System.Text.RegularExpressions.Tests.RegexMatchTests.CharClassSubtraction_DeepNesting_DoesNotStackOverflow(engine: NonBacktracking) [FAIL]
  System.PlatformNotSupportedException
  Stack Trace:
    at System.Text.RegularExpressions.Symbolic.SymbolicRegexRunnerFactory..ctor(RegexTree regexTree, RegexOptions options, TimeSpan matchTimeout)

Build Information

Build: https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_build/results?buildId=1314573
Build error leg or test failing: CharClassSubtraction_DeepNesting_DoesNotStackOverflow with NonBacktracking engine on browser-wasm
Pull request: #124125

Details

The test CharClassSubtraction_DeepNesting_DoesNotStackOverflow was added in #124995 (commit 50f4fec, merged Feb 27). It runs across all RegexEngine values via AvailableEngines_MemberData, including NonBacktracking.

On browser-wasm (single-threaded), the deep nesting with the NonBacktracking engine triggers internal threading APIs (Task.InternalWaitCore → ThrowIfMultithreadingIsNotSupported) that are not supported. The NonBacktracking engine works fine on browser-wasm for normal patterns — only this extreme nesting depth triggers the threading code path. The fix is an in-test guard that skips only NonBacktracking on Browser, keeping Interpreter and Compiled coverage.

Affects 3 browser-wasm LibraryTests jobs:

• LibraryTests browser-wasm linux Release
• LibraryTests_EAT browser-wasm linux Release
• LibraryTests browser-wasm windows Release

Not related to any PR changes ΓÇö this is a main-branch regression in test coverage.

Error Message

{
  "ErrorPattern": "[FAIL].*_DeepNesting_DoesNotStackOverflow",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1314573
Error message validated: [[FAIL].*_DeepNesting_DoesNotStackOverflow]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 3/1/2026 3:37:52 AM UTC

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