Delete unnecessary seek from FileStream.SetLengthInternal on Unix

[jkotas]

No description provided.

[stephentoub]

Looks good to me once CI is green. I'm trying to remember why all this was deemed necessary and coming up empty.

[jkotas]

I suspect that it was just copy&paste from Windows where we can avoid it as well - #43863 (comment).

[stephentoub]

    System.IO.Tests.FileStream_SetLength.InvalidLengths [FAIL]
      Assert.Throws() Failure
      Expected: typeof(System.ArgumentOutOfRangeException)
      Actual:   (No exception was thrown)
      Stack Trace:
        /_/src/libraries/Common/tests/TestUtilities/System/AssertExtensions.cs(69,0): at System.AssertExtensions.Throws[T](String expectedParamName, Action action)
        /_/src/libraries/System.IO.FileSystem/tests/FileStream/SetLength.cs(19,0): at System.IO.Tests.FileStream_SetLength.InvalidLengths()

    System.IO.MemoryMappedFiles.Tests.MemoryMappedFileTests_CreateNew.TooLargeCapacity_Unix [FAIL]
      Expected one of: (System.IO.IOException, System.ArgumentException) -> Actual: (System.ArgumentOutOfRangeException)
      Stack Trace:
        /_/src/libraries/Common/tests/TestUtilities/System/AssertExtensions.cs(212,0): at System.AssertExtensions.ThrowsAnyInternal(Action action, Type[] exceptionTypes)
        /_/src/libraries/Common/tests/TestUtilities/System/AssertExtensions.cs(222,0): at System.AssertExtensions.ThrowsAny[IOException,ArgumentException](Action action)
        /_/src/libraries/System.IO.MemoryMappedFiles/tests/MemoryMappedFile.CreateNew.Tests.cs(115,0): at System.IO.MemoryMappedFiles.Tests.MemoryMappedFileTests_CreateNew.TooLargeCapacity_Unix()
        /_/src/mono/netcore/System.Private.CoreLib/src/System/Reflection/RuntimeMethodInfo.cs(378,0): at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)

[stephentoub]

It looks like this method is poorly named, in that whereas Assert.ThrowsAny<T> allows for the exception to be T or anything derived from it, AssertExtensions.ThrowsAny<T1, T2> is requiring the concrete type of T1 or T2:

runtime/src/libraries/Common/tests/TestUtilities/System/AssertExtensions.cs

Lines 195 to 216 in 22c3105

	public static void ThrowsAny(Type firstExceptionType, Type secondExceptionType, Action action)
	{
	ThrowsAnyInternal(action, firstExceptionType, secondExceptionType);
	}
	private static void ThrowsAnyInternal(Action action, params Type[] exceptionTypes)
	{
	try
	{
	action();
	}
	catch (Exception e)
	{
	Type exceptionType = e.GetType();
	if (exceptionTypes.Any(t => t.Equals(exceptionType)))
	return;
	throw new XunitException($"Expected one of: ({string.Join<Type>(", ", exceptionTypes)}) -> Actual: ({exceptionType})");
	}
	throw new XunitException($"Expected one of: ({string.Join<Type>(", ", exceptionTypes)}) -> Actual: No exception thrown");
	}

which is then failing if the exception is actually an ArgumentOutOfRangeException.