Support inline regex flags (?i), (?m), (?s) in libcudf regex enabled APIs by davidwendt · Pull Request #24784 · NVIDIA/cudf

davidwendt · 2026-10-22T17:30:48Z

Description

Adds support for the inline regex mode modifiers (?i), (?m), and (?s) in the libcudf regex APIs (contains_re, extract, replace_re, etc.). These map to the existing IGNORECASE, MULTILINE, and DOTALL regex flags. The scoped form (?ims:regex) is also supported. Both the Thompson NFA and the Glushkov paths are supported since both consume the same generated instructions.

Modifiers may appear anywhere in the pattern and apply to the remainder of the enclosing group (Java/PCRE semantics). For example, (a(?i)b)c matches abc and aBc but not abC. Turning off flags (e.g. (?-i)) and other modifiers (e.g. (?x)) are not supported.

Tests are added for contains/matches/count and extract, and cpp/doxygen/regex.md is updated with a new Mode Modifiers section.

The cudf-polars tests are updated since (?i:...) is no longer an unsupported pattern, and a test is added comparing GPU and CPU results for patterns using inline flags (including patterns containing only flags like (?s)).

This also addresses #24759 (part of #24756) by supporting the (?s) pattern generated by Polars SQL LIKE directly in libcudf. This is an alternative to #24770 which strips leading inline flags in cudf-polars.

Checklist

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

🤖 Generated with Claude Code

Add support for the inline mode modifiers (?i), (?m), and (?s) and the scoped form (?ims:regex) in the libcudf regex parser. The modifiers turn on the IGNORECASE, MULTILINE, and DOTALL flags respectively for the remainder of the enclosing group (Java/PCRE semantics). No new regex instructions are added; the parser simply updates its flags while lexing. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

copy-pr-bot · 2026-10-22T17:30:52Z

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davidwendt · 2026-10-23T13:48:00Z

/ok to test

The (?i:...) modifier is now supported by libcudf so use (?-i:...) as the unsupported pattern instead. Add a test comparing GPU and CPU results for patterns using the (?i), (?m), and (?s) inline flags. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

davidwendt · 2026-10-23T15:30:02Z

/ok to test

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

coderabbitai · 2026-10-23T16:52:36Z

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Files selected for processing: 2

cpp/src/strings/regex/regcomp.cpp
cpp/tests/strings/contains_tests.cpp

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📝 Summary

Summary by CodeRabbit

New Features
- Regex patterns now support inline case-insensitive, multiline, and dot-all flags, including combinations and flags scoped to a group.
- Inline flags can be applied mid-pattern and affect matching behavior within the enclosing group.
Bug Fixes
- Inline regex flags are handled consistently across string matching, counting, and extraction operations.
Documentation
- Updated regex documentation to describe inline flag syntax and supported behavior.
Tests
- Added coverage for global and scoped flags, flag combinations, and unsupported syntax.

Regex patterns now support inline case-insensitive, multiline, and dot-all flags. Flags apply from their position through the enclosing group, or only within a scoped group. C++ and Python tests cover these forms and unsupported patterns.

Changes: Inline regex flags

Layer / File(s)	Summary
Parse and apply inline flags `cpp/src/strings/regex/regcomp.h`, `cpp/src/strings/regex/regcomp.cpp`	The parser recognizes inline `i`, `m`, and `s` flags, tracks flag scope across groups, and applies dot-all behavior based on current flags. `reprog::add_flags` combines inline flags with existing program flags.
Document and test inline flag behavior `cpp/doxygen/regex.md`, `cpp/tests/strings/contains_tests.cpp`, `cpp/tests/strings/extract_tests.cpp`, `python/cudf_polars/tests/expressions/test_stringfunction.py`	Documentation describes global and scoped flags. Tests cover matching, extraction, counting, and unsupported flag forms.

Priority: Normal

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

Change: Feature · Severity of issue fixed: Medium

Possibly related issues

NVIDIA/cudf#24759: The issue reports that libcudf rejects the (?s) modifier generated by cudf-polars. This change adds support for (?s) and tests inline dot-all patterns in cudf-polars.

