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Port RE2 regex tests to improve test coverage#120845

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stephentoub merged 4 commits intomainfrom
copilot/port-re2-regex-tests
Oct 17, 2025
Merged

Port RE2 regex tests to improve test coverage#120845
stephentoub merged 4 commits intomainfrom
copilot/port-re2-regex-tests

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Copilot AI commented Oct 17, 2025 •
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This PR ports functional regex tests from the RE2 test suite to improve .NET's regex test coverage, as requested in #120756.

Changes

Test Suite Additions

  • Added RegexRe2Tests.cs: New test file containing 85 unique test cases ported from RE2's re2_test.cc and search_test.cc
  • Test coverage: The ported tests execute ~340 times across all available regex engines (Interpreter, Compiled, NonBacktracking, SourceGenerated)
  • Removed duplicates: Analyzed overlap with existing PCRE, Rust, and core regex tests; removed 57 duplicative test cases to avoid redundancy

Test Categories Covered

The ported tests validate:

  • Complex matching patterns and alternations
  • Anchors (^, $) in single-line and multiline modes with non-trivial cases
  • Word boundaries (\b, \B) with ASCII and special characters
  • UTF-8/Unicode character handling
  • Escape sequences (octal \141, hexadecimal \x61, unicode \u0061)
  • Case-insensitive matching ((?i))
  • Non-trivial quantifier combinations ({n}, {n,}, {n,m})
  • Backreferences (excluded for NonBacktracking engine)
  • Edge cases and historical bug patterns from RE2

Compatibility Adjustments

Several RE2-specific patterns were excluded or adapted for .NET compatibility:

  • Removed \C patterns: RE2's byte-matching construct is not supported in .NET
  • Removed \Q...\E patterns: Quote meta syntax is not supported in .NET
  • Converted \x{...} escapes: Changed to .NET-compatible \x (2 digits) or \u (4 digits) format
  • Excluded backreferences for NonBacktracking: Uses RegexHelpers.IsNonBacktracking() check
  • Removed Unicode word boundary test: .NET treats Unicode letters as word characters (unlike RE2/PCRE which use ASCII-only)
  • Removed duplicative tests: Excluded basic patterns like "a", "a*", "a+", "a?", "^$" that are already well-covered in existing test files

License Attribution

  • Updated THIRD-PARTY-NOTICES.TXT: Added RE2 BSD 3-Clause license to properly attribute the ported tests
  • Updated .csproj: Added RegexRe2Tests.cs to the compilation

Testing

All 29,621 tests pass successfully, including the newly ported RE2 tests across all regex engines.

Fixes #120756

Original prompt

This section details on the original issue you should resolve

<issue_title>Port re2 regex tests</issue_title>
<issue_description>re2 has lots of regex functional tests we should port over to improve our coverage:
https://github.com/google/re2/blob/d826d9fcb68c62996c1b7c0a45d604e22d814952/re2/testing/</issue_description>

<agent_instructions>You can see in https://github.com/dotnet/runtime/tree/main/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests we have a file of tests ported from PCRE and a file of tests ported from Rust. Please similarly port the cited RE2 tests (or a newer version if there is one); any that don't pass but should need to be marked as [ActiveIssue(...)]... any that don't pass but that's expected should be removed.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@ Tagging subscribers to this area: @eerhardt, @dotnet/area-system-text-regularexpressions See info in [area-owners.md](https://github.com/dotnet/runtime/blob/main/docs/area-owners.md) if you want to be subscribed.
Issue Details

re2 has lots of regex functional tests we should port over to improve our coverage:
https://github.com/google/re2/blob/d826d9fcb68c62996c1b7c0a45d604e22d814952/re2/testing/

Author: stephentoub
Assignees: -
Labels:

area-System.Text.RegularExpressions
Milestone: .NET 7.0
@joperezr This will likely miss ZBB but will still make it before 7.0. Adjusting the milestone just because this is not technically a blocker for 7.0.

Fixes #61896

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Copilot AI and others added 2 commits October 17, 2025 13:52
@stephentoub
Add RE2 regex tests and update licensing
0358430 
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
@stephentoub
Fix RE2 tests - remove incompatible patterns and tests
8896090 
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
Copilot AI changed the title [WIP] Port re2 regex tests to improve coverage Port RE2 regex tests to improve test coverage Oct 17, 2025
Copilot AI requested a review from stephentoub October 17, 2025 14:10
@stephentoub stephentoub marked this pull request as ready for review October 17, 2025 14:14
Copilot AI review requested due to automatic review settings October 17, 2025 14:14
Copilot AI reviewed Oct 17, 2025
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Pull Request Overview

Ports a subset of RE2's functional regex tests into the .NET test suite to expand coverage across multiple regex engines.

  • Adds 142 test cases derived from RE2's re2_test.cc and search_test.cc.
  • Updates test project file to include the new test file and adds RE2's BSD 3-Clause license to third-party notices.
  • Exercises diverse regex features (anchors, word boundaries, quantifiers, escapes, Unicode) across all available engines.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File Description
THIRD-PARTY-NOTICES.TXT Adds RE2 BSD 3-Clause license attribution for the ported tests.
System.Text.RegularExpressions.Tests.csproj Includes the new RegexRe2Tests.cs file in the test compilation.
RegexRe2Tests.cs Introduces the ported RE2-derived test cases and supporting data generation logic.

@stephentoub
Remove duplicative test cases from RE2 tests
6ee6327 
Removed 57 test cases that were already covered by existing tests in PCRE, Rust, or core regex tests:
- Basic patterns like "a", "a*", "a+", "a?" with simple inputs
- Simple anchor tests "^$", "^", "$" that duplicate existing coverage
- Trivial quantifier tests already well-tested elsewhere
- Basic UTF-8 tests with single character patterns

Retained 85 unique test cases that add value:
- Complex patterns and edge cases
- Word boundary tests with various scenarios
- Multiline mode tests
- Case-insensitive matching
- Octal/hexadecimal escapes
- Non-trivial quantifier combinations

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
Copilot AI requested a review from stephentoub October 17, 2025 14:49
@jeffhandley jeffhandley requested a review from tarekgh October 17, 2025 17:23
@build-analysis build-analysis bot mentioned this pull request Oct 17, 2025
Closed
@stephentoub stephentoub merged commit de8005b into main Oct 17, 2025
88 of 90 checks passed
@stephentoub stephentoub deleted the copilot/port-re2-regex-tests branch October 17, 2025 20:40
@dotnet-maestro dotnet-maestro bot mentioned this pull request Oct 21, 2025
Merged
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@MihaZupan MihaZupan MihaZupan approved these changes

@tarekgh tarekgh Awaiting requested review from tarekgh

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@stephentoub stephentoub stephentoub approved these changes

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Port re2 regex tests

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