Roslyn: Control falls through switch statement case labels

[tenor]

This issue was previously reported in the old Roslyn forums.

``` C#
var i = 0;

switch (i)
{
case 0:
Console.WriteLine('0');
case 1:
Console.WriteLine('1');
case 2:
break;
}
```

The code above will compile in both scripting and interactive mode.

In interactive mode, the code will compile even if the break statement is omitted.

_Edited Code for clarity_

[redknightlois]

Fall through switch is insanely useful for high performance code.

[sharwell]

@redknightlois You can still fall through in C#, you just have to do it explicitly. The syntax looks like this:

https://github.com/DotNetAnalyzers/StyleCopAnalyzers/blob/80f056045605ef6f8e6b17c96c8267997d025f12/StyleCop.Analyzers/StyleCop.Analyzers/SpacingRules/SA1000CodeFixProvider.cs#L85

[redknightlois]

@sharwell Nice, didn't know that.
Would that emit a jump statement if the behavior would be fall through? Or better would the JIT find out and do not emit the jump at all?

[sharwell]

@redknightlois If I'm not mistaken, the C# compiler will remove unnecessary branch instructions between cases when optimization is enabled (but not when optimization is disabled because it would negatively impact the debugging experience).