[MangelMaxime]

RegexOptions.NonBacktracking is now accepted and ignored, like Compiled: it only changes performance, not match results, and V8's linear l flag is still experimental and rejects the i and u flags that .NET allows with it, so mapping to it would throw on every stock runtime.

Supersedes #4104.

[github-actions]

Python Type Checking Results (Pyright)

Metric	Value
Total errors	33
Files with errors	4
Excluded files	4
New errors	✅ No

Excluded files with errors (4 files)

These files have known type errors and are excluded from CI. Remove from pyrightconfig.ci.json as errors are fixed.

File	Errors	Status
temp/tests/Python/test_hash_set.py	18	Excluded
temp/tests/Python/test_applicative.py	11	Excluded
temp/tests/Python/test_nested_and_recursive_pattern.py	2	Excluded
temp/tests/Python/fable_modules/thoth_json_python/encode.py	2	Excluded

[Copilot]

🟢 Approval recommended

The narrow validation changes preserve existing engine behavior, add focused regression coverage, and have no identified blocking issues.

No open issues 🎉

What changed in this PR

This PR accepts and ignores RegexOptions.NonBacktracking across Fable targets, avoiding reliance on V8’s experimental linear-regex flag.

Changes:

• Allow NonBacktracking in JavaScript/TypeScript, Rust, and Dart runtime option validation without changing engine behavior.
• Add regression tests across five targets covering case-insensitive construction, static matching, and replacement.

File	Description
tests/​Rust/​tests/​src/​RegexTests.fs	Test NonBacktracking acceptance on Rust.
tests/​Python/​TestRegex.fs	Test NonBacktracking acceptance on Python.
tests/​Js/​Main/​RegexTests.fs	Test NonBacktracking acceptance on JavaScript.
tests/​Dart/​src/​RegexTests.fs	Test NonBacktracking acceptance on Dart.
tests/​Beam/​RegexTests.fs	Test NonBacktracking acceptance on BEAM.
src/​fable-library-ts/​RegExp.ts	Accept the option and update the validation message.
src/​fable-library-rust/​src/​RegExp.rs	Accept the option without changing regex configuration.
src/​fable-library-dart/​RegExp.dart	Accept the option and update the validation message.

_{Review effort: Balanced}