I'm not 100% sure that this is really the case since my understanding of Dotnet and C# is pretty limited but the [current documentation](https://github.com/actions/toolkit/blob/30e0a77337213de5d4e158b05d1019c6615f69fd/docs/problem-matchers.md#regular-expression-not-matching) seems to suggest that the problem matchers use EcmaScript-style regex syntax but I don't see the [necessary options](https://docs.microsoft.com/en-us/dotnet/api/system.text.regularexpressions.regexoptions?view=netcore-3.1#fields) being passed here: https://github.com/actions/runner/blob/6c70d53eead402ba5d53676d6ed649a04e219c9b/src/Runner.Worker/IssueMatcher.cs#L68 The default seems to be to use canonical regex synatx: https://docs.microsoft.com/en-us/dotnet/standard/base-types/regular-expression-options#default-options
I'm not 100% sure that this is really the case since my understanding of Dotnet and C# is pretty limited but the current documentation seems to suggest that the problem matchers use EcmaScript-style regex syntax but I don't see the necessary options being passed here: https://github.com/actions/runner/blob/6c70d53eead402ba5d53676d6ed649a04e219c9b/src/Runner.Worker/IssueMatcher.cs#L68
The default seems to be to use canonical regex synatx: https://docs.microsoft.com/en-us/dotnet/standard/base-types/regular-expression-options#default-options