Additional fixes for libcudf large strings support

[davidwendt]

Description

Fixes some code logic where strings offsets were hardcoded to expect int32 (or cudf::size_type).
These were found while investigating size_type/offset-type usage in libcudf.

Checklist

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

[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

• Performance

  • Improved GPU-based processing for JSON string handling, field-name matching, string joining, and n-gram tokenization.
  • Reduced host-side offset construction and improved offset processing during data transfers.

• Bug Fixes

  • Improved compatibility and correctness when working with string offsets and generated tokenization results.

• Maintenance

  • Updated copyright attributions and internal processing utilities.

Walkthrough

The PR updates JSON string-offset copying and field-name hashing to use offsetalator_factory. String joining and n-gram tokenization now use make_offsets_child_column for offset construction.

Changes

Offset handling updates

Layer / File(s)	Summary
JSON offset iterator handling cpp/src/io/json/host_tree_algorithms.cu, cpp/src/io/json/json_tree.cu	String offsets are normalized into int64_t device storage before host copying. Decoded field-name hashing and equality use offset iterators.
String and text offset construction cpp/src/strings/combine/join.cu, cpp/src/text/ngrams_tokenize.cu	String joining and n-gram tokenization use make_offsets_child_column to construct output offsets. Copyright notices and required headers are updated.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• rapidsai/cudf#23336: Migrates iterator construction in overlapping JSON and string code.
• rapidsai/cudf#23338: Updates iterator-based logic in host_tree_algorithms.cu and json_tree.cu.
• rapidsai/cudf#23607: Introduces related string-offset handling through offsetalator_factory.

Suggested labels: improvement

Suggested reviewers: vyasr, pmattione-nvidia, karthikeyann

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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 identifies additional fixes for libcudf large-string support, which matches the main changeset.
Description check	✅ Passed	The description explains that the changes fix hardcoded int32 and cudf::size_type string offsets, matching the changeset.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

🧹 Nitpick comments (1)

cpp/src/io/json/json_tree.cu (1)

577-581: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Declare the return type of d_equal.

d_equal is a generic device comparator used by cuco::static_set. Add -> bool to the lambda declaration.

As per coding guidelines, extended device lambdas passed to device algorithms must declare explicit return types.

Proposed fix

-  auto const d_equal = [char_ptr, offset_itr] __device__(auto node_id1, auto node_id2) {
+  auto const d_equal =
+    [char_ptr, offset_itr] __device__(auto node_id1, auto node_id2) -> bool {

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@cpp/src/io/json/json_tree.cu` around lines 577 - 581, Update the d_equal
device lambda declaration to explicitly specify a bool return type using
trailing-return syntax, preserving its existing comparator logic and
compatibility with cuco::static_set.

Source: Coding guidelines

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@cpp/src/io/json/json_tree.cu`:
- Around line 577-581: Update the d_equal device lambda declaration to
explicitly specify a bool return type using trailing-return syntax, preserving
its existing comparator logic and compatibility with cuco::static_set.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 3a041847-a7ab-40e5-8790-421d72decebc

📥 Commits

Reviewing files that changed from the base of the PR and between 463fba2 and 1b0c47a.

📒 Files selected for processing (4)

• cpp/src/io/json/host_tree_algorithms.cu
• cpp/src/io/json/json_tree.cu
• cpp/src/strings/combine/join.cu
• cpp/src/text/ngrams_tokenize.cu