Unrecognized escape sequence error in pattern-based record struct definition

[koddek]

When I try to build this code:

public const string Pattern2 = "^[a-zA-Z0-9._%+-]{1,64}@[a-zA-Z0-9.-]{1,255}\\.[a-zA-Z]{2,}$";
public const string Pattern3 = """^[a-zA-Z0-9._%+-]{1,64}@[a-zA-Z0-9.-]{1,255}\.[a-zA-Z]{2,}$""";

[String(minLength: 6, maxLength: 99,Pattern = Pattern1)]
public readonly partial record struct Email;

I get this error for both ways of arranging the pattern:

0>PrimitiveRepository.g.cs(35,200): Error CS1009 : Unrecognized escape sequence

[koddek]

After some more testing, I realise that the code generation fails when there are escaped characters in the pattern. Anything with the '\' character.