RegexMatchTests intermittent failures: Match_ExcessPrefix (linux-bionic x64), Match_Timeout_Throws (Windows arm64)

[ViveliDuCh]

Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1597620
Build error legs/tests failing:

• net8.0-linux-Release-x64-Mono_Release_LinuxBionic / System.Text.RegularExpressions.Tests.RegexMatchTests.Match_ExcessPrefix
• net8.0-windows-Release-arm64-CoreCLR_release / System.Text.RegularExpressions.Tests.RegexMatchTests.Match_Timeout_Throws

Pull request: #133957 (release/8.0-staging -> release/8.0 merge; not introduced by this PR)

Console logs:

• https://helixr1107v0xd1eu3ibi6ka.blob.core.windows.net/dotnet-runtime-refs-heads-release-80-staging-7d05b173a976466cbb/System.Text.RegularExpressions.Tests/1/console.b73e32bd.log?helixlogtype=result
• https://helixr18s23ayyeko0k025g8.blob.core.windows.net/dotnet-runtime-refs-heads-release-80-staging-e78e519adc7b49bca9/System.Text.RegularExpressions.Tests/1/console.fc7bbfaa.log?helixlogtype=result

Two RegexMatchTests cases failed on two unrelated architectures/runtimes (linux-bionic Mono x64, Windows arm64 CoreCLR) in the same build, with no error message captured beyond the outcome — both are timing-sensitive scenarios (excess-prefix backtracking bound, timeout-throws), consistent with CI machine load rather than a regex-engine correctness regression. Possibly related to general regex-timeout flakiness tracked in #128201, but that issue doesn't cover these exact tests/legs. Filing to track recurrence.

Error Message

{
  "ErrorMessage": "",
  "ErrorPattern": "RegexMatchTests\\.(Match_ExcessPrefix|Match_Timeout_Throws)",
  "BuildRetry": true,
  "ExcludeConsoleLog": false
}

Note

This issue was filed with AI assistance (GitHub Copilot CLI) analyzing public Azure DevOps/Helix logs.

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1597620
Error message validated: [RegexMatchTests\.(Match_ExcessPrefix|Match_Timeout_Throws)]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 9/15/2026 10:44:48 PM UTC

Report

Build	Repository	Test	Pull Request
1616110	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_ExcessPrefix	#134527
1606683	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_Timeout_Throws
1601369	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_Timeout_Throws
1599809	dotnet/runtime	System.Text.RegularExpressions.Tests.WorkItemExecution
1598686	dotnet/runtime	System.Text.RegularExpressions.Tests.WorkItemExecution
1597620	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_Timeout_Throws

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
0	1	6

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