Suggested labels: feature request, strings

Suggested reviewers: bdice, mroeschke

Merge Risk: Minimal · up to 73d43

No merge-blocking issue was identified with inline regex flags. The change is ready to merge after normal checks.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 20.83% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 24 functions across 5 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description check		The description accurately summarizes the inline regex flag support, scoped modifiers, affected APIs, tests, documentation, and related issue context.
Title check		The title clearly and concisely identifies the main change: support for inline regex flags in libcudf regex-enabled APIs.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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Inline comments:
Review comments at @cpp/src/strings/regex/regcomp.cpp:
- Line 594: Update the flag-only-group handling in lex so consumed groups
continue through the existing lexer loop instead of recursively calling lex;
preserve the current flag updates and behavior for subsequent pattern tokens.

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Reviewing files that changed from the base of the PR and between 1d8ac9c and c568e58.

📒 Files selected for processing: 6

cpp/doxygen/regex.md
cpp/src/strings/regex/regcomp.cpp
cpp/src/strings/regex/regcomp.h
cpp/tests/strings/contains_tests.cpp
cpp/tests/strings/extract_tests.cpp
python/cudf_polars/tests/expressions/test_stringfunction.py

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Process flag-only groups like (?i) in a loop at the start of the lexer instead of recursively calling lex() so a long sequence of consecutive flag groups cannot exhaust the host stack. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

TomAugspurger

python changes look good.

mhaseeb123

Approving pending .h -> .hpp file ext change

A flag-only group like (?i) is not a repeatable item so patterns like a(?i)* now throw the "nothing to repeat" error. This matches the behavior of Java, Rust, PCRE, and Perl regex engines. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

davidwendt · 2026-10-26T14:15:29Z

/merge

Renames 2 .h files in the cpp/src/strings/regex directory to .hpp files: ``` regex_program_impl.h -> regex_program_impl.hpp regcomp.h -> regcomp.hpp ``` Reference comment from a separate PR: #24784 (comment) Authors: - David Wendt (https://github.com/davidwendt) Approvers: - Muhammad Haseeb (https://github.com/mhaseeb123) - Yunsong Wang (https://github.com/PointKernel) URL: #24826

github-actions Bot added the libcudf Affects libcudf (C++/CUDA) code. label Oct 22, 2026

github-actions Bot assigned davidwendt Oct 22, 2026

davidwendt changed the title ~~Support inline regex flags (?i), (?m), (?s)~~ Support inline regex flags (?i), (?m), (?s) in libcudf regex enabled APIs Oct 22, 2026

davidwendt added 2 - In Progress Currently a work in progress improvement Improvement / enhancement to an existing function non-breaking Non-breaking change labels Oct 22, 2026

Merge branch 'main' into regex-inline

c0068af

davidwendt added 3 - Ready for Review Ready for review by team and removed 2 - In Progress Currently a work in progress labels Oct 23, 2026

github-actions Bot added Python Affects Python cuDF API. cudf-polars Issues specific to cudf-polars labels Oct 23, 2026

github-project-automation Bot added this to cuDF Python Oct 23, 2026

github-project-automation Bot moved this to Todo in cuDF Python Oct 23, 2026

Add tests for regex patterns containing only inline flags

c568e58

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

davidwendt marked this pull request as ready for review October 23, 2026 16:43

davidwendt requested review from a team as code owners October 23, 2026 16:43

davidwendt requested review from PointKernel, lamarrr and rjzamora October 23, 2026 16:43

davidwendt mentioned this pull request Oct 23, 2026

Support leading inline regex flags in cudf-polars #24770

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Comment thread cpp/src/strings/regex/regcomp.cpp Outdated

coderabbitai Bot mentioned this pull request Oct 23, 2026

Improve replace_re performance with a single regex pass #24807

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TomAugspurger approved these changes Oct 23, 2026

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Comment thread cpp/src/strings/regex/regcomp.cpp

Comment thread cpp/tests/strings/contains_tests.cpp

Comment thread python/cudf_polars/tests/expressions/test_stringfunction.py

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Comment thread cpp/src/strings/regex/regcomp.h

Merge branch 'main' into regex-inline

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rapids-bot Bot merged commit b7f2073 into NVIDIA:main Oct 26, 2026
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github-project-automation Bot moved this from Todo to Done in cuDF Python Oct 26, 2026

davidwendt deleted the regex-inline branch October 26, 2026 14:15

This was referenced Oct 26, 2026

[FEAT] Support (?s) regex from SQL LIKE in cudf-polars #24759

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Rename internal regcomp.h to regcomp.hpp #24826

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Support inline regex flags (?i), (?m), (?s) in libcudf regex enabled APIs - #24784

Support inline regex flags (?i), (?m), (?s) in libcudf regex enabled APIs#24784
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