Add float, boolean and array indexing support to Java Variant extraction

[nartal1]

Description

This PR contributes to NVIDIA/cudf-spark#15222 and NVIDIA/cudf-spark#15223.

It brings VariantUtils in line with Variant functionality subsequently merged into libcudf:

• Add floating point type support to Parquet variant field extraction #23075 added FLOAT32 and FLOAT64 extraction
• Add boolean type support to Parquet variant field extraction #23276 added BOOL8 extraction
• Add array indexing support to Parquet variant field extraction #22895 added zero-based array-index steps to Variant extraction paths

In this PR:

• added DType.FLOAT32, DType.FLOAT64, and DType.BOOL8 to the supported Variant target types
• documented the exact physical-type matching behavior for Variant decoding
• documented array-index path syntax such as $[0] and $.a[1].b
• documented null behavior for missing fields, out-of-bounds indices, container mismatches, encoded Variant nulls, and physical-type mismatches
• expanded VariantUtilsTest coverage for the newly supported types and path behavior

Variant decoding requires the encoded physical type to exactly match the requested target type. Numeric conversions are not performed. For example, a FLOAT32 Variant value cannot be extracted as FLOAT64; the result is null.

Array Indexing

Variant extraction paths now document and test zero-based array indexing:

• root array indexing: $[0]
• mixed object and array traversal: $.a[1].b
• raw extraction followed by casting
• combined extraction and casting

Testing

Expanded VariantUtilsTest coverage includes:

• direct and combined extraction of FLOAT32 and FLOAT64
• float width mismatches and truncated payloads
• direct and combined extraction of boolean true and false values
• encoded Variant nulls, input nulls, and parent struct nulls
• empty float and boolean inputs
• root and nested array indexing
• out-of-bounds array indices and container mismatches
• sliced input columns
• null argument and malformed input validation

Validation results:

• VariantUtilsTest: 32 tests, 0 failures, 0 errors

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]

This pull request requires additional validation before any workflows can run on NVIDIA's runners.

Pull request vetters can view their responsibilities here.

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: b767e1a4-e483-49d9-96eb-0515cc450705

📥 Commits

Reviewing files that changed from the base of the PR and between c563e26 and e7645f8.

📒 Files selected for processing (2)

• java/src/main/java/ai/rapids/cudf/VariantUtils.java
• java/src/test/java/ai/rapids/cudf/VariantUtilsTest.java

Included review availability: Your plan provides up to 12 included reviews per hour; 11 remain after this review.

---

📝 Walkthrough

Summary by CodeRabbit

• New Features

  • Added support for extracting FLOAT32, FLOAT64, and BOOL8 values from variants.
  • Expanded JSONPath-style extraction to support array indices and nested object-array paths.
  • Added clearer handling for null, empty, invalid, and unsupported values.

• Bug Fixes

  • Prevented incorrect numeric conversions by requiring exact physical-type matches.
  • Improved handling of invalid array indexes, truncated data, mismatched types, and sliced inputs.

Walkthrough

VariantUtils now documents and tests FLOAT32, FLOAT64, BOOL8, array-index paths, exact physical-type matching, null handling, and invalid inputs.

Changes

Variant extraction support

Layer / File(s)	Summary
Target types, paths, and encoded fixtures java/src/main/java/ai/rapids/cudf/VariantUtils.java, java/src/test/java/ai/rapids/cudf/VariantUtilsTest.java	The supported target types and extraction paths are documented. Tests add encoders and fixtures for arrays, floating-point values, booleans, and nulls.
Extraction and casting validation java/src/test/java/ai/rapids/cudf/VariantUtilsTest.java	Tests cover nested array paths, scalar casting, sliced and empty inputs, type mismatches, invalid arguments, and truncated float payloads.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to e7645

This PR adds float, boolean, and array-path Variant extraction with expanded tests; no actionable merge-blocking risk remains.

Suggested reviewers: tgravescs

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 7.50% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
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.
Title check	✅ Passed	The title clearly summarizes the main changes: float, boolean, and array-index support for Java Variant extraction.
Description check	✅ Passed	The description directly explains the supported types, array indexing, documentation updates, and expanded tests.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

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

[nartal1]

/ok to test e7645f8