpp/src/io/parquet/reader_impl_preprocess.cu

🚧 Files skipped from review as they are similar to previous changes (6)

• cpp/src/io/parquet/experimental/hybrid_scan_impl.cpp
• cpp/src/io/parquet/reader_impl_helpers.cpp
• cpp/CMakeLists.txt
• cpp/src/io/parquet/synthetic_column_helpers.hpp
• cpp/src/io/parquet/reader_impl.cpp
• cpp/src/io/parquet/synthetic_column_helpers.cu

Included review availability: Your plan provides up to 12 included reviews per hour; 9 remain after this review.

---

📝 Walkthrough

Summary by CodeRabbit

• New Features
  • Improved Parquet reading support for generated row indices, source indices, and row-group indices.
  • Added support for selected row groups, multiple input sources, and empty results.
• Bug Fixes
  • Improved index generation across concatenated Parquet inputs and row-group selections.
  • Added validation for row-group index inputs to improve reliability.
  • Improved handling of memory allocation and large-scale index generation.

Walkthrough

Changes

Parquet synthetic-column generation now uses shared CUDA helpers for row, source, and row-group indices. Reader-local implementations and declarations are removed. Reader and hybrid-scan paths pass row-group metadata to the new helpers, and CMake compiles the implementation.

Parquet synthetic columns

Layer / File(s)	Summary
Define and implement synthetic-column helpers cpp/src/io/parquet/synthetic_column_helpers.*	Adds documented helper interfaces and CUDA implementations for row-index mapping, source-index generation, and row-group indexing.
Integrate helpers into reader paths cpp/src/io/parquet/reader_impl.*, cpp/src/io/parquet/experimental/hybrid_scan_impl.cpp, cpp/CMakeLists.txt	Updates reader call sites to use the shared helpers, removes the previous reader-local synthesis methods, and adds the CUDA implementation to the build target.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Merge Risk: ⚪ Minimal · up to 6811f

This refactor has no actionable merge-blocking risk identified at the current head and is merge-ready after normal checks and review.

Suggested reviewers: vyasr, bdice

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 16.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 6 functions across 5 files. (1 skipped: 1 unsupported.)	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the main change: refactoring Parquet synthetic column helpers.
Description check	✅ Passed	The description accurately relates the changes to moving Parquet column synthesizer functions into a reusable translation unit.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

_{Comment @coderabbitai help to get the list of available commands.}