Stryker falls back to safe mode for this method

Describe the bug While running stryker the following warning was printed to the console, asking me to report this issue

[13:21:55 WRN] Stryker.NET encountered an compile error in D:\xxxx\VarUInt64.cs (at 56:22) with message: Verwendung der nicht zugewiesenen lokalen Variablen "b". (Source code: b)
[13:21:55 WRN] Safe Mode! Stryker will try to continue by rolling back all mutations in method. This should not happen, please report this as an issue on github with the previous error message.

Exception message in English: “Use of unassigned local variable”

Luckily this class does not have any external dependencies, so my guess is that it should be reproducable.

Here is the code:

using System.Diagnostics.CodeAnalysis;
using System.IO;

namespace XXXXX
{
	public static class VarUInt64
	{
		private const byte Msb0 = 0b0111_1111;
		private const byte Msb1 = 0b1000_0000;

		[SuppressMessage("Design", "CA1062:Validate arguments of public methods", Justification = "No null check for performance reasons")]
		public static int Write(Stream stream, ulong value)
		{
			ulong next;
			var cnt = 1;

			while ((next = value >> 7) != 0)
			{
				stream.WriteByte((byte)((value & Msb0) | Msb1));
				value = next;
				cnt++;
			}

			stream.WriteByte((byte)value);
			return cnt;
		}

		[SuppressMessage("Design", "CA1062:Validate arguments of public methods", Justification = "No null check for performance reasons")]
		public static int Read(Stream stream, out ulong value)
		{
			ulong b, result = 0;
			var shift = 0;
			var cnt = 0;

			while (true)
			{
				var x = stream.ReadByte();
				cnt++;

				if (x < 0)
				{
					throw new EndOfStreamException();
				}

				if (((b = (ulong)x) & Msb1) == 0)
				{
					break;
				}

				result |= (b & Msb0) << shift;
				shift += 7;
			}

			value = result | ((b & Msb0) << shift);

			return cnt;
		}
	}
}

Expected behavior stryker cli asked my to report it, but I guess the expected behaviour would be that stryker is able to mutate the Read method without entering safe mode.

Desktop:

• OS: Windows
• Type of project: core3 / xunit tests
• Framework Version: .net core 3.1
• Stryker Version: 0.16.0 (beta)

[rouke-broersma]

IMHO, I think most while(true) constructions will result in compilation issues.

Asking user to report safe mode was there to prevent the persistence of mutation process bugs that would result in triggering safe mode.

I know, but if we acknowledge that some mutations have issues we can stop asking users to report on those specific issues (if it’s possible to detect that of course).

We could exclude mutating while(true) from the default boolean mutator and create a new separate mutator for it that is not turned on by default and can be turned on manually if people want a very thorough mutation testrun?

I think especially because while(true) is such a dangerous construct it would make sense to make sure it is properly tested when possible.

[dupdob]

My comment on the ugliness of the code was referring to the minimal example, not the original code (which I failed to read). so sorry about that. I agree, Stryker should not crash, and it does not. It just fails to manage the cascading effects of the mutation, which is difficult, because while(true)allows very specific constructions.

By the way, replacing while(true)by for(;;)will remove the message.