System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens fails by not timing out

[AndyAyersMS]

Build Information

Build: https://dev.azure.com/dnceng-public/cbb18261-c48f-4abb-8651-8cdcb5474649/_build/results?buildId=1080515
Build error leg or test failing: System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens
Pull request: #116771

Error Message

Fill the error message using step by step known issues guidance.

{
  "ErrorMessage": "System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens(engine: Compiled) [FAIL]",
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1080515
Error message validated: [System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens(engine: Compiled) [FAIL]]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 6/28/2025 12:57:08 AM UTC

Report

Build	Definition	Test	Pull Request
1093242	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens
1092873	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens
1091910	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens
1089610	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens
1089039	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_Timeout_Throws
1086691	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens
1085479	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens
1085439	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens
1083263	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens
1081380	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens
1080515	dotnet/runtime	System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens	#116771

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
1	5	11

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[ericstj]

Looks like compiled regex got fast enough to not timeout 😆

    System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens(engine: Compiled) [FAIL]
      Assert.Throws() Failure: No exception was thrown
      Expected: typeof(System.Text.RegularExpressions.RegexMatchTimeoutException)
      Stack Trace:
        /_/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/Regex.Match.Tests.cs(1242,0): at System.Text.RegularExpressions.Tests.RegexMatchTests.Match_TestThatTimeoutHappens(RegexEngine engine)
        --- End of stack trace from previous location ---

We should decrease the timeout value to something smaller

runtime/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/Regex.Match.Tests.cs

Lines 1230 to 1243 in f1f1167

	private async Task Match_TestThatTimeoutHappens(RegexEngine engine)
	{
	var rnd = new Random(42);
	var chars = new char[1_000_000];
	for (int i = 0; i < chars.Length; i++)
	{
	byte b = (byte)rnd.Next(0, 256);
	chars[i] = b < 200 ? 'a' : (char)b;
	}
	string input = new string(chars);
	Regex re = await RegexHelpers.GetRegexAsync(engine, @"a.{20}^", RegexOptions.None, TimeSpan.FromMilliseconds(10));
	Assert.Throws<RegexMatchTimeoutException>(() => { re.Match(input); });
	}